U.S. patent application number 11/028854 was filed with the patent office on 2005-06-02 for quadrature oscillator and methods thereof.
This patent application is currently assigned to INTEL CORPORATION. Invention is credited to Ravi, Ashoke, Soumyanath, Krishnamurthy.
Application Number | 20050116784 11/028854 |
Document ID | / |
Family ID | 32989348 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050116784 |
Kind Code |
A1 |
Ravi, Ashoke ; et
al. |
June 2, 2005 |
Quadrature oscillator and methods thereof
Abstract
A quadrature oscillator includes a master tuned oscillator and
two injection-locked slave tuned oscillators.
Inventors: |
Ravi, Ashoke; (Hillsboro,
OR) ; Soumyanath, Krishnamurthy; (Portland,
OR) |
Correspondence
Address: |
EITAN, PEARL, LATZER & COHEN ZEDEK LLP
10 ROCKEFELLER PLAZA, SUITE 1001
NEW YORK
NY
10020
US
|
Assignee: |
INTEL CORPORATION
|
Family ID: |
32989348 |
Appl. No.: |
11/028854 |
Filed: |
January 5, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11028854 |
Jan 5, 2005 |
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10401024 |
Mar 28, 2003 |
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6850122 |
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Current U.S.
Class: |
331/45 |
Current CPC
Class: |
H03B 5/1228 20130101;
H03K 3/354 20130101; H03B 5/124 20130101; H03B 5/1215 20130101;
H03B 27/00 20130101 |
Class at
Publication: |
331/045 |
International
Class: |
H03L 007/00 |
Claims
What is claimed is:
1. A method comprising: generating quadrature signals from
substantially anti-phase output signals of a source oscillator
oscillating at a frequency, said output signals having
substantially twice said frequency, said quadrature signals having
substantially half said frequency and having a phase difference
therebetween of substantially .pi./2 radians.
2. The method of claim 1, wherein generating said quadrature
signals comprises: tuning slave oscillators coupled to said source
oscillator to have a natural self-resonant frequency within an
injection-locking range to said frequency.
3. The method of claim 1, wherein generating said quadrature
signals comprises: injecting said output signals to single-ended
inputs of tuned slave oscillators.
4. The method of claim 1, wherein generating said quadrature
signals comprises: injecting said output signals to differential
inputs of tuned slave oscillators.
5. An apparatus comprising: a quadrature oscillator including at
least a source oscillator able to oscillate at a frequency and to
produce substantially anti-phase output signals at said frequency,
said quadrature oscillator able to generate quadrature signals from
said output signals, said quadrature signals having substantially
half said frequency and having a phase difference therebetween of
substantially .pi./2 radians.
6. The apparatus of claim 5, wherein said quadrature oscillator
further includes two slave oscillators having input nodes coupled
to output nodes of said source oscillator.
7. The apparatus of claim 6, wherein said input nodes are coupled
to said output nodes via a single-ended connection scheme.
8. The apparatus of claim 6, wherein said input nodes are coupled
to said output nodes via a differential connection scheme.
9. The apparatus of claim 6, wherein the architecture of each of
said slave oscillators is similar to the architecture of said
source oscillator.
10. The apparatus of claim 6, wherein said slave oscillators are
tuned oscillators.
11. The apparatus of claim 6, wherein at least one of said slave
oscillators includes at least one shunt resonant circuit tuned to
twice said frequency.
12. The apparatus of claim 6, further comprising a matching network
coupling said slave oscillators to said source oscillator.
13. The apparatus of claim 5, wherein said source oscillator is a
tuned oscillator.
14. A communication device comprising: a dipole antenna; and a
quadrature oscillator including at least a source oscillator able
to oscillate at a frequency and to produce substantially anti-phase
output signals at said frequency, said quadrature oscillator able
to generate quadrature signals from said output signals, said
quadrature signals having substantially half said frequency and
having a phase difference therebetween of substantially .pi./2
radians.
15. The communication device of claim 14, wherein said quadrature
oscillator further includes two slave oscillators having input
nodes coupled to output nodes of said source oscillator.
16. The communication device of claim 14, wherein said
communication device is a mobile station.
