U.S. patent application number 09/198224 was filed with the patent office on 2001-08-16 for voltage controlled oscillator with adaptive closed loop coarse tune.
Invention is credited to CUNNING, MICHAEL D..
Application Number | 20010013812 09/198224 |
Document ID | / |
Family ID | 22732500 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013812 |
Kind Code |
A1 |
CUNNING, MICHAEL D. |
August 16, 2001 |
VOLTAGE CONTROLLED OSCILLATOR WITH ADAPTIVE CLOSED LOOP COARSE
TUNE
Abstract
A voltage controlled oscillator circuit incorporating a closed
loop coarse tuning mechanism. In this system, a reference
oscillator is set with the desired frequency for the voltage
controlled oscillator. A resulting voltage used to drive the
oscillator is produced by a synthesizer connected in series with a
loop filter. The resulting voltage is connected to a fine tune
input of the voltage controlled oscillator and also to the input of
an adaptive closed loop coarse tuning mechanism. The adaptive
closed loop coarse tuning mechanism is comprised of an op amp
configured in a noninverting feedback loop connected to a parallel
resistor/adapt switch loop. The loop is followed by a shunt
capacitor filter which is then connected directly to the coarse
tune input of the VCO. If the adapt switch is closed, currentfrom
the coarse amp flows through a filter and to a coarse tune port of
the VCO. The voltage resulting from the adaptive closed loop coarse
tuning mechanism overrides any voltage being received in the fine
tune port, making the coarse tune loop controlling in frequency
acquisition. Throughout the entire coarse tune process, a feedback
loop allows the synthesizer to adjust the control voltage as the
VCO gets closer to the desired frequency. After a predetermined
acquisition time, the adapt switch is opened. This virtually
eliminates the adaptive closed loop tuning mechanism from the
circuit because of the large time constant associated with the
(closed) adapt switch/resistor circuit. At that point, the fine
tune port voltage will make any minor adjustments in driving the
VCO to the desired frequency.
Inventors: |
CUNNING, MICHAEL D.; (PAOLA,
KS) |
Correspondence
Address: |
DEVON A ROLF
GARMIN INTERNATIONAL, INC.
1200 EAST 151ST STREET
OLATHE
KS
66062
US
|
Family ID: |
22732500 |
Appl. No.: |
09/198224 |
Filed: |
November 23, 1998 |
Current U.S.
Class: |
331/10 ; 331/14;
331/16; 331/17; 331/177R |
Current CPC
Class: |
H03B 2201/0208 20130101;
H03L 2207/06 20130101; H03L 7/1075 20130101; H03L 7/102
20130101 |
Class at
Publication: |
331/10 ; 331/14;
331/16; 331/17; 331/177.00R |
International
Class: |
H03L 007/093; H03B
001/00 |
Claims
What is claimed is:
1. A voltage controlled oscillator circuit, said voltage controlled
oscillator circuit comprising: a fine tune varactor; a coarse tune
varactor; and a voltage controlled oscillator.
2. The voltage controlled oscillator circuit as recited in claim 1,
wherein said coarse tune varactor is comprised of an op amp
circuit.
3. The voltage controlled oscillator circuit as recited in claim 2,
said fine tune varactor having an output connected directly to an
input of said coarse tune op amp circuit and also to a fine tune
port input of said voltage controlled oscillator.
4. The voltage controlled oscillator circuit as recited in claim 3,
wherein said op amp circuit is incorporated into a noninverting
closed loop feedback configuration.
5. The voltage controlled oscillator circuit as recited in claim 4,
further comprising of a low impedance adapt switch connected in
parallel with a resistor to an output of said noninverting closed
loop feedback of op amp.
6. The voltage controlled oscillator circuit as recited in claim 5,
wherein said resistor in parallel is of a high resistance.
7. The voltage controlled oscillator circuit as recited in claim 3,
further comprising a resistor and a shunt capacitor connected to
said output of the op amp circuit and said parallel switch and
resistor.
