Patent Publication Number: US-9413326-B2

Title: Second-order filter with notch for use in receivers to effectively suppress the transmitter blockers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/405,673 filed on Feb. 27, 2012, and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Many modern wireless communication devices (e.g., cell phones, PDAs, etc.) comprise transceivers configured to both transmit data and to receive data over radio frequencies.  FIG. 1  illustrates a wireless communication transceiver  100  comprising a duplexer  104  configured to couple a transmitter section  106  and receiver section  108  to an antenna  102 . Receiver section  108  comprises an amplifier stage  110 , a mixer  112 , and a transimpedance amplifier  114 . Amplifier stage  110  is configured to receive a radio frequency (RF) input signal as a voltage and to convert the received RF input signal to a current. The current is provided to the mixer  112 , which down-converts the RF signal to an intermediate frequency (IF) signal. The IF signal is provided to a transimpedance amplifier  114 , which converts the current into a voltage and additionally filters unwanted interferer signals. 
     To achieve high data rates, transceiver  100  may be configured to operate in full-duplex mode, wherein both transmitter section  106  and receiver section  108  use antenna  102  at the same time. During full-duplex mode operation, transmitter section  106  typically uses one carrier frequency while receiver section  108  uses another carrier frequency. Despite using different frequencies, intermodulation distortion may arise during operation of transceiver  100 . One such source of intermodulation distortion occurs when a transmitted signal leaks from transmitter section  106  to receiver section  108 , generating a transmitter blocker (i.e., a transmitter interferer signal). Once intermodulation distortion appears within receiver section  108 , there is no way of distinguishing it from the desired signal, and sensitivity of the transceiver  100  is degraded. 
    
    
     
       DRAWINGS 
         FIG. 1  illustrates a block diagram of a conventional transceiver system. 
         FIG. 2  illustrates a block diagram of some embodiments of a disclosed transceiver system having a transimpedance amplifier comprising a notch filter element configured to suppress transmitter blockers within a reception path. 
         FIGS. 3 a -3 c    illustrate graphs showing the frequency of signals along the reception path in the disclosed transimpedance amplifier circuit. 
         FIG. 4  illustrates a block diagram of some additional embodiments of a disclosed transceiver system having a transimpedance amplifier comprising a notch filter element. 
         FIG. 5 a    illustrates a block diagram of some embodiments of a disclosed transimpedance amplifier comprising a notch filter element that can be selectively activated. 
         FIG. 5 b    illustrates a block diagram of some alternative embodiments of a disclosed transimpedance amplifier having components that may be selectively bypassed. 
         FIG. 6 a    illustrates a schematic diagram of some embodiments of a disclosed transimpedance amplifier comprising a notch filter element. 
         FIG. 6 b    illustrates a schematic diagram of some alternative embodiments of a disclosed transimpedance amplifier comprising a notch filter element. 
         FIGS. 7 a   -b illustrate schematic diagrams of some embodiments of a disclosed transimpedance amplifier comprising having components configured in different orders along a differential reception path. 
         FIG. 8 a    illustrates a schematic diagram of some embodiments of a disclosed transceiver system having a tunable notch filter element. 
         FIG. 8 b    illustrates a schematic diagram of an exemplary embodiment of a variable capacitor configuration. 
         FIG. 9  is a flow diagram of an exemplary method for suppressing transmitter blockers within a reception path. 
         FIG. 10  illustrates an example of a mobile communication device, such as a mobile handset, in accordance with the disclosure. 
         FIG. 11  illustrates an example of a wireless communication network in accordance with the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The claimed subject matter is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. It may be evident, however, that the claimed subject matter may be practiced without these specific details. 
