Abstract:
Sharing one or more load inductors comprises receiving a first input signal at a first terminal of a first amplifier and amplifying the first input signal using the first amplifier. The first amplifier is coupled to one or more load inductors at a second terminal of the first amplifier and is coupled to one or more dedicated source inductors at a third terminal of the first amplifier. Also, a second input signal is received at a first terminal of a second amplifier amplifying the second input signal using the second amplifier. The second amplifier is coupled to the one or more load inductors at a second terminal of the second amplifier and is coupled to one or more dedicated source inductors at a third terminal of the second amplifier.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of priority from U.S. Provisional Application entitled “LOAD INDUCTOR SHARING”, Application No. 60/975,778 filed Sep. 27, 2007, the disclosure of which is incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]    This disclosure generally relates to the use and design of inductors in radio frequency circuitry. 
       BACKGROUND  
       [0003]    Communication systems which utilize radio frequency (RF) signals often include the use of low noise amplifiers (LNAs) to amplify portions of received RF signals. LNAs are often selected for their ability amplify the typically weak signals of RF signals while maintaining a low noise figure. Also, use of LNAs typically includes use of source and load inductors in conjunction with transistors or field effect devices. 
       SUMMARY  
       [0004]    According to one general aspect, a method for sharing one or more load inductors comprises receiving a first input signal at a first terminal of a first amplifier and amplifying the first input signal using the first amplifier. The first amplifier is coupled to one or more load inductors at a second terminal of the first amplifier and is coupled to one or more dedicated source inductors at a third terminal of the first amplifier. The method also includes receiving a second input signal at a first terminal of a second amplifier amplifying the second input signal using the second amplifier. The second amplifier is coupled to the one or more load inductors at a second terminal of the second amplifier and is coupled to one or more dedicated source inductors at a third terminal of the second amplifier. 
         [0005]    These and other implementations can optionally include one or more of the following features. For example, the method can include disabling the amplification of the first amplifier during a first time period in which the second amplifier is amplifying the second input signal and disabling the amplification of the second amplifier during a second time period in which the first amplifier is amplifying the first input signal. Disabling the amplification of the first amplifier can include switching the first terminal of the first amplifier to ground. Disabling the amplification of the first or the second amplifier can include disconnecting the one or more load inductors. Disabling the amplification of the first or the second amplifier can include disconnecting a power supply. Disabling the amplification of the first and the second amplifiers can include using a control circuit such that the control circuit is configured to switch the first terminal of the first amplifier to ground and to switch the first terminal of the second amplifier to ground 
         [0006]    Also, amplifying the first or second input signals can include using a control circuit such that the control circuit is configured to control a first switch such that the first amplifier is active and the control circuit is configured to concurrently control a second switch such that the second amplifier is not active. The control circuit can be configured to not activate the first amplifier and the second amplifier concurrently. Amplifying the first input signal using the first amplifier can include amplifying the first input signal only at times when the second amplifier is not active. The first input signal can be a first differential input signal and the second input signal can be a second differential input signal. The first amplifier can include a first differential amplifier and the second amplifier can include a second differential amplifier. The one or more load inductors can include a pair of load inductors of equal value and the one or more dedicated source inductors coupled to the third terminal of the first amplifier can include a first pair of source indictors of equal value and the one or more dedicated source inductors coupled to the third terminal of the second amplifier can include a second pair of source inductors of equal value. 
         [0007]    Further, the first input signal can have a first center frequency and the second input signal can have a second, different, center frequency. The first amplifier can be dedicated to a first frequency band with a first center frequency and the second amplifier can be dedicated to a second, different, frequency band with a second center frequency. The difference of the first and second center frequencies can be within a defined frequency bandwidth. The first and the second amplifiers are low noise amplifiers with a cascode topology. The first and the second amplifiers can be low noise amplifiers with a single transistor topology which include one transistor for a single ended input signal and two transistors for a differential input signal. The second terminal of the first amplifier can be coupled to the second terminal of the second amplifier. 
