Patent Publication Number: US-11387857-B2

Title: Dynamically reconfigurable frequency selective attenuator for radio frequency receiver front end

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a Continuation-in-Part of U.S. patent application Ser. No. 16/706,433, filed on Dec. 6, 2019, entitled “Frequency Selective Attenuator For Optimized Radio Frequency Coexistence,” which is hereby incorporated by reference in its entirety for all intents and purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates in general to wireless communications, and more particularly to a dynamically reconfigurable frequency selective attenuator for radio frequency (RF) front end that enables a low power victim wireless transceiver to coexist with a high power aggressor wireless transceiver. 
     Description of the Related Art 
     Many different wireless RF technologies may be used for several different applications operating in a common area, such as cellular networks, local area networks, home automation systems, Internet of Things (IoT), alarm systems, etc. The use of multiple wireless devices in a common area may cause communication conflicts when using the same radio frequency (RF) or overlapping frequencies. Wireless technologies in the 2.4 Gigahertz (GHz) frequency range include Wi-Fi, Zigbee, Bluetooth (including low energy version or BLE), Thread, etc. Wireless technologies in the sub-GHz frequency range, such as 800-900 Megahertz (MHz), include some lower power Wi-Fi technologies (e.g., MiWi), Z-wave, certain cellular communications (e.g., 3G, 4G, LTE), etc. 
     The performance of wireless RF transceivers of a lower powered wireless network tends to decrease when in close proximity to higher powered wireless RF transceivers of another network when operating near the same frequency levels. Wireless performance for collocated transceivers, for example, is challenging especially when one of the transmitters operates with very high power while another operates at significantly lower receive signal power levels. Two or more wireless transceivers are referred to as being “collocated” when implemented on the same printed circuit board (PCB) or within the same package or product. This is often the case for alarm systems, gateways, routers or adaptors that include Wi-Fi or LTE operating in frequencies in proximity of lower power systems that are targeting high sensitivity. A low power system is at a disadvantage because the end nodes communicate using low transmit power with low duty cycles, greatly reducing the probability of a successful communication in the presence of a high power level blocker. A signal “blocker” is a coincident signal sufficiently close to the frequency of the signal of interest being received causing various potential impairments to the desired signal, such as distortion, compression, and de-sensitization. One example includes a Zigbee device collocated with a Wi-Fi device at or near 2.4 GHz. Another example is a Z-wave device and cellular device at 800-900 MHz. 
     SUMMARY OF THE INVENTION 
     A wireless device according to one embodiment includes a receiver circuit coupled to a radio frequency receiver node, a frequency selective attenuator including an inductor and a first capacitor coupled in series between the radio frequency receiver node and a reference node, and a second capacitor coupled in parallel with the first capacitor, in which the first capacitor has a first capacitance based on a blocker frequency and in which the second capacitor has a second capacitance that linearizes the frequency selective attenuator. 
     The second capacitance of the second capacitor may be greater than the first capacitance of the first capacitor. The second capacitance of the second capacitor may be selected to reduce a voltage swing across the frequency selective attenuator. The first capacitor may be implemented as a high-quality factor capacitor and the second capacitor may be implemented as a low-quality factor capacitor. 
     The second capacitor may be programmable, in which a controller determines a frequency difference between the blocker frequency and a receive frequency and programs the second capacitance to optimize overall distortion performance when the frequency differential is below a predetermined attenuation threshold. The controller may decouple the second capacitor when the frequency differential is above the predetermined attenuation threshold. 
     The wireless device may include a transmitter circuit having an output coupled to the radio frequency receiver node, in which a controller programs the second capacitance of the second capacitor to minimize function of the frequency selective attenuator at a frequency of transmission. The controller may programs the second capacitance of the second capacitor so that the frequency selective attenuator presents as an inductive load to the transmitter circuit during a transmission mode. 
     The first capacitor may be a first digitally programmable capacitor programmed with a first digital value provided by a controller, and the second capacitor may be a second digitally programmable capacitor programmed with a second digital value provided by the controller. A memory may be programmed with first digital values each corresponding to a corresponding one of multiple blocker frequencies, and second digital values each corresponding to a difference between a receive frequency and each of the blocker frequencies. 
     A method of linearizing a frequency selective attenuator of a wireless device may include detecting presence of a blocker signal, activating a frequency selective attenuator and programming a capacitor of the frequency selective attenuator to reduce a strength of the blocker signal, determining a frequency difference between the blocker signal and a receive frequency and coupling a second capacitor to the frequency selective attenuator to linearize the frequency selective attenuator when the frequency difference is no more than an attenuation threshold. 
     The method may include programming a capacitance of the second capacitor to optimize linearization. The method may include programming a capacitance of the second capacitor to reduce a voltage swing across the frequency selective attenuator. The method may include programming a capacitance of the second capacitor based on the frequency difference. The method may include decoupling the second capacitor from the frequency selective attenuator when the frequency difference is at least a disable threshold. The method may include detecting a transmission mode of the wireless device and programming a capacitance of the second capacitor so that the frequency selective attenuator appears as an inductance at a frequency of transmission. The method may include detecting a transmission mode of the wireless device and programming a capacitance of the second capacitor to minimize functionality of the frequency selective attenuator at a frequency of transmission. The method may include applying a digital value to program a capacitance of the second capacitor. The method may include retrieving the digital value from a memory. 
     A wireless communication system according to one embodiment includes a communication packaging and a controller. The communication packaging incorporates an aggressor wireless transceiver, a victim wireless transceiver, and a host system interfaced with the aggressor wireless transceiver and the victim wireless transceiver. The victim wireless transceiver may include a receiver circuit coupled to a radio frequency transceiver node, a tunable notch filter coupled between the radio frequency transceiver node and a reference node, and a capacitor coupled between the tunable notch filter and the reference node. The controller may program the tunable notch filter with a selected blocker frequency to attenuate at least one blocker signal including at least one transmission frequency of the aggressor wireless transceiver, and may program the capacitor to linearize the tunable notch filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
         FIG. 1  is a simplified illustration of a local network including a communication system with collocated wireless transceivers, including one or more aggressor wireless transceivers and one or more victim wireless transceivers implemented according to one embodiment of the present disclosure. 
         FIG. 2  is a simplified block diagram of a victim wireless transceiver including a tunable notch filter (TNF) implemented according to one embodiment of the present disclosure which may be used as either or both of the victim transceivers of  FIG. 1 . 
         FIG. 3  is a flowchart diagram illustrating operation of the victim wireless transceiver of  FIG. 2  including operation of the controller for tuning and enabling or disabling the TNF of the wireless transceiver according to one embodiment of the present disclosure. 
         FIG. 4  is a simplified schematic and block diagram of a portion of a victim wireless transceiver implemented according to an embodiment of the present disclosure in which the TNF is configured as a tunable notch filter using only a bondwire as the inductance. 
         FIG. 5  is a simplified schematic and block diagram of a portion of another victim wireless transceiver implemented according to an embodiment of the present disclosure in which the TNF is configured as a tunable notch filter using a bondwire and a separate inductor as the inductance. 
         FIG. 6  is a simplified schematic and block diagram of a portion of another victim wireless transceiver implemented according to an embodiment of the present disclosure in which the TNF is configured as a tunable notch filter using a bondwire and an in-package inductor as the inductance. 
         FIG. 7  is a simplified schematic and block diagram of a portion of another victim wireless transceiver implemented according to another embodiment of the present disclosure in which elements of the TNF are arranged in a different order. 
         FIG. 8  is a simplified schematic diagram of a digitally programmable capacitor that may be used as the variable capacitor for any of the tunable notch filters according to one embodiment of the present disclosure. 
         FIG. 9  is a flowchart diagram illustrating a calibration process that may be performed by a victim wireless transceiver according to one embodiment of the present disclosure. 
         FIG. 10  is a flowchart diagram illustrating a blocker scan process that may be performed by a victim wireless transceiver according to one embodiment of the present disclosure. 
         FIG. 11  is a simplified schematic and block diagram of a portion of a victim wireless receiver similar to the victim wireless transceiver of  FIG. 2  including a frequency selective attenuator in the form of a TNF. 
         FIG. 12  is a simplified schematic and block diagram of a portion of another victim wireless receiver implemented according to an embodiment of the present disclosure and similar to the victim wireless transceiver of  FIG. 11  in which similar components assume identical reference numerals, further including a second variable capacitor. 
         FIG. 13  is a simplified schematic and block diagram illustrating the TNF of  FIG. 12  implemented as controlled by the controller of  FIG. 12  according to one embodiment of the present disclosure. 
