U.S. patent application number 14/929353 was filed with the patent office on 2016-02-25 for semiconductor device, radio communication terminal, and method for controlling semiconductor device.
This patent application is currently assigned to Renesas Electronics Corporation. The applicant listed for this patent is Renesas Electronics Corporation. Invention is credited to Ryo Endo.
Application Number | 20160056952 14/929353 |
Document ID | / |
Family ID | 50881433 |
Filed Date | 2016-02-25 |
United States Patent
Application |
20160056952 |
Kind Code |
A1 |
Endo; Ryo |
February 25, 2016 |
SEMICONDUCTOR DEVICE, RADIO COMMUNICATION TERMINAL, AND METHOD FOR
CONTROLLING SEMICONDUCTOR DEVICE
Abstract
A semiconductor device according to the present invention
includes a PLL circuit, in which the PLL circuit includes: a phase
difference detection unit that detects a phase difference between a
reference signal and a division signal; a filter that outputs a
control signal according to a detection result of the phase
difference detection unit; an oscillation unit that outputs an
oscillation signal of a frequency according to the control signal;
a division unit that divides the oscillation signal to output it as
the division signal; a noise intensity detection unit that detects
a noise intensity of a predetermined frequency component included
in the control signal; and a phase difference adjustment unit that
adjusts a phase difference between the reference signal and the
division signal based on the noise intensity detected by the noise
intensity detection unit.
Inventors: |
Endo; Ryo; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Renesas Electronics Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Renesas Electronics
Corporation
|
Family ID: |
50881433 |
Appl. No.: |
14/929353 |
Filed: |
November 1, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14083629 |
Nov 19, 2013 |
9197276 |
|
|
14929353 |
|
|
|
|
Current U.S.
Class: |
375/376 |
Current CPC
Class: |
H03L 7/099 20130101;
H03L 2207/50 20130101; H04B 1/40 20130101; H04B 1/1036 20130101;
H03L 7/085 20130101; H03L 7/193 20130101; H04L 7/033 20130101; H03L
7/093 20130101 |
International
Class: |
H04L 7/033 20060101
H04L007/033; H04B 1/10 20060101 H04B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2012 |
JP |
2012-266839 |
Claims
1-12. (canceled)
13. A radio communication terminal comprising: an antenna that
wirelessly transmits/receives a high-frequency signal; a PLL
circuit that generates an oscillation signal; a mixer that
demodulates the high-frequency signal to a baseband signal by using
the oscillation signal, or modulates a baseband signal to the
high-frequency signal by using the oscillation signal; and a
baseband signal processing unit that performs a predetermined
process based on the baseband signal demodulated by the mixer, or
generates the baseband signal to be modulated by the mixer
according to a result of the predetermined process, wherein the PLL
circuit includes: (a) a phase difference detection unit that
detects a phase difference between a reference signal and a
division signal; (b) a filter that outputs a control signal
according to a detection result of the phase difference detection
unit; (c) an oscillation unit that outputs the oscillation signal
of a frequency according to the control signal; (d) a division unit
that divides the oscillation signal to output it as the division
signal; (e) a noise intensity detection unit that detects a noise
intensity of a predetermined frequency component included in the
control signal; and (f) a phase difference adjustment unit that
adjusts a phase difference between the reference signal and the
division signal based on the noise intensity detected by the noise
intensity detection unit.
14. The radio communication terminal according to claim 13, wherein
the noise intensity detection unit detects the noise intensity by
performing Fourier transform of the predetermined frequency
component included in the control signal.
15. The radio communication terminal according to claim 13, wherein
the phase difference adjustment unit adjusts the phase difference
between the reference signal and the division signal using a span
of adjustable range corresponding to the noise intensity indicating
a minimum value among the plurality of noise intensities detected
in a case where the phase difference has been adjusted using a
plurality of different spans of adjustable range, respectively.
16. The radio communication terminal according to claim 13, wherein
the phase difference adjustment unit adjusts the phase difference
between the reference signal and the division signal so that the
noise intensity detected by the noise intensity detection unit
after phase difference adjustment indicates the minimum value.
17. The radio communication terminal according to claim 13, wherein
the filter is a digital low-pass filter that outputs a digital code
according to the detection result of the phase difference detection
unit as the control signal, and the oscillation unit is a digital
control oscillator that outputs the oscillation signal of a
frequency according to the digital code as the control signal.
18. The radio communication terminal according to claim 13, wherein
the PLL circuit further comprises an AD converter, the filter is a
low-pass filter that outputs the control signal of a voltage value
according to the detection result of the phase difference detection
unit, the oscillation unit is a voltage control oscillator that
outputs the oscillation signal of a frequency according to the
voltage value of the control signal, the AD converter converts the
voltage value of the control signal into a digital signal, and the
noise intensity detection unit detects a noise intensity of a
predetermined frequency component included in the digital signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2012-266839, filed on
Dec. 6, 2012, the disclosure of which is incorporated herein in its
entirety by reference.
BACKGROUND
[0002] The present invention relates to a semiconductor device such
as a high-frequency signal processing device including a PLL
circuit etc., a radio communication terminal, and a method for
controlling the semiconductor device.
[0003] A high-frequency signal processing device used for a radio
communication terminal etc. is provided with a PLL (Phase-Locked
Loop) circuit such as a digital-type PLL circuit. For example,
Japanese Unexamined Patent Application Publication No. 2011-155601
discloses a configuration of a digital-type PLL circuit.
SUMMARY
[0004] The inventor of the present application has found various
problems in developing a high-frequency signal processing device
used for a radio communication terminal etc. Each embodiment
disclosed in the present application, for example, provides a
semiconductor device suitable for the radio communication terminal.
More detailed features will be apparent from the description of the
specification and accompanying drawings.
[0005] One aspect disclosed in the specification includes a PLL
circuit, and the PLL circuit is provided with: a noise intensity
detection unit that detects a noise intensity of a predetermined
frequency component; and a phase difference adjustment unit that
adjusts a phase difference between a reference signal and a
division signal based on the noise intensity detected by the
above-described noise intensity detection unit.