     The present disclosure relates to a transceiver front-end comprising a notch filter element configured to suppress transmitter blockers (i.e., transmitter interferer signals) within a reception path. In some embodiments, the transceiver front-end comprises a differential reception path, having a first differential branch and a second differential branch. The differential reception path is configured to provide an RF differential input signal having a transmitter blocker to a transimpedance amplifier comprising a first-order active filter and a notch filter element. The notch filter element comprises a stop band corresponding to a frequency of the transmitter blocker, such that the notch filter element attenuates the transmitter blocker without degrading the signal quality of the received differential input signal. 
       FIG. 2  illustrates a block diagram of some embodiments of a disclosed transceiver system  200  having a transimpedance amplifier  208  comprising a notch filter element  212  configured to attenuate transmitter blockers (i.e., transmitter interferer signals from transmission path  202 ) within a reception path  206 . Although the transceiver circuits shown and described herein are illustrated as differential or single ended circuits, it will be appreciated that the apparatus provided herein are not limited to such circuits. Instead, the method and apparatus provided herein may be applied to both differential and single ended circuits. 
     Transceiver system  200  comprises a transmission path  202  and a reception path  206 . Transmission path  202  is configured to provide a signal for transmission (a transmitted signal) to an antenna  102  by way of a duplexer  104 . Duplexer  104  is further configured to receive an RF input signal from antenna  102 . The RF input signal is provided to reception path  206  as an RF input signal. Transmitter blockers  204  corresponding to the transmission signals frequency may leak from the transmission path  202  through the duplexer  104  to the reception path  206 . 
     Reception path  206  includes a low noise amplifier (LNA)  110 , a mixer  112 , and a transimpedance amplifier  208 . LNA  110  is configured to receive the RF input signal as a voltage and to convert it to a current that is provided to the mixer  112 , which demodulates the received RF input signal to generate an input signal comprising a received current. Transimpedance amplifier  208  comprises a multiple feedback filter having a first-order filter element  210  and a notch filter element  212 . The transimpedance amplifier  208  is configured to receive the received current from mixer  112 , to filter the received current, and to convert the received current to a voltage. In some embodiments, first-order filter element  210  may be located downstream of notch filter element  212 , while in other embodiments, first-order filter element  210  may be located upstream of notch filter element  212 . 
     As shown in  FIG. 2 , first-order filter element  210  is configured to receive the received current from mixer  112 . First-order filter element  210  filters the received current to reduce noise within the received input signal. In some embodiments, first-order filter element  210  may comprise an active low-pass filter, for example. The filtered current is output from first-order filter element  210  to notch filter element  212 , which is configured to attenuate signals within a stop band frequency corresponding to a frequency of the transmitted signal. By attenuating signals corresponding to the frequency of the transmitted signal, while passing other frequencies, transmitter blockers  204  that have leaked from the transmission path  202  to the reception path  206  are effectively removed from reception path  206 , without degrading the signal quality of the input signal received from antenna  102 . 
     In some embodiments, notch filter element  212  may comprise a tunable notch filter having an adjustable stop band frequency. A control unit  214  may be configured to generate a control signal S CTRL  that is provided to the notch filter element  212  to control one or more characteristics of the stop band frequency of the tunable notch filter. In various embodiments, the one or more characteristics may comprise a stop band center frequency and/or a stop band frequency range. By operating control unit  214  to adjust one or more characteristics of the stop band of the tunable notch filter, the transceiver system  200  can be actively adjusted to suppress transmitted signals over a range of transmission frequencies, thereby enabling suppression of a transmitter blocker in multiband communication systems. 
     It will be appreciated that by attenuating a transmitter blockers  204  that have leaked into the reception path  206 , the disclosed transceiver system  200  allows for duplexer  104  to have a relatively low isolation, thereby reducing the cost of the transceiver system  200 . Furthermore, the notch filter element  212  removes interference from the transmission path  202  while maintaining a low current consumption and input impedance (e.g., in contrast to conventional first order or second-order filters, which are often implemented at the cost of increasing the current consumption, the input impedance, and the transceiver complexity). 