17. A communication system comprising: a first communication
device; and a second communication device able to communicate with
said first communication device via a communication channel,
wherein at least one of said first communication device and said
second communication device comprises: a quadrature oscillator
including at least a source oscillator able to oscillate at a
frequency and to produce substantially anti-phase output signals at
said frequency, said quadrature oscillator able to generate
quadrature signals from said output signals, said quadrature
signals having substantially half said frequency and having a phase
difference therebetween of substantially .pi./2 radians.
18. The communication system of claim 17, wherein said quadrature
oscillator further includes two slave oscillators having input
nodes coupled to output nodes of said source oscillator.
19. The communication system of claim 18, wherein said quadrature
oscillator further comprises a matching network coupling said slave
oscillators to said source oscillator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/401,024, filed Mar. 28, 2003.
BACKGROUND OF THE INVENTION
[0002] Radio frequency (RF) transceivers may use quadrature
modulation for higher spectral efficiency. The quadrature signals
that are used for modulation and demodulation directly affect the
performance of the transceiver and thus it is desirable that the
quadrature signals be precise and have a low phase noise.
Consequently, these signals may be generated locally at the
transceiver.
[0003] In some conventional transceivers, an oscillator is used to
produce an initial frequency at four times the desired frequency of
the quadrature signals. The initial frequency is then divided down
using at least two stages of digital dividers.
[0004] It is well known that generating a high frequency signal may
be difficult due to device parasitic capacitances and inductances
in the process. This, and the fact the in some conventional
transceivers, the source oscillator oscillates at a frequency four
times higher than the desired frequency of the quadrature signals,
currently limit the quadrature signal frequencies that can be
generated. High frequency signals also tend to have a high phase
noise.
[0005] It is also known that digital dividers are high bandwidth
devices, and consequently, the quadrature signals at their output
may have more phase noise than the original signal before
division.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with objects, features and advantages
thereof, may best be understood by reference to the following
detailed description when read with the accompanied drawings in
which:
[0007] FIG. 1 is a simplified block-diagram illustration of an
exemplary communication system, in accordance with some embodiments
of the present invention;
[0008] FIG. 2A is a simplified block-diagram illustration of a
quadrature oscillator, in accordance with some embodiments of the
present invention;
[0009] FIG. 2B is a simplified exemplary illustration of waveforms
of signals in the quadrature oscillator of FIG. 2A; and
[0010] FIGS. 3-10 are schematic illustration of quadrature
oscillators, in accordance with various embodiments of the present
invention.
[0011] It will be appreciated that for simplicity and clarity of
illustration, elements shown in the figures have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements may be exaggerated relative to other elements for clarity.
Further, where considered appropriate, reference numerals may be
repeated among the figures to indicate corresponding or analogous
elements.
DETAILED DESCRIPTION OF THE INVENTION
[0012] In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of the invention. However it will be understood by those of
ordinary skill in the art that the present invention may be
practiced without these specific details. In other instances,
well-known methods, procedures, components and circuits have not
been described in detail so as not to obscure the present
invention.
[0013] It should be understood that the present invention may be
used in a variety of applications. Although the present invention
is not limited in this respect, the circuit disclosed herein may be
used in many apparatuses such as the transmitters and receivers of
a radio system. Radio systems intended to be included within the
scope of the present invention include, by way of example only,
cellular radio telephone communication systems, wireless local area
networks that meet the existing 802.11a, b, g, and future high
data-rate versions of the above, two-way radio communication
systems, one-way pagers, two-way pagers, personal communication
systems (PCS) and the like.
[0014] Types of cellular radiotelephone communication systems
intended to be within the scope of the present invention include,
although not limited to, Direct Sequence-Code Division Multiple
Access (DS-CDMA) cellular radiotelephone communication systems,
Global System for Mobile Communications (GSM) cellular
radiotelephone systems, North American Digital Cellular (NADC)
cellular radiotelephone systems, Time Division Multiple Access
(TDMA) systems, Extended-TDMA (E-TDMA) cellular radiotelephone
systems, wideband CDMA (WCDMA), General Packet Radio Service (GPRS)
systems, Enhanced Data for GSM Evolution (EDGE) systems, 3.5G and
4G systems.
[0015] FIG. 1 is a simplified block-diagram illustration of an
exemplary communication system, in accordance with some embodiments
of the present invention. A communication device 100 is able to
communicate with a communication device 110 over a communication
channel 120. It will be appreciated by persons of ordinary skill in
the art that a quadrature oscillator according to embodiments of
the present invention may be present in communication device 100
only or in communication device 110 only or in both communication
devices 100 and 110. The following description is based on the
example of both communication devices comprising a quadrature
oscillator according to one or another of the embodiments of the
present invention, although the present invention is not limited in
this respect.