         FIG. 14  is a flowchart diagram illustrating operation of the controller of the victim wireless receiver of  FIG. 12  for controlling connection of the second capacitor with capacitance C 2  according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have recognized the need to resolve conflicts between collocated or nearby wireless RF transceivers of a wireless communication system. They have therefore developed a victim wireless receiver with a frequency selective attenuator for optimized RF coexistence that enables a low power victim wireless transceiver to coexist with a high power aggressor wireless transceiver. 
       FIG. 1  is a simplified illustration of a local network  100  including a wireless communication system  102  with collocated wireless transceivers, including an aggressor wireless transceiver  104  and a victim wireless transceiver  106  implemented according to one embodiment of the present disclosure. The local network  100  also shows another aggressor wireless transceiver  110  and another victim wireless transceiver  112  that are in close proximity to each other. In this context, an aggressor wireless transceiver, including the aggressor wireless transceivers  104  and  110 , typically operates at relatively high power and/or a high duty cycle, and a victim wireless transceivers, including the victim wireless transceivers  106  and  112 , typically operates to receive low power and/or a low duty cycle signals. Although the wireless transceivers  110  and  112  are not collocated, similar wireless communication issues may arise when in close proximity with each other. 
     The wireless transceivers  104  and  106  are referred to as being collocated when implemented on the same printed circuit board (PCB) or within the same package or product and are thus in very close proximity to each other. The wireless communication system  102  may be configured as any type of wireless device such as, for example, a gateway, a router, an adapter, an alarm system, etc., in which different wireless technologies or protocols are provided within the same device or product. The wireless communication system  102  may be a gateway in which the aggressor wireless transceiver  104  is a Wi-Fi device and the victim wireless transceiver  106  may be a Zigbee device. Alternatively, the wireless communication system  102  may be an alarm system in which the aggressor wireless transceiver  104  is a cellular device (e.g., LTE) and the victim wireless transceiver  106  is a Z-wave device. Many other collocated configurations are contemplated. The wireless communication system  102  may include a host circuit  108  coupled to both of the transceivers  104  and  106 . The transceivers  104  and  106  may also share a direct communication link (DCL), such as a serial peripheral interface (SPI), an inter-integrated circuit (I 2 C) interface, or any other suitable communication interface including a custom control interface. A gateway, for example, may incorporate Internet access, such as an integrated modem or Ethernet connection from one or more gateways to a main router, or a Wi-Fi connection to the main router. The victim wireless transceiver  106  may serve as a Zigbee coordinator or the like of a home automation system supported by the wireless network  100 . 
     Wi-Fi transceivers may be implemented according to any one of the various IEEE 802.11 standards, such as 802.11a, 802.11b, 802.11g, 802.11n, etc. IEEE 802.11n, for example, may operate using 20 Megahertz (MHz) bandwidth channels and orthogonal frequency-division multiplexing (OFDM) subcarrier modulation. The wireless transceiver  106  may operate according to the IEEE 802.15.4 standard. Wi-Fi (IEEE 802.11b/g/n) supports up to 14 overlapping 20/22 MHz bandwidth channels across the 2.4 Gigahertz (GHz) ISM band with transmit power levels up to +30 dBm (decibel-milliwatts). 2.4 GHz Zigbee and other protocols (e.g., Thread), which are based on IEEE 802.15.4, support 16 non-overlapping 2 MHz bandwidth channels at 5 MHz spacing with transmit powers up to +20 dBm. Different devices using these wireless protocols may successfully operate in the local network  100 , although some communication conflicts may occur. 
     When collocated, the aggressor wireless transceiver  104  may impede the ability of the victim wireless transceiver  106  to receive communications from other victim wireless transceivers or devices in the local network  100 . Similarly, when in close proximity, the aggressor wireless transceiver  110  may impede the ability of the victim wireless transceiver  112  to receive communications from other victim wireless transceivers or devices in the local network  100 . In particular, when an aggressor wireless transceiver is transmitting at relative high power and high duty cycle, it tends to function as a blocker to collocated or closely located victim wireless transceivers operating at significantly less power levels. 
     The victim wireless transceivers  106  and  112  are configured with a frequency selective attenuator as further described herein to optimize reception to allow RF coexistence with the aggressor wireless transceivers  104  and  110 . 
       FIG. 2  is a simplified block diagram of a victim wireless transceiver  200  including a tunable notch filter (TNF)  216  implemented according to one embodiment of the present disclosure which may be used as either or both of the victim transceivers  106  or  112 . An antenna  202  for transmitting or receiving wireless RF signals is coupled through a matching network  204  to a transceiver node  205  carrying an RX input signal RXIN. Received signals are provided to an input of a low-noise amplifier (LNA)  206 , having an output providing amplified (and filtered) received signals RXO to a receive (RX) chain circuit  208  for down-converting the frequency of the received signal and converting the received signal to digital format for further processing by a processor  210 . The processor  210  outputs digital signals for transmission to a transmit (TX) chain circuit  212 , which converts to analog format and upconverts to an RF frequency for transmission. The TX chain circuit  212  has an output coupled to the input of a power amplifier (PA)  214 , which amplifies the signal for transmission by the antenna  202  via the matching network  204 . 
     The RX chain circuit  208  may include a level detector (LD)  207  and an automatic gain control (AGC) circuit  209 . The level detector  207  may actually represent one or more level detectors, in which each detector may be implemented as a peak detector, an amplitude detector, a signal level detector for determining the root-mean-square (RMS) level of an input voltage level, an envelope detector, etc., depending upon its function and where in the RX chain circuit  208  an incoming signal is being monitored. When a signal is being received, the AGC circuit  209  may adjust the gain of the LNA  206  and may also adjust other gain blocks in the RX chain circuit  208  to adjust the amplitude of the incoming signal to within a target range of an analog to digital converter (ADC) (not shown) within the RX chain circuit  208 . The LD  207  may include multiple level detectors that monitor the receive signal at different points in the receive signal chain. At least one level detector may monitor the RF level of the signal before down conversion at the transceiver node  205  or after the LNA  206 . In most cases, RF level detectors are wide band and are sensitive to blocker signals. The LD  207  may also include at least one narrow band level detector located after down conversion and reactive mostly to in-band signals. 
     In one embodiment the victim wireless transceiver  200  operates at low power (and usually low duty cycle) in which the LNA  206  and the RX chain circuit  208  are configured to detect low power signals transmitted in the wireless medium and received via the antenna  202 . A collocated or nearby aggressor wireless transceiver, such as either of the aggressor wireless transceivers  104  or  112 , may block reception of low power signals if simultaneously transmitting at a nearby frequency. The transmission by the aggressor wireless transceiver is at a relatively higher power causing the AGC circuit  209  to reduce the gain of the LNA  206  to a level that might otherwise prevent successful reception of desired low power signals if the aggressor transmit signal was not attenuated. 
     The victim wireless transceiver  200  further includes the TNF  216  coupled between the transceiver node  205  and a reference node, such as ground (GND). The TNF  216  is tuned to the transmission frequency of the collocated or nearby aggressor wireless transceiver in order to attenuate the aggressor transmit power and protect the victim front end of the victim wireless transceiver  200  including the LNA  206  and the RX chain circuit  208  from compression. When the TNF  216  is tuned correctly, the aggressor transmit power is sufficiently attenuated so that the LNA  206  may be kept at sufficient gain to detect and successfully receive desired low power signals. 
     In one embodiment, the TNF  216  may be tuned to a particular blocker frequency, such as during a calibration procedure or the like, and may also remain enabled during operation of the victim wireless transceiver  200 . It is noted, however, that multiple different blocker signals at different frequencies may be encountered so that the TNF  216  may be re-tuned during operation. In addition, since the blocker frequency is sufficiently close to the frequency of operation of the victim wireless transceiver  200 , the TNF  216  may attenuate the energy of wanted channels which may harm performance. The receive sensitivity may be degraded when TNF  216  is enabled, so that it may be turned off or disabled when not needed. 
     The victim wireless transceiver  200  includes a controller  218  coupled to the processor  210  which programs the TNF  216  via one or more program (PGM) signals to a selected blocker frequency and that further enables/disables the TNF  216  via an enable (EN) signal. Although shown as a separate circuit, the controller  218  may be incorporated into the processor  210 . For example, the firmware of the processor  210  may be programmed with the programming and enable functions of the controller  218 . The victim wireless transceiver  200  may further include a memory  220  coupled to the controller  218  for storing programmed values for programming the TNF  216 . In one embodiment, the memory  220  may be configured as a lookup table (LUT) or the like for storing a programmed value for each of one or more blocker frequencies of interest. In one embodiment, the memory  220  may be any type of non-volatile memory (NVM), such as any type of read-only memory (ROM) device, including programmable types of NVM, such as an electrically erasable programmable ROM (EEPROM) or the like. 
