PATENT DOCUMENT

Publication Number: US-9780755-B1
Application Number: US-201615268490-A
Country: US
Kind Code: B1

Title: On flex circuit desense filter for wireless communications

Abstract:
An apparatus for on flex desensing, includes a flex circuit including one or more DC traces, and at least one desense filter including a transformer having a primary winding coupled to at least one of the DC traces. Each desense filter includes one or more circuits coupled to a secondary winding of the transformer. Each of the circuits includes a variable capacitor connected in parallel with a resistor, and each desense filter is tunable to filter a desense frequency in a frequency band associated with one or more wireless communication protocols.

Claims:
What is claimed is: 
     
       1. An apparatus comprising:
 a flex circuit including one or more conductive traces; and 
 at least one desense filter including a transformer having a primary winding coupled to at least one of the one or more conductive traces, wherein each of the at least one desense filters further includes one or more circuits coupled to a secondary winding of the transformer, each of the one or more circuits includes a variable capacitor coupled to a resistor, and each of the at least one desense filters is tunable to filter noise at a desense frequency in a frequency band associated with one or more wireless communication protocols. 
 
     
     
       2. The apparatus of  claim 1 , further comprising an electromagnetic interference (EMI) shield covering the least one desense filter, wherein the at least one desense filter is positioned near an EMI noise source that generates noise at the desense frequency. 
     
     
       3. The apparatus of  claim 1 , wherein the flex circuit includes a single conductive trace coupling an EMI noise source to a power supply through the primary winding of the transformer, wherein the EMI noise source is distant from a ground potential to be filtered by a decoupling capacitor. 
     
     
       4. The apparatus of  claim 3 , wherein the EMI noise source comprises a display driver circuit coupled to one of the one or more conductive traces, wherein the display driver circuit includes a demultiplexer coupled to one of the one or more conductive traces. 
     
     
       5. The apparatus of  claim 1 , wherein a capacitance value of the variable capacitor is controlled by a control circuit and a digital-to-analog converter (DAC), and wherein the variable capacitor comprises one of a varactor diode, a transmission line stub, a discrete capacitor, or a capacitor formed by parallel conductor planes implemented on two flex layers of the flex circuit. 
     
     
       6. The apparatus of  claim 5 , wherein the transformer includes multiple secondary windings, each secondary winding being coupled to a respective circuit, wherein a capacitance of a respective circuit of each secondary winding is set to a different value corresponding to a respective desense frequency to provide a wider desense band including multiple desense frequencies, wherein the variable capacitor of the circuit is connected in parallel with the resistor. 
     
     
       7. The apparatus of  claim 1 , wherein the primary winding and the secondary winding of the transformer are implemented by loops formed by conductor traces on the flex circuit, wherein the flex circuit is bent to form a first flex circuit portion that is nearly parallel with a second flex circuit portion, and wherein the primary winding is implemented on the first flex circuit portion and the secondary winding is implemented on the second flex circuit portion. 
     
     
       8. The apparatus of  claim 1 , wherein the primary winding and the secondary winding of the transformer are implemented by loops formed by conductor traces on the flex circuit, wherein the primary winding and the secondary winding of the transformer are implemented on two separate flex layers of the flex circuit. 
     
     
       9. The apparatus of  claim 1 , wherein the one or more wireless communication protocols include at least one of Wi-Fi, Bluetooth, and long-term evolution (LTE) protocols. 
     
     
       10. An apparatus comprising:
 a multilayer flex circuit including one or more conductive traces; and 
 one or more desense filters, each desense filter comprising:
 a transformer having a primary winding and one or more secondary windings; and 
 one or more circuits coupled to the one or more secondary windings, 
 wherein the primary winding includes a center tap, at least one of the center tap or two terminals of the primary winding are coupled to a power source through one or two of the one or more conductive traces, each of the one or more circuits includes a variable capacitor coupled to a resistor, and each of the one or more desense filters is tunable to filter noise generated by an electromagnetic interference (EMI) noise source at a desense frequency in a frequency band associated with one or more wireless communication protocols. 
 
 
     
     
       11. The apparatus of  claim 10 , further comprising an EMI shield configured to protect the one or more desense filters against EMI, wherein the one or more desense filters is implemented on the multilayer flex circuit near a noise source generating noise at the desense frequency. 
     
     
       12. The apparatus of  claim 10 , wherein the multilayer flex circuit includes a single conductive trace coupling the EMI noise source to the center tap, and the two terminals of the primary winding are coupled through two traces of the one or more conductive traces to a power supply, wherein the EMI noise source is distant from a ground potential to be filtered by a decoupling capacitor. 
     
     
       13. The apparatus of  claim 10 , wherein the multilayer flex circuit includes symmetric conductive traces coupling the EMI noise source to the two terminals of the primary winding, and the center tap of the primary winding is coupled through a trace of the one or more conductive traces to a power supply, wherein the EMI noise source is too far away from a ground potential to be filtered by a decoupling capacitor. 
     
