U.S. patent application number 11/252782 was filed with the patent office on 2006-02-16 for frequency synthesizer and multi-band radio apparatus using said frequency synthesizer.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Toshiyuki Umeda, Hiroshi Yoshida.
Application Number | 20060035599 11/252782 |
Document ID | / |
Family ID | 18737740 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060035599 |
Kind Code |
A1 |
Yoshida; Hiroshi ; et
al. |
February 16, 2006 |
Frequency synthesizer and multi-band radio apparatus using said
frequency synthesizer
Abstract
There is disclosed a frequency synthesizer having an HF
synthesizer for generating a first reference frequency signal
having a variable frequency in a high-frequency band as a unit
synthesizer, an LF synthesizer for generating a second reference
frequency signal in a low-frequency band as another unit
synthesizer, and an arithmetic circuit including a mixer for
receiving the first and second reference frequency signals, a
divider for receiving the second reference frequency signal, a
mixer for receiving the first reference frequency signal and an
output signal from the divider, a divider for receiving an output
signal from the mixer, a divider for receiving an output signal
from the mixer and capable of switching a division ratio, and a
switch for switching and outputting output signals from the
dividers, wherein an output signal of the switch is outputted as a
first local signal, and an output signal from the divider is
outputted as a second local signal.
Inventors: |
Yoshida; Hiroshi;
(Yokohama-shi, JP) ; Umeda; Toshiyuki; (Inagi-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
105-8001
|
Family ID: |
18737740 |
Appl. No.: |
11/252782 |
Filed: |
October 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09931105 |
Aug 17, 2001 |
|
|
|
11252782 |
Oct 19, 2005 |
|
|
|
Current U.S.
Class: |
455/76 |
Current CPC
Class: |
H03B 21/02 20130101;
H04B 1/405 20130101 |
Class at
Publication: |
455/076 |
International
Class: |
H04B 1/40 20060101
H04B001/40 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2000 |
JP |
2000-247703 |
Claims
1-15. (canceled)
16. A frequency synthesizer comprising: a first signal generator
which outputs a first signal of which frequency is within one of a
plurality of frequency bands; a second signal generator which
outputs a second signal having a fixed frequency; a first mixer
which mixes the first and second signals and outputs a first mixed
signal; a first divider which divides the first mixed signal by a
first division ratio and outputs a first divided signal; a second
divider which divides the second signal by a second division ratio
and outputs a second divided signal; a second mixer which mixes the
first signal and the second divided signal and outputs a second
mixed signal; a third divider which divides the second mixed signal
by a third division ratio to output a first local signal; and a
switch which selects either the first divided signal or the first
local signal and outputs a second local signal; wherein said first
divider includes a first .pi./2 phase shifter and said third
divider includes a second .pi./2 phase shifter, and wherein said
switch outputs first and second phase signals having phases
different from each other by .pi./2.
17. A frequency synthesizer comprising: a first signal generator
which outputs a first signal of which frequency is within one of a
plurality of frequency bands; a second signal generator which
outputs a second signal having a fixed frequency; a first mixer
which mixes the first and second signals and outputs a first mixed
signal; a first divider which divides the first mixed signal by a
first division ratio and outputs a first divided signal; a second
divider which divides the second signal by a second division ratio
and outputs a second divided signal; a second mixer which mixes the
first signal and the second divided signal and outputs a second
mixed signal; a third divider which divides the second mixed signal
by a third division ratio to output a first local signal; a switch
which selects either the first divided signal or the first local
signal and outputs a second local signal; and a first filter
inserted between said first mixer and said first divider, and a
second filter inserted between said second mixer and said third
divider.
18. A frequency synthesizer comprising: a first signal generator
which outputs a first signal of which frequency is within one of a
plurality of frequency bands; a second signal generator which
outputs a second signal having a fixed frequency; a first mixer
which mixes the first and second signals and outputs a first mixed
signal; a first divider which divides the first mixed signal by a
first division ratio and outputs a first divided signal; a second
divider which divides the second signal by a second division ratio
and outputs a second divided signal; a second mixer which mixes the
first signal and the second divided signal and outputs a second
mixed signal; a third divider which divides the second mixed signal
by a third division ratio to output a first local signal; a switch
which selects either the first divided signal or the first local
signal and outputs a second local signal; and a fourth divider
which divides a signal output from said switch by a fourth division
ratio.
19. The frequency synthesizer of claim 16, further comprising a
fourth divider which divides a signal output from said switch by a
fourth division ratio, and a fifth divider which divides a signal
output from said switch by a fifth division ratio.
20. The frequency synthesizer of claim 16, further comprising a
sixth divider inserted between said third divider and said
switch.
21. A frequency synthesizer comprising: a first signal generator
which outputs a first signal of which frequency is within one of a
plurality of frequency bands; a second signal generator which
outputs a second signal having a fixed frequency; a first divider
which divides the second signal by a first division ratio and
outputs a first divided signal; a mixer which mixes the first
signal with the first divided signal and outputs a mixed signal; a
second divider which divides the mixed signal by a second division
ratio to output a first local signal; a third divider which divides
the second signal by a third division ratio to output a second
local signal; a fourth divider which divides the first signal by a
fourth division ratio to output a third local signal; and a first
filter inserted between said first divider and said mixer, and a
second filter inserted between said mixer and said second
divider.
22. A frequency synthesizer comprising: a first signal generator
which outputs a first signal of which frequency is within one of a
plurality of frequency bands; a second signal generator which
outputs a second signal having a fixed frequency; a first divider
which divides the second signal by a first division ratio and
outputs a first divided signal; a mixer which mixes the first
signal with the first divided signal and outputs a mixed signal; a
second divider which divides the mixed signal by a second division
ratio to output a first local signal; a third divider which divides
the second signal by a third division ratio to output a second
local signal; a fourth divider which divides the first signal by a
fourth division ratio to output a third local signal; a second
mixer which mixes a signal output from said fourth divider with a
signal output from said third divider; and a switch which outputs
either a signal output from the second mixer or a signal output
from the third divider as a second local signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2000-247703; filed Aug. 17, 2000, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a frequency synthesizer for
generating signals having a plurality of desired frequencies, and
also relates to a multi-band radio apparatus using the same.
[0004] 2. Description of the Related Art
[0005] In general, mobile communication terminals are designed for
the purpose of using in one communication system. Such a
communication system may be a PDC (Personal Digital Cellular)
mobile phone system, a mobile phone system conforming to IS-95, or
PHS (Personal Handy-phone System). It is quite usual that one
mobile communication terminal complies with only-one standard among
others of various communication systems existing in the world.
[0006] Recently, demand is raised to provide another mobile
communication terminal to cope with rapid diversifications of the
mobile communication systems. Such a terminal can solely control
transmission/reception in response to multiple, different
communication systems. For example, so-called "multi-mode terminal"
used for both the PDC mobile phone system and the PHS has already
been proposed.
[0007] In most cases, different mobile communication systems use
different frequency bands; therefore, a multi-mode terminal to deal
with them should be provided with a "multi-band radio function",
i.e., a function of transmitting/receiving data within each of
multiple frequency bands.
[0008] A direct conversion mode is known as an architecture
suitable for realizing such a multi-band radio apparatus. In the
apparatus using the direct conversion mode, received signals from
an antenna are inputted to one of quadrature demodulators.
[0009] To the quadrature demodulator, a pair of local signals for
receiver having phases different from each other by 90.degree. are
also inputted. They are generated by subjecting local signals
output from a frequency synthesizer, to the phase shift by a .pi./2
phase shifter. Note that frequencies of the local signals are set
with regard to frequencies of desired signals in the received
signals.