[0016] Although the present invention is not limited in this
respect, the system shown in FIG. 1 may be part of a cellular
communication system, with one of communication devices 100, 110
being a base station and the other a mobile station or with both
apparatuses 100, 110 being mobile stations, a pager communication
system, a personal digital assistant and a server, etc.
Communication devices 100 and 110 may each comprise a radio
frequency antenna 102, which may be, for example, a dipole antenna
or any other suitable radio frequency antenna.
[0017] Communication device 100 may comprise a transmitter 108 that
may comprise a modulator 103 and a quadrature oscillator 109.
Modulator 103 may modulate and upconvert a data signal 101 using
quadrature signals 105 and 106 generated by quadrature oscillator
109 to produce an upconverted modulated data signal 104, which
after amplification by a power amplifier (not shown) may then be
transmitted by RF antenna 102 over communication channel 120.
[0018] Communication device 110 may comprise a receiver 118 that
may comprise a demodulator 113 and a quadrature oscillator,
referenced 109 to indicate that it may be similar to quadrature
oscillator 109 of transmitter 108. Receiver 118 may receive a
modulated data signal 111 from communication channel 120 via RF
antenna 102, which may be demodulated and downconverted by
demodulator 113 using quadrature signals 105 and 106 generated by
quadrature oscillator 109.
[0019] It will be appreciated by persons of ordinary skill in the
art that communication devices 100 and 110, and in particular
transmitter 108 and receiver 118, may comprise additional
components that are not shown in FIG. 1 so as not to obscure the
invention.
[0020] FIG. 2A is a simplified block-diagram illustration of an
exemplary quadrature oscillator, in accordance with some
embodiments of the present invention. Quadrature oscillator 209 may
comprise a master tuned-oscillator 200 and two slave
tuned-oscillators 201 and 202.
[0021] The master tuned-oscillator 200 may oscillate at its natural
self-resonant frequency f.sub.M, which may be selectable from a
range of frequencies, producing two signals 203 and 204. Both
signals may have a frequency 2 f.sub.O and a phase difference of
.pi. radians therebetween.
[0022] Slave tuned-oscillators 201 and 202 may have natural
self-resonant frequencies f.sub.S1 and f.sub.S2, respectively.
Slave tuned-oscillator 201 (202) may comprise an input node 207
(208) having the property that when slave tuned-oscillator 201
(202) oscillates at its natural self-resonant frequency, only even
harmonics of the natural self-resonant frequency can exist at this
input node 207 (208). Slave tuned-oscillator 201 (202) may also
comprise an optional input node 217 (218) having the property that
when slave tuned-oscillator 201 (202) oscillates at its natural
self-resonant frequency, only even harmonics of the natural
self-resonant frequency can exist at this input node 217 (218).
Moreover, the signal at input node 217 (218) may have a phase
difference of .pi. radians from the signal at node 207 (208).
[0023] However, if a periodic signal having certain characteristics
is injected into input node 207 (208), slave tuned-oscillator 201
(202) and its output signal 205 (206) may oscillate at half of the
injected signal's frequency and not at its natural self-resonant
frequency f.sub.S1 (f.sub.S2). Moreover, output signal 205 (206)
may maintain phase relations with the signal injected at 207
(208).
[0024] If a periodic signal having certain characteristics is
injected into input node 207 (208), and in addition, a periodic
signal having similar characteristics and having a phase difference
of .pi. radians from the signal at node 207 (208) is injected into
input node 217 (218), slave tuned-oscillator 201 (202) and its
output signal 205 (206) may oscillate at half of the injection
signal's frequency and not at its natural self-resonant frequency
f.sub.S1 (f.sub.S2). This oscillation may be more immune to noise
than the oscillation induced by having an injected signal only at
one input node. Moreover, output signal 205 (206) may maintain
phase relations with the signal injected at 207 (208).
Consequently, a period of the signal at 205 (206) may contain two
periods of the signal at 207 (208).