       FIGS. 3 a -3 c    illustrate graphs showing the frequency of signals in a reception path of a disclosed filter transimpedance amplifier. 
       FIG. 3 a    illustrates a graph  300  showing a transmitter blocker  302  within a reception path. The horizontal axis represents the frequency of the transmitter blocker, while the vertical axis represents the amplitude of the voltage of the transmitter blocker. As shown in graph  300 , the transmitter blocker  302  has a frequency that is centered on a first frequency f 1 . It will be appreciated that the frequency of the transmitter blocker will depend upon the frequency of a signal transmitted by a transceiver and may vary in time. 
       FIG. 3 b    illustrates a graph  304  showing a filter response  306  of a first-order active filter comprising a low-pass filter (i.e., showing the received input signal that is output from a first-order active filter). The horizontal axis represents the frequency of a received input signal, while the vertical axis represents the amplitude of the voltage of the received input signal. As shown in graph  304 , the filter response  306  of a first-order active filter passes an input signal at low frequencies, while attenuating the received input signal at frequencies above a filter knee located at a frequency f 2 . 
       FIG. 3 c    illustrates a graph  308  showing a filter response  310  of a notch filter element (i.e., showing the received input signal that is output from the transimpedance amplifier). The horizontal axis represents the frequency of a received input signal, while the vertical axis represents the amplitude of the received input signal. The notch filter element provides for a filter response  310  having a low level of attenuation away from the notch frequency f 1 , and an increasingly large level of attenuation as the frequency moves closer to the notch frequency f 1 . Therefore, as shown in graph  308 , the input signal output from the transimpedance amplifier is attenuated around the frequency f 1 . This attenuation suppresses the transmitter blocker (e.g., shown in  FIG. 3 a   ) without substantially degrading the signal quality of the input signal. 
       FIG. 4  illustrates a block diagram of some embodiments of a disclosed transceiver system  400 . 
     Transceiver system  400  comprises a differential reception path extending from duplexer  104  to a transimpedance amplifier  402 . The differential reception path comprises a first differential branch  408  and a second differential branch  410 . In some embodiments, first and second differential branches,  408  and  410 , are configured to respectively transmit a differential N-P complementary input signal, comprising a current from duplexer  104 , to transimpedance amplifier  402 . 
     Transimpedance amplifier  402  comprises a first-order active filter  404  and a notch filter element  212 , as described above, and a second active filtering element  406 . In various embodiments, the second active filtering element  406  may comprise an integrator or a first-order active filter, for example. The second active filtering element  406  may be located upstream of the notch filter element  212 , so as to provide a filtered signal to the notch filter element  212 , or downstream of the notch filtering element  212  , so as to filter the output of the notch filter element  212 . As shown in  FIG. 4 , second active filtering element  406  is located downstream of the notch filtering element  212 . 
     Transimpedance amplifier  402  converts the input current to an output voltage that is provided at a first output node  422  on the first differential branch  408  and a second output node  424  on the second differential branch  410 . The output is provided to an amplifier element  416  configured to amplify the output of transimpedance amplifier  402 . In some embodiments, the output of amplifier element  416  is provided to an analog-to-digital converter  418  configured to convert the analog input signal to a digital signal that is subsequently provided to a digital signal processor  420 . 
     The output is further provided to a first negative feedback path  412  and a second negative feedback path  414 , which are respectively configured to generate negative feedback signals that suppress the out-of-band-transmitted signals within the differential reception path, thereby improving linearity of the transimpedance amplifier  402 . In some embodiments, the negative feedback signals, with an amplitude having an opposite polarity as the out-of-band transmitter signals, are provided by connecting opposite differential paths together. For example, first negative feedback path  412  extends from second output node  424  on second differential branch  410  to a node on first differential branch  408  at the input of first-order active filter  404 . Second negative feedback path  414  extends from first output node  422  on first differential branch  408  to a node on second differential branch  410  at the input of first-order active filter  404 . 
