Abstract:
A PWM receiver circuit receives and demodulates pulse width modulated (PWM) data signals without requiring synchronization such that no synchronization preamble need be provided with the PWM data signal. Embodiments may consume less power since there is no need to repeatedly synchronize a PLL, counter or other circuitry to the PWM data signal. Furthermore, the PWM receiver circuit operates in view of or is “tolerant” to jitter in the frequency of the PWM signal and also to a relatively wide range of intentional variation in the frequency. Interleaved operation of parallel PWM receiver circuits are utilized in some embodiments. In one embodiment currents are integrated during low and high portions of the duty cycle of the PWM data signal and the difference in the respective voltages generated through such integration used to demodulate the PWM data signal.

Description:
PRIORITY CLAIM 
     The present application claims the benefit of U.S. Provisional Patent Application No. 61/806,516, filed Mar. 29, 2013, which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to data communications, and more specifically to capturing a pulse width modulated (PWM) data input signal. 
     BACKGROUND 
     The Mobile Industry Processor Interface (MIPI) Alliance is a collaboration of mobile industry leaders having the objective of defining and promoting open standards for interfacing with mobile application processors. A mobile application processor is typically a system-on-a-chip (SoC) that executes applications in a mobile operating system environment. The MIPI Alliance establishes specifications for standard hardware and software interfaces in mobile processing environments to speed deployment of new services to mobile users. In such mobile processing environments, data is communicated between and among chips forming the SoC over high speed serial links. While this high speed serial data must be communicated, there is also a need for low speed and low power communication over these same data links, such as to transfer link management information, lower priority or speed-critical data, and possibly other types of low speed data as well. 
     Different ways or protocols for communicating this serial data have been proposed and utilized, such as protocols including a data clock or data strobe accompanying the data being communicated as well as self-clocking protocols (i.e., no separate data clock or strobe) like Pulse Width Modulation (PWM) and Pulse Width and Amplitude Modulated (PWAM). In many of these prior approaches, a phase-locked loop (PLL) or delay-locked loop (DLL) in both a transmitter transmitting the data and in a receiver receiving the data are required. In one such situation, a mobile physical layer (M-PHY) standard communicates pulse width modulated data signals, with the duty cycle of each pulse width modulated signal determining whether a binary 1 or a binary 0 is being communicated. In the present description the acronym PWM is utilized to refer to both the terms “pulse width modulation” and “pulse width modulated.” 
     One prior approach of sensing or demodulating these PWM data signals being communicated according to the M-PHY standard is to utilize a counter to generate a count value when the PWM data signal is high and a count value when the PWM data signal is low, and to compare the two counts to determine whether the PWM signal is communicating a binary 1 or a binary 0. An up/down counter could also be utilized. With this approach, however, the frequency of a clock signal that clocks the counter, or the number of phases of the clock signal, may need to be eight or more times higher than the frequency of the PWM data signal. For example, if the duty cycle of the PWM data signal may go as low as ¼ (0.25) the period or unit interval (UI) of the data signal then the clock signal would need to be twice the frequency of this signal (2×(1/(¼UI)) or eight times the frequency (1/UI) of the PWM data signal. Circuitry to generate this clock signal may consume relatively large amounts of power. Moreover, the clock signal must be synchronized with the PWM data signal so the PWM data signal must include a synchronizing preamble. Some applications, however, require that no such preamble be utilized due to bandwidth constraints. Another approach utilizes a phase locked loop (PLL) to lock onto the PWM data signal and to then appropriately sample the PWM data signal. These PLLs may consume relatively large amounts of power and also require relatively complex circuitry. Another technique is to use an analog integrator to extract the middle of a data clock period for use in data extraction, but such an approach also may consume a relatively large amount of power. Accordingly, there is a need for improved techniques of reliably capturing serial PWM data signals. 
     SUMMARY 
     In an embodiment of the present disclosure, a PWM receiver circuit operates to receive and demodulate pulse width modulated (PWM) data signals without require synchronization so no synchronization preamble need be provided with the PWM data signal. Some embodiments will consume less power, at least in particular situation. For example, during burst-then-stall intermittent communications through such PWM data signals, there is no need to repeatedly synchronize a PLL, counter or other circuitry to the PWM data signal, which would otherwise be necessary when synchronization is required. The PWM receiver circuit also does not need to generate a local clock signal from the PWM signal, such as through sampling the PWM data signal. Furthermore, the PWM receiver circuit operates in view of or is “tolerant” to jitter in the frequency of the PWM signal and also to a relatively wide range of intentional variation in the frequency. In one embodiment the PWM receiver circuit can tolerate a change in frequency of the PWM data signal of up to three times. Interleaved operation of parallel PWM receiver circuits are also utilized in other embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are signal timing diagrams illustrating a PWM data signal modulated to contain a logic 1 in  FIG. 1A  and modulated to contain a logic 0 in  FIG. 1B . 