         [0008]    According to a second general aspect, a method for sharing one or more load inductors comprises coupling a first input terminal to a first terminal of a first amplifier and coupling at least one load inductor to a second terminal of the first amplifier. The method also includes coupling one or more dedicated source inductors to a third terminal of the first amplifier and coupling a second input terminal to a first terminal of a second amplifier. The method further includes coupling the at least one load inductor to a second terminal of the second amplifier and coupling one or more dedicated source inductors to a third terminal of the second amplifier. 
         [0009]    These and other implementations can optionally include one or more of the following features. For example, the first amplifier can be dedicated to a first frequency band with a first center frequency and the second amplifier can be dedicated to a second, different frequency band with a second center frequency. The difference of the first and second center frequencies can be within a defined frequency bandwidth. The method can include coupling a first output of a control circuit to a first switch such that the control circuit is configured to use the first switch to switch between coupling or not coupling the first terminal of the first amplifier to ground and coupling a second output of the control circuit to a second switch, such that the control circuit is configured to use the second switch to switch between coupling or not coupling the first terminal of the second amplifier to ground. The control circuit can be configured to always couple at least one of the first terminal of the first amplifier and the first terminal of the second amplifier to ground when amplification is being conducted. The first and the second amplifiers can be low noise amplifiers with a cascode topology. The first and the second amplifiers can be low noise amplifiers with a single transistor topology comprising one transistor for a single ended input signal and two transistors for a differential input signal. 
         [0010]    Also, the first and second input terminals are differential input terminals, the first terminal of the first amplifier is a differential terminal, and the first terminal of the second amplifier is a differential terminal. Coupling the at least one load inductor to the second terminal of the first amplifier can include coupling a pair of load inductors of equal value to a second differential terminal of the first amplifier and coupling the at least one load inductor to the second terminal of the second amplifier can include coupling the pair of load inductors of equal value to a second differential terminal of the second amplifier. Coupling the one or more dedicated source inductors to the third terminal of the first amplifier can include coupling a first pair of source inductors of equal value to a third differential terminal of the first amplifier and coupling the one or more dedicated source inductors to the third terminal of the second amplifier can include coupling a second pair of source inductors of equal value to a third differential input terminal of the second amplifier. The method can further include coupling the second terminal of the first amplifier to the second terminal of the second amplifier. 
         [0011]    According to a third general aspect, a circuit for sharing one or more load inductors includes a first terminal of a first amplifier coupled to a first input terminal and at least one load inductor coupled to a second terminal of the first amplifier. The circuit also includes one or more dedicated source inductors coupled to a third terminal of the first amplifier and a first terminal of a second amplifier coupled to a second input terminal. The circuit further includes a second terminal of the second amplifier coupled to the at least one load inductor and a third terminal of the second amplifier coupled to one or more dedicated source inductor. 
         [0012]    These and other implementations can optionally include one or more of the following features. For example, the second terminal of the first amplifier can be coupled to the second terminal of the second amplifier. The first amplifier can be dedicated to a first frequency band and the second amplifier can be dedicated to a second, different, frequency band. The circuit can include a control circuit with an input terminal coupled to a baseband to receive instructions from the baseband, a first switch coupled to the control circuit and configured to switch between coupling or not coupling the first terminal of the first amplifier to ground, and a second switch coupled to the control circuit and configured to switch between coupling or not coupling the first terminal of the second amplifier to ground. The control circuit can be configured to always couple at least one of the first terminal of the first amplifier and the first terminal of the second amplifier to ground when amplification is being conducted. 
         [0013]    Also, the first and the second amplifiers can be low noise amplifiers with a cascode topology. The first input terminal can be a single ended input terminal and the second input terminal can be a single ended input terminal. The first and second input terminals can be differential input terminals, the first terminal of the first amplifier can be a differential terminal, and the first terminal of the second amplifier can be a second differential terminal. The first and the second amplifiers can be low noise amplifiers with a single transistor topology comprising one transistor for a single ended input signal and two single transistors for a differential input signal. The first amplifier can include a first differential amplifier and the second amplifier can include a second differential amplifier. 