     In some embodiments, the disclosed transimpedance amplifier may comprise one or more switching elements configured to selectively bypass one or more components of the transimpedance amplifier. For example, the switching elements may be configured to bypass the notch filter element and/or one or more one or more other filtering components (e.g., the first order filter and/or the second filtering element and/or feedback paths) of the transimpedance amplifier. 
       FIG. 5 a    illustrates a block diagram of some embodiments of a disclosed transimpedance amplifier  500  comprising a notch filter element  212  that can be selectively activated or bypassed. 
     As shown in  FIG. 5 a   , the transimpedance amplifier  500  comprises first and second switching elements,  502  and  504 , located upstream of notch filter element  212  and third and fourth switching elements,  506  and  508 , located downstream of notch filter element  212 . First and third switching elements,  502  and  506 , are comprised within first differential branch  408  and are configured to selectively couple the output of first-order active filter  404  to either notch filter element  212  or to a first output node  510  of transimpedance amplifier  500 . Second and fourth switching elements,  504  and  508 , are comprised within second differential branch  410  and are configured to selectively couple the output of first-order active filter  404  to either notch filter element  212  or to a second output node  512  of transimpedance amplifier  500 . 
     In some embodiments, switching elements  502 - 508  are configured to receive a switching control signal S sw  from a control unit  514 . By providing a switching control signal S sw  having a first value to switching elements  502 - 508 , notch filter element  212  and second active filtering element  406  can be selectively bypassed to get a first-order filter response if the improved performance of notch filter element  212  and second active filtering element  406  (e.g., the decreased linearity offered by the notch filter element  212 ) is not needed. By deactivating notch filter element  212  and second active filtering element  406 , power consumption of the transimpedance amplifier  500  can be reduced. Alternatively, by providing a switching control signal S sw  having a second value to switching elements  502 - 508  notch filter element  212  and integrator  406  can be selectively activated to get a second-order filter response if the improved performance of notch filter element  212  and second active filtering element  406  is needed. 
     In alternative embodiments, the switching elements  502 - 508  may be located at positions which allow the switching elements  502 - 508  to bypass the first-order active filter  404  and the notch filter element  212 . When the first-order active filter  404  and the notch filter element  212  are bypassed, the second active filtering element  406  acts as a first-order active filter. 
       FIG. 5 b    shows a schematic diagram  516  having switching elements  518 - 528  located within the feedback paths  412  and  414  and the differential reception path. The switching elements  518 - 524  within the differential reception path can bypass the active filter  406 , while switching elements  526 - 528  within the feedback paths  412  and  414  can be operated to bypass the feedback paths. In such a configuration the notch filter element  212  is selectively connected to the first and second output nodes  510  and  512  (e.g., a buffer or an analog-to-digital converter). 
       FIG. 6 a    illustrates a schematic diagram of some embodiments of a disclosed transimpedance amplifier  600  comprising a passive notch filter  606 . 
     The transimpedance amplifier  600  comprises a first-order active filter  602 . First-order active filter  602  comprises an operational amplifier  604  and an RC feedback network comprising feedback capacitors C 1  and C 1x  and feedback resistors R 1  and R 1x . A capacitor C a  is configured to filter the differential input signal at very high frequencies where the open loop gain of a standard op-amp in CMOS would not be sufficient. 
     The output of first-order active filter  602  is provided to passive notch filter  606  comprising a capacitive element connected in parallel to a resistive element. In particular, each of the differential branches,  408  and  410 , of the passive notch filter  606  comprises a first signal path comprising two resistors (e.g., R 2a  and R 2b ) connected in series and a second signal path comprising two capacitors (e.g., C 2a  and C 2b ) connected in series. The first and second signals paths are configured to introduce different phase shifts into the received differential input signal traveling through each signal path, resulting in a high degree of attenuation at the resonance frequency. In some embodiments the passive notch filter  606  further comprises a capacitor C 3  extending between the differential branches. The resonance frequency of passive notch filter  606  depends upon the values of capacitors C 2m  and/or C 3  and/or resistors R 2m  (where m=a, b, ax, or bx). 