         FIG. 2  is a schematic and functional block diagram of a PWM receiver circuit according to one embodiment of the present disclosure. 
         FIG. 3  is a timing diagram illustrating several signals in the PWM receiver circuit of  FIG. 2  during operation of this circuit. 
         FIG. 4  is more detailed schematic of one embodiment of the differential amplifier of  FIG. 2 . 
         FIG. 5  is functional block diagram of an interleaved PWM receiver circuit according to another embodiment of the present disclosure. 
         FIG. 6  is a signal timing diagram illustrating several signals in the interleaved 
       PWM receiver circuit of  FIG. 5  during operation of this circuit. 
         FIG. 7  is a functional block diagram of an electronic system including the interleaved PWM receiver circuit of  FIG. 5  according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  are signal timing diagrams illustrating a PWM data signal modulated to contain a logic 1 in  FIG. 1A  and modulated to contain a logic 0 in  FIG. 1B . The period T of the PWM data signal is indicated as a unit interval UI in the figures. The duty cycle of the PWM data signal changes depending on whether a binary logic 1 or a logic 0 is being transmitted during a given unit interval UI of the PWM data signal. For example, when a logic 1 is being communicated as shown in  FIG. 1A , the duty cycle is ⅔, with the ⅓ low portion of the data signal coming at the start of the unit interval UI and followed by the ⅔ high portion of the data signal. When a logic 0 is being communicated as shown in  FIG. 1B , the duty cycle is ⅓, with the ⅔ low portion of the data signal coming at the start of the unit interval UI and followed by the ⅓ high portion of the data signal. The duty cycle may vary from unit interval UI to unit interval, and may vary from application to application. A minimum allowable duty cycle is specified for given applications, such as ¼ of the unit interval UI, and indicates the minimum permissible duty cycle below which the PWM data signal may not fall to ensure proper demodulation of the data signal. 
     In the present description, certain details are set forth in conjunction with the described embodiments of the present disclosure to provide a sufficient understanding of the disclosure. One skilled in the art will appreciate, however, that embodiments of the disclosure may be practiced without these particular details. Furthermore, one skilled in the art will appreciate that the example embodiments described herein do not limit the scope of the present disclosure to only such embodiments, and will also understand that various modifications, equivalents, and combinations of the disclosed embodiments and components of such embodiments are within the scope of the present disclosure. Embodiments including fewer than all the components of any of the respective described embodiments may also be within the scope of the present disclosure although not expressly described in detail below. Finally, the operation of well-known components and/or processes has not been shown or described in detail below to avoid unnecessarily obscuring the present disclosure. Also note that the terms “PWM data signal” and “PWM signal” are used interchangeably herein, and are meant to indicate a signal that is pulse width modulated to communicate any type of information. Thus, the term “data” includes data, control, and any other type of information that may be communicated via the pulse width modulation of the signal. 
     Referring now to  FIG. 2 , a schematic and functional block diagram of a PWM receiver circuit  200  according to one embodiment of the present disclosure is illustrated. The PWM receiver circuit  200  includes a first constant current source IO coupled in series with a first switch S 0  and a first capacitor C 0  between a supply voltage VDD and ground, and a second constant current source I 1  coupled in series with a second switch S 1  and a second capacitor C 1  between the supply voltage and ground. In operation, the switches S 0  and S 1  are controlled by integration signals int 0  and int 1  generated responsive to edges of the received PWM data signal to integrate the constant currents provided by the current sources I 0  and I 1 , respectively, via the capacitors C 0  and C 1  during the low and high portions of the PWM data signal, and in this way develop voltages VC 0  and VC 1  across the capacitors C 0  and C 1  that are then used to demodulate the PWM data signal, as will be explained in more detail below. 
     The PWM receiver circuit  200  further includes switches S 2  and S 3  coupled in parallel across the capacitors C 0  and C 1  to discharge to voltages VC 0  and VC 1  across the capacitors to a desired reference value responsive to reset signals rst 0  and rst 1 , respectively. The reference value is ground in the embodiment of  FIG. 2  but could be some other value in other embodiments. A switch S 4  is coupled to the node defined at the interconnection of the current source I 0  and switch S 0  to discharge this node responsive to a complementary integration signal int 0 *, which is active when the switch S 0  is open responsive to the int 0  signal being inactive. This ensures that charge does not build up on this node and that such charge is not transferred to the capacitor C 0  when the switch S 0  is again closed, which could result an erroneous value for the voltage VC 0 . For the same reason, a switch S 5  is coupled to the node defined at the interconnection of the current source I 1  and switch S 1  to discharge this node responsive to an active complementary integration signal int 1 *, which occurs when the switch S 1  is open responsive to the int 1  signal being inactive. Note the switches S 0  and S 4  receive complementary control signals int 0  and int 0 * so that when the int 0  signal is inactive to turn OFF the switch S 0  then the int 0 * signal is active to turn ON the switch S 4 , and vice versa. The same is true for the switches S 1  and S 5 , which receive complementary control signals int 1  and int 1 *, in relation to the current source I 1  and capacitor C 1 . Note the switches S 0 -S 5  may be formed through any suitable circuit, and in one embodiment each of these switches is either an NMOS or a PMOS transistor. 