8. The voltage controlled oscillator circuit as recited in claim 7,
wherein said parallel resistor is of a magnitude bigger than said
resistor connected immediately in series with said parallel
resistor.
9. The voltage controlled oscillator circuit as recited in claim 8,
wherein the magnitude of difference in resistance value between
said parallel resistor and said resistor in series is at least 10
to 1.
10. The voltage controlled oscillator circuit as recited in claim
2, further comprising an output of said resistor and said shunt
capacitor connected to a coarse tune port of said voltage
controlled oscillator.
11. The voltage controlled oscillator circuit as recited in claim
1, wherein said fine tune varactor is comprised of: a frequency
generator; a synthesizer; and a loop filter.
12. The voltage controlled oscillator circuit as recited in claim
1, further comprising a prescalar input from said voltage
controlled oscillator connected to said synthesizer.
13. A voltage controlled oscillator circuit, said voltage
controlled oscillator circuit comprising: a fine tune varactor,
said fine tune varactor comprised of a frequency generator, a
synthesizer and a loop filter; a voltage controlled oscillator,
whereby said loop filter having an output connected to a fine tune
port of said voltage controlled oscillator and said voltage
controlled oscillator connected to said synthesizer via a prescalar
input line; and a coarse tune varactor, said coarse tune varactor
comprised of an op amp circuit configured in a noninverting closed
loop feedback loop, a low impedance adapt switch connected in
parallel with a resistor to an output of said noninverting closed
loop feedback of said op amp circuit, a resistor and a shunt
capacitor connected to said parallel switch and resistor, a coarse
tune port of a voltage controlled oscillator connected to an output
of said resistor and said shunt capacitor.
14. The voltage controlled oscillator circuit as recited in claim
13, wherein said voltage controlled oscillator circuit incorporated
in combination with a communication device.
15. The voltage controlled oscillator circuit as recited in claim
14, where said communication device is capable of cellular
communication.
16. The voltage controlled oscillator circuit as recited in claim
14, wherein said communication device further comprises a
navigational aid.
17. The voltage controlled oscillator circuit as recited in claim
16, wherein said navigational aid has means for acquiring and
processing global positioning system data.
18. The method of implementing an adaptive closed loop coarse
tuning mechanism with a voltage controlled oscillator, said method
comprising: selecting a desired frequency as a reference; comparing
said reference frequency to a present frequency of said voltage
controlled oscillator; producing a voltage corresponding to a phase
difference between said reference frequency and said present
voltage controlled oscillator frequency; utilizing a closed adapt
switch to drive an adaptive closed loop coarse tuning mechanism
with said voltage; continuing to drive said adaptive closed loop
coarse tune for a preset time; and opening said adapt switch to end
adaptive closed loop coarse tuning.
19. The method of implementing an adaptive closed loop coarse
tuning mechanism as recited in claim 18, wherein said selection of
a desired frequency as a reference is selected by an external
control within a communication device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] In general, this invention relates to a communication device
utilizing voltage controlled oscillators and more specifically to a
voltage controlled oscillator circuit incorporating an adaptive
closed loop coarse tuning mechanism.
[0003] 2. Description of the Related Art
[0004] Voltage controlled oscillators (VCO) are well known in the
field of communication devices. In general, the operating frequency
of a VCO is controlled by the application of a voltage to a tuning
varactor incorporated into the VCO design. Some communication
devices implement a single varicap diode to apply corresponding
reference voltages over an entire band of desired frequencies. The
problem encountered when using a single varicap diode is that the
VCO becomes sensitive to noise and experiences reference frequency
leakage in the case of high VCO gain. In some devices, this problem
is addressed by varying the closed loop bandwidth of a single loop
filter using an adapt switch to change the loop filter components.
Such single loop adaptive filtering requires multiple switches and
filters to cover a desired frequency range.