[0010] Because the quadrature demodulator multiplies the received
signals by the local signals, the desired signals are converted
into baseband signals for an I (Inphase) channel and a Q
(Quadrature phase) channel with a center frequency of 0 Hz, which
are inputted to a baseband reception section for subsequent signal
reproduction processing.
[0011] On the other hand, signals to be transmitted for the I
channel and the Q channel generated by a baseband transmission
section are inputted to the another quadrature modulator.
[0012] To a local input port of the quadrature modulator, local
signals for transmitter having phases different from each other by
90.degree., which are generated by subjecting local signals output
from the frequency synthesizer to the phase shift by the .pi./2
phase shifter are inputted.
[0013] Frequencies of the local signals are set to be equal to a
transmission frequency. As this quadrature demodulator multiplies
the transmission signals by the local signals, the frequencies of
the transmission signals are converted into a predetermined
transmission frequency.
[0014] The frequency synthesizer used in the multi-band radio
apparatus must generate local signals in various frequency bands
according to realization of the multi-band. Note that this
requirement is not limited to the direct conversion mode.
[0015] Various modes such as GSM (global system mobile
communication) using the 900 MHz band, DCS (digital cellular
system) using the 1800 MHz band, PCS (personal communication
services) using the 1900 MHz band, UMTS (universal mobile
telecommunication system) using the 2 GHz band are extensively
utilized in the world. Development of a four-band radio apparatus
supposed to be used in all of these frequency bands is desired.
[0016] When the frequency synthesizer to cope with such a four-band
radio apparatus is realized in compliance with, for instance, the
direct conversion mode, there can be considered a method for
preparing respective unit synthesizers for: GSM transmission, GSM
reception, DCS transmission, DCS reception, PCS transmission, PCS
reception, UMTS transmission and UMTS reception by analogy with the
method for constituting the frequency synthesizer in the two-band
radio apparatus which can cope with both PDS and PHS.
[0017] Since the reception frequency band of PCS and the
transmission frequency band of UMTS are nearly equal to each other,
one synthesizer can function for the both modes. That is, except
special cases, unit synthesizers whose number corresponds to a
plurality of necessary frequency bands are basically prepared.
Therefore, when a number of bands is increased, a number of the
unit synthesizers is also proportionately increased, which results
in vast hardware.
[0018] In preparing the unit synthesizers according to the
respective frequency bands in order to realize the multi-band radio
apparatus, multiple unit synthesizers are required when a number of
bands is increased. Therefore, the scale of hardware become larger,
which leads to increase in size of the multi-mode terminal and the
price and the power consumption.
BRIEF SUMMARY OF THE INVENTION
[0019] In view of the above-described problems, it is an object of
the present invention to provide a frequency synthesizer which
comprises a small number of unit synthesizers and has a small
circuit scale, and a multi-band radio apparatus using this
frequency synthesizer.
[0020] To achieve this aim, according to the present invention,
there is provided a frequency synthesizer comprising:
[0021] a first synthesizer which outputs signal of which frequency
is within one of a plurality of frequency bands;
[0022] a second synthesizer which outputs a fixed frequency
signal;
[0023] a first mixer which mixes the signal output from the first
synthesizer with the fixed frequency signal output from the second
synthesizer;
[0024] a first divider which divides a signal output from the first
mixer by a first division ratio;
[0025] a second divider which divides the fixed frequency signal
output from the second synthesizer by a second division ratio;
[0026] a second mixer which mixes the signal output from the first
synthesizer with a signal output from the second divider;
[0027] a third divider which divides a signal output from the
second mixer by a third division ratio to output a signal to be
used as a first local signal; and
[0028] a switch which outputs either a signal output from the first
divider or a signal output from the third divider as a second local
signal.
[0029] As described above, in the frequency synthesizer according
to the embodiment of the present invention, it is possible to
generate signals in a plurality of frequency bands whose number is
larger than that of the unit synthesizers by the small-scale
circuit configuration in which the two unit synthesizers are
combined with the arithmetic circuit comprising dividers and mixers
for multiplication.
[0030] According to another embodiment of the present invention,
there is provided a multi-band radio apparatus comprising:
[0031] a frequency synthesizer including: [0032] a first
synthesizer which outputs signal of which frequency is within one
of a plurality of frequency bands; [0033] a second synthesizer
which outputs a fixed frequency signal; [0034] a first mixer which
mixes the signal output from the first synthesizer with the fixed
frequency signal output from the second synthesizer; [0035] a first
divider which divides a signal output from the first mixer by a
first division ratio; [0036] a second divider which divides the
fixed frequency signal output from the second synthesizer by a
second division ratio; [0037] a second mixer which mixes the signal
output from the first synthesizer with a signal output from the
second divider; [0038] a third divider which divides a signal
output from the second mixer by a third division ratio to output a
signal to be used as a first local signal; and [0039] a switch
which outputs either a signal output from the first divider or a
signal output from the third divider as a second local signal;
[0040] a quadrature demodulator connected to the frequency
synthesizer, which demodulates a received signal by use of the
reception local signal; and
[0041] a quadrature modulator connected to the frequency
synthesizer, which modulates a signal to be transmitted by use of
the transmission local signal.
[0042] In a multi-band radio apparatus having in a radio portion a
quadrature demodulator for demodulating a received signal by a pair
of local signals having phases different from each other by
90.degree. or 45.degree. and a quadrature modulator for modulating
a pair of transmission signals having phases different from each
other by 90.degree. by using a pair of local signals having phases
different from each other by 90.degree., the frequency synthesizer
is used to generate the local signals for receiver and the local
signals for transmitter. With such a structure, for example, the
multi-band radio apparatus adopting the direct conversion mode for
both the transmission and reception systems can be realized in a
small hardware scale.
[0043] Furthermore, in a multi-band radio apparatus having in a
radio portion a quadrature demodulator for demodulating a received
signal by a pair of local signals having phases different from each
other by 90.degree. or 45.degree., a quadrature modulator for
modulating a pair of transmission signals having phases different
from each other by 90.degree. by using a pair of first local
signals having phases different from each other by 90.degree., and
a frequency converter for converting a frequency of an output
signal from the quadrature modulator by using a second local
signal, the frequency synthesizer is used to generate the local
signals. With such a structure, for example, the multi-band radio
apparatus using the direction conversion mode for the reception
system and the super heterodyne mode for the transmission system
can be realized in the small hardware scale.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0044] FIG. 1 is a block diagrams showing a structure of a
multi-band radio apparatus including a frequency synthesizer
according to a first embodiment of the present invention;
[0045] FIG. 2 is a block diagram showing a structural example of an
image suppression type mixer;
[0046] FIG. 3 is a block diagram showing a structure of a
multi-band radio apparatus including a frequency synthesizer
according to a second embodiment of the present invention;
[0047] FIG. 4A is a block diagram showing an example of a divider
also serving as a .pi./2 phase shifter;
[0048] FIG. 4B is a timing chart of the divider also serving as a
.pi./2 phase shifter;
[0049] FIG. 5 is a block diagram showing a structure of a
multi-band radio apparatus including a frequency synthesizer
according to a third embodiment of the present invention;
[0050] FIG. 6 is a block diagrams showing a structure of a
multi-band radio apparatus including a frequency synthesizer
according to a fourth embodiment of the present invention;
[0051] FIG. 7 is a block diagram showing a structure of a
multi-band receiver including a frequency synthesizer according to
a fifth embodiment of the present invention;
[0052] FIG. 8 is a block diagram showing a structure of a
multi-band receiver including a frequency synthesizer according to
a sixth embodiment of the present invention;
[0053] FIG. 9 is a block diagram showing a structure of a
multi-band receiver including a frequency synthesizer according to
a seventh embodiment of the present invention;
[0054] FIG. 10 is a block diagram showing a structure of a
frequency synthesizer according to an eighth embodiment of the
present invention;
[0055] FIG. 11 is a block diagram showing a structure of a
frequency synthesizer according to a ninth embodiment of the
present invention;
[0056] FIG. 12 is a block diagrams showing a structure of a
multi-band receiver including a frequency synthesizer according to
a tenth embodiment of the present invention;
[0057] FIG. 13 is a block diagram showing a structure of a
multi-band receiver including a frequency synthesizer according to
an eleventh embodiment of the present invention; and
[0058] FIG. 14 is a block diagram showing a structure of a
multi-band receiver including a frequency synthesizer according to
a twelfth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0059] FIG. 1 is a block diagram showing a structure of a
multi-band radio apparatus including a frequency synthesizer
according to a first embodiment of the present invention. The
multi-band radio apparatus of this embodiment is a four-band radio
apparatus adopting the direct conversion mode conform to
GSM/DCS/PCS/UMTS.