     The controller  218  is responsive to various signals indicative of conditions for enabling or disabling TNF  216  and for programming its frequency of attenuation. A signal RXS indicates the receive state of the victim wireless transceiver  200 , meaning whether the victim wireless transceiver  200  is in active transmit or receive mode of operation. A signal AGCS indicates the state of the AGC  209 , meaning the relative strength of detected signals including blocker signals. The RXS and AGCS signals may be provided by the processor  210  and are used by the controller  218  for determine whether and when to enable the TNF  216 . A signal BFREQ provided to the controller  218  indicates frequency of a blocker signal for programming the frequency of the TNF  216  if and when known. The controller  218  may also be coupled directly to a collocated aggressor wireless transceiver, such as, for example, the aggressor wireless transceiver  104 , via the DCL for direct inter-transceiver communications. 
     In one embodiment, it may be predetermined that one or more transmission channels of a collocated aggressor wireless transceiver, such as the aggressor wireless transceiver  104 , operate as strong blocker signals negatively impacting the ability of the victim wireless transceiver  106  to detect and receive desired signals. The host circuit  108  of the wireless communication system  102  detects or is otherwise is programmed with the active transmission channels and transmission timing of the aggressor wireless transceiver  104 , so that when a transmission is imminent, it may prompt the controller  218  and adjust the BFREQ signal indicative of the blocker frequency of aggressor transmission. Alternatively, or in addition, the collocated aggressor wireless transceiver may directly communicate via the DCL that transmission is imminent in which the TNF  216  may be engaged automatically with known settings. The DCL communication may simply be an indication of the power amplifier (PA) enable signal of the aggressor wireless transceiver. The DCL provides a faster communication link enabling a faster response by the victim wireless transceiver  200 . If the victim wireless transceiver  200  is not already actively receiving a signal, it may program and activate the TNF  216  accordingly. 
       FIG. 3  is a flowchart diagram illustrating operation of the victim wireless transceiver  200  including operation of the controller  218  for tuning and enabling or disabling the TNF  216  according to one embodiment of the present disclosure. After power on or reset (POR) or after waking from a sleep mode, the victim wireless transceiver  200  is initialized, the initial RX gain is set, and the TNF  216  is initially disabled. The initial RX gain typically means that the gain of the LNA  206  and other gain blocks within the RX chain  208  are set to maximum gain for detecting weak signals transmitted in the communication medium. At next block  304 , the operating mode is determined, such as either a transmit (TX) mode or a receive (RX) mode. Other operating modes may be defined but are not described. At next block  306 , it is queried whether the victim wireless transceiver  200  is in the RX mode of operation. If not, then operation advances to block  308  in which the processor  210  outputs a signal for transmission if in the TX mode, and the signal is transmitted. Operation then loops back to block  304  after successful transmission. 
     If instead it is determined at block  306  that the victim wireless transceiver  200  is in the RX mode of operation, then operation proceeds to block  310  to determine whether a signal is being received. If not, operation loops back to block  304 , and operation loops between blocks  304 ,  306  and  310  during the RX mode until a signal is detected. When an RX signal is detected, operation advances instead to block  312  in which normal receive mode operations are performed including adjusting the RX gain of the LNA  206  and/or the RX chain circuit  208  in an attempt to adjust the amplitude of the incoming signal to within a target range of the ADC of the RX chain circuit  208  as previously described. The RX gain is reduced commensurate with the strength of the signal being received. At next block  314 , while the signal is being received, the processor  210  evaluates the signal being received by the victim wireless transceiver  200 . At next block  316 , it is queried whether the signal is a “desired” signal meaning that it is intended for the victim wireless transceiver  200 . If so, operation advances to block  318 , in which the signal is acquired according to normal receive operations, and once acquired, the RX gain is reset back to initial conditions for receiving any other signals. Operation then loops back to block  304  for further operations. 
     Referring back to block  316 , if the signal is not a desired signal, meaning that it is not intended for the victim wireless transceiver  200  and may otherwise be a blocker signal, then operation advances instead to block  320  to evaluate the relative strength of the blocker signal. If the blocker signal is relatively weak or otherwise is not sufficiently strong to prevent the victim wireless transceiver  200  from receiving weak desired signals, then operation advances to block  322  in which the RX gain may be optimized for receiving desired signals in the presence of the blocker signal (which is not sufficiently strong to block desired signals). At this point, the TNF  216  remains disabled and operation loops back to block  304  for mode determination. It is noted that the RX gain may have been adjusted for the presence of the weak or mid-strength blocker signal. The victim wireless transceiver  200  may have provision, such as at block  304 , for monitoring the presence of the blocker signal so that the RX gain may be re-adjusted if and when the weaker blocker signal terminates. If so, the RX gain may be re-initialized back to maximum levels for detecting weak desired signals. 
     Referring back to block  320 , if the blocker signal is strong, meaning that the RX gain including the gain of the LNA  206  is set too low for detecting weak desired signals, then operation advances instead to block  324  in which the TNF  216  is enabled in an attempt to attenuate the strong blocker signal. The TNF  216  may be initially programmed at a default frequency, or at the frequency of a known blocker signal. As an example, the host circuit  108  may inform the controller  218  of the channel of operation of the aggressor wireless transceiver  104 , in which the controller  218  programs the TNF  216  accordingly. Assuming that the aggressor wireless transceiver  104  is transmitting causing the strong blocker signal, then activation of the TNF  216  likely attenuates the strength of the blocker signal to enable successful receive operations by the victim wireless transceiver  200 . 
     Operation then advances to block  326  in which the AGC is released to adjust or otherwise re-adjust the RX gain after the TNF  216  is enabled. Operation then advances to block  328  in which the controller  218  evaluates the AGCS signal to determine the adjusted state of the AGC  209 . If the AGCS signal indicates that the strength of the blocker signal is reduced, then operation advances to block  330  to query whether the victim wireless transceiver  200  is still in the RX mode of operation. If so, then operation advances to block  332  to query whether a desired signal is detected. If so, then operation advances to block  334  in which the desired signal is acquired, and then operation advances to block  336  in which the TNF  216  is disabled and the RX gain is reset back to initial conditions. Operation then loops back to block  304 . It is noted that if the blocker signal terminates while a desired signal is being received at block  334 , then the TNF  216  remains enabled in spite of the fact that the blocker signal has terminated to avoid undesired transients during reception of a desired signal. 
     Referring back to block  332 , if a desired signal is not detected, operation instead proceeds to block  338  to query whether the strong blocker signal is still active. If so, then operation loops back to block  330 , and operation loops between blocks  330 ,  332  and  338  while in the RX mode in the presence of the strong blocker signal attenuated by the TNF  216 . It is noted that other non-desired signals may be detected while the strong blocker signal is active, but such signals are rejected or otherwise ignored according to normal receive operation. If the strong blocker signal terminates as determined at block  338 , then operation instead proceeds to block  336  in which the TNF  216  is disabled and the RX gain reset before returning back to block  304 . 
     Referring back to block  328 , if the strength of the blocker signal is not reduced, then the TNF  216  may not be programmed to the correct frequency so that it is queried at block  340  whether the TNF  216  should be programmed to another frequency. If multiple frequencies are to be tried, then operation advances to block  342  in which the controller  218  selects another frequency and re-programs the TNF  216 . If the blocker frequency is known then the TNF  216  is tuned to the known blocker frequency. If the blocker frequency is not known, then the TNF  216  may be tuned to the most probable blocker locations depending upon which types of aggressor devices are collocated or in close proximity, such as non-co-channel most used Wi-Fi channels or LTE up-link frequencies and the like. 
     Operation then loops back to block  328  to determine whether the blocker strength is reduced. Operation may loop between blocks  328 ,  340  and  342  until the TNF  216  is programmed to the correct frequency to attenuate the strength of the blocker signal. If so, then operation can proceed to block  330  to receive desired signals. If the blocker signal terminates during this process, then although not specifically shown, operation advances to block  336  to disable the TNF  336  and reset the RX gain before returning to block  304 . If instead the blocker signal remains active and the TNF  216  has been programmed with all known or otherwise available frequencies, then operation instead advances to block  344  in which an error process may be performed. It is noted that the TNF  216  is specifically designed within the operating frequency range of the victim wireless transceiver  200  so that a programmed frequency of the TNF  216  should be available to attenuate the strong blocker signal under normal conditions. After block  344 , operation advances to block  336  previously described before returning back to block  304 . 
     As previously described, the LD  207  may include a wideband RF level detector sensitive to the blocker and blocker attenuation and a narrow band level detector more sensitive to attenuation of the in-band wanted signal. Although not specifically described in  FIG. 3 , even if the TNF  216  is successfully attenuates a blocker signal, the TNF  216  may nonetheless be disabled if the TNF  216  also attenuates the wanted signal by more than a desired amount. In other words, attenuation of the wanted signal should not exceed a predetermined level for the TNF  216  to be enabled. 