[0005] As an alternative solution, the problem of noise and
frequency leakage is overcome by dividing the frequency band into
sub-bands using either diode switches or dual tuning diodes from
two varicap diodes, one for coarse tuning and the other for fine
tuning. When using dual tuning diodes, the coarse tune varactor is
normally controlled open loop using a D/A converter. A problem with
this approach, however, is that the voltage produced by the D/A
converter for each individual communication device must be
calibrated over the entire band, substantially increasing the
overall system cost per unit. As an alternative, the VCO is
sometimes installed with microstrip line etching containing
precalibrated frequencies for the entire band. The microstrips are
driven by an adapt switch connected directly to the VCO. However,
initial calibration of the microstrip etching requires laser
trimming which equates to a large up front cost, thereby also
substantially increasing the cost per unit. Because single varicap
adaptive filtering does not effectively reduce noise without
multiple components and because a D/A converter and microstrip line
etching increase overall system costs, a need exists for a less
expensive, single unit coarse tuning mechanism.
SUMMARY OF THE INVENTION
[0006] Based on the above noted deficiencies in the related art, it
is an object of the present invention to eliminate the need for
individual calibration per unit of the coarse tune voltage across a
band of desired frequencies. It is the further object to reduce VCO
gain while eliminating the need for a D/A converter and without
sacrificing resolution. Still another object is to allow for
adaptive VCO sensitivity without the need and implementation of
switching diodes. Finally, it is the object to offer a noise
reduction advantage over single loop adaptive filtering used in
VCOs.
[0007] These and other objects of the present invention are
achieved by the incorporation of an adaptive closed loop coarse
tuning mechanism into a voltage controlled oscillator (VCO)
circuit. Particularly, a reference oscillator is set with the
desired frequency for the VCO. The resulting wave form is sent to a
synthesizer, which is connected in series with the reference
oscillator. The synthesizer then compares the reference frequency
to the frequency at which the VCO is currently set and a charge
pump within the synthesizer converts any phase difference between
the two frequencies into a corresponding current that is
proportional to the phase difference. If there is no phase
difference, the charge pump will not emit a current, as the VCO is
presently at the desired frequency. Therefore, the greater the
phase difference, the higher the current the charge pump will
produce.
[0008] Connected in series with the synthesizer is a loop filter
which receives the incoming current from the synthesizer and
produces a corresponding voltage. This voltage is applied directly
to the fine tune port of the VCO. In addition, the adaptive closed
loop coarse tuning mechanism is connected in parallel with the fine
tune port and develops the same voltage, which is the reference
voltage for the coarse tune.
[0009] The adaptive closed loop coarse tuning mechanism consists of
an op amp configured in a noninverting feedback loop connected to a
parallel resistor/adapt switch. The switch is followed in series by
a shunt capacitor filter which is connected directly to the coarse
tune input of the VCO. When the adapt switch is closed, the voltage
produced by the coarse amp flows through the filter and to the
coarse tune port of the VCO. The voltage resulting from the
adaptive closed loop coarse tune overrides any voltage being
received in the fine tune port making the coarse tune loop
controlling in frequency acquisition. This process is known as the
wide band (fast lock) mode. After a preset time has expired, the
adapt switch is opened thereby effectively eliminating the coarse
tune circuit from the loop because of a large time constant
associated with the parallel adapt switch/resistor circuit. At that
point, the fine tune port voltage will make any minor adjustments
in driving the VCO to the desired frequency. This process is known
as the narrow band (low noise) mode.