[0060] A received signal from an antenna 1 is inputted to a
quadrature demodulator 2 including two mixers 2A and 2B. When this
received signal is multiplied by local signals having phases
0.degree. and 90.degree. inputted from a frequency synthesizer 10A
to local input ports of the mixers 2A and 2B through a .pi./2 phase
shifter 4, baseband received signals Ir and Qr for an I channel and
a Q channel are generated. The baseband received signals Ir and Qr
are inputted to a non-illustrated baseband processing stage.
[0061] On the other hand, baseband transmission signals It and Qt
for the I channel and the Q channel output from the baseband
processing stage are inputted to a quadrature modulator 3 including
two mixers 3A and 3B. When these signals are multiplied by local
signals having phases 0.degree. and 90.degree. inputted from the
frequency synthesizer 10A to local input ports of the mixers 3A and
3B through a .pi./2 phase shifter 5, RF transmission signals for
the I channel and the Q channel are generated. The RF signals for
the I channel and the Q channel are combined with each other and
transmitted through the antenna 1.
[0062] The frequency synthesizer 10A will now be described.
[0063] The frequency synthesizer 10A comprises an HF synthesizer 11
for generating a first reference frequency signal having a variable
frequency in a high-frequency band and an LF synthesizer 12 for
generating a second reference frequency signal in a low-frequency
band as unit synthesizers. Here, the terms "high-frequency band"
and "low-frequency band" relatively mean that a frequency in the
latter band is lower than that in the former band. The HF
synthesizer 11 and the LF synthesizer 12 are constituted by using,
for example, PLLs.
[0064] In the frequency synthesizer 10A of this embodiment, by
using the following arithmetic circuit to perform arithmetic
operations including frequency division and multiplication to the
reference frequency signals output from the HF synthesizer 11 and
the LF synthesizer 12 as two unit synthesizers having different
frequency bands, output signals having a plurality of necessary
frequencies are generated as transmission/local signals in each of
GSM/DCS/PCS/UMTS modes.
[0065] To a first mixer 13, an output signal from the HF
synthesizer 11 as the first reference frequency signal and an
output signal from the LF synthesizer 12 as the second reference
frequency signal are inputted. The output signal from the LF
synthesizer 12 is also inputted to a first divider 14 having a
division ratio "2". An output signal from the HF synthesizer 11 and
an output signal from the first divider 14 are inputted to a second
mixer 15. An output signal from the first mixer 13 is inputted to a
second divider 16 having a division ratio "2", and an output signal
from the second mixer 15 is inputted to a third divider 17 whose
division ratio can be switched between "2" and "4".
[0066] A switch 18 switches an output signal from the second
divider 16 and an output signal from the third divider 17. An
output signal from the switch 18 is outputted as a local signal and
inputted to the quadrature demodulator 2 through the .pi./2 phase
shifter 4. An output signal from the third divider 17 is further
outputted as a local signal and inputted to the quadrature
modulator 3 through the .pi./2 phase shifter 5.
[0067] An output signal frequency of the HF synthesizer 11, an
output signal frequency of the LF synthesizer 12,
enabling/disabling the operation of the second mixer 15, the
division ratio of the third divider 17 and the changeover operation
of the switch 18 are controlled by a controller 19 in accordance
with an operation mode of the multi-band radio apparatus. It is to
be noted that the output signal frequency of the LF synthesizer 12
may be fixed in this embodiment and control executed by the
controller 19 is not necessarily required except on/off switching
of the LF synthesizer 12. Moreover, a control signal line from the
controller 19 to the second mixer 15 is omitted in FIG. 1.
[0068] The operation of the frequency synthesizer 10A will now be
concretely described in accordance with each operation mode of the
multi-band radio apparatus hereinafter. For explaining the
operation of the frequency synthesizer 10A, Table 1 shows a
concrete frequency structure of four bands, i.e., GSM/DCS/PCS/UMTS.
TABLE-US-00001 TABLE 1 GSM DCS PCS UMTS Transmission 880-915
1710-1785 1850-1910 1920-1980 frequency MHz MHz MHz MHz Reception
925-960 1805-1880 1930-1990 2110-2170 frequency MHz MHz MHz MHz
[0069] [GSM Transmission Mode]
[0070] At first, in case of performing transmission in the GSM
mode, the output signal frequency of the HF synthesizer 11 is
determined as a value within a frequency range of 3520 MHz to 3660
MHz in accordance with the transmission frequency, the second mixer
15 is disabled (allowing the output signal from the HF synthesizer
11 to pass without change), and the division ratio of the third
divider 17 is determined as "4". As a result, from the frequency
synthesizer 10A is outputted a local signal having a frequency of
880 MHz to 915 MHz obtained by dividing the frequency of 3520 MHz
to 3660 MHz by four by the third divider 17, and this local signal
is inputted to the quadrature demodulator 3 through the .pi./2
phase shifter 5.
[0071] [GSM Reception Mode]
[0072] At second, in case of performing reception in the GSM mode,
the output signal frequency of the HF synthesizer 11 is determined
as a value within a frequency range of 3700 MHz to 3840 MHz in
accordance with the transmission frequency, the second mixer 15 is
disabled (allowing the output signal from the HF synthesizer 11 to
pass without change), the division ratio of the third divider 17 is
determined as "4", and the switch 18 is moved to the lower side
(selecting the output signal of the third divider 17). As a result,
a local signal having a frequency of 925 MHz to 960 MHz obtained by
dividing the frequency of 3700 MHz to 3840 MHz by four by the third
divider 17 is outputted from the frequency synthesizer 10A through
the switch 18, and this local signal is inputted to the quadrature
demodulator 2 through the .pi./2 phase shifter 4.
[0073] In the GSM mode, since communication is carried out in the
TDMA (time division multiple access) system, transmission and
reception are not simultaneously carried out. Transmission and
reception are changed over by switching the output signal frequency
of the HF synthesizer 11 in accordance with the timing of
transmission/reception as described above.