[0025] Signal 203, having a frequency of 2 f.sub.O, may be injected
into node 207 of slave tuned-oscillator 201 through an optional
matching network 210. If slave tuned-oscillator 201 is tuned to
have its resonant frequency f.sub.S1 sufficiently close, for
example, within an injection-locking range, to f.sub.O, and the
amplitude of signal 203 is within an appropriate range, then slave
tuned-oscillator 201 may oscillate at half of the frequency of
signal 203, namely at f.sub.O. Slave tuned-oscillator 201 may then
generate output signal 205 at frequency f.sub.O and maintain a
phase relation with signal 203. In other words, slave
tuned-oscillator 201 is `locked` to signal 203.
[0026] Similarly, signal 204, having a frequency of 2 f.sub.O, may
be injected into node 208 of slave tuned-oscillator 202 through
optional matching network 210. If slave tuned-oscillator 202 is
tuned to have its natural self-resonant frequency f.sub.S2
sufficiently close, for example, within an injection-locking range,
to f.sub.O, and the amplitude of signal 204 is within an
appropriate range, then slave tuned-oscillator 202 may oscillate at
half of the frequency of signal 204, namely at f.sub.O. Slave
tuned-oscillator 202 may then generate output signal 206 at
frequency f.sub.O and maintain a phase relation with signal 204. In
other words, slave tuned-oscillator 202 is `locked` to signal
204.
[0027] In addition, signal 203 may be injected into node 218 of
slave tuned-oscillator 202 through optional matching network 210,
and signal 204 may be injected into node 217 of slave
tuned-oscillator 201 through optional matching network 210.
[0028] Reference is now made briefly to FIG. 2B, which is a
simplified exemplary illustration of a waveform of signals 203,
204, 205 and 206 of FIG. 2A, when slave tuned-oscillator 201 is
locked to signal 203 and slave tuned-oscillator 202 is locked to
signal 204. Signals 203 and 204 may have a period T and may be
opposite in direction, reflecting a frequency of 2 f.sub.O and a
phase difference of .pi. radians. Signals 205 and 206 may have a
period 2T, reflecting a frequency of f.sub.O.
[0029] Signal 205 may maintain phase relations with signal 203,
having direction changes 240 occurring T1 seconds after low-to-high
changes 245 of signal 203. Signal 206 may maintain phase relations
with signal 204, having direction changes 250 occurring T2 seconds
after low-to-high changes 255 of signal 204. When slave
tuned-oscillator 201 is locked to signal 203 and slave
tuned-oscillator 202 is locked to signal 204, then T1 equals T2,
resulting in phase quadrature, that is, a phase difference of
.pi./2 radians between signals 205 and 206. Since signals 205 and
206 are generated by two tuned circuits that are locked together,
the phase noise may be reduced by a factor related to the square of
the quality factor of the resonant circuits ("tanks").
[0030] In FIGS. 3-10, quadrature oscillators according to various
exemplary embodiments of the present invention will now be
described. These exemplary quadrature oscillators include exemplary
embodiments of master tuned-oscillators and slave tuned-oscillators
corresponding to the master tuned-oscillators and slave
tuned-oscillators of FIG. 2A.
[0031] In FIGS. 3, 4, 5, 7, and 8, a master tuned-oscillator is
coupled to slave tuned-oscillators with single-ended inputs,
possibly using appropriate matching networks. In FIGS. 6, 9, and
10, a master tuned-oscillator is coupled to slave tuned-oscillators
with differential inputs.
[0032] The master tuned-oscillators illustrated in FIGS. 3, 7, and
10 are tuned to oscillate at 2 f.sub.O in order to generate output
signals 203 and 204 oscillating at 2 f.sub.O. In contrast, in FIGS.
4, 5, 6, 8 and 9, since output signals 203 and 204 are generated at
second-harmonic nodes, master tuned-oscillator is tuned to
oscillate at f.sub.O to produce output signals 203 and 204
oscillating at 2 f.sub.O.
[0033] FIG. 3 is a schematic illustration of a quadrature
oscillator 309, in accordance with some embodiments of the present
invention. Quadrature oscillator 309 may comprise a master
tuned-oscillator 300 and slave tuned-oscillators 301 and 302, and
may optionally comprise a matching network 310.
[0034] Master tuned-oscillator 300 may comprise two pairs of
cross-coupled transistors 316, a tank 314, and a transistor 318.