     
       14. The apparatus of  claim 10 , wherein the transformer includes multiple secondary windings coupled to multiple respective circuits tunable to multiple respective desense frequencies to achieve a wider desense band including multiple desense frequencies, and wherein the variable capacitor of the circuit is connected in parallel with the resistor. 
     
     
       15. The apparatus of  claim 10 , further comprising a control circuit and a digital-to-analog converter (DAC) to control a capacitance value of the variable capacitor, and wherein the variable capacitor comprises one of a varactor diode, a transmission line stub, a discrete capacitor, or a capacitor formed by parallel conductor planes implemented on two flex layers of the multilayer flex circuit. 
     
     
       16. The apparatus of  claim 10 , wherein the primary winding and the one or more secondary windings of the transformer are implemented by loops formed by conductor traces on the multilayer flex circuit, wherein the flex circuit is a bent flex circuit including a first flex circuit portion that is nearly parallel with a second flex circuit portion, and wherein the primary winding is implemented on the first flex circuit portion and the one or more secondary windings are implemented on the second flex circuit portion. 
     
     
       17. The apparatus of  claim 10 , wherein the primary winding and the one or more secondary windings of the transformer are implemented by loops formed by conductor traces on two separate flex layers of the multilayer flex circuit. 
     
     
       18. A method comprising:
 implementing at least one desense filter on a flex circuit that includes one or more conductive traces coupling an electromagnetic interference (EMI) noise source to a power supply; and 
 shielding the at least one desense filter wherein implementing a respective one of the at least one desense filter comprises:
 providing a transformer having a primary winding coupled to at least one of the one or more of the conductive traces and one or more secondary windings; 
 coupling each of the one or more secondary windings to a respective circuit including a variable capacitor connected in parallel with a resistor; and 
 tuning the respective circuit to filter noise at a desense frequency in a frequency band associated with one or more wireless communication protocols. 
 
 
     
     
       19. The method of  claim 18 , further comprising implementing the primary winding and the one or more secondary windings of the transformer using loops formed by conductor traces on the flex circuit, wherein the flex circuit is a bent flex circuit, and wherein the method further comprises implementing the primary winding and the one or more secondary windings, respectively, on a first and a second portion of the bent flex circuit on opposite sides of a bent section. 
     
     
       20. The method of  claim 18 , further comprising implementing the primary winding and the one or more secondary windings of the transformer by loops formed by conductor traces on two separate flex layers of the flex circuit, and wherein tuning the respective circuit to filter the desense frequency comprises tuning a capacitance of the variable capacitor of the respective circuit.