[0074] [DCS Transmission Mode]
[0075] At third, in case of performing transmission in the DCS
mode, the output signal frequency of the HF synthesizer 11 is
determined as a value within a frequency range of 3610 MHz to 3760
MHz in accordance with the transmission frequency, the output
signal frequency of the LF synthesizer 12 is determined as 380 MHz,
the second mixer 15 is enabled, and the division ratio of the third
divider 17 is determined as "2". An output signal of the LF
synthesizer 12 is divided by two to be 190 MHz and then inputted to
the second mixer 15.
[0076] In the second mixer 15, when the output signal from the HF
synthesizer 11 and the output signal from the second divider 14 are
multiplied together and a difference in frequency of the both
signals is detected, an output signal having a frequency within a
frequency range of 3420 MHz to 3570 MHz is obtained in accordance
with the transmission frequency. By dividing the output signal
having a frequency of 3420 MHz to 3570 MHz from the second mixer 15
by two in the third divider 17, the frequency synthesizer 10A
outputs a local signal having a frequency of 1710 MHz to 1785 MHz,
and this output signal is inputted to the quadrature modulator 3
through the .pi./2 phase shifter 5.
[0077] [DCS Reception Mode]
[0078] Subsequently, in case of performing reception in the DCS
mode, the output signal frequency of the HF synthesizer 11 is
determined as a value in a frequency range of 3610 MHz to 3760 MHz
in accordance with the reception frequency, the second mixer 15 is
disabled (allowing the output signal from the HF synthesizer 11 to
pass without change), the division ratio of the third divider 17 is
determined as "2", and the switch 18 is moved to the lower side
(selecting the output signal from the third divider 17). As a
result, the frequency synthesizer 10A outputs through the switch 18
the local signal having a frequency of 1805 to 1880 MHz obtained by
dividing the frequency of 3610 MHz to 3760 MHz by two in the second
divider 17, and this output signal is inputted to the quadrature
demodulator 2 through the .pi./2 phase shifter 4.
[0079] In the DCS mode, since communication is effected in the TDMA
mode as similar to the GSM mode, transmission and reception are not
simultaneously carried out. Transmission and reception are changed
over by switching disabling/enabling of the second mixer 15 in
accordance with the timing of transmission/reception as described
above.
[0080] [PCS Transmission Mode]
[0081] Next, in case of carrying out transmission in the PCS mode,
the output signal frequency of the HF synthesizer 11 is determined
as a value within a frequency range of 3700 MHz to 3820 MHz in
accordance with the transmission frequency, the second mixer 15 is
disabled (allowing the output signal from the HF synthesizer to
pass without change), and the division ratio of the third divider
17 is determined as "2". As a result, the frequency synthesizer 10A
outputs a local signal having a frequency of 1850 MHz to 1910 MHz
obtained by dividing the frequency of 3700 MHz to 3820 MHz by two
in the third divider 17, and this output signal is inputted to the
quadrature modulator 3 through the .pi./2 phase shifter 5.
[0082] [PCS Reception Mode]
[0083] Then, in case of performing reception in the PCS mode, the
output signal frequency of the HF synthesizer 11 is determined as a
value within a frequency range of 3860 MHz to 3980 MHz in
accordance with the transmission frequency, the second mixer 15 is
disabled (allowing the output signal from the HF synthesizer 11 to
pass without change), the division ratio of the third divider 7 is
determined as "2", and the switch 18 is moved to the lower side
(selecting the output signal from the third divider 17). As a
result, the frequency synthesizer 10A outputs through the switch 18
a local signal having a frequency of 1930 MHz to 1990 MHz obtained
by dividing the frequency of 3860 MHz to 3980 MHz by two in the
second divider 17, and this output signal is inputted to the
quadrature demodulator 2 through the .pi./2 phase shifter 4.
[0084] Although there are several PCS modes, since communication is
carried out in the TDMA system in case of a mode similar to the GSM
mode, transmission and reception are not simultaneously performed.
Transmission and reception are changed over by switching the output
signal frequency of the HF synthesizer 11 in accordance with the
timing of transmission/reception.
[0085] [UMTS Transmission Mode]
[0086] Then, in case of carrying out transmission in the UMTS mode,
the output signal frequency of the HF synthesizer 11 is determined
as a value within a frequency range of 3840 MHz to 3960 MHz in
accordance with the transmission frequency, the second mixer 15 is
disabled (allowing the output signal of the HF synthesizer 11 to
pass without change), and the division ratio of the third divider
17 is determined as "2". As a result, the frequency synthesizer 10A
outputs a local signal having a frequency of 1920 MHz to 1980 MHz
obtained by dividing the frequency of 3840 MHz to 3960 MHz by two
in the third divider 17, and this output signal is inputted to the
quadrature modulator 3 through the .pi./2 phase shifter 5.
[0087] [UMTS Reception Mode]
[0088] Subsequently, in case of performing reception in the UMTS
mode, the output signal frequency of the HF synthesizer 11 is
determined as a value within a frequency range of 3840 MHz to 3960
MHz in accordance with the transmission frequency, the output
signal frequency of the LF synthesizer 12 is determined as 380 MHz,
the first mixer 13 is enabled, and the switch 18 is moved to the
upper side (selecting the output signal of the second divider 16).
In the first mixer 13, a signal having a frequency of 4220 MHz to
4340 MHz is obtained by multiplying the output signal from the HF
synthesizer 11 and the output signal from the LF synthesizer 12
together. Consequently, the frequency synthesizer 10A outputs
through the switch 18 a local signal having a frequency of 2110 MHz
to 2170 MHz obtained by dividing the frequency of 4220 MHz to 4340
MHz by two in the second divider 17, and this output signal is
inputted to the quadrature demodulator 2 through the .pi./2 phase
shifter 4.
[0089] In case of the UMTS mode, since the CDMA/FDD (code division
multiple access/frequency division duplex) system is adopted,
transmission and reception are simultaneously carried out.
According to the structure of this embodiment, it is possible to
simultaneously output the local signals for receiver and
transmitter having frequencies required for
transmission/reception.
[0090] As mentioned above, in the frequency synthesizer 10A of this
embodiment, with the simple structure that the two unit
synthesizers, i.e., the HF synthesizer 11 and the LF synthesizer 12
are prepared and the mixers 13 and 15, the dividers 14, 16 and 17,
and the switch 18 are combined with these synthesizers, it is
possible to generate all frequencies required for
transmission/reception in each mode of GSM/DCS/PCS/UMTS. Therefore,
when a number of unit synthesizers whose circuit scale is large is
greatly reduced, the hardware scale can be considerably
minimized.
[0091] FIG. 2 shows a structural example of an image suppression
type mixer which is suitable as the first mixer 13 and the second
mixer 15 depicted in FIG. 1. This mixer comprises .pi./2 phase
shifters 21 and 22, multipliers 23 and 24, and an adder-subtracter
25. This mixer basically multiplies an output signal from the HF
synthesizer 11 and an output signal from the LF synthesizer 12 (or
a signal obtained by further dividing an output signal from the LF
synthesizer 12 by the divider 14) and outputs a signal having a
frequency indicative of a sum or a difference of the output signals
of the both synthesizers 11 and 12.
[0092] In this case, as shown in FIG. 2, the .pi./2 phase shifters
21 and 22 are used to branch each of output signals from the both
synthesizers 11 and 12 into two, and the two multipliers 23 and 24
are then used to carry out the above-described multiplication
operation. In addition, the adder-subtracter 25 is used to add (or
subtract) the output signals from the multipliers 23 and 24. As a
result, the image suppression effect can be obtained. Since
approximately 30 dB can be obtained as an image suppression ratio,
an image suppression filter which is usually required on a
subsequent stage of the mixer can be eliminated in the mixer having
the structure shown in FIG. 2.
