Abstract:
A primary side wireless power transmitter inductively couplable to a secondary side wireless power receiver for receiving communications from the secondary side wireless power receiver through the inductive coupling having a primary side tank circuit receiving a signal from the secondary side wireless power receiver. A phase delay or time delay circuit generates a fixed delay clock signal from a signal utilized to excite the primary side tank circuit. A sample and hold circuit samples a tank circuit voltage utilizing the fixed phase or time delayed clock signal. A comparator is coupled to an output of the sample and hold circuit for extracting data or commands from the signal stream. A method of operating a primary side wireless 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 is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority from U.S. Provisional Application No. 61/916,643, filed Dec. 16, 2013; U.S. Provisional Application No. 61/916,655; and U.S. Provisional Application No. 61/916,669 filed Dec. 16, 2013, which are incorporated herein by reference in their entirety for all purposes. This application is related to U.S. application Ser. No. 14/501,850, filed Sep. 30, 2014; U.S. patent application Ser. No. 14/502,048, filed Sep. 30, 2014, filed on even date, which are incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD 
     The invention relates to recovery of data or commands in a signal stream received from a wireless power receiver in a wireless power transmitter. 
     BACKGROUND 
     The explosion of small portable electronic devices such as cell phones has led to the desire to be able to recharge the device without the necessity of attaching a cord to the device. A solution that accomplishes this task is known as “wireless power”. 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 for wireless power transmission utilizes two electromagnetically coupled coils to form a transformer through which power is transferred from the primary 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 the 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 the 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 by the system, for example. 
       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 controller  108  which could be combined into a single integrated circuit with the power stage  106 . The receiver side  122  comprises a rectifier circuit  124  to output a DC voltage and a voltage conditioning circuit  126  which is operated by the receiver controller  128  to supply power to a load  130 , which may be a rechargeable battery being recharged by the system, for example. 
     As shown  FIG. 1 , power flows from left to right from the transmitter to the receiver and communications flows 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. The low-level signals are noisy because of the noise generated by the power transmission portion of the system. 
     The Wireless Power Consortium (WPC) defines a standard for such wireless power transmission. In a WPC defined wireless charging system, the power transmitter detects the signal from the power receiver as a modulation of current through and/or voltage across the primary circuit through a V/I circuit  110 . In other words, the power receiver and the power transmitter use amplitude modulated power signals to provide a power receiver to power transmitter communication channel. 
     The WPC defined communication channel assumes that the incoming power signal is always amplitude modulated. However, that may not be a valid assumption. Accordingly, there is a need for a reliable, low-cost and easily integratable solution for detecting information being sent from the receiver to the transmitter in a wireless power system. 
     SUMMARY 
     It is a general object of the invention to provide for recovery of data or commands in a signal stream in a wireless power transmitter. 
     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 control for receiving communications from the secondary side wireless power receiver through the inductive coupling comprises a primary side tank circuit being excited into oscillation by an excitation signal, the tank circuit receiving a signal from the secondary side wireless power receiver. A delay circuit generates a fixed delay clock signal from the excitation signal. A sample and hold circuit samples a tank circuit voltage utilizing the fixed delayed clock signal. A comparator is coupled to an output of the sample and hold circuit for extracting data or commands from the signal stream. 
     In an aspect, a method of operating a primary side wireless 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 exciting a tank circuit into oscillation utilizing an excitation signal. A signal stream is received from the wireless power receiver in a primary side tank circuit. A fixed delay clock signal is generated. The tank circuit voltage is sampled utilizing the fixed delayed clock in holding the sample value. A threshold voltage signal is generated from the signal stream signal. Data is extracted from the signal stream utilizing the threshold voltage signal. 
     In an aspect, a wireless power transfer system comprises a transmitter for transmitting electrical energy through a first inductive coil electromagnetically coupled to a second inductive coil and a receiver. A circuit in the receiver couples a resistor or capacitor across the second inductive coil to generate data or command signals in the first inductive coil. A sample and hold circuit samples a value of signal in the first inductive coil and holds the value, the sample being taken at a fixed delay from the excitation signal for the first coil. A comparator coupled to an output of the sample and hold circuit extracts data or commands from a signal stream. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Further aspects of the invention will appear from the appending claims and from the following detailed description given with reference to the appending drawings. 