       FIG. 4  is a simplified schematic and block diagram of a portion of a victim wireless transceiver  400  implemented according to an embodiment of the present disclosure in which the TNF  216  is configured as a tunable notch filter  416  using only a bondwire as an inductor  434 . The victim wireless transceiver  400  is configured in a similar manner as the victim wireless transceiver  200  in which similar components assume identical reference numerals. The victim wireless transceiver  400  is shown provided on a semiconductor chip or semiconductor die  450  which is further mounted on a semiconductor package  460  (e.g., standard package). The victim wireless transceiver  400  includes the transceiver node  205 , the LNA  206 , the tunable notch filter  416 , the memory  220 , and the controller  218  which are shown provided on the semiconductor die  450 . It is understood that remaining portions of the victim wireless transceiver  400 , such as the RX and TX chain circuits  208  and  212 , the processor  210 , and the PA  214  are included but not shown. Although not shown, external components, such as the matching network  204  and the antenna  202  may also be included and coupled in a similar manner as the victim wireless transceiver  200 . The semiconductor package  460  and one or more of the external components may be mounted on a printed circuit board (PCB) or the like (not shown). 
     The tunable notch filter  416  includes a switch  430 , a variable capacitor  432  with capacitance C, and the inductor  434  with inductance L. The switch  430  has one terminal coupled to the transceiver node  205  and another terminal coupled to one terminal of the variable capacitor  432 , which has its other terminal coupled to one terminal of the inductor  434  at a conductive pad  436  of the semiconductor die  450 . The other terminal of the inductor  434  is coupled to a GND connection of the semiconductor package  460 . The switch  430  is illustrated as a single-pole, single-throw (SPST) switch having a control terminal controlled by an enable (EN) signal from the controller  218 . The switch  430  may be implemented as a transistor device, such as, for example, a CMOS device such as an N-type or P-type bipolar junction transistor (BJT) or a PMOS or NMOS transistor or the like. In one embodiment, EN is asserted (e.g., pulled high) to close the switch  430  to enable or activate the tunable notch filter  416  by coupling it to the transceiver node  205 . The tunable notch filter  416  is disconnected or disabled when EN is de-asserted (e.g., pulled low) opening the switch  430 . 
     The variable capacitor  432  may be implemented as a programmable capacitor that is programmed by a digital program (PGM) value provided by the controller  418 . As an example, the variable capacitor  432  may be implemented by multiple capacitors coupled in parallel activated by corresponding switches each controlled by corresponding bit of the digital PGM value such as shown in  FIG. 8 . The programmed capacitance is a value C. 
     The inductor  434  is shown configured as a conductive bondwire connected between the conductive pad  436  of the semiconductor die  450  and the conductive GND connection of the underlying semiconductor package  460 , in which the bondwire has an inductance L. A bondwire configuration is appropriate if the bondwire has a suitable value of inductance L that when combined with the capacitance C is programmable within a blocker frequency range of blockers that may negatively impact the frequency range of operation of the victim wireless transceiver  200 . In addition, the variable capacitor  432  is configured to have a sufficient quality factor Q to appropriately attenuate the blocker frequency without significantly impacting the operating frequency range of the victim wireless transceiver  400 . 
     For example, a bondwire implementing the inductor  434  having an inductance L=1 nano-Henry (nH) and a programmable capacitor implementing the variable capacitor  332  programmed with a capacitance of C=4.35 pico-Farads (pF) with a Q value of approximately 30 resonating at 2.412 GHz is suitable for attenuating a Wi-Fi signal at the center of Wi-Fi channel 1 6 decibels (dB) more than the center of 15.4 channel 25 at 2.475 GHz. Another example is a European configuration of Z-wave in the 868 MHz frequency band in close proximity of the LTE uplink band 5 (824-849 MHz) and 7 (880-915 MHz). 
       FIG. 5  is a simplified schematic and block diagram of a portion of another victim wireless transceiver  500  implemented according to an embodiment of the present disclosure in which the TNF  216  is configured as a tunable notch filter  516  using a bondwire and a physical inductor  572  as the inductance. The victim wireless transceiver  500  is configured in a similar manner as the victim wireless transceiver  400  in which similar components assume identical reference numerals. The victim wireless transceiver  500  is also shown provided on the semiconductor die  450  upon which the transceiver node  205 , the LNA  206 , a portion of the tunable notch filter  416 , the memory  220 , and the controller  218  are implemented. It is understood that remaining portions of the victim wireless transceiver  400 , such as the RX and TX chain circuits  208  and  212 , the processor  210 , and the PA  214  are included but not shown. Although not shown, external components, such as the matching network  204  and the antenna  202  may also be included and coupled in a similar manner as shown in  FIG. 2 . The semiconductor die  450  is mounted on the semiconductor package  460  in a similar manner previously described. 
     The tunable notch filter  516  is configured in substantially similar manner as the tunable notch filter  416  including the switch  430 , the variable capacitor  432 , and the inductor  434  coupled in substantially similar manner. The controller  218  programs the variable capacitor  432  via PGM in similar manner and enables or disables the tunable notch filter  516  in similar manner via EN. Also, the inductor  434  is included and provided has a bondwire having an inductance L 1  and having one terminal coupled to the conductive pad  436 . The other terminal of the inductor  434 , however, is not coupled directly to GND but instead is coupled to one terminal of the inductor  572  via an external conductor  540 , in which the inductor  572  is mounted on an external PCB  570 . The semiconductor package  460  may also be mounted on the PCB  570 . The inductor  572  may be implemented as a physical inductor with inductance L 2  and has its other terminal coupled to a separate GND connection. In this case, the inductor  572  is mounted on the PCB  570  external to the semiconductor package  460  and the inductance of the notch filter inductor is L 1 +L 2 . 
       FIG. 6  is a simplified schematic and block diagram of a portion of another victim wireless transceiver  600  implemented according to an embodiment of the present disclosure in which the TNF  216  is configured as a tunable notch filter  616  using a bondwire and an in-package physical inductor  662  as the inductance. The victim wireless transceiver  600  is configured in a similar manner as the victim wireless transceiver  500  in which similar components assume identical reference numerals. The victim wireless transceiver  600  is also shown provided on the semiconductor die  450  upon which the transceiver node  205 , the LNA  206 , a portion of the tunable notch filter  416 , the memory  220 , and the controller  218  are implemented. It is understood that remaining portions of the victim wireless transceiver  400 , such as the RX and TX chain circuits  208  and  212 , the processor  210 , and the PA  214  are included but not shown. Although not shown, external components, such as the matching network  204  and the antenna  202  may also be included and coupled in a similar manner as the victim wireless transceiver  200 . The semiconductor die  450  is mounted on the semiconductor package  460  in a similar manner previously described. 
     The tunable notch filter  616  is configured in substantially similar manner as the tunable notch filter  516  including the switch  430 , the variable capacitor  432 , and the inductor  434  coupled in substantially similar manner. The controller  218  programs the variable capacitor  432  via PGM in similar manner and enables or disables the tunable notch filter  616  in similar manner via EN. The inductor  434  is included and provided has a bondwire having an inductance L 1  and having one terminal coupled to the conductive pad  436 . The other terminal of the inductor  434  is coupled to one terminal of the inductor  662  mounted as a physical inductor on the semiconductor package  460  rather than on an external PCB. The inductor  662  is also a physical inductor with inductance L 2  and has its other terminal coupled to a separate GND connection of the semiconductor package  460 . Again, the inductance of the notch filter inductor is L 1 +L 2 . 
       FIG. 7  is a simplified schematic and block diagram of a portion of another victim wireless transceiver  700  implemented according to another embodiment of the present disclosure in which elements of the TNF  216  are arranged in a different order. The victim wireless transceiver  700  is configured in a similar manner as the victim wireless transceiver  500  in which similar components assume identical reference numerals. The victim wireless transceiver  700  is also shown provided on a semiconductor die  750  upon which the transceiver node  205 , the LNA  206 , a portion of the tunable notch filter  716 , the memory  220 , and the controller  218  are implemented. It is understood that remaining portions of the victim wireless transceiver  700 , such as the RX and TX chain circuits  208  and  212 , the processor  210 , and the PA  214  are included but not shown. The semiconductor die  750  is mounted on the semiconductor package  760  in a similar manner as the semiconductor die  450  and the semiconductor package  460 . 