         [0014]    Further, the at least one load inductor coupled to the second terminal of the first amplifier can include a pair of load inductors of equal value coupled to a differential second terminal of the first differential amplifier and a differential second terminal of the second differential amplifier. The one or more dedicated source inductors coupled to the third terminal of the first amplifier can include a first pair of source inductors of equal value coupled to a differential third terminal of the first amplifier and the third terminal of the second amplifier coupled to the one or more dedicated source inductors can include a second pair of source inductors of equal value coupled to a differential third terminal of the second amplifier. 
         [0015]    According to a third general aspect, a system with shared one or more load inductors comprises an output terminal of an antenna coupled to input terminals of two or more RF filters and an output terminal of the RF filters coupled to two or more low noise amplifiers (LNAs). The system also includes a shared load inductor coupled to each of the two or more LNAs, such that a shared load inductor is an inductor coupled to more than one LNA and dedicated source degeneration inductors coupled to each of the two or more LNAs, such that a dedicated source degeneration inductor is an inductor coupled to no more than one LNA. The system further includes one or more outputs of the two or more LNAs coupled to a first set of one or more input terminals of a first set of one or more mixers and an output of a first local oscillator coupled to a second set of one or more input terminals of the first set of mixers. The system additionally includes a set of output signals of the first set of mixers filtered by one or more IF filters and one or more output signals of the one or more IF filters amplified by one or more IF amplifiers. Finally, the system includes one or more outputs of the one or more IF amplifiers mixed with an output signal of a second local oscillator by a second set of one or more mixers with outputs coupled to a baseband for further processing and one or more terminals of a first LNA of the two or more LNAs coupled to one or more terminals of a second LNA of the two more LNAs. 
         [0016]    The described implementations may be compatible with digital algorithms used in communication systems. Some implementations also may, for example, provide for reduced cost, power and size of circuitry. In particular, by requiring fewer inductors on, for example, silicon, the coupling effects and noise may be reduced for better performance. Load sharing of inductive elements may be able to enable integration to achieve monolithic transceivers or full radios. 
         [0017]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS  
         [0018]      FIG. 1  is a schematic of an example of a circuit with dedicated inductors. 
           [0019]      FIGS. 2A and 2B  are schematics of examples of circuits employing load inductor sharing. 
           [0020]      FIG. 3  is a schematic of an example of a circuit employing single-ended load inductor sharing. 
           [0021]      FIG. 4  is a schematic of an example of a circuit employing load inductor sharing for a group of amplifiers. 
           [0022]      FIG. 5  is a schematic of an example of a multiband low intermediate frequency (IF) receiver. 
           [0023]      FIG. 6  is a schematic of an example of a direct-conversion receiver. 
       
    
    
     DETAILED DESCRIPTION  
       [0024]    Generally, in multi-band and/or multi-standard receivers, a low-noise amplifier (LNA) circuit can be included for each frequency band. In some implementations described here, two or more load inductors for close frequencies may be shared by, for example, directly or indirectly electrically connecting the load inductors to multiple circuit components. Sharing two or more load inductors may decrease the required space, cost of the circuit, and power consumed compared to using separate load inductors for each LNA. 
         [0025]    Load inductor sharing may be employed with LNAs for a number of communication systems. Sharing may be used in, for example, GSM, Extended Global System for Mobile Communication (EGSM), DCS and PCS communications standards. For example, various implementations in quad-band communication standards such as GSM, may reduce required cost and power consumption of the LNA by approximately 25%. The load inductor sharing techniques also may be used in or applied to, for example, multiple stage cascode topology, a single transistor or other topology LNAs, both I and Q phases of the signals, wireless or wireless RF transceivers for 2 or more close frequency bands, wideband code division multiple access (WCDMA) and/or 2G, 3G, 4G wireless standards. 