Description:
TECHNICAL FIELD 
     The present description relates generally to integrated circuits, and more particularly, to an on flex circuit desense filter for wireless communications. 
     BACKGROUND 
     Many mobile communication devices such as phones, tablets, and phablets are equipped with high-speed links capable of providing high definition video and/or high data-rate storage. The use of more sensitive, wide-band, and/or smart antennas in these communication devices is becoming more and more widespread. The higher sensitivity and the broader bandwidth of these antennas make them more susceptible to electro-magnetic interference (EMI), in particular, the EMI noise generated by various circuitry of the communication device itself. 
     For example, the EMI noise generated by a display driver or a power-management integrated circuit (PMIC) of a mobile communication device can cause ˜3 dB broadband noise in a frequency band of a wireless communication protocol (e.g., LTE, Wi-Fi, or Bluetooth) which can lead to dropped calls or reduced connectivity. When the noise source is far from the RF ground, filtering the noise by decoupling capacitors connecting noisy traces to ground is not an option. Therefore, as the noise travels through the exposed flex traces, it radiates to the antennas, causing desense. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain features of the subject technology are set forth in the appended claims. However, for purposes of explanation, several embodiments of the subject technology are set forth in the following figures. 
         FIG. 1  is a high-level diagram illustrating an example of a system architecture in which the subject technology operates. 
         FIG. 2  illustrates an example schematic diagram including a desense filter, in accordance with one or more aspects of the subject technology. 
         FIG. 3  illustrates a schematic diagram of an exemplary secondary winding circuit of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 4  illustrates a schematic diagram of an exemplary secondary winding circuit of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 5  is a diagram illustrating an example on-flex implementation of primary and secondary windings of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 6  is a chart illustrating example plots of frequency response of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 7  is a chart illustrating example plots of frequency response of the desense filter of  FIG. 2  in accordance with one or more aspects of the subject technology. 
         FIG. 8  is a diagram illustrating an exemplary implementation of primary and secondary windings of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 9  is a diagram illustrating an exemplary implementation of primary and secondary windings of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 10  is a diagram illustrating an example implementation of the variable capacitor of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 11  is a diagram illustrating an example implementation of the variable capacitor of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 12  is a diagram illustrating an example on-flex implementation of the variable capacitor of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. 
         FIG. 13  is a chart illustrating example plots of frequency response of the desense filter of  FIG. 12 , in accordance with one or more aspects of the subject technology. 
         FIG. 14  illustrates a schematic diagram including an example of a desense filter, in accordance with one or more aspects of the subject technology. 
         FIG. 15  illustrates a schematic diagram including an example of a desense filter, in accordance with one or more aspects of the subject technology. 
         FIG. 16  is a flow diagram illustrating a method of providing a desense filter, in accordance with one or more aspects of the subject technology. 
         FIG. 17  is a flow diagram illustrating of a method of implementing the desense filter of the method of  FIG. 16 , in accordance with one or more aspects of the subject technology. 
         FIG. 18  is a block diagram illustrating an example wireless communication device, in accordance with one or more implementations of the subject technology. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology may be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, the subject technology is not limited to the specific details set forth herein and may be practiced without one or more of the specific details. In some instances, structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology. 
     In one or more aspects of the subject technology, solutions for filtering electro-magnetic interference EMI noise, referred to as desense noise, is generated by a noise source and propagated through conductor traces (e.g., of a flex circuit) are provided. The generated EMI noise can cause desensing of antenna(s) of a transceiver over one or more frequencies of the communication frequency band of the transceiver. The desense filters of the subject technology can substantially reduce the desense noise at or near the location where it is generated. The disclosed filters can be readily implemented on the same flex circuit, the conductor traces of which are connected to the noise source. 
       FIG. 1  is a high-level diagram illustrating an example of a system architecture  100  in which the subject technology operates. The system architecture  100  may include a number of analog and digital circuitry including circuit  1  through circuit N. For example, circuit  1  through circuit N can include one or more radio-frequency (RF) transmitter and/or receiver circuits, processors, memory, power management units, driver circuits, digital-to-analog converter (DAC), analog-to-digital converter (ADC), and/or other circuits that can generate a significant amount of noise. In some aspects, the system architecture  100  corresponds to a wireless communication device such as a mobile phone, a tablet, a watch, a wireless headphone, or other wireless communication devices. Many of the noise generating circuits can be located near a ground potential (e.g., RF ground), such that the generated noise can be effectively directed to the RF ground through a suitable coupling capacitor. 