[0010] These as well as other novel advantages, details,
embodiments, features, and objects of the present invention will be
apparent skilled in the art from the following detailed description
of the invention, the attached claims and accompanying drawings,
listed herein below, which are useful in explaining the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Objects and features of the invention noted above are
explained in more detail with reference to the drawings, and in
which like reference numerals are used to indicate like parts in
the various views:
[0012] FIG. 1 is a schematic of the voltage controlled oscillator
with an adaptive closed loop coarse tuning mechanism circuit of the
present invention;
[0013] FIG. 2 is a flow diagram of frequency acquisition utilizing
an adaptive closed loop coarse tuning mechanism circuit of the
present invention;
[0014] FIG. 3 is a schematic of the adaptive closed loop coarse
tuning mechanism circuit of the present invention during the wide
band fast lock acquisition mode; and
[0015] FIG. 4 is a schematic of the adaptive closed loop coarse
tuning mechanism circuit of the present invention during narrow
band low noise mode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] For better understanding of the present invention, reference
may be had to the following detailed description taken in
conjunction with the appended claims and accompanying drawings. In
essence, the present invention enables a voltage controlled
oscillator to acquire a desired frequency with the use of a coarse
tune varactor. At the same time, the coarse tune varactor is
implemented without the need to calibrate the coarse tune voltage
across the desired band of frequencies, without sacrificing VCO
sensitivity and resolution and without the implementation of a D/A
converter.
[0017] In the preferred embodiment, FIG. 1 represents the voltage
controlled oscillator (VCO) circuit designated generally by
reference numeral 10. The VCO circuit includes a reference
oscillator 11 connected in series with a synthesizer 12 which is
connected in series with a loop filter 13. Typically, the loop
filter 13 is comprised of a resistor and a capacitor. The output of
the loop filter 13 is connected directly to the fine tune port 23
of the VCO 24.
[0018] Connected in parallel to the fine tune port is the adaptive
closed loop coarse tuning mechanism 25, designated generally by
reference numeral 25. Within the adaptive closed loop coarse tuning
mechanism 25 is a coarse amp 14 configured in a noninverting
feedback loop with the loop filter 13 output connected to the
positive input of the coarse amp 14. The noninverting feedback loop
of the coarse amp 14 is configured with a 10 K.OMEGA. resistor 15
and a 1 K.OMEGA. 16 resistor. It will be appreciated by someone
skilled in the relevant art that other combinations of resistor
values could be substituted for those identified. At the output of
the coarse amp 14 is an adapt switch 21 of little or no resistance
and, in parallel, a 1 M.OMEGA. resistor 18. In series with the
adapt switch 21/resistor 18 loop is a 50 K.OMEGA. resistor 19. This
resistor 19 is used in conjunction with a parallel 0.1 .mu.F shunt
capacitor 20 to filter out additional noise. The output of the
resistor 19 and shunt capacitor 20 is connected to the coarse tune
port 22 of the VCO 24. The VCO 24 then relays its frequency back to
the synthesizer 14 via the prescalar input line 26.
[0019] In general, FIG. 2 represents a flow diagram of the
implementation of the adaptive closed loop coarse tuning mechanism.
External controls (not shown) load the reference oscillator 11 with
the frequency desired for the VCO 24 as represented in Step S200.
The resulting wave form is sent to the synthesizer 12 which also
contains the present VCO 24 frequency as loaded in the prescalar
input line 26. The synthesizer 12 internally divides down both
frequencies and compares the reference frequency to the VCO 24
frequency. The phase difference, if any, between the wave forms
causes a charge pump within the synthesizer 14 to produce a current
proportional to the phase difference. The loop filter 13, connected
in series, receives the current produced by the charge pump and a
resulting voltage appears as the current flows into a capacitor
located within the loop filter 13.
[0020] The resulting voltage is sensed by the fine tune port 23 of
the VCO 24, which begins to drive the VCO 24. In parallel to the
fine tune port 23 is the coarse amp 14 of the adaptive closed loop
coarse tuning mechanism 25. If the adapt control switch 21 of the
coarse tune amp is closed, the voltage from filtered coarse 13
drives the coarse amp 14. The closing of the adapt switch initiates
the wide band fast lock mode as represented in FIG. 2 by Step
S210.