     The tunable notch filter  716  includes similar components and operates in a similar manner. The tunable notch filter  716  also includes the switch  430 , the variable capacitor  432 , and the conductive pad  436  coupled a different manner. In this case, one terminal of the switch  430  is coupled to GND and its other terminal is coupled to one terminal of the variable capacitor  432 , having its other terminal coupled to the conductive pad  436 . The conductive pad  436  is coupled to one terminal of a physical inductor  772  mounted on a separate PCB  770  via a bondwire  740  having an inductance L 1 . The inductor  772  may also be a physical inductor with inductance L 2 . The other terminal of the inductor  772  is coupled to a node  774  on the PCB  770 , which is coupled to the transceiver node  205  via an off-chip conductor  776  and a conductive pad  438  of the semiconductor die  750 . The matching network  204  is shown mounted on the PCB  770  between the conductive pad  774  and another conductive pad  778 , which may be further coupled to the antenna  202  (not shown in  FIG. 7 ). Again, the inductance of the notch filter inductor is L 1 +L 2 . 
     The controller  218  programs the variable capacitor  432  via PGM in similar manner and enables or disables the tunable notch filter  716  in similar manner via EN. In this case, however, the tunable notch filter  716  is enabled or disabled by selectively coupling the tunable notch filter  716  to GND rather than selectively coupling the tunable notch filter  716  to the transceiver node  205 . Nonetheless, operation of the tunable notch filter  716  is substantially similar. Although the inductor  772  is shown mounted on the PCB  770 , it may also be mounted on the semiconductor package  760  in a similar manner as shown by the inductor  662  in  FIG. 6 . 
     The arrangement of the components or elements of the tunable notch filters  416 ,  516  and  616 , in which the switch  430  selectively couples an LC series circuit connected to GND to the transceiver node  205 , operates in similar manner as the arrangement shown by the tunable notch filter  716 , in which the switch  430  selectively couples an LC series circuit connected to the transceiver node  205  to GND. The element ordering in any of these TNF configurations may be rearranged to allow the most optimal implementation. For example, the configuration of the tunable notch filters  416 ,  516  and  616  may be rearranged similar to that of the tunable notch filter  716 , or the tunable notch filter  716  may be rearranged similar to that of the tunable notch filters  416 ,  516  and  616 , in order to achieve the most optimal implementation for a given application. 
     A selection from among the various configurations of the TNF  216  implemented as a notch filter as shown in  FIGS. 4-7  may depend on the target notch frequency and the packaging technology of the semiconductor die. If appropriate, the notch inductor may be implemented solely with a bondwire (e.g., tunable notch filter  416 ) or at least partly implemented with a bondwire (e.g., tunable notch filters  516  and  616 ). The notch inductor may be implemented solely as a physical inductor (e.g., tunable notch filter  716 ) or in combination with a bondwire (e.g., tunable notch filters  516  and  616 ). The physical inductor may be integrated on the die (e.g., tunable notch filter  616 ) or on a separate PCB (e.g., tunable notch filters  516 ,  616  or  716 ). 
     The amount of attenuation increases with higher Q implementations and can be maintained over process variations by using calibration of the tuning capacitors. If higher selectivity is needed for an application, a very high quality inductor may be used to implement the trap to realize frequency selectivity within 60-70 MHz, which is less than 3% of the center frequency. On-chip inductors may not be feasible to realize a Q level of 30 at 2.5 GHz. Bondwire inductors are an option to achieve a Q level greater than 20, yet bondwires tend to be restricted to low inductance values. In order to reduce the minimum attenuation and increase selectivity, off-chip high quality inductors for an LC trap with Q&gt;50 may be configured. The LC trap may be automatically tuned as the location of the notch needs to be very accurate. 
       FIG. 8  is a simplified schematic diagram of a digitally programmable capacitor  800  that may be used as the variable capacitor  432  for any of the tunable notch filters described herein according to one embodiment of the present disclosure, in which PGM is a digital value PGM&lt;0:N&gt;. Each bit of PGM includes an inverted counterpart PGM&lt;0:N&gt; B in which “B” is appended to denote inverted bits. The programmable capacitor  800  includes a pair of capacitor terminals  802  and  804  representing the terminals of the programmable capacitor  800 . For example, the capacitor terminal  802  may be coupled to one terminal of the switch  430  and the capacitor terminal  804  may be coupled to the conductive pad  436 . 
     The programmable capacitor  800  includes a series of N+1 capacitors C 0 , C 1 , CN and a corresponding series of N+1 N-channel transistor switches N 0 -NN, in which each capacitor is coupled in series with the current terminals of a corresponding one of the transistor switches between the capacitor terminals  802  and  804 . Thus, C 0  is coupled in series with N 0  between the terminals  802  and  804 , C 1  is coupled in series with N 1  between the terminals  802  and  804 , and so on, up to CN, which is coupled in series with NN between the terminals  802  and  804 , each forming one of multiple switch-capacitor pairs coupled in parallel between the capacitor terminals  802  and  804 . One terminal of each of the capacitors C 0 -CN is coupled to the capacitor terminal  802 . In each case, the drain terminal of each of the transistor switches N 0 -NN is coupled to the other terminal of a corresponding one of the capacitors C 0 -CN, and the source terminal is coupled to the capacitor terminal  804 . Each of the transistor switches N 0 -NN has a gate terminal receiving a corresponding one of N+1 program bits PGM&lt;0&gt;, PGM&lt;1&gt;, PGM&lt;N&gt; from the controller  218 . 
     A series of N+1 resistors R are further provided, each having one terminal coupled to the junction between the resistor-transistor switch pairs between the capacitor terminals  802  and  804 . The other terminal of each resistor R is coupled to one current terminal of a corresponding one of a series of N+1 pass gates (a.k.a., transmission gates) G 0 , G 1 , . . . , GN. It is noted that the resistance value of the resistors R is chosen to be substantially higher than the ON resistance of the N-channel transistor switches N 0 -NN. The other current terminal of each of the pass gates G 0 -GN is coupled to a bias voltage VB. Each pass gate G 0 -GN is shown implemented as a parallel combination of a P-channel transistor and an N-channel transistor, in which the source terminal of one of the transistors of each pass gate is coupled to the drain terminal of the other, and vice-versa. Each pass gate includes a P-gate control terminal (gate terminal of internal P-channel transistor) and an N-gate control terminal (gate terminal of internal N-channel transistor). The P-gate control terminal of each pass gate G 0 -GN receives a corresponding one of the program bits PGM&lt;0&gt;-PGM&lt;N&gt;. The corresponding N-gate control terminal of each pass gate G 0 -GN receives a corresponding one of inverted program bits PGM&lt;0&gt;_B-PGM&lt;N&gt;_B. 
     In operation of the programmable capacitor  800 , each program bit PGM&lt;0&gt; PGM&lt;N&gt; is asserted high to turn on the corresponding transistor switch N 0 -NN to connect the corresponding capacitor C 0 -CN between the capacitor terminals  802  and  804 , and to turn off the corresponding pass gate G 0 -GN. Each of the control bits PGM&lt;0&gt;-PGM&lt;N&gt; is negated low to turn off the corresponding one of the transistor switch N 0 -NN to remove or decouple the corresponding capacitor C 0 -CN from the capacitor terminal  804  and to turn on the corresponding pass gate G 0 -GN to instead couple the capacitor to VB. For example, when PGM&lt;0&gt; is asserted high, N 0  is turned on so that C 0  is coupled between the capacitor terminals  802  and  804 , while the corresponding pass switch G 0  is turned off to isolate C 0  from VB. When PGM&lt;0&gt; is negated low, N 0  is turned off so that C 0  is isolated from the capacitor terminal  804 , while the corresponding pass switch G 0  is turned on to connect C 0  to VB. Thus, the control bits PGM&lt;0&gt;-PGM&lt;N&gt; collectively form the digital program value PGM used to couple selected ones of the capacitors C 0 -CN in parallel in which the capacitances of the selected capacitors add to select the corresponding capacitance for the programmable capacitor  800 . The non-selected ones of the capacitors C 0 -CN are tied off to the bias voltage to remove and isolate them from the circuit. 
     The capacitances of the capacitors C 0 -CN are selected based on the applicable frequency range of use for the particular wireless transceiver and the inductance of the corresponding bondwire or inductor or both. In one embodiment, the capacitances of the capacitors C 0 -CN are substantially equal to each other. In another embodiment, the capacitances of the capacitors C 0 -CN are binarily distributed to potentially provide a wider range of frequencies. The number of capacitors N may be selected to achieve the desired resolution or level of accuracy to more accurately tune and attenuate blocker frequencies. 
     The controller  218  enables the programmable capacitor  800  by asserting the program bits PGM&lt;0&gt;-PGM&lt;N&gt; of the digital program value PGM to a desired value. The controller  218  may disable the programmable capacitor  800 , or effectively remove it from the circuit, by asserting each of the program bits PGM&lt;0&gt;-PGM&lt;N&gt; to a zero value. It is appreciated that the additional switch  430  may be used in each case to disable the corresponding tunable notch filter  416 ,  516 ,  616 , or  716 . The switch  430  may be eliminated when using the programmable capacitor  800  in which PGM is asserted to a digital zero value to disable the programmable capacitor  800  and thus the corresponding tunable notch filter. 