     A differential amplifier  202  has inputs coupled to the capacitors C 0  and C 1  and operates to generate a differential voltage Vdiff responsive to these voltages, where the differential voltage Vdiff=VC 1 −VC 0 . A latched comparator  204  receives the differential voltage Vdiff and operates, in response to an evaluation signal eval, to generate a data output signal RxOut having a value that is determined by the differential voltage. The value of the data output signal RxOut indicates whether the PWM data signal being demodulated is communicating a logic 0 or a logic 1, as will be described in more detail below with reference to  FIG. 3 . In the PWM receiver circuit  200 , the current sources I 0  and I 1  are matched currents sources that each provide the same current I to charge the corresponding capacitor C 0  and C 1 . The capacitors C 0  and C 1  too are matched capacitors having equal values. The term “matched” is understood by those skilled in the art to mean components that are identical or nearly identical. For example, the current sources I 0 , I 1  provide approximately the same or substantially the same current I, where any differences are extremely small so as to not adversely affect the operation of the circuit  200 . The current sources I 0 , I 1  have substantially the same operating characteristics as well, where an example of such an operating characteristic is a temperature coefficient of the current I, and in this way any variation in the current I over temperature will be the same for each current source. 
     In operation, the PWM receiver circuit  200  integrates the constant current I from the current source I 0  over the low period or portion of the received PWM data signal and integrates the current I from the current source I 1  over the high period or portion of the PWM data signal. The PWM data signal has a period or unit interval UI as discussed with reference to  FIGS. 1A and 1B , and over the low portion of the unit interval (i.e., the time during which the PWM data signal is low) the constant current I from the current source I 0  is integrated through the capacitor C 0 , and over the high portion of the unit interval (i.e., the time during which the PWM data signal is high) the constant current I from the current source I 1  is integrated through the capacitor C 1 . As a result, at the end of the unit interval UI, the voltages VC 0  and VC 1  across the capacitors C 0  and C 1  have values that together indicate whether the PWM data signal is communicating a logic 1 or a logic 0. More specifically, the sign of the difference of the voltages (VC 1 −VC 0 ) determines whether the PWM data signal is communicating a logic 1 or a logic 0. This is true because when the PWM data signal has a higher duty cycle (i.e., when the high portion of the signal is greater than the low portion as shown in  FIG. 1A ), the voltage VC 1  is greater than the voltage VC 0  at the end of the unit interval UI, and accordingly a logic 1 will be decoded or demodulated by the PWM receiver circuit  200 . Conversely, when the PWM data signal has lower duty cycle (i.e., when the low portion of the signal is greater than the high portion as shown in  FIG. 1B ), the voltage VC 1  is less than the voltage VC 0  at the end of the unit interval UI, and accordingly a logic 0 will be decoded or demodulated by the PWM receiver circuit  200 . 
     In operation of the PWM receiver circuit  200 , the current I is integrated through the capacitors C 0  and C 1  for the low and high portions of the PWM data signal and the voltages are stored or held on these capacitors for comparison by the latched comparator  204  after the unit interval has elapsed since the unit interval is required to generate the two voltages VC 0  and VC 1 . This approach has the advantage over charging and discharging of a single capacitor during the two phases or portions of the PWM data signal because the charging and discharging currents of such a single capacitor are difficult to match so that they are equal. This is true because with MOS technology, charging of the single capacitor would typically be done using a PMOS transistor while discharging would typically be done using an NMOS transistor. The differences between such NMOS and PMOS devices inherently makes it difficult to match the charge and discharge currents where a single capacitor used. 
     The differential amplifier  202  generates the differential voltage Vdiff having a sign indicating whether the PWM data signal is communicating a logic 1 or a logic 0. This differential voltage Vdiff is output by the amplifier  202  and provided to the latched comparator  204 . In one embodiment, the latched-comparator  204  is formed by a sense amplifier type latch (i.e., NMOS and PMOS transistors forming cross-coupled inverters to thereby form the latch) followed by an SR latch for storing the data output signal RxOut. 