[0093] Other embodiments according to the present invention will
now be described. In each drawing of the following embodiments,
like reference numerals denote the same constituent parts as those
in FIG. 1 to avoid tautological explanation, and a characteristic
part of each embodiment will be mainly described.
Second Embodiment
[0094] FIG. 3 shows a structure of a multi-band radio apparatus
including a frequency synthesizer according to a second embodiment
of the present invention. In the frequency synthesizer 10B of this
embodiment, the second and third dividers 16 and 17 in the
frequency synthesizer 10A in FIG. 1 are substituted by dividers 26
and 27 which also serve as the .pi./2 phase shifters, and a switch
28 capable of simultaneously switching signals for two channels is
used in place of the switch 18.
[0095] FIG. 4 shows an example of the circuit diagram of dividers
also serving as the .pi./2 phase shifters which are used as the
dividers 26 and 27. This divider is realized with two D type flip
flops DFF1 and DFF2 as main constituted parts as shown in FIG. 4A.
When clock signals are inputted to clock input terminals CK and
_CK, a signal I and a signal. Q obtained by dividing, the clock
signal by two are output from a terminal I, _I and a terminal Q,
_Q. Although the clock signal, the signal I and the signal Q are
treated as differential signals in FIG. 4A, the signal I and the
signal Q have a phase difference of 90.degree. as shown in FIG. 4B
illustrating only positive phase signals. That is, the divider
shown in FIG. 4A also has a function of the .pi./2 phase
shifter.
[0096] Therefore, when the divider shown in FIG. 4A is used for the
dividers 26 and 27, the signal I and the signal Q outputted from
the dividers 26 and 27 can be used as the local signal inputted to
the local input port of the quadrature demodulator 2 or the local
signal inputted to the local input port of the quadrature modulator
3 as shown in FIG. 3. In addition, the .pi./2 phase shifters 4 and
5 shown in FIG. 1 are no longer necessary. The switch 28 is
constituted so as to be capable of simultaneously switching the
signal I and the signal Q outputted from the dividers 26 and 27
also serving as the .pi./2 phase shifters.
Third Embodiment
[0097] FIG. 5 shows a structure of a multi-band radio apparatus
including a frequency synthesizer according to a third embodiment
of the present invention. In the first embodiment, description that
the filter on the subsequent stage of the mixer can be eliminated
by using such an image suppression type filter as shown in FIG. 2
has been given. However, it is needless to say that inserting the
filter to the subsequent stage of the mixer may be preferable
depending on unnecessary spurious specifications of the output
signal from the frequency synthesizer.
[0098] In the frequency synthesizer 10C of this embodiment,
band-pass filters 31 and 32 are inserted to the subsequent stages
of the mixers 13 and 15. These filters 31 and 32 may be constituted
by combining discrete components such as a coil (L), a capacitor
(C) or a resistor (R), or by using filter components formed as
modules such as an LC laminated filter, a dielectric filter, or an
SAW (surface acoustic wave) filter. Additionally, these filters can
be realized in a simpler structure by constituting the band-pass
filters 31 and 32 by low-pass filters or high-pass filters
depending on the frequency concern.
Fourth Embodiment
[0099] In the direct conversion mode, in order to suppress
deterioration of the reception characteristic caused due to
generation of the DC offset, a harmonic mixer may be used in the
quadrature demodulator on the reception side. The harmonic mixer is
different from a regular mixer, and a signal having a frequency
which is 1/2 of the reception frequency is used as a local
signal.
[0100] FIG. 6 shows a structure in case of using the harmonic mixer
in the quadrature demodulator 2 as a fourth embodiment according to
the present invention. In the frequency synthesizer 10D of this
embodiment, a fourth divider 33 is inserted on the subsequent stage
of the switch 18. The division ratio of the fourth divider 33 is
"2" and used for generating a local signal having a frequency which
is 1/2 of the reception frequency and required in the quadrature
demodulator 2 having the harmonic mixer structure.
[0101] Incidentally, when utilizing the harmonic mixer, since a
phase difference of the local signals to be supplied to the two
mixers must be 45.degree. in the quadrature demodulator 2, the
.pi./2 phase shifter 6 is used in place of the .pi./2 phase shifter
4 shown in FIG. 1.
Fifth Embodiment
[0102] FIG. 7 shows a structure according to a fifth embodiment of
the present invention obtained by improving the fourth embodiment
illustrated in FIG. 6. In the frequency synthesizer 10E of this
embodiment, second and third dividers 26 and 27 also serving as the
.pi./2 phase shifters and the switch 18 capable of simultaneously
switching signals for two channels are used as similar to the
second embodiment illustrated in FIG. 3, and a fifth divider 34
having the division ratio of "2" which also functions as the .pi./2
phase shifter is added as well as the fourth divider 33 depicted in
FIG. 6.
[0103] By dividing each of signals having a phase 0.degree.
outputted from the second and third dividers 26 and 27 by two in
the fourth divider 33 through the switch 28, these signals are
outputted as the local signals having a phase 0.degree.. Further,
by dividing each of signals having a phase 90.degree. outputted
from the dividers 26 and 27 by two by the fifth divider 34 which
also functions as the .pi./2 phase shifter through the switch 28,
these signals are outputted as the local signals having a phase
45.degree..
[0104] As described above, according to this embodiment, since the
two local signals having a phase difference of .pi./2 in total are
obtained, the FIG. 6 .pi./2 phase shifter 6 used in the fourth
embodiment can be eliminated.
Sixth Embodiment
[0105] FIG. 8 shows another structural example in case of using the
harmonic mixers in the quadrature demodulator 2 as a sixth
embodiment according to the present invention. In the frequency
synthesizer 10F of this embodiment, the first divider 26 having the
division ratio "2" depicted in FIG. 7 is substituted by a divider
41 having the division ratio "4", and a fourth divider 42 having
the division ratio "2" is inserted between the third divider 27 and
the switch 28. Moreover, the dividers 33 and 34 illustrated in FIG.
7 are removed.
[0106] According to this embodiment, since the dividers 41 and 42
can also function as the .pi./4 phase shifters, the effects similar
to those of the fifth embodiment shown in FIG. 7 can be obtained
because the .pi./4 phase shifter required for the harmonic mixers
can be eliminated.
Seventh Embodiment
[0107] All of the first to sixth embodiments mentioned above are
examples in which the present invention is applied to the
multi-band radio apparatus using the direct conversion mode in both
the transmission system and the reception system. Description will
now be given as an example that the present invention is applied to
the multi-band radio apparatus in which the direct conversion mode
is used only in the reception system and the super heterodyne mode
is used in the transmission system as shown in FIG. 9 as a seventh
embodiment according to the present invention.
[0108] In FIG. 9, a frequency converter 7 is inserted between the
quadrature modulator 3 of the transmission system and the antenna
1. In this case, the quadrature modulator 3 is used as an
intermediate frequency converter. That is, baseband transmission
signals It and Qt for the I channel and the Q channel are converted
into intermediate frequency signals by the quadrature modulator 3,
then up-converted by the frequency converter 7, and supplied to the
antenna 1.
[0109] The frequency converter 7 is constituted by phase
comparators 71a to 71c, down converters 72a to 72c, an up
converters 72d and VCOs (voltage control oscillators) 73a to 73c.