[0006] According to the above-described one embodiment, a good
quality semiconductor device, a good quality radio communication
terminal, and a method for controlling the semiconductor device can
be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The above and other aspects, advantages and features will be
more apparent from the following description of certain embodiments
taken in conjunction with the accompanying drawings, in which:
[0008] FIG. 1A is an external view showing one example of a radio
communication terminal pertaining to a first embodiment;
[0009] FIG. 1B is an external view showing one example of a radio
communication terminal pertaining to a first embodiment;
[0010] FIG. 2 is a block diagram showing an internal structure of
the radio communication terminal pertaining to the first
embodiment;
[0011] FIG. 3 is a block diagram showing a specific configuration
example of an RF subsystem provided in the radio communication
terminal pertaining to the first embodiment;
[0012] FIG. 4 is a diagram showing a configuration example of a
digital-type PLL circuit pertaining to the first embodiment;
[0013] FIG. 5 is a flowchart showing operation of the digital-type
PLL circuit pertaining to the first embodiment;
[0014] FIG. 6 is a table for explaining the operation of the
digital-type PLL circuit pertaining to the first embodiment;
[0015] FIG. 7 is a graph showing a relation between a degree of
phase difference adjustment made by a phase difference adjustment
unit CTL1 and a detection result (noise intensity) obtained by a
noise intensity detection unit FT1;
[0016] FIG. 8 is a diagram showing a configuration example of a PLL
circuit pertaining to a second embodiment;
[0017] FIG. 9 is a block diagram showing a configuration of a
digital-type PLL circuit that the present inventor has
examined;
[0018] FIG. 10 is a graph showing a relation between an oscillation
frequency and a phase error of the digital-type PLL circuit that
the present inventor has examined;
[0019] FIG. 11 is a graph showing a relation between an offset
frequency and a phase noise of the digital-type PLL circuit that
the present inventor has examined;
[0020] FIG. 12 is a graph showing a relation between an offset
frequency and a phase noise of the digital-type PLL circuit that
the present inventor has examined; and
[0021] FIG. 13 is a graph showing a relation between a frequency
and an electric power (a noise) of the digital-type PLL circuit
that the present inventor has examined.
DETAILED DESCRIPTION
<Previous Examination By Inventor>
[0022] Before the embodiments of the present invention are
explained, the contents of the previous examination that the
present inventor conducted will be explained.
[0023] A high-frequency signal processing device used for a radio
communication terminal etc. is provided with a PLL circuit such. as
a digital-type PLL circuit as described above.
[0024] FIG. 9 is a block diagram showing a configuration of a
digital-type PLL circuit that the present inventor has examined.
The digital-type PLL circuit shown in FIG. 9 is provided with: a
digital phase difference detector DPFD; a digital low-pass filter
DLPF; a digital control oscillator DCO; an amplifier AMP; a divider
DIV1; and a multi-modulus divider (division unit) MMD.
[0025] The digital phase difference detector DPFD detects a phase
difference between a reference oscillation signal Fref and a
division oscillation signal Fdiv. The digital low-pass filter DLPF
outputs a digital code (control signal) according to a detection
result of the digital phase difference detector DPFD. The digital
control oscillator DCO outputs an oscillation signal Fosc1 of a
frequency according to the digital code output from the digital
low-pass filter DLPF. The oscillation signal Fosc1 is amplified by
the amplifier AMP. The divider DIV1 divides (for example,
half-divides) the oscillation signal Fosc1 amplified by the
amplifier AMP, and outputs it as an oscillation signal Fosc2. The
multi-modulus divider MMD divides the oscillation signal Fosc2 with
a division ratio not more than a decimal point, and outputs it as
the division oscillation signal Fdiv.
[0026] Here, a spurious noise is generated in a spurious frequency
Fspur expressed by the following Expression (1) by means of
coupling between an oscillator-related signal (for example, the
oscillation signal Fosc1 or Fosc2) and a reference signal (for
example, the reference oscillation signal Fref). It is conceived
that the coupling is, for example, caused by the oscillator-related
signal propagating to a reference signal side through a signal line
of a power source voltage VDD or a ground voltage VSS.
Fspur=|N.times.Fosc-M.times.Fref| (1)
[0027] It is to be noted that Fspur indicates the spurious
frequency (a spurious offset frequency), Fosc indicates a frequency
of the oscillator-related signal (for example, the oscillation
signal Fosc1 or Fosc2), Fref indicates a frequency of the reference
oscillation signal Fref, and that both M and N indicate arbitrary
integers.
[0028] Here, the smaller Fspur, M, and N are, the stronger the
coupling becomes, and the larger the spurious noise becomes. Since
the spurious noise generated in a band of the digital-type PLL
circuit in a specific channel among such spurious noises is not
attenuated by the digital low-pass filter DLPF, it deteriorates a
phase error characteristic in the specific channel. That is, the
digital-type PLL circuit of FIG. 9 had a problem of deteriorating
the phase error characteristic in the specific channel due to an
effect of the spurious noise generated in the PLL band in the
specific channel.
[0029] FIG. 10 is a graph showing one example of a relation between
an oscillation frequency and a phase error of the digital-type PLL
circuit that the present inventor has examined. As shown in FIG.
10, the phase error characteristic has deteriorated by not less
than 1 [degrms] in a specific channel.
[0030] FIG. 11 shows a case where a spurious frequency is higher
than a cutoff frequency Fc of the digital low-pass filter DLPF. In
this case, the digital low-pass filter DLPF needs to sufficiently
reduce the cutoff frequency Fc (for example, reduce it to not more
than 10 kHz), and to remove (attenuate) a spurious noise generated
in the spurious frequency Fspur. However, it is not preferable to
reduce the cutoff frequency Fc since a settling time (a time until
the oscillation signal Fosc1 stabilizes) is lengthened due to a
narrower band.
[0031] FIG. 12 shows a case where the spurious frequency is lower
than the cutoff frequency Fc of the digital low-pass filter
DLPF.
[0032] In this case, it is conceived to make the cutoff frequency
Fc lower in order to remove the spurious frequency. However, in the
high-frequency signal processing device, since a transmission
signal needs to be output by a high electric power, the cutoff
frequency cannot be made lower. In other words, since it is
necessary to make the digital-type PLL circuit hold a wide band
(for example, 80 kHz), the spurious noise generated in the spurious
frequency Fspur cannot be removed.
[0033] As shown in examples of FIGS. 11 and 12, the spurious noise
generated in the specific channel may not be removed by the digital
low-pass filter DLPF. In such case, it is required that
deterioration of the phase error characteristic in the specific
channel be suppressed by suppressing the spurious noise by means of
a method other than the method using the digital low-pass filter
DLPF.
[0034] Furthermore, in an example shown in FIG. 9, there is a
plurality of (two in the example) paths of coupling between the
oscillator-related signal (for example, the oscillation signal
Fosc1 or Fosc2) and the reference signal (for example, the
reference oscillation signal Vref). Along with this plurality,
there is also a plurality of spurious frequencies calculated by
Expression (1).
[0035] FIG. 13 is a graph showing a relation between a frequency
and an electric power (a noise) of the digital-type PLL circuit
that the present inventor has examined. As shown in FIG. 13, a
harmonic M times as high as the reference oscillation signal Fref
is coupled with a fundamental wave of the oscillator-related signal
(Fosc1 here) Fosc, and thereby a large spurious noise is
generated.