     In some aspects, a sub-circuit  102  of the system architecture  100  includes a noise source  130 , a power source  140 , a bypass capacitor  142 , conductor traces  110 , an RF ground  144 , and an EM shield  120 . In one or more aspects, the sub-circuit  102  is implemented on a flex circuit such as a multi-layer flex circuit including conductor traces (e.g.,  110 ) routed through various layers of the flex circuit. The noise source  130  can generate EMI noise  135  and is coupled to the power source  140  via a conductor trace  110 - 1 . In some aspects, noise source  130  is sufficiently far from the RF ground  144  such that bypassing the generated EMI noise  135  through a bypass capacitor to the RF ground in not practical. The bypass capacitor  142  is coupled in parallel with the power source  140  (e.g., battery) and can provide a path to the RF ground  144  for any noise reaching the power source  140 . A portion of the conductor traces  110 , may be covered by the EM shield  120 , which may be used to shield a sensitive portion of the sub-circuit  102  against outside interferences. The exposed portions of the conductor trace  110  including the DC carrying conductor trace  110 - 1  can act as an antenna and radiate the EMI noise generated by the noise source  130 . Such EMI noise can desense an antenna of the system, at least for a number of frequencies or a portion of a frequency-band of a communication protocol. 
     In some aspects, the noise source  130  can be a display driver of a wireless communication device (e.g., a mobile phone) that can be at a far distance from a backplane RF ground and may operate at a high data-rate (e.g., within the range of about 1.2 to 2.7 Gbps). Such a high data-rate display driver can generate a significant amount (e.g., about 3 dB) of broadband noise in the frequency-band of, for example, long-term-evolution (LTE) communication protocol (e.g., at about 2300 GHz). In one or more aspects, the noise source  130  can be a power management integrated circuit (PMIC) of a wireless communication device that is implemented on a flex circuit and is far from the backplane RF ground. For example, in small wireless communication devices such as watches, the PMIC can be far from the backplane RF ground and cannot be shielded due to the small available footprint. The EMI noise generated by the PMIC can be broadband noise that interfere with the frequency-band of the Wi-Fi (e.g., about 2.4 GHz band) and Bluetooth (e.g., about 2.4-2.485 GHz) communication protocols. 
       FIG. 2  illustrates an example schematic diagram  200  including a desense filter  210 , in accordance with one or more aspects of the subject technology. The schematic diagram  200  includes the noise source  205 , a desense filter (apparatus)  210 , a shield  240 , a conductor trace  250 , and the power source  140 . In some aspects, the noise source  205  can be a display driver circuit or a PMIC that is far from the RF ground  144  and is coupled via the conductor trace  250  of a flex circuit (e.g., a multi-layer flex circuit) to the power source  140 . The desense filter  210  is positioned as close as possible to the noise source  205 . 
     The desense filter  210  includes a transformer having a primary winding  212  and a secondary winding  232 . The terminals of the primary winding  212  are connected through the conductor trace  250  to the power source  140  and the noise source  205 . The secondary winding  232  is coupled in parallel with an RC circuit  230 , which can include a variable capacitor  234  and a resistor  236 . The secondary winding  232  forms a resonant circuit with the variable capacitor  234  that can trap the noise energy and cause the noise energy to be dissipated as heat in the resistor  236 . In some aspects, the primary and secondary windings  212  and  232  can be implemented on different layers of the multi-layer flex circuit, as explained below. In some aspects, multiple desense filters similar to the desense filter  210  can be applied. In one or more implementations, each of the desense filters may be tuned to a different desense frequency to provide a wider desense band including multiple desense frequencies. 
       FIG. 3  illustrates a schematic diagram of an exemplary secondary winding circuit  300  of the desense filter  210  of  FIG. 2 , in accordance with one or more aspects of the subject technology. The secondary circuit  300  includes the secondary winding  232 , a resistor  306 , a variable capacitor  304 , and a DAC circuit  308  controlled by a control circuit  310 . In the embodiment shown as the secondary circuit  300  the resistor  306  and the variable capacitor  304  are connected in series with the secondary winding  232 . The impedance of the resonant circuit formed by the inductance of the secondary winding  232  and the variable capacitor  304  can be reduced to nearly zero Ohm at a resonance frequency (f r )=1/2π√LC), where L and C are the inductance and capacitance of the secondary winding  232  and the variable capacitor  304 , respectively. Therefore, the energy of the noise at a noise frequency f n (˜f r ) is almost entirely dissipated in the resistor  306 . 
     The resonant frequency of the secondary circuit  300  can be tuned to the noise frequency f n  by changing the capacitance (C) of the variable capacitor  304 . The tuning can be achieved through the use of the DAC circuit  308 , the digital input (e.g., N bits) of which is provided by the control circuit  310 . In some embodiments, the control circuit  310  includes a processor, such as a general processor or a microcontroller. In some implementations, the control circuit  310  may operate based on a feedback, for example, from a current passing through the secondary circuit  300  and change the digital input of the DAC circuit  308  to set the current to a desired (e.g., highest) value. 