       FIG. 3  is a timing diagram illustrating signals in the PWM receiver circuit of  FIG. 2  during the above-described operation of the circuit. The PWM data signal input to the PWM receiver circuit  200  is in the form of a low voltage differential signal (LVDS) where the PWM receiver circuit is being used to decode or demodulate signals being communicated according to the M-PHY standard of the MIPI alliance. In this situation, LVDS signal would be converted to a CMOS level signal through an LVDS limiting amplifier (not shown in  FIG. 2 ) to thereby generate the PWM_IN signal shown in  FIG. 3 . The PWM_IN signal thus corresponds to the PWM data signal discussed above with reference to  FIGS. 1 and 2 , and as used in the below description as well. The PWM_IN signal is effectively used as a clock to control the operation of the PWM receiver circuit  200  in generating the data output signal RxOut. Also note that control circuitry (not shown in  FIG. 2 ) generates the control signals illustrated in  FIG. 3  to control operation of the PWM receiver circuit  200 . One skilled in the art will understand suitable circuitry that may be utilized to generate these control signals and thus, for the sake of brevity and so as to not obfuscate the present disclosure, the detailed structure of this control circuitry is not described in more detail herein. 
     In operation, the PWM data signal (PWM_IN) goes low at a time t 0  to initiate operation of the PWM receiver circuit  200  in the modulating a single bit encoded by the signal over a unit interval UI of the signal. Also assume initially that the reset signals switches S 2 -S 5  are closed (i.e., reset signals rst 0 , rst 1  and complementary integration signals int 0 *, int1* are active high) and thus the voltages VC 0  and VC 1  across capacitors C 0  and C 1  are at (i.e. at ground) initially. In response to the PWM_IN signal going low at time t 0 , the reset signal rst 0  goes low opening the switch S 2 . In addition, the low edge of the PWM_IN signal causes the complementary integration signal int 0 * (not shown in  FIG. 3 ) to go in active low, opening the switch S 4 , and causes the integration signal int 1  to go active high closing the switch S 0  to thereby couple the current source  10  to the capacitor C 0 . As seen in  FIG. 3 , this results in charging of the capacitor C 0  with the current I from the current source I 0  at time t 0  and this charging results in the voltage VC 0  beginning to increase at time t 0 . 
     This charging of the capacitor C 0  and increase of the voltage VC 0  continues during the low portion of the unit interval UI until a time t 1  at which the PWM_IN signal goes high. In response to this rising edge of the PWM_IN signal at the time t 1 , the integration signal int 0  goes inactive low, opening the switch S 03  and terminating the charging of the capacitor C 0 . As seen in  FIG. 3 , the generated voltage VC 0  across the capacitor C 0  is maintained after the time t 1 , as will be described in more detail below. The complementary integration signal int 0 * (not shown) also transitions active high at the same time to thereby close the switch S 4 . Also, in response to this rising edge of the PWM_IN signal at the time t 1 , the reset signal rst 1  goes inactive low, opening the switch S 3  to allow charging of the capacitor C 1 . The integration signal int 1  also goes active high at the time t 1 , closing the switch S 1  and thereby coupling the current source I 1  to the capacitor C 1 . The int 1  signal (not shown) also goes inactive low at the time t 1  opening the switch S 5 . The charging of the capacitor C 1  with the current I from the current source I 1  starts at time t 1  and this charging results in the voltage VC 1  (dotted line) beginning to increase at time t 1 . 
     This charging of the capacitor C 1  and increase of the voltage VC 1  continues during the high portion of the unit interval UI until a time t 2  at which time the PWM_IN signal again goes low, indicating the end of the unit interval. At this point, the voltage VC 1  across the capacitor C 1  is maintained as is the voltage VC 0  across the capacitor C 0 . The differential amplifier  202  ( FIG. 2 ) generates the differential voltage Vdiff in response to the voltages VC 1  and VC 0 , where Vdiff=(VC 1 −VC 0 ). This differential voltage Vdiff is input to the latched comparator  204  ( FIG. 2 ). At a time t 3 , which occurs an delay time to of the differential amplifier  202  after the PWM_IN signal goes low at time t 2 , the eval signal goes high, causing the latched comparator  204  ( FIG. 2 ) to generate at a time t 4  the data output signal RxOut having a value indicating a logic 0 or a logic 1 for the PWM_IN signal over the unit interval UI. The time t 4  is a delay time tL of the latched comparator  204  after the set signal goes active at t 3 . In the example of  FIG. 2 , the RxOut signal would indicate the PWM_IN signal communicates a logic 0 (see  FIG. 1B ) over the unit interval UI. Note the time t 4  is a set up time TL after the time t 3  when the eval signal goes active high, and corresponds to the time needed for the latched comparator  204  to generate the RxOut signal and for this signal to be sufficiently settled or set up so that it can be reliably read by an external circuit (not shown) coupled to receive the RxOut signals. 
     The eval signal stays active high until a time t 5 , at which time the eval signal goes inactive low to terminate operation of the latched comparator  204 . In addition, at the time t 5  the reset signals rst 0  and rst 1  go active high to turn on the switches S 2  and S 3 , respectively, and thereby discharge the capacitors C 0  and C 1 . This is seen in  FIG. 3  through the voltages VC 0  and VC 1  across the capacitors C 0  and C 1  decreasing starting at the time t 5  until they are discharged a discharge time tD later at a time t 6 , where tD is the discharge time of the capacitors C 0 , C 1 . After the time t 6 , the PWM receiver circuit  200  is ready to decode or demodulate the PWM_IN signal over another unit interval UI of the signal. 
     The control signals shown in  FIG. 3  control the discharge of capacitors C 0  and C 1  through the signals rst 0  and rst 1  respectively. The integration of the currents I 0 , I 1  on the capacitors C 0 , C 1  is controlled by the int 0  and int 1  signal, respectively, as just described, and the latching of the difference of integrated voltages, Vdiff=VC 1 −VC 0 , is controlled by the eval signal. 
     The common mode voltage VCM, of the voltages VC 0  and VC 1  varies with the duration of the unit interval UI as follows: 
     
