Abstract:
A circuit for setting a threshold level for extracting data from a signal stream includes a terminal couplable to the signal stream. A peak detector is coupled to the terminal. A valley detector is coupled to the terminal. A comparator is coupled to outputs of the peak detector and the valley detector for generating a threshold voltage for extracting data or commands from the signal stream. A method of extracting data from a signal stream including: peak detecting the signal stream to generate a first signal; valley detecting the signal stream to generate a second signal; combining the first and second signals to generate a threshold signal; and extracting data from the signal stream utilizing the threshold level signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/916,655 (TI-74615); Provisional Patent Application No. 61/916,669 (TI-74616) filed Dec. 16, 2013; and U.S. Provisional Patent Application No. 61/916,643 (TI-74614) filed on Dec. 16, 2013, which are incorporated herein by reference in its entirety and for all purposes. This application is also related to U.S. patent application Ser. No. XX/XXX,XXX (TI-74614); U.S. patent application Ser. No. XX/XXX,XXX (TI-74615); and U.S. patent application Ser. No. XX/XXX,XXX (TI-74613), filed on even date, which are incorporated herein by reference in their entireties and for all purposes. 
     
    
     FIELD 
       [0002]    The invention relates to extracting data or commands from a noisy signal and, more particularly, to a circuit for setting a threshold voltage level for extracting the data or commands. 
       BACKGROUND 
       [0003]    Extracting data or commands from a noisy signal is a difficult task. Noisy data can occur when data is transmitted on a long cable or a radio link. Another situation in which data needs to be extracted from a noisy signal occurs in wireless power transmission. The term “wireless power” as utilized herein refers to the transmission of electrical energy from a power source to an electrical load without interconnecting wires. A common form of wireless power transmission utilizes two electromagnetically coupled coils to form a transformer through which power is transferred from the transmitting side to the receiving side. The transmitter may take the form of a pad having a coil embedded therein. The receiver may be built into a cellular telephone, for example, with a receiving side coil built into the back thereof. Although there is no direct contact between the transmitting and receiving coils, the close proximity of the coils and a judicious use of shielding allows for efficient transfer of energy from the transmitting side to the receiving side to operate a load, which may be a rechargeable battery being recharged through the system, for example. 
         [0004]      FIG. 1  shows a block diagram of a prior art wireless power transmission system, generally as  100 . The system comprises a transmitter side  102  and a receiver side  122 . The transmitter side  102  comprises a circuit  104  for rectifying an AC input into a DC voltage which is fed into a power stage  106  for generating a high frequency signal. The high frequency signal is coupled across a transformer  120  to the receiver side  122 . The power stage  106  is controlled by a controller  108  which contains a threshold setting circuit  110 . The threshold setting circuit  110  could be external to the controller  108 . The power stage  106  and the controller  108  could be combined into a single integrated circuit. The receiver side  122  comprises a rectifier circuit  124  to output a DC voltage to a voltage conditioning circuit  126  which is operated by the receiving controller  128  to supply power to a load  130 , which may be a rechargeable battery being recharged by the system, for example. 
         [0005]    As shown in  FIG. 1 , power flows from left to right from the transmitter to the receiver and communications flow from right to left from the receiver to the transmitter. The communication signals may be command signals to adjust the power level from the transmitter or other parameters, for example. The communication signals may be generated by coupling a resistor or capacitor across the receiving coil to generate signals which can be recognized by the controller on the transmitting side. These low level signals are noisy because of the noise generated by the power transmission portion of the system. 