     The output of notch filter  606  is provided to a second filtering element  608  comprising an active integrator configured to increase the gain of transimpedance amplifier  600 . The active integrator comprises an operational amplifier  610  and feedback capacitors C 4  and C 4x  respectively extending from first and second differential output nodes of the active integrator to first and second differential input nodes of the active integrator. 
     In some embodiments, first and second negative feedback paths  412  and  414  comprise additional RC filtering elements  612  and  614 . Each RC filtering element,  612  or  614 , comprises an additional capacitor (e.g., C 5 ) and a resistor (e.g., R 4 ) connected in parallel. The additional capacitor adjusts the passive function of the filter (making it more stable), while the additional resistor defines the DC gain of transimpedance amplifier  600  (e.g., if differential input current is I 1 , DC voltage generated by the transimpedance amplifier is equal to I 1  x R 4 ). 
       FIG. 6 b    illustrates an alternative embodiment of a schematic diagram of some embodiments of a disclosed transimpedance amplifier  616  comprising a passive notch filter  606 . 
     Transimpedance amplifier  616  has a second filtering element  608  comprising a first order filter element, such that transimpedance amplifier  616  has two first-order RC active filters. In particular, the first order filter element has an operational amplifier  618  and an RC feedback network comprising feedback capacitors C 4  and C 4x  and feedback resistors R 5  and R 5x . 
     It will be appreciated that the order of elements within the disclosed reception chain may vary in different embodiments.  FIGS. 7 a -7 b    illustrates some embodiments of transimpedance amplifier components positioned in different orders. It will be appreciated that the schematic diagrams of  FIGS. 7 a -7 b    are not limiting embodiments, but rather are examples of possible ordering of components that may be implemented. 
       FIG. 7 a    illustrates a transimpedance amplifier  700  having a second filtering element  608  (shown as an integrator) located upstream of the notch filter element  606  and a first-order active filter  602  located downstream of the notch filter element  606 . By interchanging the order of the second filtering element  608  and the first-order active filter  602 , relative to the transimpedance amplifier  700  of  FIG. 6 a   , the notch filter element  606  is configured to receive a signal from a second filtering element  608  and to provide a filtered signal to the first order active filter  602 . 
       FIG. 7 b    illustrates a transimpedance amplifier  702  having input resistive elements, R i  and R ix , on the differential paths. The resistors R i , R ix , convert the input resistance to a current, such that the transimpedance amplifier  702  acts as a filter whose input is not a current but a voltage. This allows for the transimpedance amplifier  702  to not have to be placed at the output of a mixer (e.g., mixer  112 ). 
       FIG. 8 a    illustrates a schematic diagram of some embodiments of a disclosed transceiver system  800  having a passive, tunable notch filter element  802 . 
     Tunable notch filter element  802  comprises an adjustable stop band frequency. A control unit  804  may be configured to control one or more characteristics of the stop band frequency of the tunable notch filter element  802 . By operating control unit  804  to change the stop band of the tunable notch filter element  802 , the transceiver system  800  can suppress transmitter blockers over a range of operating modes having different transmitter and/or receiver frequencies. This allows for the transceiver system  800  to be used in multiband phones, which are configured to transmit and/or receive data over a plurality of frequency bands (e.g., it allows the phone to operate over a plurality of mobile communication protocols such as LTE, GSM, CDMA, etc.). 