       
         
           
             
               
                 
                   VCM 
                   = 
                   
                     
                       I 
                       × 
                       UI 
                     
                     
                       2 
                       × 
                       C 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The value C represents the value of each of the capacitors CO and C 1 . This common mode voltage VCM results in a rail to rail common mode input capable differential amplifier being used in one embodiment of the differential amplifier  202 . The differential voltage Vdiff also changes with the duration of the unit interval UI and variation of the duty cycle of the PWM input. When the duty cycle approaches 50%, the differential voltage Vdiff may become very small, making it potentially difficult to decode or demodulate via the latched comparator  204 . As a result, in one embodiment the value of the integrating current I (i.e., current provided by current sources I 0  and I 1 ) and value of the capacitors is chosen to maintain the following relation: 
                   Vdiff   =         I   ·          Δ   ⁢           ⁢   T            C     ≥       Voffset_latch   AV_amp     +   Voffset_amp               (   2   )               
where, Voffset_latch is the sum of offset and the required input overdrive of the latched comparator, and Voffset_amp and AV_amp are an input referred offset voltage and a voltage gain of the differential amplifier, respectively, and the term ΔT is the difference of major and minor duration (major duration is larger of low or high portion of the PWM_IN signal and the minor duration is the smaller of the low or high portion) of a unit interval UI and is given by the following equation:
 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     T 
                   
                   = 
                   
                     2 
                     · 
                     
                       
                         
                           Duty_Cycle 
                           ⁢ 
                           _In 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           % 
                         
                         - 
                         50 
                       
                       100 
                     
                     · 
                     UI 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Other factors that may be utilized in selecting values for the integrating current I and capacitors C 0 , C 1  include accommodating variation of absolute time due to the variation of the unit interval UI and the variation of the duty cycle of the PWM_IN signal caused by degradation over the transmission line and jitter of the transmission circuit. This is done by limiting the integrated voltages VC 0 , VC 1  across capacitors C 0 , C 1  over the maximum minor duration of the degraded PWM_IN signal below the value of the supply voltage Vdd as indicated below: 
     
       
         
           
             
               
                 
                   
                     