         [0026]      FIG. 1  is a schematic of an example of a circuit  100  with dedicated load inductors for two LNAs  105   a  and  105   b . The circuit  100  includes components for processing at least two bands within a multi-band receiver and specifically includes two inputs  110   a  and  110   b , inductors  122 - 138 , transistors  142 - 148 , and two outputs  150   a - 150   b . The two inputs  110   a  and  110   b  can follow an antenna (not shown) or one or more RF filters (not shown) in the receiver, such as a surface acoustic wave (SAW) band select filter. The two outputs  150   a  and  150   b  can be the output amplified signals of two different bands and can be connected to one or more following mixers (not shown) of the receiver. 
         [0027]    Transistors  142  and  144  form a first differential LNA  105   a  that uses a first set of inductors  122 - 128 . Transistors  146  and  148  form a second differential LNA  105   b  that uses a second set of inductors  132 - 138 . The transistors  142  and  144  of the first differential LNA  105   a  are coupled to a dedicated set of load inductors  122  and  124 , which are not coupled to the transistors  146  and  148  of the second differential LNA  105   b . Similarly, the transistors  146  and  148  of the second differential LNA  105   b  are coupled to a dedicated set of load inductors, inductors  132  and  134 , which are not coupled to the transistors  142  and  144  of the first differential LNA  105   a . As such, the circuit  100  requires space and power for the eight inductors  122 - 138 . 
         [0028]      FIG. 2A  is a schematic of an example of a LNA circuit  200 A employing load inductor sharing for two LNAs  243 A and  247 A. Specifically, LNA circuit  200 A includes two LNAs  243 A and  247 A for processing two close frequency bands within a multi-band receiver and specifically includes two differential inputs  210 A and  211 A, load inductors  232 A and  234 A, source degeneration inductors  226 A,  228 A,  236 A, and  238 A, transistors  242 - 248 A, and one differential output  250 A. The two differential inputs  210 A and  211 A can follow an antenna or one or more RF filters, such as a SAW band select filter. The outputs  250 A are the output amplified signals, which can represent the active band and can be coupled to a following mixer. 
         [0029]    Transistors  242 A and  244 A form a first LNA  243 A, which uses a first set of inductors. The first set of inductors includes shared load inductors  232 A and  234 A and dedicated (not shared) source degeneration inductors  226 A and  228 A. Transistors  246 A and  248 A form a second LNA  247 A, which uses a second set of inductors. The second set of inductors also includes shared load inductors  232 A and  234 A and dedicated source degeneration inductors  236 A and  238 A. Therefore, shared load inductors  232 A and  234 A are used by both the first and second LNAs  243 A and  247 A. As such, the LNA circuit  200 A can require less available space and power for the load inductors of the first and second LNAs  243 A and  247 A than the circuit  100  of  FIG. 1 . Moreover, the use of dedicated source degeneration inductors in conjunction with shared load inductors can strike a balance between the benefits of sharing load inductors described above and the potential for increase of noise and decrease of circuit performance that may accompany the sharing of load inductors. 
         [0030]    In various implementations, when the first LNA  243 A is active, the second LNA  247 A is shut off with transistors  242 A and  244 A acting like open circuits. A non-active LNA can be shut-off using various methods, such as, switching an input of the LNA to ground, disconnecting the load inductors, or disconnecting the power supply. These are merely examples of methods for shutting off an LNA. In various implementations, the method and circuits can be applied to LNAs to use GSM 850 MHz and GSM 900 MHz frequency bands, DCS 1800 MHz frequency bands and PCS 1900 MHz frequency bands, WCDMA frequency bands, or other close frequency bands. When sharing load inductors for the LNAs, the load inductors may need to be able to cover the frequency bandwidths of all LNAs. Therefore, there can be an equivalent bandwidth of a maximum frequency which can be the maximum frequency of all frequency bands and a minimum frequency, which can be the minimum frequency of all frequency bands sharing load inductors. In general, if the difference of the center frequencies of the frequency bands is less than a desired frequency bandwidth, the load inductor sharing can be used for the LNAs. The desired frequency bandwidth can be a function of the bandwidths and the center frequencies of the frequency bands and a quality factor of the shared load inductors. As an example, the desired frequency bandwidth for the GSM 850 MHz and EGSM 900 MHz bands is approximately 100 MHz. The frequency difference between the center frequencies of these two bands is within this bandwidth. 