       FIG. 4  illustrates a schematic diagram of an exemplary secondary winding circuit  400  of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. In some aspects, the transformer of the desense filter  210  of  FIG. 2  has multiple (e.g., M) secondary windings  232  (e.g.,  232 - 1 ,  232 - 2  . . .  232 -M) as shown in the secondary circuit  400 . Each secondary winding (e.g.,  232 - 1 ) is coupled in series or in parallel with an RC circuit  424 - 1  of multiple RC circuits (e.g.,  424 - 1 ,  424 - 2  . . .  424 -M). In some implementations, each of the RC circuit  424  may be tuned to a different desense frequency to provide a wider desense band including multiple desense frequencies. In one or more aspects, each of the secondary windings  232  can be implemented on a separate layer of the multilayer flex circuit. In some implementations, the variable capacitor of each RC circuit  424  is controlled by a separate DAC circuit. 
       FIG. 5  is a diagram illustrating an example on-flex implementation  500  of primary and secondary windings of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. As explained above, exposed (unshielded) portions of one or more conductor traces of a flex circuit  510  may radiate the noise generated by a noise source such as a display driver or a PMIC of a wireless communication device. The subject technology enables drastically reducing this noise near the source by implementing an apparatus (desense filter)  502  on the flex circuit  510 . 
     In some aspects, the apparatus  502  includes a transformer, the primary winding and secondary windings of which can be implemented, respectively, as loops  512  and  522  on one or more layers of the flex circuit  510 . The primary loops  512  are connected at nodes  505  and  515  to a conductor trace of the flex circuit  510  that is coupled to the noise source. The nodes of the secondary loop  522  are coupled to a resistor  514  and a variable capacitor  516 , which may or may not be implemented on the flex circuit  510 . The flex circuit  510  can be multi-layer flex circuit having a number of (e.g., 4) layers (e.g.,  510 - 1  through  501 - 4 ). The flex circuit  510  may include fencing vias  530  that pass through all four layers of the flex circuit and can play a role in shielding the flex circuit against, for example, substrate mode EMI. In some aspects, the primary loops  512  and the secondary loop  522  may be implemented using conductor traces on layers  510 - 2  and  510 - 3  of the multi-layer flex circuit  510 . The capacitance of the variable capacitor  516  and the resistance of the resistor  514  can be suitably chosen to maintain the desense frequency of the desense filter at a desired location on the frequency band of a wireless communication protocol, as explained below. 
       FIG. 6  is a chart illustrating example plots  610  through  617  of the frequency response  600  of the desense filter  210  of  FIG. 2 , in accordance with one or more aspects of the subject technology. As explained above the frequency response of the desense filter  210  is dependent on a value of the capacitance of the variable capacitor (e.g.,  304  of  FIG. 3 ). Plots  610  through  617  show the frequency response for a range of capacitor values from about 2 pF to about 1 pF. The frequency responses are the result of simulation of the desense filter using a high-frequency electromagnetic field simulation program such as the known high-frequency structural simulator (HFSS). The highest desense (dB) achieved by the filter is about −8 dB, which is more than enough to attenuate the measured noise of about 3 dB at the desired frequency. The tunable frequency range of the desense filter by changing the capacitance of the variable capacitor is about 700 MHz in the 2.4 GHz band of Wi-Fi, Bluetooth, and/or LTE communication protocols. 
       FIG. 7  is a chart illustrating example plots of frequency response  700  of the desense filter  210  of  FIG. 2  in accordance with one or more aspects of the subject technology. The plots (e.g.,  720  and  730 ) of  FIG. 7  are obtained by using HFSS to simulate the desense filter. The plots of the frequency response  700  are similar to the plots of the frequency response  600   FIG. 6 , except that in the case of  FIG. 7 , instead of varying the capacitance of the variable capacitance (e.g.,  516  of  FIG. 5 ), the resistance of the resistor (e.g.,  514  of  FIG. 5 ) is changed. The variation in resistance has no effect on the resonance frequency (1/2π√LC) of the desense filter, and changes the amount of the noise energy that is dissipated by the resistor. Accordingly, as the resistance value changes from about 500Ω to about 8 kΩ, as represented by plots  720  and  730 , the amount of highest desense changes from about −5.5 dB to about −10 dB, which are sufficiently high to combat the 3 dB noise in the 2.4 GHz band of Wi-Fi, Bluetooth, and/or LTE communication protocols. 
       FIG. 8  is a diagram illustrating an exemplary implementation  800  of primary and secondary windings of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. In one or more aspects, such as the implementation  800 , the primary winding  804  and the secondary windings  806  of the transformer of the desense filter (e.g.,  210  of  FIG. 2 ) are implemented by spiral inductors on two different layers of a multi-layer flex circuit  802  of  FIG. 8 , where the magnetic coupling between the two windings is through the inter-layers of the flex circuit  802 . The primary winding  804  and the secondary windings  806  can be implemented using on-flex conductor traces. 
       FIG. 9  is a diagram illustrating an exemplary implementation  900  of primary and secondary windings of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. In some aspects, such as the implementation  900 , a flex circuit  912  may be a bent flex circuit that allows the primary winding  914  and the secondary windings  916  formed as spiral inductors on flat sections of the flex circuit  912  on both sides of the bend, as shown in  FIG. 9 . The primary winding  914  and the secondary windings  916  can be implemented using on-flex conductor traces. The magnetic coupling between the primary winding  914  and the secondary windings  916  can partially be through a gap (e.g., air gap) between the two flat sections of the flex circuit  912 . The implementation of the transformer of the desense filter is not limited to the implementations discussed above. Other approaches, such as the use of discrete components, can be implemented. 