                       I 
                       · 
                       Tminor_max 
                     
                     C 
                   
                   ≤ 
                   
                     Vdd 
                     - 
                     Vdiff 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     To address various PWM gears as specified in the M-PHY standard, in one embodiment of the circuit  200  the integrating currents I and the gain bandwidth of the differential amplifier  202  are programmable. “Gears” correspond to different bit rates, data rates or speeds at which the PWM_IN signal may be communicated and multiple gears may be provided pursuant to the M-PHY specification. While gears up to G 7  are defined in the M-PHY specification it is expected that gears up to G 5  will be more widely used. Once the integrating current I and gain of the amplifier  202  are programmed for a particular gear, the PWM receiver circuit  200  in one embodiment is capable of handling up to a three times peak-to-peak variation of the unit interval UI by using the design equations (1)-(4) above. The PWM receiver circuit  200  is also able to demodulate a logic 1 from a PWM_IN signal with a duty cycle between 75% and 60%, and similarly is able to demodulate a logic 0 from a PWM_IN signal with a duty cycle between 25% and 40%. 
       FIG. 4  is more detailed schematic of one embodiment of the differential amplifier  202  of  FIG. 2 . The amplifier  202  is a rail-to-rail common mode input capable differential amplifier and includes a number of NMOS transistors N 1 -N 2 , PMOS transistors P 1 -P 6 , resistors R 1 , R 2 , and current sources I 3 , I 4  coupled as shown between the supply voltage Vdd and ground. A pair of the NMOS transistors N 1 , N 2  and a pair of the PMOS transistors P 5  receive the inputs to the amplifier  202 , which are the voltages VC 0  and VC 1  across the capacitors C 0  and C 1 , respectively. The amplifier  202  generates outputs O+, O− in response to the input voltages VC 0  and VC 1  and these outputs are applied as the differential voltage Vdiff to the latched comparator  204  ( FIG. 2 ). 
     Referring back to  FIG. 3 , there is a need to hold the charges on the capacitors C 0 , C 1  for the times (tA+tL), to amplify it via differential amplifier  202 , to resolve or decode the differential voltage via the latched comparator  204 . Then at time t 5  after the RxOut signal has been output, the capacitors C 0 , C 1  must be discharged fully, which takes some more time (tD, from t 5  to t 6 ) before the next integration phase of the PWM receiver circuit  200  can be initiated. The “integration” phase” corresponds to the times from t 0 -t 6  in  FIG. 3  and thus the next unit interval UI of the PWM_IN signal cannot begin to be demodulated until just after the time t 6 . The time interval t 0 -t 6  is long enough, however, that before this time elapses for a given unit interval UI being demodulated, the next unit interval of the PWM_IN signal has started. In other words, the interval (t 0 -t 6 ) is greater than the unit interval UI, which of course must be true since the entire unit interval UI is needed to integrate current I on capacitors C 0 , C 1  for the low and high portions of the PWM_IN signal. As a result, the next integration phase (i.e., integration of the next unit interval UI of the PWM_IN signal) must be done with a separate set of capacitors C 0 , C 1 , differential amplifier  202 , and latched comparator  204 , namely with a separate PWM receiver circuit  200 . This means that a time interleaving technique may be employed with several PWM receiver circuits  200  that operate in an interleaved manner to demodulate successive unit intervals UI of the PWM_IN signal. 
       FIG. 5  is functional block diagram of an interleaved PWM receiver circuit  500  according to another embodiment of the present disclosure. In this embodiment, a LVDS-to-CMOS converter receives the LVDS input signal and converts this to the PWM_IN signal, as discussed above. The PWM_IN signal is then applied to a timing and control generator circuit  504  which, in response to the PWM_IN signal, generates a number of control signals to control the overall operation of the circuit  500 . The PWM_IN signal functions as a clock signal to clock the generator circuit  504 , as will be explained in more detail below. The generator circuit  504  includes a number of receiver stages  506 - 0  to  506 -(N−1), where each stage corresponds to the PWM receiver circuit  200  of  FIG. 2 . Thus, N is a number that determines the number of receiver stages  506  in the interleaved PWM receiver circuit  500 , and the number N varies in different embodiments of the present disclosure. In response to the PWM_IN signal, which as mentioned above clocks the generator circuit  504 , the generator circuit generates the required control signals rst 0 [N−1:0], rst 1 [N−1:0], int 0 [N−1:0], int 0 *[N−1:0], int 1 [N−1:0], int 1 *[N−1:0], and eval[N−1:0] to control the operation of these receiver stages  506  in an interleaved manner. A multiplexer  508  receives the data output signals RxOut 1  to RxOutn form the stages  506 - 0  to  506 -(N−1) and the generator circuit  504  also generates multiplexer selection signals Sel[N−1:0] to select which of these output signals is provided by the multiplexer as the output of the interleaved PWM receiver circuit  500 . The timing and control generator circuit  504  may be formed using counters, such as a ring counter, and state machines, and delays operating responsive to the PWM_IN signal being used as a clock signal to clock the generator circuit, and thus for the sake of brevity, the generator circuit  504  will not be described in more detail herein. The generator circuit  504  also outputs a clock output signal CkOut, which is a delayed version of the PWM_IN signal, and thus the outputs generated by the interleaved PWM receiver circuit  500  are the selected output RxOut from the selected stage and the CkOut signal. 
     The required number N of interleaved stages  506  is determined by the following equation, rounded off to the next higher integer: 
                   Nstage   =       ceiling   ⁢           ⁢       tA   +   tL   +   tD       UI   ⁢           ⁢   min         +   1             (   5   )               
where the time to is the delay time of the differential amplifier  202 , the time tL is the delay time of the latched comparator  204 , the time tD is the discharge time of the capacitors C 0 , C 1 , and the value UImin is the minimum target unit interval UI for a given gear of operation. In one embodiment, three stages  506 - 0 ,  506 - 1 ,  506 - 2  (i.e., N=3) of time interleaving are found to be sufficient for the highest data rate, PWM-Gear- 7  of the M-PHY specification.
 