         [0031]      FIG. 2B  is a schematic of an example of a LNA circuit  200 B employing load inductor sharing between two LNAs  243 B and  247 B. The LNA circuit  200 B of  FIG. 2B  is similar to the LNA circuit  200 A of  FIG. 2A  while further including a control circuit  260 B. In particular, the LNA circuit  200 B includes two LNAs  243 B and  247 B for processing two close frequency bands within a multi-band receiver and specifically includes two differential inputs  210 B and  211 B, load inductors  232 B and  234 B, source degeneration inductors  226 B,  228 B,  236 B, and  238 B, transistors  242 - 248 B, switches  261 - 264 B and one differential output  250 B. 
         [0032]    Output terminals of the control circuit  260 B can be coupled to the controls of the switches  261 - 264 B. An input terminal of the control circuit  260 B can be coupled to the baseband to receive instructions to activate the LNAs  243 B and  247 B. Input terminals of the switches  261 - 264 B are coupled to ground. The switches  261 - 264 B can be switched to connect or disconnect each of the input terminals of the first and second differential LNAs  243 B and  247 B to ground. The LNAs  243 B and  247 B can be activated or deactivated by the switches  261 - 264 B controlled by the control circuit  260 B. Other implementations may overlap the activation of the first and second LNAs  243 B and  247 B. 
         [0033]    Also, other implementations may use the control circuit  260 B to manipulate LNA activation through use of other terminals of the first and second LNAs  243 B and  247 B. For example, the control circuit can be configured to alternately switch the shared load inductors  232 B and  234 B to the first or the second LNAs  243 B and  247 B. The LNAs  243 B and  247 B can be deactivated by disconnecting the shared load inductors, therefore disconnecting the LNAs  243 B and  247 B from the power supply. 
         [0034]      FIG. 3  is a schematic of an example of an amplifier circuit  300  employing single-ended load inductor sharing between two transistors  345  and  346 . Specifically, the single-ended amplifier circuit  300  includes a first transistor  345  that forms a first amplifier and a second transistor  346  forms a second amplifier. Both transistors  345  and  346  share a load inductor  332  and use dedicated source degeneration inductors  335  and  336 , respectively. The output  350  can be an amplified active band output signal. When the first LNA is active, the second LNA can be shut off with the second transistor  346  acting like an open circuit and vice versa using techniques such as those described with respect to  FIG. 2B , such as, for example, the switches  261 B and  263 B controlled by the control circuit  260 B. The single-ended amplifier circuit  300  can employ the load inductor sharing techniques while further reducing power requirements, size, and cost requirements. Also, circuitry of the single-ended amplifier circuit  300  can be reduced in some implementations by a factor of about two when compared to differential LNA designs, such as, for example, the LNA circuit  200 A of  FIG. 2A . 
         [0035]      FIG. 4  is a schematic of an example of a multiple LNA circuit  400  employing load inductor sharing for a group of LNAs. In particular, the multiple LNA circuit  400 , as shown, includes three LNAs  461 - 463 . The multiple LNA circuit  400  can be adapted to share load inductors for LNAs within close frequency bands. One implementation shares load inductors with LNAs that have center frequencies approximately within 10% of each other. 
         [0036]    Each of the LNAs  461 - 463  are dedicated to a separate frequency band. The multiple LNA circuit  400  includes differential inputs  410   a ,  410   b , and  410   c  for LNAs  461 ,  462 , and  463 , respectively. The multiple LNA circuit  400  also includes a shared pair of load inductors  401  and  402  and dedicated pairs of source degeneration inductors  411  and  412 ,  421  and  422 , and  431  and  432 . The differential output  450  can be a differential amplified active band output signal. The LNAs  461 - 463  can be circuits of single transistor, multiple transistors, cascode topology or other topologies. When one LNA is active, the other LNAs can be shut off and acting like an open circuit by switching LNA inputs to ground or by other methods, including, for example, the methods described with respect to  FIG. 2B . In this manner, a load inductor may be shared between amplifiers of different frequency bands such that a load inductor in one moment can be used in amplifier hardware dedicated to a first frequency band and in another moment can be used in amplifier hardware dedicated to a second frequency band. By sharing only one pair of load inductors for multiple LNAs, the power, noise, size and cost can be further reduced. 