[0036] When there is a plurality of spurious types, a large
spurious noise can be generated in each of these pluralities of
spurious types. In such a case, it is required that the spurious
noise against which measures need to be taken be previously
specified, the specified spurious noise be suppressed, and that
thereby deterioration of the phase error characteristic in the
specific channel be suppressed.
[0037] Hereinafter, embodiments will be explained with reference to
drawings. It is to be noted that since the drawings are simple, the
technical scope of the embodiments must not be interpreted narrowly
on the ground of the description of the drawings. In addition,
components which are the same as each other are indicated by the
same symbol, and an overlapping explanation is omitted.
[0038] Although the following embodiments will be explained,
divided into a plurality of sections or embodiments if necessary
for convenience, except for a case shown particularly clearly,
these embodiments are not mutually unrelated, and one embodiment
has relationships, such as being a modified example, an application
example, detailed explanation, supplementary explanation, or the
like with some or all of the other embodiments. In addition, in the
following embodiments, when referring to the number of components
etc. (including the number, a numeric value, an amount, a range,
etc.), they may not be limited to the specific number but may not
be less than or more than the specific number except for a case
where they are particularly clearly expressed and where they are
theoretically clearly limited to a specific number.
[0039] Furthermore, in the following embodiments, an element
(including an operation step etc.) is not necessarily
indispensable, except for a case where it is particularly clearly
expressed and where it is considered to be theoretically clearly
indispensable, etc. Similarly, in the following embodiments, when a
shape, a positional relationship, etc. of a component etc. are
referred to, what substantially resembles or is similar to the
shape shall be included, except for the case where it is
particularly clearly expressed and where it is considered to be
theoretically clearly not right to include it. This statement also
applies to the above-mentioned number of components etc. (including
the number, a numeric value, an amount, a range, etc.).
First Embodiment
[0040] First, with reference to FIGS. 1A and 1B, a description will
be given of a radio communication terminal suitable as an
electronic device to which a semiconductor device pertaining to the
embodiment is applied. FIGS. 1A and 1B are external views showing a
configuration example of a radio communication terminal 500. It is
to be noted that FIGS. 1A and 1B show a case where the radio
communication terminal 500 is a smartphone. However, the radio
communication terminal 500 may be another radio communication
terminal, such as a feature phone (for example, a folding mobile
phone terminal), a mobile game terminal, a tablet PC (Personal
Computer), and a notebook PC. In addition, it should be noted that
the semiconductor device pertaining to the embodiment can also be
applied to an electronic device other than the radio communication
terminal.
[0041] FIG. 1A shows one main surface (front surface) of a housing
501 that forms the radio communication terminal 500. At the front
surface of the housing 501, a display device 502, a touch panel
503, some manipulation buttons 504, and a camera device 505 are
arranged. FIG. 1B shows the other main surface (back surface) of
the housing 501. A camera device 506 is arranged at the back
surface of the housing 501.
[0042] The display device 502 is an LCD (Liquid Crystal Display),
an OLED (Organic Light-Emitting Diode) display, or the like, and it
is arranged so that a display surface thereof is located at the
front surface of the housing 501. The touch panel 503 is arranged
as to cover the display surface of the display device 502, or is
arranged on a back surface side of the display device 502, and
detects a position of the display surface contacted by a user. That
is, the user can intuitively manipulate the radio communication
terminal 500 by touching the display surface of the display device
502 with a finger, a dedicated pen (generally called a stylus), or
the like. In addition, the manipulation button 504 is used for
auxiliary manipulation of the radio communication terminal 500. It
is to be noted that such manipulation buttons may not be provided
depending on the radio communication terminal.
[0043] The camera device 506 is a main camera arranged so that a
lens unit thereof is located at the back surface of the housing
501. Meanwhile, the camera device 505 is a sub-camera arranged so
that a lens unit thereof is located at the front surface of the
housing 501. It is to be noted that such sub-camera may not be
provided depending on the radio communication terminal.
<Internal Configuration of Radio Communication Terminal
500>
[0044] Next, an internal configuration of the radio communication
terminal 500 pertaining to the embodiment will be explained with
reference to FIG. 2. FIG. 2 is a block diagram showing one example
of the internal configuration of the radio communication terminal
500 pertaining to the embodiment. As shown in FIG. 2, the radio
communication terminal 500 includes: an application processor 601;
a baseband processor 602; an RF (Radio Frequency) subsystem 603; a
memory 604; a battery 605; a PMIC (Power Management Integrated
Circuit) 606; a display unit 607; a camera unit 608; a manipulation
input unit 609; an audio IC 610; a microphone 611; and a speaker
612.
[0045] The application processor 601 reads a program stored in the
memory 604, and performs processing for achieving various functions
of the radio communication terminal 500. For example, the
application processor 601 executes an OS (Operating System) program
from the memory 604, and executes an application program that uses
the OS program as an operational base.
[0046] The baseband processor 602 performs baseband processing
including encoding (for example, error correction encoding of a
convolutional code, a turbo code, etc.) processing or decoding
processing with respect to data that the radio communication
terminal 500 transmits and receives. More specifically, the
baseband processor 602 receives transmission data from the
application processor 601, applies encoding processing to the
received transmission data, and transmits it to the RF subsystem
603. In addition, the baseband processor 602 receives reception
data from the RF subsystem 603, applies decoding processing to the
received reception data, and transmits it to the application
processor 601.
[0047] The RF subsystem 603 performs modulation processing or
demodulation processing on data that the radio communication
terminal 500 transmits and receives. More specifically, the RF
subsystem 603 performs modulation processing of the transmission
data received from the baseband processor 602 by a carrier to
generate a transmission signal, and outputs the transmission signal
through an antenna. In addition, the RF subsystem 603 receives a
reception signal through the antenna, performs demodulation
processing of the reception signal by the carrier to generate
reception data, and transmits the reception data to the baseband
processor 602.
[0048] In the memory 604, a program and data that are utilized by
the application processor 601 are stored. In addition, the memory
604 includes a nonvolatile memory that holds stored data even
though a power source is interrupted, and a volatile memory in
which the stored data is cleared when the power source is
interrupted.
[0049] The battery 605 is an electric cell, and is utilized when
the radio communication terminal 500 operates without using an
external power source. It is to be noted that the radio
communication terminal 500 may utilize a power source of the
battery 605 also when the external power source is connected
thereto. In addition, it is preferable to utilize a secondary
battery as the battery 605.