       FIG. 10  is a diagram illustrating an example implementation  1000  of the variable capacitor of the desense filter  210  of  FIG. 2 , in accordance with one or more aspects of the subject technology. The variable capacitor (e.g.,  304  of  FIG. 3 ) can be implemented in a variety of ways. In some aspects, the variable capacitor can be implemented by transmission line stubs. For example, in the implementation  1000 , the transmission line stub  1004  can act as a variable capacitor, the capacitance of which can be varied, for instance, by adjusting its length L. An input impedance of a transmission line stub is given as: X sc =j Z 0  tan (βL), where β=δ2π/λ can be positive or negative. The parameters Z 0 , L, and λ are the characteristic impedance of the transmission line  1002 , the length of the stub, and a corresponding wavelength, respectively. The resistance  1008  of the filter is depicted as the load impedance Z L . In some implementations, the transmission line  1002  can be used to implement the inductance of the secondary winding of the transformer, by selecting a length l of the transmission line such that tan (βl) becomes positive. 
       FIG. 11  is a diagram illustrating an example implementation  1100  of the variable capacitor of the desense filter of  FIG. 2 , in accordance with one or more aspects of the subject technology. In the implementation  1100  of  FIG. 11 , the variable capacitor  1112  is implemented by two conductor pads  1114  and  1116  formed on two sides of a layer of a flex circuit. In some aspects, the two conductor pads  1114  and  1116  can be separated by more than one layer of the flex circuit. As is well known, the amount of capacitance depends on the area of the two conductor pads  1114  and  1116  and thickness and dielectric constant of the dialectic material of the flex circuit. The top conductor pad  1114  is coupled to a terminal  1118  of the secondary winding  1120  of the desense filter transformer. Similarly, the bottom conductor pad  1116  is coupled to another terminal of the secondary winding  1120 . In some implementations, the variable capacitor (e.g.,  304  of  FIG. 3 ) can be implemented using a varactor diode (e.g., a reversed biased Schottky diode). In some aspects, the varactor diode can be a discrete element. In a varactor diode, the capacitance is formed by the depletion region of the reversed biased P-N junction of the diode. 
       FIG. 12  is a diagram illustrating an example on-flex implementation  1200  of the variable capacitor  1112  of the desense filter  1220 , in accordance with one or more aspects of the subject technology. In some aspects, the desense filter  1220  is similar to the desense filter  210  of  FIG. 2  and is implemented on a flex circuit  1210 . The flex circuit  1210  can be a multi-layer flex circuit having a number of (e.g., 4) layers (e.g.,  1210 - 1  through  1201 - 4 ). As discussed above, the variable capacitor  1112  can be implemented on two layers of the flex circuit  1210 . In the embodiment shown in  FIG. 12 , the conductor pads  1114  and  1116  are formed on layers  1210 - 2  and  1210 - 3  of the flex circuit  1210 . 
       FIG. 13  is a chart illustrating example plots of frequency response  1300  of the desense filter  1220  of  FIG. 12 , in accordance with one or more aspects of the subject technology. The frequency response  1300  is similar to the frequency response  600  of  FIG. 6  described above, except that in the frequency response  1300 , the plots (e.g.,  1310  through  1350 ) are for different values of the length of the conductor pads (e.g.,  1114  and  1116  of  FIG. 11 ), which are varied between 0.9 mm (e.g., plot  1310 ) and 0.1 mm (e.g., plot  1350 ). As explained above, the larger length of the conductor pads results in larger areas and consequently larger capacitance C, which leads to a lower resonance frequency (f r =1/2π√LC) of the highest desense point of the frequency response  1300 . The tuning based on length of the conductor pads can cover a frequency range of about 900 MHz within the 2.4 GHz band of the Wi-Fi, Bluetooth, and/or LTE communication protocols. 
       FIG. 14  illustrates a schematic diagram  1400  including an example of a desense filter  1410 , in accordance with one or more aspects of the subject technology. The schematic diagram  1400  includes the noise source  1402 , a desense filter (apparatus)  1410 , a shield  1440 , a conductor trace  1442 , a power source  1450 , and a bypass capacitor  1452 . In some aspects, the noise source  1402  can be a display driver circuit or a PMIC that is far from the RF ground  1454  and is coupled via the conductor trace  1442  of a flex circuit (e.g., a multi-layer flex circuit) to the power source  1450 . The desense filter  1410  is positioned as close as possible to the noise source  1402 . 
     The desense filter  1410  includes a transformer having a primary winding  1430  and a secondary circuit  1420 . The terminals  1432  and  1434  of the primary winding  1430  are connected to two symmetric conductor (e.g. DC) traces of the flex circuit to the noise source  1402 . A center tap  1436  of the primary winding  1430  is coupled via the conductor trace  1442  to the power source  1450 . The primary winding is acting as a balun and converts a single ended signal (e.g., of  1442 ) to a differential ended signal coupled to the noise source  1402 . The secondary circuit  1420  is similar to the secondary circuit  220  of  FIG. 2 , and includes the secondary winding couple to an RC circuit including a variable capacitor (e.g., similar to  234  of  FIG. 2 ) and a resistor (e.g., similar to  236  of  FIG. 2 ). In some aspects, the primary windings  1430  and the secondary circuit  1420  can be implemented similar to the implementations shown and discussed with respect to  FIGS. 3, 5, 11, and 12  above. The tuning of the desense filter  1410  can be done similar to the tuning of the desense filters  210  of  FIG. 2 and 1210  of  FIG. 12 , as described with respect to frequency responses  600 ,  700 , and  1300  of  FIGS. 6, 7, and 13 , respectively. The filter  1410  can be covered with the shield  1440  to prevent magnetic coupling with other nearby circuits. 