     For example, control unit  804  may be configured to adjust tunable notch filter element  802  to attenuate a stop band center frequency centered upon 100 MHz in a first operating mode and a stop band center frequency centered upon 120 MHz in a second operating mode. Control unit  804  may also be configured to adjust the range of the stop band frequency of tunable notch filter element  802 . For example, since each operating mode has a different duplex distance between transmitter and receiver, control unit  804  may be configured to adjust the range of the stop band of tunable notch filter element  802  to attenuate a stop band frequency having a range of 40 MHz in a first operating mode (e.g., from 80-120 MHz) and a stop band frequency having a range of 20 MHz in a second operating mode (e.g., from 110-130 MHz). 
     In some embodiments, control unit  804  is configured to tune the stop band frequency of tunable notch filter element  802  based upon the operating mode of the transmission path  202 . For example, in a multiband telephone configured to operate over a plurality of frequency bands, different operating mode will have a different duplex frequency. Based upon the operating mode, control unit  804  is configured to generate a control signal S CTRL , which is provided to tunable notch filter element  802 . The control signal S CTRL  tunes tunable notch filter element  802  to a frequency that corresponds to the transmitter signal frequency, so as to attenuate transmitter blocker signals within the reception path. In some embodiments, the control unit  804  comprises a memory element  806  configured to store one or more predetermined characteristics of the stop band frequency associated with different operating modes. The control unit  804  may be configured to detect an active operating mode, to read data corresponding to the active operating mode from the memory element  806 , and to generate the control signal S CTRL  based upon the read data. 
     In other embodiments, control unit  804  may be configured to detect a frequency of a transmitted signal. Based upon the detected frequency of the transmitted signal, control unit  804  is configured to generate a control signal S CTRL , which is provided to tunable notch filter element  802 . The control signal S CTRL  tunes tunable notch filter element  802  to a frequency that corresponds to the transmitter signal frequency, so as to attenuate transmitter blocker signals within the reception path. 
     Tunable notch filter element  802  may comprise one or more tunable capacitors C 2m ′, C 3  and/or tunable resistors R 2m ′. The tunable capacitors C 2m ′, C 3  and/or resistors R 2m ′are tuned by the control signal S CTRL  to change one or more characteristics of the stop band frequency of tunable notch filter element  802 . In some embodiments, the tunable capacitors and/or resistors may comprise switched capacitors and/or resistors. In other embodiments, the tunable capacitors and/or resistors may comprise other types of variable capacitors and/or resistors. 
       FIG. 8 b    illustrates a schematic diagram  808  of an exemplary implementation of a tunable capacitor. 
     Schematic diagram  808  comprises a plurality of capacitors C 1k , . . . , C nk  and a plurality of transmission gates T gate   _   1 , . . . , T gate   _   n . Transmission gates T gate   _   1 , . . . , T gate   _   n  are connected to a wire configured to provide a control word S CTRLn . The control word S CTRLn  selectively activates transmission gates to provide a variable capacitance between input node IN and output node OUT. For example, when transmission gates T gate   _   1  and T gate   _   2  are activated, capacitors C 1k  and C 2k  are connected in series with each other resulting in an overall capacitance of C total =C 1k +C 2k . When a transmission gate is deactivated the total capacitance of the variable capacitor C k  is decreased. For example, when transmission gate T gate   _   1  is activated, capacitors C 1k  provides an overall capacitance of C total ′=C 1k &lt;C total    
     Therefore, if the control word S CTRLn  turns on transmission gate T gate   _   1  and T gate   _   2 , capacitor C k  will have an effective capacitance that results in a first stop band frequency. However, if control word S CTRLn  turns on transmission gate T gate   _   1 ) capacitor C k  will have a smaller effective capacitance that results in a second, different stop band frequency. 
     In some embodiments, control signal S CTRLn  may a digital control word having a plurality of n data bits is provided to a selection circuit  810 . Based upon values of the plurality of n data bits in the received control word, the selection circuit  810  sends an activation voltage to selected transmission gates, thereby activating the selected transmission gates and increasing the effective capacitance of capacitor C k . 
       FIG. 9  is a flow diagram of an exemplary method  900  for suppressing a transmitter interferer signals within differential branches of a reception path. 