[0050] The PMIC 606 generates an internal power source from the
battery 605 or the external power source. The internal power source
is given to each block of the radio communication terminal 500. At
this time, the PMIC 606 controls a voltage of the internal power
source for every block that receives a supply from the internal
power source. The PMIC 606 performs voltage control of the internal
power source based on an instruction from the application processor
601. Furthermore, the PMIC 606 can also control supply and
interruption of the internal power source for every block. In
addition, when the external power source is supplied, the PMIC 606
also performs charge control to the battery 605.
[0051] The display unit 607 is, for example, a liquid crystal
display device, and displays various images in accordance with
processing in the application processor 601. On the display unit
607, a user interface image in which the user gives an operation
instruction to the radio communication terminal 500, a camera
image, a moving image, or the like is displayed.
[0052] The camera unit 608 acquires an image in accordance with an
instruction from the application processor. The manipulation input
unit 609 is a user interface that the user manipulates to give a
manipulation instruction to the radio communication terminal 500.
The audio IC 610 decodes voice data transmitted from the
application processor 601 to drive the speaker 612, also encodes
voice information obtained from the microphone 611 to generate
voice data, and outputs the voice data to the application processor
601.
<Specific Configuration Example of RF Subsystem 603>
[0053] FIG. 3 is a block diagram showing a specific configuration
example of the RF subsystem 603. The RF subsystem 603 shown in FIG.
3 is provided with: a high-frequency signal processing device RFIC;
power amplifier circuits (electric power amplifier circuits) HPA1
and HPA2; a duplexer DPX; an antenna switch ANTSW; and an antenna
ANT. It is to be noted that the baseband processor 602 is also
shown in FIG. 3.
[0054] Although not particularly limited, the baseband processor
602 and the high-frequency signal processing device RFIC are
realized by individual semiconductor chips formed in a CMOS
manufacturing process, respectively, and the power amplifier
circuits HPA1 and HPA2, the duplexer DPX, and the antenna switch
ANTSW are, for example, realized by appropriately mounting a
plurality of parts on one module wiring substrate (typically, a
ceramic substrate).
<<High-frequency Signal Processing Device RFIC>>
[0055] The high-frequency signal processing device RFIC is provided
with: a transmission circuit block TXBK; a reception circuit block
RXBK; and a control unit for both transmission and reception. In
the control unit, the following are included: a microcomputer unit
MCU; a transmitting bus control unit BSCTL_TX; a receiving bus
control unit BSCTL_RX; a reset control unit RSCTL; and a front-end
control unit FEMCTL. The microcomputer unit MCU includes a central
processing circuit (processor unit), a memory unit, etc., and
controls the whole high-frequency signal processing device RFIC
while appropriately communicating with the baseband processor
602.
[0056] The transmitting bus control unit BSCTL_TX is connected to
various circuits in the transmission circuit block TXBK through a
bus, and performs control of the transmission circuit block TXBK
based on a command from the microcomputer unit MCU. The receiving
bus control unit BSCTL_RX is connected to various circuits in the
reception circuit block RXBK through a bus, and performs control of
the reception circuit block RXBK based on a command from the
microcomputer unit MCU. When, for example, detecting power-on or
receiving a reset command directed to the high-frequency signal
processing device RFIC from outside, the reset control unit RSCTL
appropriately controls power supply, operation clock supply, etc.
to various circuits in the high-frequency signal processing device
RFIC. The front-end control unit FEMCTL is controlled by the
microcomputer unit MCU through the transmitting bus control unit
BSCTL_TX and the receiving bus control unit BSCTL_RX, and, for
example, performs control of activation/deactivation of the power
amplifier circuits HPA1 and HPA2, control of the antenna switch
ANTSW, etc.
[0057] The transmission circuit block TXBK is provided with: a
transmitting logic circuit LOG_TX; DA converters DAC1 to DAC3; a
transmitting digital-type PLL circuit DPLL_TX; transmitting mixer
circuits MIX_TX1 and MIX_TX2; a variable gain amplifier circuit
PGA1; and an automatic power control circuit APC. The DA converter
DAC1, the mixer circuit MIX_TX1, and the variable gain amplifier
circuit PGA1, for example, serve as processing circuits directed to
W-CDMA (Wideband Code Division Multiple Access) (or HSDPA (High
Speed Downlink Packet Access) that serves as an extended standard
of the W-CDMA) or LTE (Long Term Evolution). The DA converter DAC2
and the mixer circuit MIX_TX2, for example, serve as processing
circuits directed to GSM (registered trademark) (Global System for
Mobile Communications).
[0058] In W-CDMA (HSDPA) and LTE, for example, more than ten
frequency bands prescribed between a 700 MHz band to a 2.6 GHz band
are appropriately used. In W-CDMA (HSDPA), phase and amplitude
modulation schemes, such as QPSK (Quadrature Phase Shift Keying),
HPSK (Hybrid Phase Shift Keying), and 16 QAM (Quadrature Amplitude
Modulation) are used, and in LTE, phase and amplitude modulation
schemes, such as QPSK, 16 QAM, and 64 QAM are used. In GSM, for
example, a 850 MHz band (GSM850), a 900 MHz band (GSM900), a 1.8
GHz band (DCS (Digital Cellular System) 1800), and a 1.9 GHz band
(PCS (Personal Communications Service) 1900) are used. The GSM850
and GSM900 are called low bands of GSM or the like, and the DCS1800
and PCS1900 are called high bands of GSM or the like. In GSM, for
example, phase (frequency) modulation schemes, such as GMSK
(Gaussian filtered Minimum Shift Keying) and 8 PSK are used.
[0059] The transmitting logic circuit LOG_TX receives a
transmission data signal (transmission baseband signal) from the
baseband processor 602 through a differential interface circuit
LVDS, and performs predetermined digital processing (for example,
10B8B encoding, generation processing of a modulating digital
baseband signal (phase information etc.), etc.). The DA converter
DAC1 converts the modulating digital baseband signal from the
transmitting logic circuit LOG_TX into an analog baseband signal
TXDAT, The digital-type PLL circuit DPLL_TX generates a local
signal (a local oscillation signal or a carrier signal) LO_TX
having a predetermined transmission carrier frequency. The mixer
circuit MIX_TX1 modulates and up-converts (performs frequency
conversion of) the analog baseband signal TXDAT from the DA
converter DAC1 using the local signal LO_TX from the digital-type
PLL circuit DPLL_TX. The variable gain amplifier circuit PGA1
amplifies an output signal of the mixer circuit MIX_TX1 by a
predetermined gain, and outputs it toward the power amplifier
circuit HPA1.