Tank 314 may comprise capacitors 311 and inductors 312 connected in
parallel. The natural self-resonant frequency f.sub.M of master
tuned-oscillator 300 may be determined by the properties of
capacitors 311 and inductors 312. Inductors 312 may have a fixed
inductance, while capacitors 311 may be variable and controlled for
the purpose of tuning the natural self-resonant frequency f.sub.M.
Cross-coupled transistors 316 may create a negative resistance path
to cancel out any losses in tank 314. Transistor 318 may be a tail
current source, receiving a biasing signal 320 at its gate 322. A
node 324 may have the property that only even harmonics of the
natural self-resonant frequency f.sub.M can exist at this node.
[0035] Natural self-resonant frequency f.sub.M of master
tuned-oscillator 300 may be tuned to be 2 f.sub.O, namely, signals
203 and 204 may be of frequency 2 f.sub.O.
[0036] Slave tuned-oscillator 301 (302) may comprise two pairs of
cross-coupled transistors 336 (356), a tank 334 (354) and a
transistor 338 (358). Tank 334 (354) may comprise capacitors 330
(350) and inductors 332 (352) connected in parallel. The natural
self-resonant frequency f.sub.S1 (f.sub.S2) of slave
tuned-oscillator 301 (302) may be determined by the properties of
capacitors 330 (350) and inductors 332 (352). Inductors 332 (352)
may have a fixed inductance, while capacitors 330 (350) may be
variable and controlled for the purpose of tuning the natural
self-resonant frequency f.sub.S1 (f.sub.S2). Cross-coupled
transistors 336 (356) may create a negative resistance path to
cancel out any losses in tank 334 (354). Transistor 338 (358) may
be a tail current source receiving a biasing signal 340 (360) at
its gate 342 (362). Natural self-resonant frequency f.sub.S1
(f.sub.S2) of slave tuned-oscillators 301 (302) may be tuned to be
sufficiently close to f.sub.O. Moreover, the signal injected at an
input node 207 (208) may have the appropriate amplitude, and
consequently slave tuned-oscillator 301 (302) may lock to the
signal at input node 207 (208).
[0037] A single-ended connection scheme, an exemplary embodiment of
which is shown by matching network 310, may be used to couple
master tuned-oscillator 300 and slave tuned-oscillators 301 and
302. Matching network 310 may couple signal 203 to input node 207
and signal 204 to input node 208. Capacitors 370 of matching
network 310 may block the direct current (DC) components and pass
the alternate current (AC) components of signals 203 and 204.
Although the present invention is not limited in this respect,
capacitors 370 may be Metal-Insulator-Metal (MiM) capacitors
available as an add-on for Complementary-Metal-Oxide-Sem-
iconductor (CMOS), vertical mesh Metal-Metal capacitors. Matching
network 310 may optionally comprise buffers 372 coupled to
capacitors 370 to minimize kickback of signals into master
tuned-oscillator 300.
[0038] FIG. 4 is a schematic illustration of a quadrature
oscillator 409, in accordance with some embodiments of the present
invention. Quadrature oscillator 409 may comprise a master
tuned-oscillator 400 and slave tuned-oscillators 301 and 302, and
may optionally comprise matching network 310.
[0039] Master tuned-oscillator 400 is similar to master
tuned-oscillator 300, and may have differences as described
below.
[0040] Master tuned-oscillator 400 may contain a tail current
source transistor 410 that may require an additional biasing signal
414 and may create a node 412. As with node 324, node 412 may have
the property that only even harmonics of the natural self-resonant
frequency f.sub.M can exist at this node. Moreover, the signal at
node 412 may have a phase difference of .pi. radians from the
signal at node 324.
[0041] Provided that master tuned-oscillator 400 is tuned to
oscillate at frequency f.sub.M=f.sub.O, nodes 324 and 412 may
develop the second harmonic of f.sub.M, namely 2 f.sub.O, and may
oscillate with a phase difference of .pi. radians. Consequently
nodes 324 and 412 may be used as sources for signals 204 and 203,
respectively.
[0042] FIG. 5 is a schematic illustration of a quadrature
oscillator 509, in accordance with some embodiments of the present
invention. Quadrature oscillator 509 may comprise master
tuned-oscillator 400 and slave tuned oscillators 501 and 502, and
may optionally comprise matching network 310.
[0043] Slave tuned oscillators 501 and 502 are similar to slave
tuned-oscillators 301 and 302, respectively, and may have
differences as described below.