       FIG. 15  illustrates a schematic diagram  1500  including an example of a desense filter  1510 , in accordance with one or more aspects of the subject technology. The desense filter  1510  is similar to the desense filter  1410  of  FIG. 41 , except for connections of the primary winding  1430 . As shown in  FIG. 15 , in the implementation shown in the schematic diagram  1500 , the center tap  1436  of the primary winding  1430  is coupled via a conductor trace  1502  to the noise source  1402 . The terminals  1134  and  1432  of the primary winding  1430  are connected through conductor  1520  and  1522  to the power source  1450  and a second bypass capacitor  1532 , respectively. In some aspects, the desense filter  1510  can be implemented using similar implementations as shown and discussed with respect to  FIGS. 3, 4, 8, and 9  above. The tuning of the desense filter  1510  can be done similar to the tuning of the desense filters  210  of  FIG. 2 and 1210  of  FIG. 12 , as described with respect to frequency responses  600 ,  700 , and  1300  of  FIGS. 6, 7, and 13 , respectively. The filter  1510  can be covered with the shield  1440  to prevent magnetic coupling with other nearby circuits. 
       FIG. 16  is flow diagram illustrating a method  1600  of providing a desense filter, in accordance with one or more aspects of the subject technology. The method  1600  starts with implementation of at least one desense filter (e.g.,  210  of  FIG. 2 ) on a flex circuit (e.g.,  510  of  FIG. 5 ) that includes one or more DC traces (e.g.,  110  of  FIG. 1 ) that couples an EM noise source (e.g.,  130  of  FIG. 1 ) to a DC power supply (e.g.,  140  of  FIG. 1 ) ( 1610 ). The desense filter is shielded (e.g., using  240  of  FIG. 2 ) ( 1620 ). 
       FIG. 17  is a flow diagram illustrating of a method  1700  of implementing the desense filter of the method  1600  of  FIG. 16 , in accordance with one or more aspects of the subject technology. The implementation of the desense filter (e.g.,  210  of  FIG. 2 ) is performed by providing a transformer having a primary winding (e.g.,  212  of  FIG. 2 ) coupled to at least one DC trace (e.g.,  250  of  FIG. 2 ) and one or more secondary windings (e.g.,  232  of  FIG. 2 ) ( 1712 ). The implementation of the desense filter further includes coupling each of the one or more secondary windings (e.g.,  232 - 1 , through  232 -M of  FIG. 4 ) to a respective RC circuit (e.g.,  424 - 1 , through  424 -M of  FIG. 4 and 230  of  FIG. 2 ) including a variable capacitor (e.g.,  234  of  FIG. 2 ) connected in parallel with a resistor (e.g.,  236  of  FIG. 2 ) ( 1714 ), and tuning the respective RC circuit to filter a desense frequency (e.g., as shown in frequency responses  600 ,  700 , and  1300  of  FIGS. 6, 7, and 13 ) in a frequency band (e.g., 2.4 GHz) associated with one or more wireless communication protocols (e.g., Wi-Fi, LTE, and Bluetooth) ( 1716 ). 
       FIG. 18  is a block diagram illustrating an example wireless communication device  1800 , in accordance with one or more implementations of the subject technology. The wireless communication device  1800  may comprise a radio-frequency (RF) antenna  1810 , a receiver  1820 , a transmitter  1830 , a baseband processing module  1840 , a memory  1850 , a processor  1860 , a local oscillator generator (LOGEN)  1870 , a PMIC  1880 , and a display driver  1890  connected to a display (not shown). In various embodiments of the subject technology, one or more of the blocks represented in  FIG. 18  may be integrated on one or more semiconductor substrates. For example, the blocks  1820 - 1870  may be realized in a single chip or a single system on a chip, or may be realized in a multi-chip chipset. 
     The receiver  1820  may comprise suitable logic circuitry and/or code that may be operable to receive and process signals from the RF antenna  1810 . The receiver  1820  may, for example, be operable to amplify and/or down-convert received wireless signals. In various embodiments of the subject technology, the receiver  1820  may be operable to cancel noise in received signals and may be linear over a wide range of frequencies. In this manner, the receiver  1820  may be suitable for receiving signals in accordance with a variety of wireless standards, Wi-Fi, WiMAX, Bluetooth, and various cellular standards. In various embodiments of the subject technology, the receiver  1820  may not require any SAW filters and few or no off-chip discrete components such as large capacitors and inductors. 
     The transmitter  1830  may comprise suitable logic circuitry and/or code that may be operable to process and transmit signals from the RF antenna  1810 . The transmitter  1830  may, for example, be operable to up-convert baseband signals to RF signals and amplify RF signals. In various embodiments of the subject technology, the transmitter  1830  may be operable to up-convert and amplify baseband signals processed in accordance with a variety of wireless standards. Examples of such standards may include Wi-Fi, WiMAX, Bluetooth, and various cellular standards. In various embodiments of the subject technology, the transmitter  1830  may be operable to provide signals for further amplification by one or more power amplifiers. 
     The duplexer  1812  may provide isolation in the transmit band to avoid saturation of the receiver  1820  or damaging parts of the receiver  1820 , and to relax one or more design requirements of the receiver  1820 . Furthermore, the duplexer  1812  may attenuate the noise in the receive band. The duplexer may be operable in multiple frequency bands of various wireless standards. 
     The baseband processing module  1840  may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to perform processing of baseband signals. The baseband processing module  1840  may, for example, analyze received signals and generate control and/or feedback signals for configuring various components of the wireless communication device  1800 , such as the receiver  1820 . The baseband processing module  1840  may be operable to encode, decode, transcode, modulate, demodulate, encrypt, decrypt, scramble, descramble, and/or otherwise process data in accordance with one or more wireless standards. 