[0060] The DA converter DAC2 converts the modulating digital
baseband signal from the transmitting logic circuit LOG_TX into the
analog baseband signal TXDAT. The mixer circuit MIX_TX2 modulates
and up-converts the analog baseband signal TXDAT from the DA
converter DAC2 using the local signal LO_TX from the digital-type
PLL circuit DPLL_TX, and outputs it toward the power amplifier
circuit HPA2. The automatic power control circuit APC controls the
power amplifier circuits HPA1 and HPA2 through the DA converter
DAC3 so that output powers thereof become target values. It is to
be noted that since a modulation scheme in which envelope
fluctuations occur is used in W-CDMA (HSDPA) and LTE unlike
constant envelope modulation in a GSM mode (GMSK modulation), the
RF subsystem is provided with the variable gain amplifier circuit
PGA1. In addition, for example, a transmission carrier frequency in
the digital-type PLL circuit DPLL_TX, a gain of the variable gain
amplifier circuit PGA1, and a target value of an output power in
the automatic power control circuit APC are set by the
microcomputer unit MCU through the transmitting bus control unit
BSCTL_TX.
[0061] The reception circuit block RXBK is provided with: low noise
amplifier circuits LNAa and LNAb; receiving mixer circuits MIX_RXa
and MIX_RXb; low-pass filters LPFa and LPFb; variable gain
amplifier circuits PGAa and PGAb; AD converters ADCa and ADCb;
digital filters DFLTa and DFLTb; a receiving digital-type PLL
circuit DPLL_RX; and a receiving logic circuit LOG_RX. Here, what
is called a reception diversity configuration is employed, and two
types of paths from the low noise amplifier circuit to the digital
filter are provided. It is to be noted that reception diversity is
a mechanism where a plurality of antennas are prepared, inputs are
selected and synthesized, and thereby a signal intensity is
increased.
[0062] Both of the low noise amplifier circuits LNAa and LNAb
amplify a reception power signal RX input through the duplexer DPX
and the antenna switch ANTSW by a low noise. The digital-type PLL
circuit DPLL_RX generates a local signal (a local oscillation
signal or a carrier signal) LO_RX having a predetermined reception
carrier frequency. The mixer circuits MIX_RXa and MIX_RXb
demodulate and down-convert (perform frequency conversion of)
output signals of the low noise amplifier circuits LNAa and LNAb
using the local signal LO_RX from the digital-type PLL circuit
DPLL_RX, respectively, and output analog baseband signals RXDAT.
The low-pass filters LPFa and LPFb remove unnecessary high
frequency components in the analog baseband signals RXDAT from the
mixer circuits MIX_RXa and MIX_RXb, respectively.
[0063] The variable gain amplifier circuits PGAa and PGAb amplify
output signals of the low-pass filters LPFa and LPFb by a gain to
which input ranges of the AD converters ADCa and ADCb have been
added, respectively. The AD converters ADCa and ADCb convert analog
signals from the variable gain amplifier circuits PGAa and PGAb
into digital baseband signals, respectively. The digital filters
DFLTa and DFLTb perform filtering processing, such as interpolation
and decimation, of the digital baseband signals from the AD
converters ADCa and ADCb, respectively. The receiving logic circuit
LOG_RX performs predetermined digital processing (for example,
8B10B decoding etc.) of digital signals from the digital filters
DFLTa and DFLTb, and outputs the results to the baseband processor
602 through the differential interface circuit LVDS as reception
data signals (reception baseband signals). It is to be noted that,
for example, a reception carrier frequency in the digital-type PLL
circuit DPLL_RX is set by the microcomputer unit MCU through the
receiving bus control unit BSCTL_RX.
<<Power Amplifier Circuits HPA1 and HPA2>>
[0064] The power amplifier circuits HPA1 and HPA2 are, for example,
achieved by an LDMOSFET (Laterally Diffused Metal Oxide
Semiconductor Field Effect Transistor), an HBT (Hetero-junction
Bipolar Transistor), etc. The power amplifier circuit HPA1
amplifies an output signal of the variable gain amplifier circuit
PGA1 in the above-mentioned high-frequency signal processing device
RFIC, and outputs it to the duplexer DPX and the antenna switch
ANTSW as a transmission power signal TX. The power amplifier
circuit HPA2 amplifies an output signal of the transmitting mixer
circuit MIX_TX2 in the above-mentioned high-frequency signal
processing device RFIC, and outputs it to the duplexer DPX and the
antenna switch ANTSW as the transmission power signal TX.
[0065] It is to be noted that, for example, an electric power
detection circuit (coupler) or the like, though not shown, is
provided in output nodes of the power amplifier circuits HPA1 and
HPA2, and that the above-mentioned automatic power control circuit
APC controls output powers of the power amplifier circuits HPA1 and
HPA2 by comparing a target value from the microcomputer unit MCU
with a detection result of the electric power detection circuit. In
addition, although for example, one power amplifier circuit HPA1 is
representatively shown here as being directed to W-CDMA or the
like, actually, the plurality of power amplifier circuits HPA1 are
provided in order to deal with wide frequency bands, such as the
700 MHz band to the 2.6 GHz band, and the plurality of
mixer-circuits MIX_TX1 or the like are also provided in the
high-frequency signal processing device RFIC according to the power
amplifier circuits HPA1. The same is true on the power amplifier
circuit HPA2 and further, the same is also true on the low noise
amplifier circuits LNAa and LNAb in the high-frequency signal
processing device RFIC.
<<Duplexer DPX and Antenna Switch ANTSW>>
[0066] The duplexer DPX is, for example, achieved by SMD (Surface
Mount Device) parts, a wiring pattern on a module wiring substrate,
etc., and separates a transmission frequency band from a reception
frequency band. The antenna switch ANTSW is, for example, achieved
by an MMIC (Monolithic Microwave IC) using a compound semiconductor
substrate of gallium arsenide (GaAs) etc. and an SOI (Silicon on
Insulator) substrate, etc., and appropriately controls a connection
destination of the antenna ANT. Usually, combination of the antenna
ANT and the transmission power signal TX or the reception cower
signal RX is performed through the antenna switch ANTSW in
accordance with a TDD (Time Division Duplex) scheme in GSM, and it
is performed through the duplexer DPX in accordance with an FDD
(Frequency Division Duplex) scheme in W-CDMA and LTE.
[0067] As described above, it becomes easy to realize a smaller
area, a lower power source voltage, higher performance (higher
speed), etc. by applying the digital-type PLL circuits DPLL_TX and
DPLL_RX in the high-frequency signal processing device RFIC.
However, these digital-type PLL circuits, as described above,
deteriorate a phase error characteristic in a specific channel due
to an effect of a spurious noise generated in a PLL band in the
specific channel, if no measures are taken. Consequently, in the
digital-type PLL circuit pertaining to the first embodiment, the
above problem is solved by suppressing a coupling strength by
adjusting the phase difference between the Fref and the Fosc.