       FIG. 9  is a flowchart diagram illustrating a calibration process that may be performed by a victim wireless transceiver according to one embodiment of the present disclosure. The calibration process may be performed by any victim wireless transceiver including those described herein, such as the wireless transceivers  106  or  112  of  FIG. 1 , the victim wireless transceiver  200  of  FIG. 2 , or any of the wireless transceivers  400 ,  500 ,  600 , or  700  of  FIG. 4, 5, 6 , or  7 , respectively, that may be a victim to transmissions of aggressor wireless transceivers. The calibration process is typically performed during manufacturing before being operated in the field. 
     At first block  902  the victim wireless transceiver is configured into a loopback mode. This means that the TX chain circuit  212  is active for transmitting via the PA  214  while the RX chain circuit  208  including the LD  207  is also enabled to detect the level (e.g., peak level) of the signal being transmitted by the PA  214 . At next block  904  the PA  214  transmits at a first or next frequency within a target frequency range. The target frequency range includes the frequencies of operation of the victim wireless transceiver, and may include nearby frequencies that are sufficiently close to the operating frequency to cause blocking interference. The TX chain circuit  212  is configured to adjust and generate any number of frequencies within the applicable frequency range. For example, for 2.4 GHz Wi-Fi, the applicable frequencies may include Wi-Fi center MHz frequencies of  2412 ,  2417 ,  2422 , etc. for each of the up to 11-14 Wi-Fi channels. The applicable frequencies may include other frequency ranges depending upon the wireless technology employed, such as, for example, any sub-GHz frequencies including, for example, those in the 800-900 MHz range. 
     At next block  906 , the TNF  216  is enabled and the controller  218  sweeps through multiple capacitance values of the variable capacitor  432  until the LD  207  detects a minimum transmit power level. The TNF  216  may be configured in any suitable manner, such as according to any of the tunable notch filters  416 ,  516 ,  616 ,  716  described herein. Also the variable capacitor  432  may be configured in an suitable manner, such as according to the programmable capacitor  800 . For the programmable capacitor  800 , for example, the controller  218  adjusts the digital program value PGM&lt;0:N&gt; to step through multiple capacitance values for adjusting the notch frequency of the notch filter accordingly. It is noted that not all capacitance values may be selected; instead, since the frequency is known, only those capacitance values at or near the transmitted frequency may be selected. The LD  207  detects the amplitude or strength of the signal being transmitted by the PA  214  as possibly attenuated by the TNF  216 . When the capacitance is adjusted so that the TNF  216  is programmed at about the same attenuation frequency as the frequency being transmitted by the PA  214 , the LD  207  reaches a minimum value. 
     At next block  908 , the PGM value corresponding with the minimum level detected by the LD  207  is stored into the memory  220  for the corresponding value of the frequency being transmitted. In this manner, when an aggressor wireless transceiver transmits at this same frequency otherwise blocking the victim wireless transceiver, the controller  218  may retrieve this stored PGM value, program the TNF  216  accordingly, and enable the TNF  216  to attenuate the blocking frequency. With reference back to  FIG. 3 , it is noted that if the blocker is not sufficiently attenuated at block  328 , another PGM value may be retrieved or the controller  218  may tweak PGM at block  340  until the blocker signal is attenuated by a maximum amount. 
     At next block  910 , it is queried whether to calibrate for another frequency and if so, operation loops back to block  904  in which the next frequency is selected for transmission. Operation is repeated in subsequent loops until all of the desired frequency values have been calibrated, and then operation is completed. 
       FIG. 10  is a flowchart diagram illustrating a blocker scan process that may be performed by a victim wireless transceiver according to one embodiment of the present disclosure. The blocker scan process may be performed by any victim wireless transceiver including those described herein, such as the wireless transceivers  106  or  112  of  FIG. 1 , the victim wireless transceiver  200  of  FIG. 2 , or any of the wireless transceivers  400 ,  500 ,  600 , or  700  of  FIG. 4, 5, 6 , or  7 , respectively, that may be a victim to transmissions of aggressor wireless transceivers. The blocker scan process is a form of energy scan that may be performed when the wireless transceiver is operating in the field and in a specific environment in which blocker signals may be present. 
     At first dock  1002 , the victim wireless transceiver is temporarily taken offline and the TNF  216  is disabled. At next block  1004 , the RX chain circuit  208  is adjusted to monitor the first (or the next) frequency of operation. Although not specifically shown, the RX chain circuit  208  includes a programmable local oscillator or the like that may be adjusted to a selected frequency. The RX chain circuit  208  then monitors the transmitted energy in the transmission medium at the selected frequency. The selected frequency includes any one of one or more frequencies within the frequency range operation of the victim wireless transceiver. The AGC  209  may be operated to detect signals being transmitted. 
     At next block  1006 , the level of the LD  207  is compared with a blocker threshold level BTH. BTH is a threshold signal strength level of possible blocker signals that may negatively impact receive operation of the victim wireless transceiver. At next block  1008 , the level of the LD  207  is compared with BTH. If the LD level exceeds BTH meaning that a strong blocker signal may be present at that frequency, then operation advances to block  1010  in which the blocker frequency value is stored into the memory  220 . Operation then advances to block  1012  to query whether another frequency should be evaluated, and if so, operation loops back to block  1004  to evaluate the next frequency. Referring back to block  1008 , if the LD level does not exceed BTH meaning that a strong blocker signal may not be present at that frequency, then operation advances directly to block  1012 . Operation loops in this manner for each frequency of interest, and corresponding blocker frequencies are stored into the memory  220 . 
     If no other frequencies are to be tested as determined at block  1012 , operation advances instead to block  1014  to determine whether another pass of the frequencies may be warranted. The blocker scan may need to be performed for multiple passes to more likely capture blocker signals intermittently being transmitted. If another pass is desired, then operation advances to block  1016  in which the RX chain circuit  208  is reset back to monitor the first frequency, and operation loops back to block  1006  previously described. Operation repeats for as many scan passes as may be deemed necessary to potentially detect blocker signals in the wireless area. When a sufficient number of passes are done, blocker scan operation is completed. 
     Although not specifically shown, after the blocker scan operation is completed, the victim wireless transceiver may perform a self calibration process similar to the calibration process of  FIG. 9 . For each of the blocker signal frequencies stored within the memory  220 , the victim wireless transceiver may program the RX chain circuit  208  to that frequency, enable the TNF  216 , and sweep through applicable capacitance values (e.g., by stepping through multiple values of PGM) while monitoring the LD  207  to determine the value of PGM that attenuates that blocker signal. The corresponding PGM value may then be stored into the memory  220  corresponding to that blocker signal frequency. 
     The blocker scan process may be performed on a periodic basis, but does take the device offline for a period of time. A coordinator of multiple devices, such as, for example, the victim wireless transceiver  106  managing multiple devices, such as including the victim wireless transceiver  112 , may periodically instruct each of multiple devices of a given configuration to perform the block scan process as an energy scan for the local wireless area. Each device, including the coordinator, may be taken offline, one at a time, to scan the energy within its locale and generate a report that includes blocker signals at corresponding frequencies. Each device may then report back to the coordinator, that generates a corresponding energy map of the local wireless network. This information may be used by the coordinator to instruct each subservient device to program its local TNF  216  for applicable blocker frequencies. 
     It is noted that the TNF  216  may be used for alternative purposes other than attenuating an unwanted or blocker signal. A very strong wanted signal may be received in which the gain blocks of the RX chain  208  are unable to reduce the power level of the wanted signal to the desired range of the ADC within the RX chain circuit  208 . As an example, a very high power transmitter transmitting a wanted signal may be brought too close to the victim wireless receiver. In such a scenario, the TNF  216  may be tuned to the transmission frequency of the wanted signal and used to attenuate the desired signal by an amount that enables the RX chain  208  to successfully receive the desired signal. 
       FIG. 11  is a simplified schematic and block diagram of a portion of a victim wireless receiver  1100  similar to the victim wireless transceiver  200  including a frequency selective attenuator in the form of a tunable notch filter (TNF)  1102 . The antenna  202  is coupled through the matching network  204  to the transceiver node  205  further coupled to a receiver circuit  1104  and a transmitter circuit  1106 . The transceiver node  205  may be coupled to the input of the receiver circuit  1104  and the output of the transmitter circuit  1106  via a conductive wire (or trace or bondwire)  1108  and one or more conductive pads in a similar manner previously described. Although not specifically shown, the receiver circuit  1104  and the transmitter circuit  1106  may be implemented in a similar manner as previously described, such as including the LNA  206 , the RX chain circuit  208 , the TX chain circuit  212 , the PA  214 , and the processor  210  among other components and circuits. 