[0044] Slave tuned-oscillator 501 (502) may contain a tail current
source transistor 510 (512) that may receive a biasing signal at an
input node 514 (516) and may create a node 507 (508). Node 507
(508) may have similar properties to those of node 207 (208),
namely, if slave tuned-oscillator 501 (502) oscillates in its
natural self-resonant frequency f.sub.S1 (f.sub.S2), only even
harmonics of the natural self-resonant frequency can exist at this
node. Moreover, the signal at node 507 (508) may have a phase
difference of .pi. radians from the signal at node 207 (208).
[0045] When a periodic signal of 2 f.sub.O frequency and adequate
amplitude is injected into node 207 (208), node 507 (508) may
oscillate at frequency 2 f.sub.O and may have a phase that is .pi.
radians apart from the injected signal at node 207 (208).
[0046] It will be appreciated by persons of ordinary skill in the
art that the architecture of slave tuned-oscillators 501 and 502 is
similar to that of master tuned-oscillator 400. Consequently, the
total phase noise associated with quadrature oscillator 509 may be
reduced relative to that associated with quadrature oscillator
409.
[0047] FIG. 6 is a schematic illustration of a quadrature
oscillator 609, in accordance with some embodiments of the present
invention. Quadrature oscillator 609 may comprise master
tuned-oscillator 400 and slave tuned-oscillators 501 and 502, and
may optionally comprise a matching network 610.
[0048] A differential connection scheme, an exemplary embodiment of
which is shown by matching network 610, may be used to couple
master tuned-oscillator 400 and slave tuned-oscillators 501 and
502. Matching network 610 may couple signal 203 to input node 207
of slave tuned-oscillator 501 and to input node 508 of slave
tuned-oscillator 502, and may also couple signal 204 to input node
208 of slave tuned-oscillator 502 and to input node 507 of slave
tuned-oscillator 501.
[0049] Matching network 610 may comprise capacitors 370 for input
nodes 207 and 208, and capacitors 614 for input nodes 507 and 508.
Matching network 610 may also optionally comprise buffers 372 for
input nodes 207 and 208, and buffers 612 for input nodes 507 and
508.
[0050] When a periodic signal of 2 f.sub.O frequency and adequate
amplitude is injected into node 207 (208), node 507 (508) may
oscillate at frequency 2 f.sub.O and may have a phase that is .pi.
radians apart from the injected signal at node 207 (208).
[0051] Furthermore, when a periodic signal of 2 f.sub.O frequency
and adequate amplitude is injected into node 507 (508), slave
tuned-oscillator 501 (502) and its output signal 205 (206) may
oscillate at half of the injection signal's frequency and not at
its natural self-resonant frequency f.sub.S1 (f.sub.S2), and may
maintain phase relations with the signal injected at node 507
(508).
[0052] Furthermore, when periodic signals of 2 f.sub.O frequency,
adequate amplitudes and a phase difference of .pi. radians are
injected into nodes 207 and 507 (208 and 508), slave
tuned-oscillator 501 (502) may oscillate at f.sub.O frequency and
maintain phase relations with the injected signals. This behavior
is the same, but more immune to noise, than in the case of a signal
injected solely into node 207 (208) or 507 (508).
[0053] It will be appreciated by persons of ordinary skill in the
art that since quadrature oscillator 609 incorporates a
differential connection scheme, the total phase noise associated
with quadrature oscillator 609 may be less than that of quadrature
oscillator 509, which incorporates a single-ended connection
scheme.
[0054] FIG. 7 is a schematic illustration of a quadrature
oscillator 709, in accordance with some embodiments of the present
invention. Quadrature oscillator 709 may comprise master
tuned-oscillator 300 and slave tuned-oscillators 701 and 702, and
may optionally comprise a matching network 710.
[0055] Gate 342 (362) of tail current source transistor 338 (358)
may be used at tuned oscillator 701 (702) as input node 207 (208).
The amplitude of the signal at input node 207 (208) may be smaller
than the minimum amplitude required to force slave tuned-oscillator
701 (702) to oscillate at f.sub.O. (In this embodiment, the natural
self-resonant frequency f.sub.M of master tuned-oscillator 300 may
be tuned to be 2 f.sub.O, namely, signals 203 and 204 may be of
frequency 2 f.sub.O.) Slave tuned oscillator 701 (702) may
therefore optionally comprise a shunt resonant circuit 730 (732),
tuned to 2 f.sub.O frequency. Shunt resonant circuit 730 (732) may
be coupled to a node 770 (772), matching the amplitude requirements
of slave tuned-oscillator 701 (702) to the amplitude of the signal
at input node 207 (208).