     It will be appreciated that while the method  900  is illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the disclosure herein. Also, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. 
     At  902  the method operates a transceiver front-end to receive an input signal having a transmitter blocker. The transceiver front-end may receive an input signal comprising an RF input signal at an RF antenna coupled to a differential reception path having first and second differential branches. 
     At  904  the method operates a first filtering element to filter the received input signal. In some embodiments, the first filtering element comprises a first-order active filter. The first order active filter may operate as a low-pass filter configured to pass low-frequency components of the received signal while attenuating components with frequencies higher than a cutoff frequency. 
     At  906  the method operates a notch filter element to attenuate a stop band of the received input signal corresponding to a transmitter signal frequency. By attenuating a range of frequencies (i.e., a stop band) that corresponds to a transmitter frequency, frequencies of transmitter blockers within a reception path are suppressed without degrading the signal quality of a received input signal. 
     At  908  the method operates a second active filtering element to filter the received input signal. In some embodiments, the second active filtering element may comprise an integrator, such that operating the integrator integrates the output of the notch filter element. 
     At  910  the method may operate a negative feedback path to provide the output of the second active filtering element as a negative feedback signal to an input terminal of the first filtering element, in some embodiments. 
     At  912  the method may operate a control unit to determine a frequency range of transmitter blockers, in some embodiments. In some embodiments, the frequency range of the transmitter blockers may be determined by measuring the transmitted signal frequency from a transmission path of a transceiver circuit, for example. In other embodiments, the frequency range of the transmitter blockers may be determined by determining an active operating mode and reading data corresponding to the active operating mode from a memory element configured to store frequency ranges associated with an active operating mode. 
     At  914  the method may operate the control unit to adjust the stop band frequency of the notch filter element based upon the determined frequency range of the transmitter blockers. 
       FIG. 10  illustrates an example of a mobile communication device  1000 , such as a mobile phone handset for example, configured to implement one or more embodiments provided herein. In one configuration, mobile communication device  1000  includes at least one processing unit  1002  and memory  1004 . Depending on the exact configuration and type of mobile communication device, memory  1004  may be volatile (such as RAM, for example), non-volatile (such as ROM, flash memory, etc., for example) or some combination of the two. Memory  1004  may be removable and/or non-removable, and may also include, but is not limited to, magnetic storage, optical storage, and the like. In some embodiments, computer readable instructions in the form of software or firmware  1006  to implement one or more embodiments provided herein may be stored in memory  1004 . Memory  1004  may also store other computer readable instructions to implement an operating system, an application program, and the like. Computer readable instructions may be loaded in memory  1004  for execution by processing unit  1002 , for example. Other peripherals, such as a power supply  1008  (e.g., battery) and a camera  1010  may also be present. 
     Processing unit  1002  and memory  1004  work in coordinated fashion along with a transceiver  1012  to wirelessly communicate with other devices by way of a wireless communication signal. To facilitate this wireless communication, a wireless antenna  1020  is coupled to transceiver  1012 . During wireless communication, transceiver  1012  may use frequency modulation, amplitude modulation, phase modulation, and/or combinations thereof to communicate signals to another wireless device, such as a base station for example. The previously described high resolution phase alignment techniques are often implemented in processing unit  1002  and/or transceiver  1012  (possibly in conjunction with memory  1004  and software/firmware  1006 ) to facilitate accurate data communication. However, the high resolution phase alignment techniques could also be used in other parts of mobile communication device. 
     To reduce noise within transceiver  1012 , the mobile communication device  1000  also may include a transimpedance amplifier having a first-order filter  1014  and a notch filter element  1016 , as previously described. The notch filter element  1016  operates to attenuate a range of frequencies (i.e., a stop band) that corresponds to the frequencies of a transmitter blocker within a reception path, while passing other frequencies. A control unit  1018  may be configured to send control signals to notch filter element  1016  to control one or more characteristics of the stop band of notch filter element  1016 . In some embodiments, processing unit  1002  comprises control unit  1018 . 