[0021] FIG. 3 is a schematic of the adaptive closed loop coarse
tuning mechanism in wide band fast lock mode. Because the adapt
switch 21 has little or no resistance, a short circuit exists and
all of the current produced by the coarse amp 14 feedback loop
flows directly to the filter resistance 19 bypassing the parallel
resistor 18. At this point, the voltage produced by the coarse amp
14 is filtered by the series resistor 19, and shunt capacitor 20.
The output of the filter is directly connected to the coarse tune
input 22 of the VCO 24. The filtered voltage produced by the coarse
amp 14 drives the VCO 24. Throughout the entire coarse tune period,
the VCO 24 will relay its changing frequency via the prescalar
input line 26 to the synthesizer which will adjust the reference
current accordingly.
[0022] The adaptive closed loop coarse tuning mechanism 25 will
continue to drive the VCO 24 for a predetermined period, referred
to as the adapt time, at which time the adapt switch 21 will open.
As represented in FIG. 2, Step S220 continuously examines whether
the adapt time has elapsed. If the adapt time has elapsed, the
system proceeds to Step 230 as described below. However, if the
adapt time has not elapsed, the system cycles back to Step S210 and
remains in wide band fast lock mode. The adapt time is a function
of the dynamics and characteristics of the individual components of
the communication device and will be determined and programmed
during the construction of the communication device. The primary
goal of the adapt time is to establish a maximum quantum of tune in
which coarse tune frequency can acquire any frequency in the
desired bandwidth.
[0023] When the adapt switch 21 is open, the adaptive closed loop
coarse tuning mechanism is in narrow band low noise mode as
represented in FIG. 2 by Step S230. While in the narrow band low
noise mode, the closed loop coarse tuning mechanism has a slow
response and virtually no effect on the tuning of the VCO 24. FIG.
4 is a schematic of the adaptive closed loop coarse tuning
mechanism in narrow band low noise mode. Because the adapt switch
21 is open, an open circuit exists on the top of the parallel
circuit and no current can flow. Therefore, all current being
produced by the coarse amp 14 must flow through the bottom parallel
resistor 18. Because the parallel resistor 18 is of a high
resistance, the current flowing through it will produce a high
voltage drop. This high voltage drop across the parallel resistor
18 leaves little or no voltage remaining to drive the coarse tune
input 22 of the VCO 24. Consequently, the coarse tune input has
been effectively eliminated from operation. Instead, the fine tune
input 23, which is still receiving the voltage produced by the loop
filter 13, will drive the VCO 24 through the fine tune port 23 to
make any minor adjustments to achieve the desired frequency. The
synthesizer 14 will continue to produce current until the VCO 24
frequency is equal to the reference frequency.
[0024] In the preferred embodiment of the present invention, the
voltage controlled oscillator circuit implementing the adaptive
closed loop coarse tuning mechanism is used in combination with a
portable telephone, such as a cellular telephone, and operates as
the primary mechanism for acquiring the cellular frequencies for
that portable device. Additionally, in accordance with the present
invention, the voltage controlled oscillator circuit is combined in
a device having both voice communication and navigational features.
Such a device has the ability to acquire and process navigational
data, such as global positioning information and also to establish
and receive cellular communications, or their equivalent.
[0025] In the foregoing specification, the present invention has
been described with reference to specific exemplary embodiments
thereof. The invention is considered to have been described in such
full, clear, concise and exact terms as to enable a person of
ordinary skill in the art to make and use the same. It will be
apparent to those skilled in the art, that a person understanding
this invention may conceive of changes or other embodiments or
variations, which utilize the principles of this invention without
departing from the broader spirit and scope of the invention as set
forth in the appended claims. All are considered with the sphere,
spirit and scope of the invention. The specification and drawings
are, therefore, to be regarded in an illustrative rather than
restrictive sense. Accordingly, it is not intended that the
invention be limited except as may be necessary in view of the
appended claims or their equivalents, which particularly point out
and distinctly claim the subject matter applicants regard as their
invention.
* * * * *