     The processor  1860  may comprise suitable logic, circuitry, and/or code that may enable processing data and/or controlling operations of the wireless communication device  1800 . In this regard, the processor  1860  may be enabled to provide control signals to various other portions of the wireless communication device  1800 . The processor  1860  may also control transfers of data between various portions of the wireless communication device  1800 . Additionally, the processor  1860  may enable implementation of an operating system or otherwise execute code to manage operations of the wireless communication device  1800 . In some aspects, the processor  1860  may partially or entirely perform the functionality of the control circuit  310  of  FIG. 3 . 
     The memory  1850  may comprise suitable logic, circuitry, and/or code that may enable storage of various types of information such as received data, generated data, code, and/or configuration information. The memory  1850  may comprise, for example, RAM, ROM, flash, and/or magnetic storage. In various embodiment of the subject technology, information stored in the memory  1850  may be utilized for configuring the receiver  1820  and/or the baseband processing module  1840 . 
     The local oscillator generator (LOGEN)  1870  may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to generate one or more oscillating signals of one or more frequencies. The LOGEN  1870  may be operable to generate digital and/or analog signals. In this manner, the LOGEN  1870  may be operable to generate one or more clock signals and/or sinusoidal signals. Characteristics of the oscillating signals such as the frequency and duty cycle may be determined based on one or more control signals from, for example, the processor  1860  and/or the baseband processing module  1840 . 
     In operation, the processor  1860  may configure the various components of the wireless communication device  1800  based on a wireless standard according to which it is desired to receive signals. Wireless signals may be received via the RF antenna  1810  and amplified and down-converted by the receiver  1820 . The baseband processing module  1840  may perform noise estimation and/or noise cancellation, decoding, and/or demodulation of the baseband signals. In this manner, information in the received signal may be recovered and utilized appropriately. For example, the information may be audio and/or video to be presented to a user of the wireless communication device, data to be stored to the memory  1850 , and/or information affecting and/or enabling operation of the wireless communication device  1800 . The baseband processing module  1840  may modulate, encode and perform other processing on audio, video, and/or control signals to be transmitted by the transmitter  1830  in accordance with various wireless standards. 
     The PMIC  1880  may provide power for and manage power distribution to various modules and components of the communication device  1800 . The display driver  1890  may be coupled to a display of the communication device  1800 . In some implementations, the display driver  1890  may be implemented or be coupled to a flex circuit. 
     In some aspects, the PMIC  1880  and/or the display driver  1890  may generate EMI noise within the frequency band of the Wi-Fi, Bluetooth and/or LTE communication protocols. The communication device  1800  can use the desense filter (e.g.,  210  of  FIG. 2 ) of the subject technology, as described above, to prevent the EMI noise from the PMIC  1880  and/or the display driver  1890 , or other noise sources (e.g., any other circuitry of the communication device  1800  that is far from an RF ground and cannot be coupled through a coupling capacitor to the RF ground) from desensing the antenna  1810 . 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the subject disclosure. 
     The predicate words “configured to”, “operable to”, and “programmed to” do not imply any particular tangible or intangible modification of a subject, but, rather, are intended to be used interchangeably. For example, a processor configured to monitor and control an operation or a component may also mean the processor being programmed to monitor and control the operation or the processor being operable to monitor and control the operation. Likewise, a processor configured to execute code can be construed as a processor programmed to execute code or operable to execute code. 
     A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as a “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to a configuration may apply to all configurations, or one or more configurations. A phrase such as a configuration may refer to one or more configurations and vice versa. 
     The word “example” is used herein to mean “serving as an example or illustration.” Any aspect or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. 
     All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.

Metadata:
Filing Date: 20160916
Publication Date: 20171003
Grant Date: 20171003
Priority Date: 20160916
Inventors: Omid-Zohoor Kasra M.
DEVINCENTIS MARC JOSEPH
SACCHETTO PAOLO
JEONG YOUCHUL
Assignee: APPLE INC
CPC Classifications: [{"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W4/008", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03H1/0007", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K9/0081", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03J5/0209", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H2210/025", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2092", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H7/09", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H7/09", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03H1/0007", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F27/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03J5/0209", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03H1/0007", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 59928566