Patent Publication Number: US-2005116784-A1

Title: Quadrature oscillator and methods thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a divisional application of U.S. patent application Ser. No. 10/401,024, filed Mar. 28, 2003. 
    
    
     BACKGROUND OF THE INVENTION  
      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.  
      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.  
      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.  
      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  
      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:  
       FIG. 1  is a simplified block-diagram illustration of an exemplary communication system, in accordance with some embodiments of the present invention;  
       FIG. 2A  is a simplified block-diagram illustration of a quadrature oscillator, in accordance with some embodiments of the present invention;  
       FIG. 2B  is a simplified exemplary illustration of waveforms of signals in the quadrature oscillator of  FIG. 2A ; and  
       FIGS. 3-10  are schematic illustration of quadrature oscillators, in accordance with various embodiments of the present invention. 
    
    
      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  
      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.  
      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.  
      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.  
       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.  
      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.  
      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 .  
      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 .  
      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.  
       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 .  
      The master tuned-oscillator  200  may oscillate at its natural self-resonant frequency f M , which may be selectable from a range of frequencies, producing two signals  203  and  204 . Both signals may have a frequency 2 f O  and a phase difference of π radians therebetween.  
      Slave tuned-oscillators  201  and  202  may have natural self-resonant frequencies f S1  and f 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 π radians from the signal at node  207  ( 208 ).  
      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&#39;s frequency and not at its natural self-resonant frequency f S1  (f S2 ). Moreover, output signal  205  ( 206 ) may maintain phase relations with the signal injected at  207  ( 208 ).  
      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 π 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&#39;s frequency and not at its natural self-resonant frequency f S1  (f 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 ).  
      Signal  203 , having a frequency of 2 f 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 S1  sufficiently close, for example, within an injection-locking range, to f 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 O . Slave tuned-oscillator  201  may then generate output signal  205  at frequency f O  and maintain a phase relation with signal  203 . In other words, slave tuned-oscillator  201  is ‘locked’ to signal  203 .  
      Similarly, signal  204 , having a frequency of 2 f 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 S2  sufficiently close, for example, within an injection-locking range, to f 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 O . Slave tuned-oscillator  202  may then generate output signal  206  at frequency f O  and maintain a phase relation with signal  204 . In other words, slave tuned-oscillator  202  is ‘locked’ to signal  204 .  
      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 .  
      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 O  and a phase difference of π radians. Signals  205  and  206  may have a period  2 T, reflecting a frequency of f O .  
      Signal  205  may maintain phase relations with signal  203 , having direction changes  240  occurring T 1  seconds after low-to-high changes  245  of signal  203 . Signal  206  may maintain phase relations with signal  204 , having direction changes  250  occurring T 2  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 T 1  equals T 2 , resulting in phase quadrature, that is, a phase difference of π/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”).  
      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 .  
      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.  
      The master tuned-oscillators illustrated in  FIGS. 3, 7 , and  10  are tuned to oscillate at 2 f O  in order to generate output signals  203  and  204  oscillating at 2 f 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 O  to produce output signals  203  and  204  oscillating at 2 f O .  
       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 .  
      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 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 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 M  can exist at this node.  
      Natural self-resonant frequency f M  of master tuned-oscillator  300  may be tuned to be 2 f O , namely, signals  203  and  204  may be of frequency 2 f O .  
      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 S1  (f 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 S1  (f 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 S1  (f S2 ) of slave tuned-oscillators  301  ( 302 ) may be tuned to be sufficiently close to f 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 ).  
      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-Semiconductor (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 .  
       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 .  
      Master tuned-oscillator  400  is similar to master tuned-oscillator  300 , and may have differences as described below.  
      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 M  can exist at this node. Moreover, the signal at node  412  may have a phase difference of π radians from the signal at node  324 .  
      Provided that master tuned-oscillator  400  is tuned to oscillate at frequency f M =f O , nodes  324  and  412  may develop the second harmonic of f M , namely 2 f O , and may oscillate with a phase difference of π radians. Consequently nodes  324  and  412  may be used as sources for signals  204  and  203 , respectively.  
       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 .  
      Slave tuned oscillators  501  and  502  are similar to slave tuned-oscillators  301  and  302 , respectively, and may have differences as described below.  
      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 S1  (f 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 π radians from the signal at node  207  ( 208 ).  
      When a periodic signal of 2 f O  frequency and adequate amplitude is injected into node  207  ( 208 ), node  507  ( 508 ) may oscillate at frequency 2 f O  and may have a phase that is π radians apart from the injected signal at node  207  ( 208 ).  
      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 .  
       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 .  
      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 .  
      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 .  
      When a periodic signal of 2 f O  frequency and adequate amplitude is injected into node  207  ( 208 ), node  507  ( 508 ) may oscillate at frequency 2 f O  and may have a phase that is π radians apart from the injected signal at node  207  ( 208 ).  
      Furthermore, when a periodic signal of 2 f 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&#39;s frequency and not at its natural self-resonant frequency f S1  (f S2 ), and may maintain phase relations with the signal injected at node  507  ( 508 ).  
      Furthermore, when periodic signals of 2 f O  frequency, adequate amplitudes and a phase difference of π radians are injected into nodes  207  and  507  ( 208  and  508 ), slave tuned-oscillator  501  ( 502 ) may oscillate at f 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 ).  
      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.  
       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 .  
      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 O . (In this embodiment, the natural self-resonant frequency f M  of master tuned-oscillator  300  may be tuned to be 2 f O , namely, signals  203  and  204  may be of frequency 2 f O .) Slave tuned oscillator  701  ( 702 ) may therefore optionally comprise a shunt resonant circuit  730  ( 732 ), tuned to 2 f 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 ).  
      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.  
       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 .  
      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.  
      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 )  
      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.  
       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 .  
      Slave tuned oscillators  901  and  902  are similar to slave tuned-oscillators  801  and  802 , respectively, and may have differences as described below.  
      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 .  
      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 .  
      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.  
      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.  
      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.