Hereinafter, the digital-type PLL circuit will be specifically
explained.
<Specific Configuration Example of Digital-Type PLL Circuit
Pertaining to First Embodiment>
[0068] FIG. 4 is a block diagram showing a configuration example of
a digital-type PLL circuit 1 pertaining to the first embodiment,
The digital-type PLL circuit 1 shown in FIG. 4 is, for example,
applied to each of the digital-type PLL circuits DPLL_TX and
DPLL_RX that are provided in the high-frequency signal processing
device RFIC shown in FIG. 3.
[0069] The digital-type PLL circuit 1 shown in FIG. 4 is provided
with: a digital phase difference detector (phase difference
detection unit) DPFD; a frequency setting logic unit LOG_FSET; a
digital control oscillator (oscillation unit) DCO; the amplifier
AMP; the divider DIV1; and the multi-modulus divider (division
unit) MMD.
<<Digital Phase difference Detector DPFD>>
[0070] The digital phase difference detector DPFD detects the phase
difference between the reference oscillation signal (reference
signal) Fref having a reference oscillation frequency (for example,
26 MHz) generated by a crystal oscillation circuit etc and the
division oscillation signal (division signal) Fdiv generated by the
multi-modulus divider MMD.
[0071] Specifically, the digital phase difference detector DPFD is
provided with: a power source regulator LDO; a frequency difference
detection counter FCNT; and a time difference detection circuit
TDC. The power source regulator LDO generates a power source
voltage of the digital-type PLL circuit 1. The frequency difference
detection counter FCNT counts the reference oscillation signal Fref
and the division oscillation signal Fdiv, respectively, and thereby
detects the frequency difference therebetween. The time difference
detection circuit TDC, for example, has plural stages of unit delay
circuits (CMOS inverter circuits), and detects the phase difference
between the division oscillation signal Fdiv and the reference
oscillation signal Fref. Specifically, for example, the time
difference detection circuit TDC sequentially delays the division
oscillation signal Fdiv in the unit delay circuits, synchronously
latches an output of each unit delay circuit to the reference
oscillation signal Fref, and detects the phase difference in view
of the latch result. The smaller a delay amount of the unit delay
circuit becomes along with the miniaturization of a CMOS
manufacturing process, the higher the accuracy of the phase
difference detection result achieved.
<<Frequency Setting Logic Unit LOG_FSET>>
[0072] The frequency setting logic unit LOG_FSET is provided with:
an automatic band selection unit ABS; an adder ADD; the digital
low-pass filter (filter) DLPF; an decoder DEC; the noise intensity
detection unit FT1; and the phase difference adjustment unit CTL1.
The automatic band selection unit ABS, for example, detects a
frequency difference between the division oscillation signal Fdiv
and the reference oscillation signal Fref by counting the division
oscillation signal Fdiv by means of the reference oscillation
signal Fref, and outputs a trimming signal (frequency adjustment
signal) TRM having a digital code according to the frequency
difference. The adder ADD synthesizes a detection result (a digital
output of the frequency difference detection counter FCNT) of the
frequency difference and a detection result (a digital output of
the time difference detection circuit TDC) of the phase difference
by the digital phase difference detector DPFD.
[0073] The digital low-pass filter DLPF applies averaging
processing to the digital code output from the adder ADD. The
decoder DEC decodes (performs code conversion of) the digital code
(control signal) serving as a processing result of the digital
low-pass filter DLPF, and outputs a fine signal (frequency
adjustment signal) FNE and a fractional signal (frequency
adjustment signal) FRC serving as an actual digital code (for
example, ON/OFF information of a switch) for frequency setting.
[0074] The noise intensity detection unit FT1 detects the noise
intensity (intensity of the spurious noise) SL of a predetermined
frequency component included in the digital code (control signal)
output from the digital low-pass filter DLPF. For example, the
noise intensity detection unit FT1 detects the noise intensity SL
in the predetermined frequency by performing Fourier transform of
the predetermined frequency component included in the digital code
(control signal) output from the digital low-pass filter DLPF.
[0075] The phase difference adjustment unit CTL1 adjusts the phase
difference between the reference oscillation signal Fref and the
division oscillation signal Fdiv based on a detection result (the
noise intensity SL in the predetermined frequency) of the noise
intensity detection unit FT1.
[0076] Specifically, in a phase difference adjustment mode, the
phase difference adjustment unit CTL1 adjusts the phase difference
between the reference oscillation signal Fref and the division
oscillation signal Fdiv using a plurality of different spans of
adjustable range, respectively. In addition, in the phase
difference adjustment mode, the noise intensity detection unit FT1
detects the plurality of noise intensities SL in a case where the
phase difference is adjusted using the plurality of different spans
of adjustable range, respectively. Additionally, in a normal
operation mode, the phase difference adjustment unit CTL1 adjusts
the phase difference using a span of adjustable range corresponding
to the noise intensity SL indicating a minimum value among the
plurality of noise intensities SL. That is, the phase difference
adjustment unit CTL1 adjusts the phase difference between the
reference oscillation signal. Fref and the division oscillation
signal Fdiv so that the detection result of the noise intensity
detection unit FT1 after phase difference adjustment indicates the
minimum value.
[0077] In the example of FIG. 4, the phase difference adjustment
unit CTL1 generates an adjustment signal (a digital value) based on
the detection result (noise intensity SL in the predetermined
frequency) of the noise intensity detection unit FT1, and outputs
it to the adder ADD. The adder ADD adds a synthesis result (digital
code) of an output of the digital phase difference detector DPFD to
the adjustment signal (digital value) from the phase difference
adjustment unit CTL1, and outputs the addition result. As a result,
the phase difference between the reference oscillation signal Vref
and the division oscillation signal Fdiv is adjusted by a phase
difference corresponding to the adjustment signal (digital value).
A detailed description of operation of the noise intensity
detection unit FT1 and the phase difference adjustment unit CTL1
will be given later.
<<Digital Control Oscillator DCO>>
[0078] The digital control oscillator DCO is provided with: two
PMOS transistors (hereinafter simply referred to as transistors)
MP1 and MP 2 connected in a cross-coupled manner (one gate is
connected to an other drain): two NMOS transistors (hereinafter
simply referred to as transistors) MN1 and MN2 connected in the
cross-coupled manner; a coil L1; and three types of capacitance
banks CBK1 to CBK3. Sources of the transistors MP1 and MP2 are
connected to the power source voltages VDD, sources of the
transistors MN1 and MN2 are connected to ground power source
voltages VSS, drains of the transistors MP1 and MN1 are connected
to a node Nrfp, and drains of the transistors MP2 and MN2 are
connected to a node Nrfn.