     To improve a user&#39;s interaction with the mobile communication device  1000 , the mobile communication device  1000  may also include a number of interfaces that allow the mobile communication device  1000  to exchange information with the external environment. These interfaces may include one or more user interface(s)  1022 , and one or more device interface(s)  1024 , among others. 
     If present, user interface  1022  may include any number of user inputs  1026  that allow a user to input information into the mobile communication device  1000 , and may also include any number of user outputs  1028  that allow a user to receive information from the mobile communication device  1000 . In some mobile phone embodiments, the user inputs  1026  may include an audio input  1030  (e.g., a microphone) and/or a tactile input  1032  (e.g., push buttons and/or a keyboard). In some mobile phone embodiments, the user outputs  1028  may include an audio output  1034  (e.g., a speaker), a visual output  1036  (e.g., an LCD or LED screen), and/or tactile output  1038  (e.g., a vibrating buzzer), among others. 
     Device interface  1024  allows a device such as camera  1010  to communicate with other electronic devices. Device interface  1024  may include, but is not limited to, a modem, a Network Interface Card (NIC), an integrated network interface, a radio frequency transmitter/receiver, an infrared port, a USB connection, or other interfaces for connecting mobile communication device  1000  to other mobile communication devices. Device connection(s)  1024  may include a wired connection or a wireless connection. Device connection(s)  1024  may transmit and/or receive communication media. 
       FIG. 11  illustrates one embodiment of a wireless network  1000  over which a mobile communication device (e.g., mobile communication device  1000  in  FIG. 10 ) in accordance with this disclosure may communicate. The wireless network  1100  is divided into a number of cells (e.g.,  1102   a,    1102   b , . . . ,  1102   d ), wherein each cell has one or more base stations (e.g.,  1104   a,    1104   b , . . . ,  1104   d , respectively). Each base station may be coupled to a carrier&#39;s network  1106  (e.g., a packet switched network, or a circuit switched network such as the public switched telephone network (PSTN)) via one or more wirelines  1108 . 
     A mobile device  1110  (e.g., mobile communication device  1000 ) or other mobile device, having a transceiver comprising a notch filter element, may establish communication with the base station within that cell via one or more of frequency channels used for communication in that cell. The communication between a mobile handset or other mobile device  1110  and a corresponding base station often proceeds in accordance with an established standard communication protocol, such as LTE, GSM, CDMA or others. When a base station establishes communication with a mobile handset or other mobile device, the base station may establish communication with another external device via the carrier&#39;s network  1106 , which may then route communication though the phone network. 
     Those skilled in the art will realize that mobile communication devices such as mobile phones may in many instances upload and download computer readable instructions from a network through the base stations. For example, a mobile handset or other mobile device  1110  accessible via network  1106  may store computer readable instructions to implement one or more embodiments provided herein. The mobile handset or other mobile device  1110  may access a network and download a part or all of the computer readable instructions for execution. 
     The term “computer readable media” as used herein includes computer storage media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions or other data. Memory (e.g.,  1004  in  FIG. 10 ) is an example of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, Digital Versatile Disks (DVDs) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which may be used to store the desired information. The term “computer readable media” may also include communication media. Communication media typically embodies computer readable instructions or other data in a “modulated data signal” such as a carrier wave or other transport component and includes any information delivery media. The term “modulated data signal” may include a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. 
     Although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. Further, it will be appreciated that identifiers such as “first” and “second” do not imply any type of ordering or placement with respect to other elements; but rather “first” and “second” and other similar identifiers are just generic identifiers. In addition, it will be appreciated that the term “coupled” includes direct and indirect coupling. The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements and/or resources), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. In addition, the articles “a” and “an” as used in this application and the appended claims are to be construed to mean “one or more”. 
     Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”