         [0006]      FIG. 2  shows a prior art circuit for setting a voltage threshold level for extracting the data or commands from this noisy signal, generally as  110 . The data or command signals are applied at terminal  202  and charge the capacitor  206  via resistor  204 . A comparator  208  receives this threshold voltage and utilizes it to extract the data from a noisy signal, as is well known in the art. A problem with the circuit as illustrated in  FIG. 3 , is that the data or commands in wireless power transmission systems trends occur at intervals, so that the voltage across capacitor  206  is lost. Therefore, every time data is sent, the capacitor must be recharged before the appropriate threshold is generated. This is shown in  FIG. 3  where data transmission starts after idle and the threshold signal Thr starts charging with the first data pulse. The threshold does not reach a value allowing the data to be retrieved until several pulses have passed. Thus, data in those first pulses is lost. This is illustrated in greater detail in  FIGS. 4 ,  5  and  6 . In these figures, the axis is time in milliseconds and the ordinate is volts.  FIG. 4  illustrates the incoming data  402 .  FIG. 5  illustrates the charging of the threshold generating capacitor at  502  and  FIG. 6  shows the data loss  602  from the pulses  604 . A typical circuit might have a resistor of 30 mega ohms and a capacitor of 200 pF, for example. Increasing the size of the capacitor or resistor would reduce the charge lost when the circuit is at idle, but having large capacitors or resistors on a chip requires a large area on the chip and having external components increases the cost and size of the circuit. 
         [0007]    Another known technique for extracting the threshold value is to utilize an ADC circuit driving a microprocessor and extracting the data utilizing a software routine (not shown). This is an expensive solution. 
         [0008]    Thus, there is the need for a low cost, highly integratable threshold circuit that reaches its full threshold value quickly so that no data is lost. 
       SUMMARY 
       [0009]    It is a general object to provide full recovery of data or command signals from a noisy signal stream. 
         [0010]    In an aspect, a circuit for setting a threshold level for extracting data from a signal stream comprises a terminal couplable to the signal stream. A peak detector is coupled to the terminal. A valley detector is coupled to the terminal. The peak detector output and valley detector output are combined to generate a threshold. A comparator is coupled to the threshold voltage for extracting data or commands from the signal stream. 
         [0011]    In an aspect, a method of extracting data from a signal stream comprises peak detecting the signal stream to generate a first signal. Valley detecting the signal stream to generate a second signal. Combining the first and second signals to generate a threshold signal. Extracting data from the signal stream utilizing the threshold level signal. 
         [0012]    In an aspect, in a primary side wireless power transmitter for being inductively coupled to a secondary side wireless power receiver for supplying power to the wireless power receiver to power a load coupled to the wireless power receiver, a primary side controller for receiving communications from the secondary side wireless power receiver through the inductive coupling comprises a peak detector receiving a signal stream from the secondary side wireless power receiver. A valley detector receiving a signal stream from the secondary side wireless power receiver. A comparator coupled to the threshold voltage for extracting data or commands from the signal stream. 
         [0013]    In an aspect, a method of operating a primary side wireless power transmitter inductively coupled to a secondary side wireless power receiver for supplying power to the wireless power receiver to power a load coupled to the receiver comprises peak detecting a signal stream from the wireless power receiver to generate a first signal. Valley detecting the signal stream to generate a second signal. Generating a threshold voltage signal from the first and second signals. Extracting data from the signal stream utilizing the threshold voltage signal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]    Further aspects of the invention will appear from the appending claims and from the following detailed description given with reference to the appending drawings. 