[0079] The coil L1 is connected between the nodes Nrfp and Nrfn.
The capacitance bank CBK1 is provided with: a capacitance element
(for example, an MOS capacity) C11 having one end connected to the
node Nrfp; a capacitance element C12 having one end connected to
the node Nrfn; and a switch SW10 that is connected between the
other end of the capacitance element C11 and the other end of the
capacitance element C12. Although a set of circuits including the
capacitance elements C11 and C12, and the switch SW10 are here
representatively shown, actually, plural sets of such circuits are
provided between the nodes Nrfp and Nrfn. Additionally, ON/OFF of
the switch SW10 included in each set of such circuits is controlled
by the trimming signal TRM from the automatic band selection unit
ABS. It is to be noted that capacitance values of the capacitance
elements included in the plurality of sets of circuits,
respectively, need not necessarily be the same, and that weighting,
such as twice, four times, eight times, and . . . , may be
appropriately made on the basis of the capacitance element C11
(=C12).
[0080] Similarly, the capacitance bank CBK2 is provided with: a
capacitance element C21 having one end connected to the node Nrfp;
a capacitance element C22 having one end connected to the node
Nrfn; and a switch SW20 that is connected between the other end of
the capacitance element C21 and the other end of the capacitance
element C22, and plural sets of such circuits are provided between
the nodes Nrfp and Nrfn. ON/OFF of the switch SW20 included in the
each set is controlled by the fine signal FNE from the decoder DEC.
Similarly, the capacitance bank CBK3 is provided with: a
capacitance element C31 having one end connected to the node Nrfp;
a capacitance element C32 having one end connected to the node
Nrfn; and a switch SW30 that is connected between the other end of
the capacitance element C31 and the other end of the capacitance
element C32, and plural sets of such circuits are provided between
the nodes Nrfp and Nrfn. ON/OFF of the switch SW30 included in the
each set is controlled by the fractional signal FRC from the
decoder DEC.
[0081] Such digital control oscillator DCO serves as an LC
resonance-type oscillation circuit including the coil L1 and the
capacitance banks CBK1 to CBK3, and outputs the oscillation signal
Fosc1 complementary to the nodes Nrfp and Nrfn. At this time, the
transistors MP1 and MP2 and the transistors MN1 and MN2 function as
negative resistances. An oscillation frequency of the oscillation
circuit is controlled by ON/OFF of each switch in the capacitance
banks CBK1 to CBK3, and contributes as a parameter with which the
capacitance element included in a set in which the switch has been
controlled to be ON defines an oscillation frequency. Here, a
relation of each capacitance element in the capacitance banks CBK1
to CBK3 is expressed by C11 (=C12)>C21 (=C22)>C31 (=C32), and
for example, the oscillation frequency is adjusted in a unit of 2
MHz by the trimming signal TRM, in a unit of 20 kHz by the fine
signal FNE, and in a unit of 1.25 kHz by the fractional signal FRC,
respectively.
<<Divider DIV1>>
[0082] The divider DIV1 half-divides the oscillation signal Fosc1
amplified by the amplifier AMP to output it as the oscillation
signal Fosc2 (for example, approximately 2 GHz). Note that since
the divider DIV1 is provided to lower the frequency of the
oscillation signal to a level where the multi-modulus divider MMD
is able to operate, it need not be provided if there is no
necessity of lowering the frequency of the oscillation signal.
<<Multi-Modulus Divider MMD>>
[0083] The multi-modulus divider MMD divides the oscillation signal
Fosc2 using a division ratio with accuracy substantially not more
than a decimal point to output as the division oscillation signal
Fdiv (for example, approximately 26 MHz) by dividing and averaging
the oscillation signal Fosc2 using a division ratio that changes in
chronological order.
(Operation of Digital-Type PLL Circuit 1 Pertaining to the
Embodiment)
[0084] Next, operation of the digital-type PLL circuit 1 pertaining
to the embodiment will be explained with reference to FIGS. 5, 6,
and 7. FIG. 5 is a flowchart showing the operation of the
digital-type PLL circuit 1. FIG. 6 is a table for explaining the
operation of the digital-type PLL circuit 1. FIG. 7 is a graph
showing a relation between a degree of phase difference adjustment
made by the phase difference adjustment unit CTL1 and a detection
result (noise intensity SL in a predetermined frequency) obtained
by the noise intensity detection unit FT1. It is to be noted that
numerical values used in the following explanation are represented
with decimal numbers unless otherwise noted.
[0085] It is to be noted that the digital-type PLL circuit 1
suppresses a spurious noise generated at a predetermined frequency
in the phase difference adjustment mode, before performing an
oscillation operation in the normal operation mode. Here, the
predetermined frequency, for example, means a specific channel etc.
near a center frequency of a band where the phase error
characteristic has largely deteriorated due to an effect of the
spurious noise. Hereinafter, operation of the digital-type PLL
circuit 1 in the phase difference adjustment mode will be mainly
explained.
[0086] First, in an initial state, a loop variable I is set to be
"0", a PFDoffset (a degree of phase difference adjustment by the
phase difference adjustment unit CTL1, i.e., a value of an
adjustment signal) is set to be "0", and a MinSL (a minimum value
of the noise intensity SL) is set to be a maximum value of a
digital code (DC) output from the digital low-pass filter DLPF
(step S101 of FIG. 5). After that, the digital-type PLL circuit 1
starts a calibration operation (an operation in the phase
difference adjustment mode) (step S102 of FIG. 5).
[0087] Next, the digital low-pass filter DLPF outputs a digital
code (DC) according to the phase difference between the reference
oscillation signal Fref and the division oscillation signal Fdiv
(step S103 of FIG. 5).
[0088] Next, it is determined whether or not the loop variable I=8
(step S104 of FIG. 5). For example, when the loop variable I=8 (YES
in step S104 of FIG. 5), the program proceeds to processing instep
S110. On the other hand, when the loop variable I.noteq.8 (NO in
step S104 of FIG. 5), the program proceeds to processing in step
S105. Here, although the loop variable I is compared with 8 in step
S104, it may be compared with a value smaller or larger than 8
according to the number of loops.
[0089] Here, since the loop variable I=0 (I.noteq.8) (NO in step
S104 of FIG. 5), PFDoffset is set to be 64 (=16.times.I+64) LSB
(step S105 of FIG. 5). As a result, the phase difference between
the reference oscillation signal Vref and the division oscillation
signal Fdiv is adjusted by a phase difference corresponding to a
digital value 64 LSB (for example, a phase of the division
oscillation signal Fdiv is advanced).