Suffixes a, b and c indicate systems for GSM, DCS and PCS, and the
up converter 72d is used for UMTS. The phase comparators 71a to 71c
compare output signals from VCOs 73a to 73c with output signals
from down converters 72a to 72c, and output signals indicative of
phase differences between these signals. Oscillation frequencies of
the VCOs 73a to 73c are controlled by the output signals from the
phase comparators 71a to 71c. The down converters 72a to 72c
down-convert output signals from the VCOs 73a to 73c by using a
first local signal inputted from the later-described frequency
synthesizer 100A.
[0110] This structure seems to be complicated transmission system
structure as compared with the multi-band radio apparatus adopting
the direct conversion mode, but the quadrature modulator 3 of the
transmission system can be shared by all the modes. Further, when
the direct conversion mode is used in both transmission and
reception, although the output signal frequency of the quadrature
modulator 3 coincides with the transmission frequency, the output
frequency of the quadrature modulator 3 becomes the intermediate
frequency in this embodiment.
[0111] When the super heterodyne mode is adopted in the
transmission mode in this way, the structure of the frequency
synthesizer is changed by the intermediate frequency of the
transmission system. However, if the intermediate frequency is 380
MHz in GSM/DCS and 190 MHz in PCS/UMTS, the frequency synthesizer
can be realized by the most simplest structure. Output signal
frequencies of the frequency synthesizer in this case will be shown
in Table 2 in order. TABLE-US-00002 TABLE 2 GSM DCS PCS UMTS
Transmission 380 380 190 190 first LO MHz MHz MHz MHz Transmission
500-535 2090-2165 2040-2100 2110-2170 second LO MHz MHz MHz MHz
Reception LO 925-960 1805-1880 1930-1990 2110-2170 MHz MHz MHz
MHz
[0112] The frequency synthesizer 100A of this embodiment shown in
FIG. 9 is configured to generate such frequencies. The frequency
synthesizer 100A comprises an HF synthesizer 101 for generating a
first reference frequency signal in a high-frequency band and an LF
synthesizer 102 for generating a second reference frequency signal
in a low-frequency band for unit synthesizers. In the frequency
synthesizer 100A, output signals having necessary frequencies are
generated by performing arithmetic operations including
multiplication and frequency division by the following arithmetic
circuit with respect to the reference frequency signals outputted
from the HF synthesizer 101 and the LF synthesizer 102 as two unit
synthesizers having different frequency bands.
[0113] An output signal from the LF synthesizer 102 is divided by
the first divider 103 having the division ratio "4". The first
mixer 104 multiplies an output signal from the HF synthesizer 101
and an output signal from the first divider 103 together. An output
signal from the first mixer 104 is divided by a second divider 105
having the division ratio "2" and then inputted to the quadrature
demodulator 2 through the .pi./2 phase shifter 4 as a local
signal.
[0114] The output signal from the LF synthesizer 102 is also
divided by a third divider 17 which can switch the division ratio
between "2" and "4", and then inputted to the quadrature modulator
3 as a transmission first local signal. Furthermore, the output
signal from the HF synthesizer 101 is inputted to the frequency
converter 7 through a fourth divider 107 having the division ratio
"4" as a transmission second local signal.
[0115] The output signal frequency of the HF synthesizer 101, the
output signal frequency of the LF synthesizer 102,
enabling/disabling the first mixer 104, enabling/disabling the
second divider 105, the division ratio of the third divider 106,
and enabling/disabling the fourth divider 107 are controlled by a
controller 110 in accordance with an operation mode of the
multi-band radio apparatus. The output signal frequency of the LF
synthesizer 102 may be fixed in this embodiment, and control
effected by the controller 110 is not necessarily required.
Moreover, a control signal line from the controller 110 to the
mixer 104 is eliminated in FIG. 9.
[0116] The operation of the frequency synthesizer 100A will now be
concretely described in accordance with each operation mode of the
multi-band radio apparatus.
[0117] [GSM Transmission Mode]
[0118] At first, in case of performing transmission in the GSM
mode, the output signal frequency of the HF synthesizer 101 is
determined as a value within a frequency range of 2000 MHz to 2140
MHz in accordance with the transmission frequency, the output
signal frequency of the LF synthesizer 102 is determined as 760
MHz, and the division ratio of the third divider 106 is determined
as "2". In this case, the frequency synthesizer 100A outputs a
signal having a frequency of 380 MHz obtained by dividing 760 MHz
by two in the third divider 106, and this signal is inputted to the
quadrature modulator 3 as a transmission first local signal.
[0119] In addition, a signal having a frequency of 500 MHz to 535
MHz obtained by dividing the output signal frequency 2000 MHz to
2140 MHz of the HF synthesizer 101 by four using the fourth divider
107 is outputted as a transmission second local signal and inputted
to the frequency converter 7.
[0120] [GSM Reception Mode]
[0121] Subsequently, in case of performing reception in the GSM
mode, the output signal frequency of the HF synthesizer 101 is
determined as a value within a frequency range of 2040 MHz to 2110
MHz in accordance with the transmission frequency, the output
signal frequency of the LF synthesizer 102 is determined as 760
MHz, and the mixer 104 is enabled. The output signal from the LF
synthesizer 102 is divided by two to be 190 MHz by the first
divider 103 and then inputted to the mixer 104.
[0122] In the mixer 104, the output signal from the HF synthesizer
101 and the output signal from the first divider 103 are multiplied
together, and a difference frequency component of the both signals
is extracted. As a result, an output signal having a frequency in a
frequency range of 1850 MHz to 2300 MHz is obtained in accordance
with the transmission frequency. When the output signal having a
frequency of 1850 MHz to 2300 MHz from the second mixer 15 is
divided by in the second divider 105, a signal having a frequency
of 925 MHz to 1785 MHz is outputted from the frequency synthesizer
100A as the local signal and then inputted to the quadrature
demodulator 2 through the .pi./2 phase shifter 4.
[0123] In the GSM mode, since communication is effected in the TDMA
system, transmission and reception are not simultaneously carried
out. Transmission and reception are changed over by switching the
output signal frequency of the HF synthesizer 101 in accordance
with the timing of transmission/reception.
[0124] [DCS Transmission Mode]
[0125] Then, in case of carrying out transmission in the DCS mode,
the output signal frequency of the HF synthesizer 101 is determined
as a value in a frequency range of 2090 MHz to 2165 MHz in
accordance with the transmission frequency, the output signal
frequency of the LF synthesizer 102 is determined as 760 MHz, the
division ratio of the third divider 106 is determined as "2", and
the fourth divider 107 is disabled (allowing the output signal from
the HF synthesizer 101 to pass without being divided). In this
case, the frequency synthesizer 100A outputs a signal having a
frequency of 380 MHz obtained by dividing 760 MHz by two in the
third divider 106 as a transmission first local signal, and this
signal is inputted to the quadrature modulator 3.
[0126] Moreover, the output signal having a frequency of 2090 MHz
to 2165 MHz from the HF synthesizer 101 is output as a transmission
second local signal without being divided by the fourth divider 107
and inputted to the frequency converter 7.
[0127] [DCS Reception Mode]
[0128] Subsequently, in case of performing reception in the DCS
mode, the output signal frequency of the HF synthesizer 101 is
determined as a value in a frequency range of 1995 MHz to 2070 MHz
in accordance with the reception frequency, the output signal
frequency of the LF synthesizer 102 is determined as 760 MHz, the
third divider 103 is enabled, the mixer 104 is enabled, and the
second divider 105 is disabled (allowing the output signal from the
mixer 104 to pass without being divided). The output signal from
the LF synthesizer 102 is divided by four to be 190 MHz in the
second divider 103 and then inputted to the mixer 104.