           [0015]      FIG. 1  is a diagram of a wireless power system according to the prior art; 
           [0016]      FIG. 2  is a schematic of an RC threshold detection circuit in accordance with the prior art; 
           [0017]      FIG. 3  shows the signal output of the circuit  FIG. 2 ; 
           [0018]      FIG. 4  shows the data input to the circuits of  FIGS. 2 ,  8  and  12 ; 
           [0019]      FIG. 5  shows the threshold signal of the prior art RC threshold detection circuit; 
           [0020]      FIG. 6  shows the output of the prior art circuit shown in  FIG. 2 ; 
           [0021]      FIG. 7  shows an embodiment constructed according to the principles of the present disclosure; 
           [0022]      FIG. 8  shows the peak/valley detector of the embodiment of  FIG. 7 ; 
           [0023]      FIG. 9  shows the data output of the circuit of  FIG. 8 ; 
           [0024]      FIG. 10  shows the threshold signal of the circuit of  FIG. 8 ; 
           [0025]      FIG. 11  shows the data output of the circuit shown  FIG. 8 ; 
           [0026]      FIG. 12  shows an alternate embodiment constructed according to the principles of the present disclosure; 
           [0027]      FIG. 13  shows the data output of the circuit of  FIG. 12 ; and 
           [0028]      FIG. 14  shows an embodiment constructed according to the principles of the disclosure utilizing fast-attack slow-decay filters. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 7  shows an embodiment, generally as  700 . The embodiment  700  is generally similar to the circuit shown in  FIG. 1 , with the exception of the threshold setting device  710 . In the embodiment  700 , the transmitter side  702  comprises a circuit  704  for rectifying an AC input into a DC voltage which is fed into a power stage  706  for generating a high frequency signal which is coupled across a transformer  720  to the receiver side  722 . The power stage  706  is controlled by a controller  708  which contains a threshold setting circuit  710 . The threshold setting circuit  710  is different from the RC circuit  110  in  FIG. 1  and is replaced by a peak/valley detector circuit in accordance with one aspect constructed according to the principles of the present disclosure, which will be explained in greater detail hereinafter. The receiver side  722  comprises a rectifier circuit  724  to output a DC voltage to a voltage conditioning circuit  726  which is operated by the receiving side controller  728  to supply power to a load  730 , which may be a rechargeable battery being recharged by the system, for example. 
         [0030]      FIG. 8  shows the peak/valley detector circuit  710  in greater detail. Peak detector  802  and valley detector  814  are coupled to receive the data (or command) signal stream. The data (or command) signal is coupled to the non-inverting input of amplifier  801  in peak detector circuit  802  and to the non-inverting input of amplifier  815  of valley detector circuit  814 . The output of the peak detector  802  is coupled through diode  804  to the inverting input thereof. A capacitor  806  is coupled between the inverting input of the amplifier  801  and a reference voltage, represented by ground. The output of amplifier  815  is coupled through diode  816  to the inverting input thereof. The inverting input is also coupled via capacitor  810  to the reference potential represented by ground. A pair of resistors  808  and  812  are coupled in series between the inverting input to the amplifier  801  and inverting input to the amplifier  815 . A node  809  is at the junction of the two resistors. Node  809  is coupled to the inverting input of comparator  818 , the non-inverting input of which is coupled to receive the data. The recovered data is at the output of the comparator  818 . This circuit allows smaller capacitors and resistors to be used, for example, a 100 pF capacitor with 5 mega ohm resistors. 
         [0031]      FIG. 9  shows the recovered data between the two idle states as well as the outputs of the peak detector and valley detector where the signal PK is at the output of the peak detector  802  after the diode  804  in  FIG. 8  and the signal VY is at the output of the valley detector  814  after the diode  816  in  FIG. 8 . The threshold generated at node  809  is shown as the signal Thr in  FIG. 9 . The threshold signal Thr is shown as rapidly increasing at  902 . It should be noted that when no data signal is present, the RC circuits are isolated by diodes  804  and  816  and the capacitors  806  and  810  will discharge to the idle level of the data through the resistors  808  and  812 . 
         [0032]      FIG. 10  shows the threshold voltage Thr generated by the embodiments of  FIG. 8  and shown in  FIG. 9  in greater detail.  FIG. 11  shows the recovered data at the output of comparator  818 . Even though the threshold voltage shown in  FIG. 10  is not as smooth as the threshold voltage  502  shown in  FIG. 5 , no data is lost, as can be seen by comparing signals  1102  of  FIGS. 11 and 402  of  FIG. 4 . 