[0090] Next, the noise intensity detection unit FT1 performs
Fourier transform of a predetermined frequency component included
in the digital code output from the digital low-pass filter DLPF,
and outputs the noise intensity (intensity of the spurious noise)
SL in the predetermined frequency (step S106 of FIG. 5). In the
example, as shown in FIGS. 6 and 7, when PFDoffset=64 LSB, the
noise intensity SL=200 LSB.
[0091] Next, it is determined whether or not the noise intensity
SL<MinSL (step S107 of FIG. 5). For example, when the noise
intensity SL<MinSL (YES in step S107 of FIG. 5), the program
proceeds to processing in step S108. On the other hand, when it is
not established that the noise intensity SL<MinSL (NO in step
S107 of FIG. 5), the program proceeds to processing of step S109
without performing processing of step S108.
[0092] Here, since the noise intensity SL (=200 LSB)<MinSL (=a
maximum value or the DC) (YES in step S107 of FIG. 5), MinSL is set
to be 200 LSB (the noise intensity SL at this time), and MinOffset
is set to be 64 LSB (PFDoffset at this time) (step S108 of FIG.
5).
[0093] After that, the loop variable I increases only by "1" (step
S109 of FIG. 5), and the program returns to processing in step
S104. Processing in steps S104 to S109 is repeated until it is
established that the loop variable I=8.
[0094] In the example, as shown in FIGS. 6 and 7, when
PFDoffset=160 LSB (i.e., I=6), the smallest noise intensity SL=20
LSB.
[0095] Accordingly, at the time of it being established that the
loop variable I=8, MinSL is set to be 20 LSB, and MinOffset is set
to be 160 LSB.
[0096] When it is established that the loop variable I=8 (YES in
step S104 of FIG. 5), the digital-type PLL circuit 1 stops the
calibration operation (the operation in the phase difference
adjustment mode) (step S110 of FIG. 5). Additionally, the
digital-type PLL circuit 1 sets PDFoffset (the degree of phase
difference adjustment by phase difference adjustment unit CTL1,
i.e., the value of the adjustment signal) in the normal operation
mode to be a final value 160 LSB of Minoffset (step S111 of FIG.
5). After that, the digital-type PLL circuit 1 starts an
oscillation operation in the normal operation mode (step S112 of
FIG. 5). Such processing is performed, and thereby the spurious
noise generated in the specific channel (predetermined frequency)
is effectively suppressed.
[0097] As described above, the digital-type PLL circuit 1
pertaining to the embodiment can suppress the spurious noise
generated in the PLL band in the specific channel. As a result of
this, deterioration of the phase error characteristic in the
specific channel is suppressed.
[0098] It is to be noted that if a channel and a spurious type are
previously determined, Fourier transform may just be performed only
at a specific frequency, and thus a circuit scale is reduced.
Second Embodiment
[0099] FIG. 8 is a block diagram showing a configuration example of
a digital-type PLL circuit 2 pertaining to a second embodiment. The
PLL circuit 2 shown in FIG. 8 is a PLL circuit in which analog
control is employed in a part thereof unlike the digital-type PLL
circuit 1 shown in FIG. 4. Hereafter, the digital-type PLL circuit
2 will be specifically explained.
[0100] The PLL circuit 2 shown in FIG. 8 is provided with: a phase
difference detector PFD; a low-pass filter (filter) LPF; a voltage
control oscillator (oscillation unit) VCO; a divider (division
unit) DIV2; an AD converter ADC2; a noise intensity detection unit
FT2; and a phase difference adjustment unit CTL2.
[0101] The digital phase difference detector PFD detects the phase
difference between the reference oscillation signal Fref and the
division oscillation signal Fdiv. The low-pass filter LPF outputs a
control voltage according to a detection result of the phase
difference detector PFD. The voltage control oscillator VCO outputs
the oscillation signal Fosc1 of a frequency according to the
control voltage. The divider DIV2 divides the oscillation signal
Fosc1, and outputs it as the division oscillation signal Fdiv.
[0102] The AD converter ADC2 converts the control voltage (analog
signal) output from the low-pass filter LPF into a digital signal,
and outputs it.
[0103] The noise intensity detection unit FT2 detects the noise
intensity (the intensity of the spurious noise) SL of a
predetermined frequency component included in an output signal of
the AD converter ADC2. For example, the noise intensity detection
unit FT2 performs Fourier transform of the predetermined frequency
component included in the output signal of the AD converter ADC2,
and thereby detects the noise intensity SL in the predetermined
frequency.
[0104] The phase difference adjustment unit CTL2 adjusts the phase
difference between the reference oscillation signal Fref and the
division oscillation signal Fdiv based on a detection result (the
noise intensity SL in the predetermined frequency) of the noise
intensity detection unit FT2.
[0105] Specifically, in the phase difference adjustment mode, the
phase difference adjustment unit CTL2 adjusts the phase difference
between the reference oscillation signal Fref and the division
oscillation signal Fdiv using a plurality of different spans of
adjustable range, respectively. In addition, in the phase
difference adjustment mode, the noise intensity detection unit FT2
detects the plurality of noise intensities SL in a case where the
phase difference is adjusted using the plurality of different spans
of adjustable range, respectively. Additionally, in the normal
operation mode, the phase difference adjustment unit CTL2 adjusts
the phase difference using a span of adjustable range corresponding
to the noise intensity SL indicating a minimum value among the
plurality of noise intensities SL. That is, the phase difference
adjustment unit CTL2 adjusts the phase difference between the
reference oscillation signal Fref and the division oscillation
signal Fdiv so that the detection result of the noise intensity
detection unit FT2 after phase difference adjustment indicates the
minimum value. As a result, the spurious noise generated in the
specific channel (predetermined frequency) is effectively
suppressed.
[0106] As described above, the PLL circuit 2 pertaining to the
embodiment can suppress the spurious noise generated in the PLL
band in the specific channel similarly to the case of the
digital-type PLL circuit 1 pertaining to the first embodiment. As a
result of this, deterioration of the phase error characteristic in
the specific channel is suppressed.
[0107] Hereinbefore, although the invention made by the present
inventor has been specifically explained based on the embodiments,
it is needless to say that the present invention is not limited to
the previously mentioned embodiments, and that various changes can
be made without departing from the spirit of the invention.
[0108] The first and second embodiments can be combined as
desirable by one of ordinary skill in the art.
[0109] While the invention has been described in terms of several
embodiments, those skilled in the art will recognize that the
invention can be practiced with various modifications within the
spirit and scope of the appended claims and the invention is not
limited to the examples described above.
[0110] Further, the scope of the claims is not limited by the
embodiments described above.
[0111] Furthermore, it is noted that, Applicant's intent is to
encompass equivalents of all claim elements, even if amended later
during prosecution.
* * * * *