[0129] In the mixer 104, by multiplying the output signal from the
HF synthesizer 101 and the output signal from the first divider 103
together, an output signal having a frequency in a frequency range
of 1805 MHz to 1880 MHz is obtained in accordance with the
reception/transmission frequency. The output signal having a
frequency of 1805 MHz to 1880 MHz from the mixer 105 is outputted
from the frequency synthesizer 100A as a local signal without being
divided by the second divider 105, and inputted to the quadrature
demodulator 2 through the .pi./2 phase shifter 4.
[0130] In the DCS mode, since communication is carried out in the
TDMA system as similar to the GSM mode, transmission and reception
are not simultaneously performed. Transmission and reception is
changed over by switching the frequency of the HF synthesizer 10 in
accordance with the timing of transmission/reception.
[0131] [PCS Transmission Mode]
[0132] Then, in case of effecting transmission in PCS, the output
signal frequency of the HF synthesizer 101 is determined as a value
within a frequency range of 2040 MHz to 2100 MHz in accordance with
the transmission frequency, the output signal frequency of the LF
synthesizer 102 is determined as 760 MHz, the division ratio of the
third divider 106 is determined as "4", and the fourth divider 107
is disabled (allowing the output signal from the HF synthesizer 101
to pass without being divided). In this case, the frequency
synthesizer 100A outputs a signal having a frequency of 190 MHz
obtained by dividing 760 MHz by four in the third divider 106 as a
transmission first local signal, and this signal is inputted to the
quadrature modulator 3.
[0133] Furthermore, the output signal having a frequency of 2040
MHz to 2100 MHz from the HF synthesizer 101 is outputted as a
transmission second local signal without being divided by the
fourth divider 107, and inputted to the frequency converter 7.
[0134] [PCS Reception Mode]
[0135] Then, in case of carrying out reception in PCS, the output
signal frequency of the HF synthesizer 101 is determined as a value
within a frequency range of 2120 MHz to 2180 MHz in accordance with
the transmission frequency, the output signal frequency of the LF
synthesizer 102 is determined as 760 MHz, the mixer 104 is enabled,
the second divider 105 is enabled, and the fourth divider 107 is
disabled (allowing the output signal of the HF synthesizer 101 to
pass without being divided). The output signal from the LF
synthesizer 102 is divided by four to be 190 MHz in the first
divider 103 and then inputted to the mixer 104.
[0136] In the mixer 104, by multiplying the output signal from the
HF synthesizer 101 and the output signal of the first divider 103
together, there is obtained an output signal having a frequency
within a frequency range of 1930 MHz to 2100 MHz in accordance with
the transmission frequency. The output signal having a frequency of
1930 MHz to 2100 MHz from the second mixer 104 is outputted from
the frequency synthesizer 100A as a local signal without being
divided by the second divider 105, and inputted to the quadrature
demodulator 2 through the .pi./2 phase shifter 4.
[0137] In the PCS mode, since communication is carried out in the
TDMA system as similar to the GSM mode, transmission and reception
are not simultaneously performed. Transmission and reception are
changed over by switching the output signal frequency of the HF
synthesizer 101 in accordance with the timing of
transmission/reception.
[0138] [UMTS Transmission Mode]
[0139] Subsequently, in case of effecting transmission in the UMTS
mode, the output signal frequency of the HF synthesizer 101 is
determined as a value within a frequency range of 2110 MHz to 2170
MHz in accordance with the transmission frequency, the output
signal frequency of the LF synthesizer 102 is determined as 760
MHz, the division ratio of the third divider 106 is determined as
"4", and the fourth divider 107 is disabled (allowing the output
signal from the HF synthesizer 101 to pass without being divided).
In this case, the frequency synthesizer 100A outputs a signal
having a frequency of 190 MHz obtained by dividing 760 MHz by four
in the third divider 106 as a transmission first local signal, and
this signal is inputted to the quadrature modulator 3.
[0140] Moreover, the output signal having a frequency of 2110 MHz
to 2170 MHz from the HF synthesizer 101 is outputted as a
transmission second local signal without being divided by the
fourth divider 107, and inputted to the frequency converter 7.
[0141] [UMTS Reception Mode]
[0142] Then, in case of performing reception in the UMTS mode, the
output signal frequency of the HF synthesizer 101 is determined as
2110 MHz to 2170 MHz similarly as in transmission, the mixer 104 is
disabled (allowing the output signal from the mixer 104 to pass
without modification), and the second divider 105 is disabled
(allowing the output signal of the mixer 104 to pass without being
divided). The output signal of the LF synthesizer 102 is divided by
four to be 190 MHz in the first divider 103, and then passes
through the mixer 104 without modification. In addition, this
signal is outputted from the frequency synthesizer 100A as a local
signal without being divided by the second divider 105, and
inputted to the quadrature demodulator 2 through the .pi./2 phase
shifter 4.
[0143] In case of the UMTS mode, since communication is carried out
in the CDMA/FDD system, transmission and reception are
simultaneously effected. According to the structure of this
embodiment, the transmission first and second local signals and the
local signal for receiver which have frequencies required for
transmission/reception can be simultaneously outputted at this
moment.
[0144] As described above, in the frequency synthesizer 100A in
this embodiment, with the structure that only the HF synthesizer
101 and the LF synthesizer 102 are prepared as the unit
synthesizers and the dividers 103, 105, 106 and 107 and the mixer
104 are combined with these synthesizers, it is also possible to
generate all frequencies required for transmission/reception in
each mode of GMS/DCS/PCS/UMTS. Therefore, great reduction in a
number of the unit synthesizers having a large circuit scale can
considerably decrease the hardware scale.
[0145] In addition, since the transmission first local signal
having 0.degree. and 90.degree. obtained by necessarily dividing
the output signal from the LF synthesizer 102 by four or two in the
third divider 106 is supplied to the quadrature modulator 3 in the
transmission system, the divider 106 can also serve as the .pi./2
phase shifter.
Eighth Embodiment
[0146] FIG. 10 shows a structure of a frequency synthesizer
according to an eighth embodiment of the present invention. In the
eighth embodiment, although a filter on the subsequent stage of the
mixer 104 can be eliminated by using such an image suppression type
filter as shown in FIG. 2, it is needless to say that insertion of
the filter to the subsequent stage of the mixer 104 or the
subsequent stage of the first divider 103 may be preferable
depending on unnecessary spurious specifications of the output
signal of the frequency synthesizer.
[0147] In the frequency synthesizer 100B of this embodiment,
band-pass filters 108 and 109 are inserted to the subsequent stage
of the first divider 103 and the subsequent stage of the mixer 104,
respectively. These filters 108 and 109 may be configured by
combining discrete components such as a coil (L), a capacitor (C)
or a resistor (R), or filter components formed into modules such as
an LC laminated filter, a dielectric filter or an SAW (surface
acoustic wave) filter may be used for these filters. Additionally,
the present invention can be realized with a simpler structure by
configuring the band-pass filters 31 and 32 by low-pass filters or
high-pass filters depending on frequency concerns.
Ninth Embodiment
[0148] FIG. 11 shows a structure of a frequency synthesizer
according to a ninth embodiment of the present invention. In the
frequency synthesizer 100C of this embodiment, a second LF
synthesizer 120 is added. In the frequency synthesizer 100A
according to the seventh embodiment depicted in FIG. 9, a signal
having a frequency of 190 MHz is generated by dividing an output
signal having a frequency of 760 MHz from the LF synthesizer 102 by
the first divider 103. On the other hand, in this embodiment, the
newly provided second LF synthesizer 120 is used to generate a
signal having a frequency of 190 MHz.