       FIG. 6  is a signal timing diagram illustrating the control signals in the interleaved PWM receiver circuit  500  of  FIG. 5  during operation of this circuit. As seen in this timing diagram, the select signals, Sel[2:0] (i.e., Sel[N−1:0] and N=3 so Sel[3-1:0]) are generated from the falling edges of the PWM_IN signal as seen for the Sel[ 2 ] signal at time t 1 , the Sel[ 0 ] signal at time t 1 , and the Sel[ 1 ] signal at time t 2 . This naming convention is skewed by one unit interval UI, namely the 0th PWM bit (i.e., the PWM_IN signal during the 0th unit interval (t 0 -t 1 ) and designated bit[ 0 ] in  FIG. 6 ) generates the Sel[ 2 ] signal. The 1st PWM bit (i.e., the PWM_IN signal during the second unit interval (t 1 -t 2 ) and designated bit[ 1 ] in  FIG. 6 ) generates the Sel[ 0 ] signal. The 2nd PWM bit (i.e., the PWM_IN signal during the third unit interval (t 2 -t 3 ) and designated bit[ 2 ] in  FIG. 6 ) generates the Sel[ 1 ] signal. The operation of the circuit  500  continues cyclically in this manner and this way the decoded or demodulated RxOut 0  for bit  0  is output from the multiplexer  508  out when the Sel[ 0 ] signal is high. Referring to  FIG. 6 , the Sel[ 0 ] signal goes high at time t 1  and the bit[ 0 ] is output a short time later and by time t 2 . The Sel[ 1 ] signal goes high at time t 2  and the bit[ 1 ] is output a short time later and by time t 3 , and in the same way the Sel[ 2 ] signal goes high at time t 3  and the bit[ 2 ] is output a short time later and by time t 4 . In operation, the control generator circuit  504  generates these select signals Sel[2:0] responsive to the incoming PWM_IN signal and generates the remainder of the controls signals rst 0 [N−1:0], rst 1 [N−1:0], int 0 [N−1:0], int 0 *[N−1:0], int 1 [N−1:0], int 1 *[N−1:0], and eval[N−1:0] from the Sel[2:0] signals, PWM_IN signal and delayed versions thereof. The voltage signals VC 0 [i]) and VC 1 [i] represent the voltages are across the integrating capacitors C 0 , C 1  (see  FIG. 2 ) of ith receiver circuit stage, and are shown for the first receiver stage  506 - 0  (VC 0 [ 0 ], VC 1 [ 0 ]) and the second receiver stage  506 - 1  (VC 0 [ 1 ], VC 1 [ 1 ]).  FIG. 6  thus shows the difference between the integration voltages VC 0 [ 0 ], VC 1 [ 0 ] in the receiver stage  506 - 0  while receiving PWM bit  0  (time t 0 -t 1 ) and in the receiver stage  506 - 1  while receiving the PWM bit  1  (time t 1 -t 2 ). The discharge of these integration voltages VC 0 , VC 1  for each of the stages  506 - 0  and  506 - 1  are also seen in  FIG. 6 . In  FIG. 6  only control signals and integrating voltages for two stages  506 - 0  and  506 - 1  are shown by way of example. The same signals for the third receiver stage  506 - 2  can be derived easily from the timing diagram of  FIG. 6  and will be understood by those skilled in the art. In addition, the demodulation of a second PWM bit  3  (time t 3 -t 4 ) by the receiver stage  506 - 0  starting at time t 3  is also seen in  FIG. 6 . This illustrates that with the three receiver stages  506 - 0 ,  506 - 1 , and  506 - 2  the PWM_IN signal (i.e., PWM bits) can be demodulated in real time with the interleaved PWM receiver circuit  500 . 
     The operation of the PWM receiver circuit  200  of  FIG. 2  and interleaved PWM receiver circuit  500  of  FIG. 5  illustrate that each of these embodiments has a very useful characteristic for demodulating the PWM_IN signal. Every PWM data bit (i.e., the PWM_IN signal over each unit interval UI) is separately extracted during the unit interval UI for that bit, and thus variation of the unit interval UI over consecutive PWM data bits is tolerable. The embodiment of  FIG. 5  with three receiver stages  506 - 0 ,  506 - 1 ,  506 - 2  can tolerate three times the variation in consecutive unit intervals and still demodulate each bit. Thus, the jitter requirement of a clock of the driving a PWM transmitter that providing the PWM_IN signal is relaxed to a great extent. A very crude oscillator in the PWM transmitter thus may suffice, which is allowed to vary over process, unclean supply voltage, and temperature, up to three times in duration of a nominal unit interval UI. 
     In addition, with the circuits  200  and  500  there is no need to “lock” onto the incoming bit stream (i.e., the PWM_IN signal). It is much faster, typically a few 100 nS, to turn on the current sources I 0 , I 1 , the differential amplifier  202 , and the latched comparator  204 , this it takes for a PLL or a DLL to “lock,” as will be appreciated by those skilled in the art. Thus, switching between power down and normal data burst modes of reception is faster than in PWM receivers using a PLL or DLL. This results in a substantial reduction in the average power consumption of the receiver  200 / 500  when bursts of data are sent interspersed with sleep modes (not data) of operation. Finally, note that the retrieved clock (CkOut) from the interleaved PWM receiver circuit  500  is equally varying as the PWM_IN signal, but this does not matter as long as a correct depth of a first-in-first-out (FIFO) buffer is chosen in the next higher level (LINK layer) of serial communication to transfer received data (RxOut 0  to RxOutN) to a processor for subsequent processing. 
       FIG. 7  is a functional block diagram of an electronic system or device  700  including or more of the interleaved PWM receiver circuit  500  of  FIG. 5  according to one embodiment of the present disclosure. The electronic device  700  also may include one or more of the PWM receiver circuit  200  of  FIG. 2 . The electronic device  700  includes processing circuitry  702  coupled to a touch controller  704  that controls a touch screen  706  to detect touches or touch points P(X,Y,Z) applied on or above a touch panel  708  of the touch screen. In this way a user (not shown) of the electronic device  700  interfaces with and controls the operation of the electronic device. The electronic system or device  700  may be any type of electronic system, such as a computer system, a tablet computer, a smart phone, a portable music or video player, and so on. For the present description, the electronic device  700  is assumed to be a smart phone by way of example. 