     The TNF  1102  is shown implemented in a similar manner as tunable notch filter  716  of the victim wireless transceiver  700 , although the TNF  1106  may alternatively be implemented as other the tunable notch filters  216 ,  416 ,  516 , and  616  described herein. The TNF  1102  includes an inductor  1110  having one end coupled to the transceiver node  205  and another end coupled to one end of a variable capacitor  1112  through a conductive wire (or trace or bondwire)  1114  and one or more conductive pads in a similar manner as previously described. As shown, one end of the variable capacitor  1112  is coupled to a conductive pad  1116  and the other end is coupled to GND. The inductor  110  is shown having an inductance L although the inductance L represents the entire inductance of the TNF  1102  including any conductance of the conductive wire  1114 . The variable capacitor  1112  is shown having a capacitance C. The controller  218  and the memory  220  are shown for detecting blocker signals and programming the variable capacitor  1112  accordingly in a similar manner previously described. 
     A large or strong blocker signal  1120  is shown being received by the antenna  202  of the victim wireless receiver  1100 , which generates a large blocker current I_BLOCKER flowing through the TNF  1102 . It is assumed that the controller  218  has programmed the variable capacitor  1112  at the frequency level of the blocker signal  1120 . A sinusoidal graphic  1122  represents a relatively large voltage appearing on the conductive pad  1116  and thus across the variable capacitor  1112  as a result of the blocker signal  1120 . Another sinusoidal graphic  1124  represents a relatively small voltage appearing at the transceiver node  205  as a result of the blocker signal  1120 . The relative sizes of the sinusoidal graphics  1122  and  1124  illustrate that most of the energy of the blocker signal  1120  is absorbed by the TNF  1102  illustrating correct operation of the TNF  1102 . For Receiver front end circuits, the ability to provide frequency selectivity is a very useful property as has been shown herein. Frequency selectivity allows the receiver circuit  1104  of the victim wireless receiver  1100  to have higher gain for desired signals compared to interferer signals and improves the dynamic range of the receiver circuit  1104 . 
     Another useful property of a receiver front end, however, is linear attenuation. Linear attenuation also improves the dynamic range of a receiver particularly when the interferer signal is close to the desired signal. In such cases, distortion caused by receiver circuit non-linearities is suppressed by engaging the linear attenuator. When the interfering signal is close by, particularly 3 rd  order distortion terms fall into desired signal band and limit the dynamic range of a receiver. Passive LC-based circuits, such as the TNF  1102 , are an attractive choice for such frequency selective attenuators. Since it is desirable to have the capacitance C programmable and software controllable, it is implemented on-chip (e.g., on the semiconductor die  450  or  750  or the like). The capacitance C may be implemented using a capacitor bank (e.g., the digitally programmable capacitor  800 ) that has a high-quality factor (or high-Q factor) since it directly determines the frequency selectivity achievable. It is assumed that in cases of strong interferer or blocker signals from co-located chips (example would be co-located Wi-Fi or similar with BLE/Zigbee or the like), the frequency location of the interferer may be known and hence the capacitor  1112  can be tuned to its frequency. 
     Although not specifically shown, one method of providing a high-Q factor of the digitally programmable capacitor  800  is to provide relatively large channel transistor switches N 0 -NN with large current capacity. 
     In practice, achievable Q limits the selectivity that can be achieved. When interferer signals are close by, the frequency selectivity that can be achieved may be limited. A magnitude of input impedance ZIN of the TNF  1102  from the transceiver node  205  may be determined according to the following equation (1): 
                   ZIN   =       ω   ⁢   L     +     1     ω   ⁢   C       +   R             (   1   )               
in which ω is the frequency in radians and R represents finite losses in the inductances and the capacitance of the TNF  1102 . At
 
               ω   =     1     LC         ,         
ZIN=K. The configuration of the TNF  1102  offers the attenuation by providing an extremely low impedance at the blocker frequency. In this configuration, however, it is difficult to linearize the attenuation because even though it provides a low impedance at the transceiver node  205 , there are large voltage swings across the programmable capacitors of the variable capacitor  1112  as shown. This is because the LC circuit sinks large currents (I_BLOCKER) from the blocker signal and creates a large voltage swing across the variable capacitor  1112 . Large swings amplify the non-linearities that result in degraded distortion performance. These non-linearities may result from the large channel transistor switches N 0 -NN used in the programmable capacitors and/or electrostatic discharge (ESD) structures that are used for implementing the TNF  1102  structure on-chip. Hence, even though the TNF  1102  can provide selectivity when there is frequency separation between desired and interferer channels, when the blocker signal is sufficiently close by, its own distortion can become a bottleneck for the receiver circuit  1104 .
 
       FIG. 12  is a simplified schematic and block diagram of a portion of a victim wireless receiver  1200  implemented according to an embodiment of the present disclosure and similar to the victim wireless transceiver  1100  in which similar components assume identical reference numerals. The TNF  1102  is replaced by a modified TNF  1202  including the variable capacitor  1112  (with capacitance referred to as C 1 ) and also including an additional variable capacitor  1212  with capacitance C 2 . The controller  218  is replaced by a controller  1218  and the memory  220  is replaced by a memory  1220  with differences as further described herein. The antenna  202  is coupled through the matching network  204  to the transceiver node  205  further coupled to the receiver circuit  1104  and the transmitter circuit  1106  via the conductive wire  1108  and one or more conductive pads in a similar manner previously described. 
     The controller  1218  may receive the RXS, AGCS, and BFREQ signals and may operate in substantially the same manner previously described for programming the variable capacitor  1112 . Also, the memory  1220  may store programmed values for programming the variable capacitor  1112  in substantially the same manner and may be any type of NVM, such as any type of ROM device, including programmable types of NVM, such as an EEPROM or the like. Thus, the TNF  1202  is programmed substantially at the frequency of the blocker signal  1120  to enhance the ability of the receiver circuit  1104  to detect desired signals. As previously noted, however, when the frequency of the blocker signal  1120  is sufficiently close to frequency of the desired receive signals, distortion may be increased potentially interfering with the same desired receive signals. 
     The second variable capacitor  1212  is included to enhance linear attenuation to reduce the distortion. The variable capacitor  1212  has a capacitance C 2  that is selected to deliberately mistime the overall LC network of the TNF  1202 . This mistuning introduced by C 2  plays an important role in linearizing the TNF  1202  by reducing the voltage swing that appears across the variable capacitors  1112  and  1212  as illustrated by a sinusoidal graphic  1222 . Note that the graphic  1222  is smaller than the graphic  1122  representing that the added capacitance C 2  reduces the voltage swing at the conductive pad  1116  thereby reducing distortion and increasing linear attenuation. For the same power of the blocker signal  1120  at the antenna  202 , a smaller I_BLOCKER current flows through the capacitors  1112  and  1212  and the overall higher value of the combined capacitance C 1  and C 2  attenuates the signal swing across the capacitor combination. 
     The addition of the capacitance C 2  changes ZIN to a modified magnitude value ZIN MOD  according to the following equation (2): 
                     ZIN   MOD     =       ω   ⁢           ⁢   L     +     1     ω   ⁡     (       C   ⁢   1     +     C   ⁢   2       )         +     R   MOD               (   2   )               
in which R MOD  represents finite losses in the inductances and the capacitance of the TNF  1202  with the addition of the capacitance C 2 . By choosing an appropriate value of the capacitance C 2 , small ZIN MOD  values can still be realized but more importantly, the presence of C 2  linearizes ZIN and prevents the TNF  1202  from adding significant distortion.
 
       FIG. 13  is a simplified schematic and block diagram illustrating the TNF  1202  implemented as controlled by the controller  1218  according to one embodiment of the present disclosure. The inductor  1110  representing total inductance L is coupled between the transceiver node  205  and the conductive pad  1116 . The variable capacitor  1112  is coupled in series with a switch  1302  between the conductive pad  1116  and GND. In addition, the variable capacitor  1212  is coupled in series with a switch  1304  between the conductive pad  1116  and GND. The controller  1218  provides a first set of one or more program signals PGM 1  to program the variable capacitor  1112 , and provides a second set of one or more program signals PGM 2  to program the variable capacitor  1212 . The memory  1220  includes a first set of digital values for programming the capacitance C 1 , and includes a second set of digital values for programming the capacitance C 2 . The controller  1218  provides a first enable signal EN 1  to the switch  1302  to selectively enable or disable the TNF  1202  in a similar manner previously described. The controller  1218  provides a second enable signal EN 2  to the switch  1304  to selectively add the variable capacitor  1212  with capacitance C 2  in parallel with C 1 . 