         [0037]    The disclosed techniques can be used with wireless communication systems. For example, the disclosed techniques can be used with receivers and transceivers, such as the receiver and/or transceiver architectures for superheterodyne receivers, image-rejection (e.g., Hartley, Weaver) receivers, zero-intermediate frequency (IF) receivers, low-IF receivers, direct-up transceivers, two-step up transceivers, and other types of receivers and transceivers for wireless and wireline technologies.  FIGS. 5 and 6  are schematics demonstrating two examples of systems in which the inductor sharing techniques described above can be used. 
         [0038]    In particular,  FIG. 5  is a schematic of an example of a multiband low-IF receiver  500 . A RF signal arriving at an antenna  536  passes through an array of RF filters  537 , an array of LNAs  538  comprising pairs of LNAs for two close frequency bands, such as, for example, 850 MHz GSM and 900 MHz EGSM (Extended GSM) bands, and 1800 MHz DCS (Digital Cellular System) and 1900 MHz PCS bands into a mixer  540 , which performs image rejection and produces a low IF RF signal by mixing it with the signal produced by the first LO  541 . The array of LNAs  538  can use the inductor sharing techniques described above. For example, in various implementations, the array of LNAs  538  can share inductors connected to the source of the LNA&#39;s metal-oxide semiconductor field effect transistors (MOSFETs) or other transistors. One implementation is to share one pair of load inductors between the 850 MHz GSM LNA and the 900 MHz EGSM LNA, and another pair of load inductors between the 1800 MHz DCS LNA and the 1900 MHz PCS LNA. 
         [0039]    The undesired mixer products in the IF signal are rejected by an IF filter  542 . The filtered IF signal then enters an IF amplifier stage  543 , after which the output feeds into the second mixer  544  that translates it down to the baseband frequency by mixing it with the signal produced by a second LO  545 . The signal is then sent to the baseband for processing. Tuning into a particular channel within the band-limited RF signal is accomplished by varying the frequency of each LO  541  and  545 . 
         [0040]    In another example,  FIG. 6  is a schematic of an example of a direct-conversion receiver  600 . In the receiver  600 , an antenna  646  couples a RF signal through a first array of bandpass RF filters  647  into an array of LNAs  648 . The array of LNAs  648  can use the inductor sharing techniques described above. For example, in various implementations, the array of LNAs  648  can share inductors connected to the drain of the LNA&#39;s MOSFETs or other transistors. 
         [0041]    The signal then proceeds through a second array of RF filters  649 , yielding a band-limited RF signal, which then enters a mixer  650  and mixes with an LO frequency produced by an LO  651 . The output of the mixer  650  is coupled into a low pass analog filter  652  before proceeding into baseband information signal for use by the remainder of the communications system. 
         [0042]    A non-active LNA can be shut off like an open circuit by switching the LNA inputs to ground, by disconnecting the LNA from the power supply and/or from the load inductors or by any digital or analog control circuits. The load and source inductors can be spiral inductors or any other shape and type inductors designed manually or by software programs. 
         [0043]    In some implementations, circuit components can be exchanged from the disclosed figures with minimal change in circuit functionality. Various topologies for circuit models can be used. The exemplary designs may use various process technologies, such as CMOS or BiCMOS (Bipolar-CMOS) process technology, or Silicon Germanium (SiGe) technology. The circuits can be single-ended or fully-differential circuits. 
         [0044]    The system can include other components. Some of the components may include computers, processors, clocks, radios, signal generators, counters, test and measurement equipment, function generators, oscilloscopes, phase-locked loops, frequency synthesizers, phones, wireless communication devices, and components for the production and transmission of audio, video, and other data. The number and order of variable gain and filter stages can vary.