     The touch display  708  may be a liquid crystal display (LCD), and also includes a number of touch sensors  710  positioned on the touch display to detect touch points P(X,Y,Z), with only three touch sensors being shown merely by way of example and to simply the figure. There are typically many more touch sensors  710 , as will be appreciated by those skilled in the art. These touch sensors  710  are usually contained in a transparent sensor array that is then mounted on a surface of the touch display  708 . The number and locations of the sensors  710  can vary as can the particular technology or type of sensor, with typical sensors being resistive, vibration, capacitive, or ultrasonic sensors. In the embodiment of  FIG. 7 , the sensors are considered to be capacitive sensors by way of example. 
     In operation of the touch screen  706 , a user (not shown) generates a touch point P(X,Y,Z) through a suitable interface input, such as a touch event, hover event, or gesture event, using either his or her finger or an input device, such as an intelligent input device like an active stylus. The terms touch event, hover event, and gesture event will now be briefly described. A touch event is an interface input where the user&#39;s finger or input device is actually touching the surface of the touch display  708 , while hover and gesture events the user&#39;s finger or input device is within a sensing range above the surface of the touch display but is not touching the surface of the display. In a hover event the finger or input device may be stationary or moving while in a gesture event the finger or intelligent input device is moving in a singular or a plurality of predefined motions or constraints. The X-axis, Y-axis, and Z-axis are shown in  FIG. 7  with the Z-direction being out of the page and orthogonal to the surface (i.e., the XY plane) of the touch display  708 . Thus, for a given touch point P(X,Y,Z), the X and Y values indicate the location of the touch point on the surface of the touch display  708  while the Z value indicates the distance of the user&#39;s finger or input device from the surface, or simply whether the input device or finger is within the sensing range (Z=0 for touch events) from the surface. 
     In response to a touch point P(X,Y,Z), the sensors  710  generate respective signals that are provided to the touch controller  704  which, in turn, processes these signals to generate touch information TI for the corresponding touch point. The touch information TI that the touch controller  704  generates for each touch point P(X,Y,Z) includes location information and event information identifying the type of interface input, namely whether the touch point P(X,Y,Z) corresponds to a touch event, hover event, gesture event, or some other type of event recognized by the touch controller. The location information includes an X-coordinate and a Y-coordinate that together define the XY location of the touch point P(X,Y,Z) on the surface of the touch display  708 . 
     Where the sensors  710  are capacitive sensors, the sensors are typically formed as an array of sensors from transparent patterned orthogonal conductive lines (not shown) formed on the surface, or integrated as part of, the touch display  708 . The intersections of the conductive lines form individual sensors or “sensing points,” and the touch controller  704  scans these sensing points and processes the generated signals to identify the location and type of touch point or points P(X,Y,Z). The detailed operation of such an array of capacitive sensors  710  and the touch controller  708  in sensing the location and type of touch point P(X,Y,Z) will be understood by those skilled in the art, and thus, for the sake of brevity, will not be described in more detail herein. 
     The processing circuitry  702  is coupled to the touch controller  704  to receive the generated touch information TI, including the location of the touch point P(X,Y,Z) and the corresponding type of detected interface event (touch event, hover event, gesture event) associated with the touch point. The processing circuitry  704  executes applications or “apps”  712  that control the electronic device  700  to implement desired functions or perform desired tasks. These apps  712  executing on the processing circuitry  702  interface with a user of the electronic device  700  through the touch controller  704  and touch screen  706 , allowing a user to start execution of or “open” the app and to thereafter interface with the app through the touch display  708 . 
     The processing circuitry  702  represents generally the various types of circuitry contained in the electronic device  700  other than the touch screen  706  and touch controller  704 . Where the electronic device  700  is a smart phone, for example, the processing circuitry  702  would typically include a processor, memory, Global Positioning System (GPS) circuitry, Wi-Fi circuitry, Bluetooth circuitry, and so on. The processing circuitry  702  also includes the interleaved PWM receiver circuit  500  for communicating with components within the electronic device  700  or external to the electronic device. The touch controller  704  is also shown as including the interleaved PWM receiver circuit  500 , and thus in the example of  FIG. 7  the processing circuitry  702  and touch controller  704  could communicate with either through a serial communications link over which PWM_IN data signals are communicated as described above in detail with reference to  FIGS. 106 . 
     Even though various embodiments and advantages of the present disclosure have been set forth in the foregoing description, the present disclosure is illustrative only, and changes may be made in detail and yet remain within the broad principles of the present disclosure. Moreover, the functions performed by various components described above can be combined to be performed by fewer elements, separated and performed by more elements, or combined into different functional blocks depending upon the nature of the electronic system to which the present disclosure is being applied, as will be appreciated by those skilled in the art. At least some of the components described above may be implemented using either digital or analog circuitry, or a combination of both, and also, where appropriate, may be realized through software executing on suitable processing circuitry. It should also be noted that the functions performed by various components discussed above can be combined and performed by fewer elements or separated and performed by additional elements depending on the nature of the electronic device  700 . Therefore, the scope of protection for the present disclosure is to be defined and limited only by the appended or subsequently submitted claims.