     The configuration of the TNF  1202  and the controller  1218  shown in  FIG. 3  provides at least three modes of operation based on presence or absence of a blocker signal and the relative frequency of the blocker signal when present. First, a disable mode is defined such that when a blocker signal is not present during a receive mode of operation, then the controller  1218  asserts EN 1  and EN 2  to open the switches  1302  and  1304  to effectively disable the TNF  1202 . Second, a frequency selective mode is defined such that when a blocker signal is present that may interfere with reception operation, the controller  1218  asserts EN 1  to close switch  1302 , asserts PGM 1  to program the variable capacitor  1112 . As previously described, PGM 1  is selected based on the frequency of the blocker signal to program the capacitance C 1  to sufficiently attenuate the blocker signal from interfering with reception of desired receive signals. In the frequency selective mode, however, the frequency of the blocker signal is sufficiently distant from the receive frequency such that any distortion introduced by the TNF  1202  is sufficiently low so that the capacitance C 2  is not necessary. Thus, in the frequency selective mode, the controller  1218  asserts EN 2  to open switch  1304  to remove the variable capacitor  1212 . 
     Third, an attenuation mode is defined when a blocker signal is present and very close to the receive frequency. In the attenuation mode, EN 1  and EN 2  are both asserted to close the switches  1302  and  1304  to add both capacitances C 1  and C 2 . The controller  1218  provides PGM 1  to program the capacitance C 1  in the same manner based on the frequency of the blocker signal to sufficiently attenuate the blocker signal from interfering with reception of desired receive signals. In addition, the controller  1218  provides PGM 2  to program the capacitance C 2  to optimize linear attenuation to optimize distortion performance. 
     The determination between selecting between the frequency selective mode and the attenuation mode is based on the frequency difference between the receive frequency and the blocker frequency. In one embodiment, the controller  1218  determines a frequency difference between the blocker frequency and the receive frequency and compares the difference with at least one predetermined threshold. When the frequency difference is greater than a disable threshold, then the controller  1218  selects the disable mode and disables both of the capacitors  1112  and  1212 . When the frequency difference is less than the disable threshold but still greater than an attenuation (or distortion) threshold ATH, then the controller  1218  selects the frequency selective mode. When the frequency difference is less than the attenuation threshold ATH, then the controller  1218  selects the attenuation mode. 
     The specific value of the capacitance C 2  when enabled may vary depending upon the relative distance between the receive frequency and the blocker frequency. Performance values may be empirically measured for a given configuration and corresponding values programmed into the memory  1220  for programming the capacitance C 2 . In this manner, the memory  1220  stores digital values for programming both C 1  and C 2  in the different modes of operation. C 2  is typically greater than C 1 . In one specific embodiment for a 2.4 GHz configuration, C 1  may be 2 picoFarads (pF) whereas C 2  may be 3-5 pF depending upon various factors. 
     The variable capacitor  1112  may be configured as the digitally programmable capacitor  800  with as high a quality factor (HIGH-Q) as possible on the integrated circuit (IC) upon which it is fabricated. In one embodiment, the series of N+1 N-channel transistor switches N 0 -NN may be made sufficiently large to maximize or optimize the quality factor. Since the variable capacitor  1212  is only used to provide attenuation, however, it may be configured with a relative low quality factor (LOW-Q) which allows ease of design in terms of implementation of the switches, such as smaller switches with lower parasitic capacitance. In one embodiment, variable capacitor  1212  may also be configured as the digitally programmable capacitor  800  with a low quality factor (LOW-Q). In one embodiment, the series of N+1 N-channel transistor switches N 0 -NN need not be very large and may be made much smaller than the corresponding switches of the HIGH-Q capacitance C 1  of the variable capacitor  1112 . 
     In the configurations described herein, the transmitter and receiver circuits are connected to the same transceiver node  205 , which is common for BLE or Zigbee transceivers and the like. In such cases, if the receiver uses a frequency selective attenuator such as when the TNF  1202  is tuned close to desired channel frequency, it is prohibitive for the transmitter to transmit since it shunts the transmit signal path to the antenna. The switches  430  or  1302  and  1304  or the switches provided within the programmable capacitor may be used in some embodiments to turn off or disconnect the variable capacitors  1112  and  1212  of the frequency selective attenuator in the transmit mode of operation. For example, the on-chip capacitances C 1  and C 2  may be disconnected using the switches  1302  and  1304 , but parasitic capacitance may cause signal peaking at the transceiver node  205  when the power amplifier of the transmitter chain is transmitting and the signal swings across the capacitances C 1  and C 2  may turn impractical to be handled at the receiver. The switches  1302  and  1304  may be insufficient to disconnect the capacitance of the TNF  1202 . 
     In configurations in which the switches  430  or  1302  and  1304  are impractical and not provided such that the TNF  1202  remains connected during transmission, the controller  1218  may be configured to increase the capacitance of C 2  to be significantly greater than C 1  to provide a favorable impedance for the transmitter circuit  1106 . Such an impedance can be treated as part of transmit matching network and allows co-existence of the transmitter power amplifier and receiver circuit when using same transceiver node  205 . In this manner, the capacitance C 2  may be selected to present an inductive load to the power amplifier of the transmitter circuit  1106  at the frequency of operation, in which the inductive load can be absorbed as part of the transmitter matching network. In such embodiment, the controller  1218  programs the capacitance C 2  of the variable capacitor  1212  at a sufficiently high value during the transmission mode of operation. In a specific configuration for which C 1  is about 2 pF, C 2  may be increased to 9 pF or any value sufficient to overcome resonance created by L and C 1  of the TNF  1202 . In this case, ZIN MOD  of equation (2) still applies except that ωL&gt;&gt;1/ω(C 1 +C 2 ) since C 2  is substantially increased. 
       FIG. 14  is a flowchart diagram illustrating operation of the controller  1218  of the victim wireless receiver  1200  for controlling connection of the second capacitor  1212  with capacitance C 2  of the TNF  1202  according to one embodiment of the present disclosure. At first block  1402 , it is queried whether the TNF  1202  is enabled. In one embodiment, the TNF  1202  may be enabled by asserting the EN 1  signal to close the switch  1302  to connect the capacitor  1112  to GND. In another embodiment, the switch  1302  may not be provided so that the TNF  1202  remains enabled during operation so that block  1402  may be skipped. If the TNF  1202  is not enabled, operation loops at block  1402  until it is enabled. If the TNF  1202  is enabled, operation advances to determine whether the victim wireless receiver  1200  is in the receive mode of operation. If so, operation advances to block  1406 . At this point, it is assumed that the capacitor  1112  is connected and programmed to tune the TNF  1202  at a blocker frequency during the receive mode of operation. 
     At block  1406 , the controller  1218  determines the frequency difference (FD) between the receive frequency and the blocker frequency (if a blocker frequency is present). At next block  1408 , it is queried whether FD is less than or equal to the attenuation threshold ATH. If not, meaning that FD is greater than ATH, then operation proceeds to block  1410  in which the capacitor  1212  is disabled, such as by asserting EN 2  to open the switch  1304  to disconnect to the capacitor  1212 , and operation is completed for the current iteration such as when the current receive mode of operation is completed. In this case, either a blocker frequency is not present in which the TNF  1202  is in the disable mode, or the TNF  1202  is in the frequency selective mode in which the frequency of the blocker signal is sufficiently distant from the receive frequency such that any distortion introduced by the TNF  1202  is sufficiently low so that the capacitance C 2  is not necessary. 
     Referring back to block  1408 , if FD ATH, then operation advances instead to block  1412  in which the controller  1218  enables the capacitor  1212 , such as by asserting EN 2  to close the switch  1304 , and the capacitance C 2  is programmed based on FD and possibly other factors to linearize the TNF  1202  as previously described, and operation is completed for the current iteration. This is the attenuation mode in which a blocker signal is present and very close to the receive frequency. In the attenuation mode, both capacitances C 1  and C 2  are used to both attenuate the blocker signal and to optimize linear attenuation to optimize distortion performance. 
     Referring back to block  1404 , if the receive mode is not active, then operation instead proceeds to block  1414  to determine whether the victim wireless receiver  1200  is in the transmit (TX) mode of operation. If not, then operation loops back to block  1402 . If the victim wireless receiver  1200  is in the TX mode, then operation advances instead to block  1416  in which the controller  1218  enables the capacitor  1212 , such as by asserting EN 2  to close the switch  1304 , and the controller  1212  programs the capacitance C 2  to minimize the impact of the capacitance C 1 , and operation is completed for the current iteration. In this case, the capacitance C 1  cannot otherwise be disabled so that the capacitance C 2  is increased to overcome resonance created by L and C 1  of the TNF  1202 , e.g., ωL&gt;&gt;1/ω(C 1 +C 2 ). 
     The present description has been presented to enable one of ordinary skill in the art to make and use the present invention as provided within the context of particular applications and corresponding requirements. The present invention is not intended, however, to be limited to the particular embodiments shown and described herein, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed. Many other versions and variations are possible and contemplated. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for providing the same purposes of the present invention without departing from the spirit and scope of the invention.