[0149] Although an output signal from the divider 103 shown in FIG.
9 has rectangular waves, an output signal from the second LF
synthesizer 120, i.e., a signal inputted to the mixer 104 can have
sinusoidal waves according to this embodiment. As compared with the
case where the output signal of the divider 103 is inputted to the
mixer 104 as shown in FIG. 9, it is possible to reduce the
necessity of adding the band restriction by the filter 108 such as
shown in FIG. 10.
Tenth Embodiment
[0150] FIG. 12 shows a structure of a multi-band radio apparatus
including a frequency synthesizer according to a tenth embodiment
of the present invention. Giving description as to a difference of
this embodiment from the seventh to ninth embodiments, in the
frequency synthesizer 100D of this embodiment, an HF synthesizer
111 for generating a signal having a frequency which is twice as
high as that of the HF synthesizer 101 is used; the first divider
for dividing an output signal from the LF synthesizer 102 is
changed from the divider 103 having the division ratio "4" to the
divider 113 having the division ratio "2"; the second divider for
dividing an output signal from the mixer 104 is changed to the
divider 115 capable of switching the division ratio between "2" and
"4"; and the fourth divider for dividing an output signal from the
HF synthesizer 111 is changed to the divider 117 capable of
switching the division ratio between "2" and "8".
[0151] In the frequency synthesizer 101A having the structure shown
in FIG. 9, since a signal to be outputted to the reception side is
not necessarily divided by two, the .pi./2 phase shifter 4 is
required on the local signal input side of the quadrature
demodulator 2. However, since the divider for dividing a frequency
by two is also necessarily provided in the reception system in the
structure of the frequency synthesizer 100 according to this
embodiment, this divider can also function as the .pi./2 phase
shifter.
Eleventh Embodiment
[0152] FIG. 13 shows a structure of a multi-band radio apparatus
including a frequency synthesizer according to an eleventh
embodiment of the present invention. In the structure using the
direct conversion mode in the reception system and the super
heterodyne mode in the transmission system as similar to the
seventh to tenth embodiments, this embodiment corresponds to a case
of using the harmonic mixers in the quadrature demodulator 2 in the
reception system similarly as described in the fourth embodiment.
In this case, the frequency synthesizer 100E can be realized by a
fewer constituent elements.
[0153] The frequency synthesizer 100E in this embodiment is
different from the frequency synthesizer 100A shown in FIG. 9 of
the seventh embodiment in that the second divider 105 is
substituted by the divider 115 capable of switching the division
ratio between "2" and "4". Further, in case of utilizing the
harmonic mixers, since a phase difference of the local signals
supplied to the two mixers in the quadrature demodulator 2 must be
set to 45.degree., the .pi./2 phase shifter 4 shown in FIG. 9 is
substituted by the .pi./4 phase shifter 6.
[0154] As to the operation of this frequency synthesizer 100E, in
description of the operation of the seventh embodiment, the divider
115 in FIG. 13 is operated with the division ratio "4" when the
divider 105 is activated, and the divider 115 is operated with the
division ratio "2" when the divider 105 is disabled (allowing the
output signal from the mixer 104 to pass without being divided). As
a result, it is possible to obtain from the divider 115 the local
signal having a frequency which is 1/2 of the reception frequency
required in the quadrature demodulator 2 having the harmonic mixer
structure.
Twelfth Embodiment
[0155] FIG. 14 shows a structure of a multi-band radio apparatus
including a frequency synthesizer according to a twelfth embodiment
of the present invention. Although all of the frequency
synthesizers 101A to 100E described in the seventh to eleventh
embodiments are configured to adopt the super heterodyne mode in
the transmission system, the frequency synthesizer 100F of this
embodiment corresponds to an example in which the super heterodyne
mode is adopted in the transmission system for each mode of
GSM/DCS/PCS and the direct conversion mode is adopted for only the
UMTS mode.
[0156] The structure of the frequency synthesizer 100F of this
embodiment is similar to that of the frequency synthesizer 100A
shown in FIG. 9 but very different in that switches 121 and 122 and
a second mixer 123 are added. Further, the output signal frequency
of the LF synthesizer 102 is changed from 760 MHz to 380 MHz, and
hence the first divider is changed to the divider 115 having the
division ratio "2" and the third divider is changed to the divider
116 having the division ratio "2", respectively.
[0157] The added second mixer 123 multiplies an output signal from
the HF synthesizer 101 by a signal transmitted through the fourth
divider 107, and multiplies an output signal from the LF
synthesizer 102 by a signal subjected to division by two in the
third divider 116. The switches 121 and 122 are provided for
switching an output signal from the divider 116 and an output
signal from the second mixer 123 and outputting a resulting signal
as a transmission first local signal.
[0158] In this frequency synthesizer 100F, although the same
operation as that of the frequency synthesizer 100A shown in FIG. 9
is carried out in the three modes of GSM/DCS/PCS, the local signal
matched with the transmission frequency required for the direct
conversion mode can be obtained by the added second mixer 123 in
the UMTS mode. That is, the switches 121 and 123 are changed over
so as not to energize the mixer 123 in case of the GSM/DCS/PCS
modes, and they are changed over so as to energize the mixer 123 in
the UMTS mode.
[0159] Giving further concrete description as to the operation in
case of performing transmission in the UMTS mode, the output signal
frequency of the HF synthesizer 101 is determined as a value within
a frequency range of 2110 MHz to 2170 MHz in accordance with the
transmission frequency, the output signal frequency of the LF
synthesizer 102 is determined as 380 MHz, and the fourth divider
107 is disabled (allowing the output signal from the HF synthesizer
101 to pass without being divided).
[0160] In this case, the frequency synthesizer 100F outputs the
local signal having the same frequency as the transmission
frequency of 1920 MHz to 1990 MHz (see Table 1) obtained by
multiplying in the second mixer 123 a signal having a frequency of
190 MHz obtained by dividing 380 MHz by two in the third divider
116 and a signal having a frequency of 2110 MHz to 2170 MHz from
the HF synthesizer 101 which has passed through the fourth divider
107. This output signal is inputted to the quadrature modulator 3.
At this moment, the frequency converter 7 is controlled to be
disabled (allowing the output signal from the quadrature modulator
3 to pass without modification).
[0161] Although the above has described the case the present
invention is applied to the multi-band radio apparatus conform to
the four modes of GSM/DCS/PCS/UMTS in the foregoing embodiments,
the present invention can be also applied to the multi-band radio
apparatus conform to arbitrary two modes or three modes of these
four modes. Furthermore, the present invention includes a
multi-band radio apparatus conform to five communication modes that
another communication mode is added to these four modes, or any
other apparatus as long as it has a structure for generating
signals (local signals) in a plurality of (three or more) frequency
bands exceeding a number of unit synthesizers by combining at least
two unit synthesizers including the HF synthesizer and the LF
synthesizer with the arithmetic circuit comprising of the dividers
and the mixers.
[0162] As described above, according to the frequency synthesizer
of the present invention, it is possible to generate signals in a
plurality of frequency bands exceeding a number of unit
synthesizers with a small circuit scale structure comprising two
unit synthesizers for basically producing reference frequency
signals in a high-frequency band and a low-frequency band.
[0163] Furthermore, this frequency synthesizer can be used to
realize a multi-band radio apparatus which can be utilized in two
or more frequency bands with a small hardware scale.
[0164] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
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