[0056] A single-ended connection scheme, an exemplary embodiment of
which is shown by matching network 710, may be used to couple
master tuned-oscillator 300 and slave tuned-oscillators 701 and
702. Matching network 710 comprising capacitors 370 may couple
signal 203 to input node 207 and signal 204 to input node 208. In
contrast with matching network 310 of FIG. 3, matching network 710
may not comprise buffers 372 since the input impedance of gates 342
and 362 may be high. Matching network 710 may comprise resistors
711 and 712 to inject DC biasing signals 722 and 724 to the gates
342 and 362 of tail current source transistors 338 and 358,
respectively.
[0057] FIG. 8 is a schematic illustration of a quadrature
oscillator 809, in accordance with some embodiments of the present
invention. Quadrature oscillator 809 may comprise master
tuned-oscillator 400 and slave tuned-oscillators 801 and 802, and
may optionally comprise matching network 710.
[0058] Slave tuned oscillators 801 and 802 are similar to slave
tuned-oscillators 701 and 702 of FIG. 7 respectively, and may have
differences as described below.
[0059] Slave tuned-oscillator 801 (802) may contain tail current
source transistor 510 (512) that may require an additional biasing
signal at node 514 (516) and may create a node 507 (508)
[0060] As in quadrature oscillator 509 of FIG. 5, the architecture
of slave tuned-oscillators 801 and 802 is similar to that of master
tuned-oscillator 400. Consequently, the total phase noise
associated with quadrature oscillator 809 may be reduced.
[0061] FIG. 9 is a schematic illustration of a quadrature
oscillator 909, in accordance with some embodiments of the present
invention. Quadrature oscillator 909 may comprise master
tuned-oscillator 400 and slave tuned-oscillators 901 and 902, and
may optionally comprise a matching network 910.
[0062] Slave tuned oscillators 901 and 902 are similar to slave
tuned-oscillators 801 and 802, respectively, and may have
differences as described below.
[0063] A shunt resonant circuit 930, that may be similar to shunt
resonant circuit 730, may be coupled to node 507 of slave
tuned-oscillator 901. A shunt resonant circuit 932, that may be
similar to shunt resonant circuit 732, may be coupled to node 508
of slave tuned-oscillator 902.
[0064] A differential connection scheme, an exemplary embodiment of
which is shown by matching network 910, may be used to couple
master tuned-oscillator 400 and slave tuned-oscillators 901 and
902. Matching network 910 may couple signal 203 to input node 207
of slave tuned-oscillator 901 and to input node 516 of slave
tuned-oscillator 902, and may also couple signal 204 to input node
208 of slave tuned-oscillator 902 and to input node 514 of slave
tuned-oscillator 901.
[0065] Matching network 910 may comprise capacitors 370 for input
nodes 207 and 208, and may also comprise resistors 711 and 712 to
couple DC biasing signals 722 and 724 to the gates 342 and 362 of
tail current source transistors 338 and 358, respectively.
Moreover, matching network 910 may comprise capacitors 914 for
input nodes 514 and 516, and may also comprise resistors 920 and
922 to couple DC biasing signals 924 and 926 to the gates of tail
current source transistors 510 and 512, respectively.
[0066] It will be appreciated by persons of ordinary skill in the
art that since quadrature oscillator 909 incorporates a
differential connection scheme, the total phase noise associated
with quadrature oscillator 909 may be less than that of quadrature
oscillator 809, which incorporates a single-ended connection
scheme.
[0067] While certain features of the invention have been
illustrated and described herein, many modifications,
substitutions, changes, and equivalents will now occur to those of
ordinary skill in the art. As one non-limiting example of these
many modifications and changes, a quadrature oscillator 1009 shown
in FIG. 10 may comprise master tuned-oscillator 300 and slave
tuned-oscillators 501 and 502, and may optionally comprise matching
network 610. It is, therefore, to be understood that the appended
claims are intended to cover all such modifications and changes as
fall within the true spirit of the invention.
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