         [0033]    A second embodiment is shown in  FIG. 12  generally as  1200 . In  FIG. 12 , peak detector  1202  and valley detector  1214  are coupled to receive the data (or command) signal stream. In  FIG. 12 , the data (or command) signal is coupled to the non-inverting input of amplifier  1201  and to the non-inverting input of amplifier  1215 . The output of the amplifier  1201  is coupled through diode  1204  to the inverting input thereof. A capacitor  1206  is coupled between the inverting input to amplifier  1201  and a reference voltage, represented by ground. The output of amplifier  1215  is coupled through diode  1216  to the inverting input thereof. The inverting input is also coupled via capacitor  1210  to a reference voltage represented by ground. A pair of resistors  1208  and  1212  are coupled in series between the inverting input to the peak detector  1202  and the inverting input to the valley detector  1214 . A node  1209  is at the junction of the two resistors. Node  1209  is coupled to the inverting input of comparator  1218 . In this embodiment, a preamplifier  1220  is coupled to receive the data at a non-inverting input thereof The threshold signal at node  1209  is coupled via resistor R to the inverting input of the preamplifier  1220 . The output of the preamplifier  1220  is coupled through a resistor  20 R of the preamplifier  1220 . This establishes the preamplifier as a high gain amplifier. The output of preamplifier  1220  is coupled to the non-inverting input of comparator  1218 . This circuit allows smaller capacitors and resistors to be used, for example, a 100 pF capacitor and resistors with 5 mega ohm resistors. The recovered data appears at the output of comparator  1218 . 
         [0034]      FIG. 13  shows the output of the comparator  1218 . As can be seen, data is recovered between the two idle states. The signal PK represents the signal at the output of the peak detector  1202  after diode  1204  and the signal VY represents the signal at the output of valley detector  1214  after diode  1216 . The threshold signal Thr is shown as rapidly increasing at  1302 . It should be noted that when no data signal is present, the RC circuits are isolated by diodes  1204  and  1216  and the capacitors  1206  and  1210  will discharge to the idle level of the data through the resistors  1208  and  1212 . 
         [0035]      FIG. 14  shows another embodiment of the circuit  710 . In  FIG. 14 , the amplifier  801  is replaced with a low value resistor  1401  having one end coupled to the data command stream and the other end coupled to a diode  1404 . The data stream is also coupled via a low value resistor  1415 , which replaces amplifier  815 , to a diode  1416 . The anode of diode  1404  is coupled via a high value resistor to a node  1409 . A capacitor  1406  is coupled between the junction of the anode of diode  1404  and high value resistor  1408  and ground. A high value resistor  1412  is coupled between the cathode of diode  1416  and node  1409 . A capacitor  1410  is coupled between the node formed by the cathode of diode  1416  and the high value resistor  1412  and ground. 
         [0036]    In this embodiment, the circuit  710  is constructed using fast-attack, slow-decay filters. In  FIG. 14 , the fast-attack, slow-decay filter circuit is shown in detail. The data or command signal stream is coupled to RC filters with different time constants for rising and falling signals. Each RC filter consists of a lower value resistor, a higher value resistor, a capacitor and a blocking element. The blocking element allows higher current flow in one direction than the other and can be a diode, such as diodes  1404  and  1416 . 
         [0037]    In operation, the fast attack, slow decay filter  1402  output rises close to the high level of the data or command signal. Similarly, a fast decay, slow-attack filter  1414  output falls close to the low level of the data or command signal. When the signal returns to idle, the output of the fast-attack, slow-decay filter slowly decays to the idle level and the output of the fast-decay, slow-attack filter slowly rises to the level of the data or command signal. In this circuit, the high-value resistors serve two functions. One function is to create a threshold signal from the output of the fast-attack, slow-decay filter and the output of the fast-decay, slow-attack filter. The other function is to slowly change the output of the filters so that they are slowly returned to the idle level of the data or command signal. 
         [0038]    Although the invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made thereto without departing from the spirit and scope of the invention as defined by the appended claims. For example, the circuit can be applied to recover data from other noisy signals, and not just in wireless power systems.