         FIG. 1  is a diagram of a wireless power system according to the prior art; 
         FIG. 2  is a graph showing the tank waveform in a wireless power system; 
         FIG. 3  is a graph showing the tank waveform in which the two signals in a wireless power system have the same amplitude; 
         FIG. 4  is a block diagram of an embodiment constructed according to the principles of the present disclosure; 
         FIG. 5  shows an alternate embodiment constructed according to the principles of the present disclosure; and 
         FIGS. 6-12  show waveforms for the circuits illustrated in  FIGS. 4 and 5 . 
     
    
    
     DETAILED DESCRIPTION 
     In order to have a reliable communication channel, the system must tolerate system parameter variations including variations in the coupling coefficient (K) of between 0.2 and 0.7, and variation in the receiver load from 5 ohms to 1 kilo ohm, transmit and receive coil inductance variation due to shielding, effects of the battery effects of a magnet used to center the receiving device on the transmitting pad and manufacturing tolerances over the entire range of operating frequency from 110 kHz to 205 kHz. 
     The WPC defined communication channel assumes that the incoming signal is always amplitude modulated. However, the present inventors have discovered that this information may be lost because of its low value (i.e. 200 mV) which may be further reduced when the power signal level (which can be 70 Vpp) is divided down to a voltage level that can be handled by an integrated circuit, as this signal, which rides on the power signal, will also be reduced. This low level signal can be masked by changes in the load current. Accordingly, the inventors have determined that the signal data may lie within the phase of incoming carrier signal, rather than the amplitude. Therefore, a traditional amplitude demodulator channel is inadequate to solve the problems described above. 
       FIG. 2  shows the tank signal waveform of the power transmitter where data is being sent from the receiver to the transmitter, generally as  200 . In  FIG. 2 , the load resistance is 100 ohms, the coefficient of coupling K is 0.7, the secondary (receiver) side capacitor, utilized to transmit data or commands back to the transmitter (primary) side, is 22 nF. The primary side inductance is 9.36 μH and the secondary side inductance is 16 μH with the circuit having an operating frequency of 155 kHz. Waveform  202  is without the capacitor being coupled across the secondary side of receiver coil and the waveform  204  shows the same signal with the capacitor coupled across the secondary side receive coil to transmit information. Under these circumstances, there is a difference in amplitude between the two waveforms and the information in the signal can be amplitude detected. 
       FIG. 3  shows the tank signal waveform of a power transmitter generally as  300 . In  FIG. 3 , the load resistance is 5 ohms, the coupling coefficient is 0.2, the capacitance is 22 nF, the primary side inductor is 9.36 μH, the secondary side inductor is 16 μH and the operating frequency is 155 kHz. As can be seen, the peaks of the waveforms with and without capacitance being switched in at the secondary side, are identical at  306 . The exploded view shows the signal  302  which is the signal without the capacitor being switched in across the receiver side coil and the signal  304  which shows the capacitor switched in across the coil. Therefore, it may be very difficult to detect the data when the signal peaks are essentially identical utilizing amplitude demodulation. 
       FIG. 4  shows an embodiment of a solution to this problem generally as  400 . In  FIG. 4 , the tank waveform from the transmitter side tank circuit is coupled via resistor divider  402 ,  404  to a capacitor  406 . The resistor divider  402 ,  404  divides of the voltage across the tank circuit, which may be as much as 70 V peak to peak, to a voltage level that can be handled by an integrated circuit. Capacitor  406  blocks the DC level of the input waveform from affecting the setpoint of a buffer circuit  412 , the non-inverting input of which is coupled to the capacitor  406 . This allows the setpoint of the buffer  412  to be set via the resistor divider  408 ,  410  between a reference voltage and ground. The inventors have found it to be advantageous to utilize the voltage just slightly above 0 V, for example, 100 or 200 mV as the setpoint for the buffer  412 . In addition, the circuit may be operated at a higher voltage than may be used for other portions of the transmitter circuit, for example 4 V rather than 3.3 V. The combination of these two features allows for an increased voltage swing of the measured data or commands in the signal stream. Buffer  412  has its output coupled to the inverting input thereof so that it has a gain of unity. The output of buffer  412  is coupled to a sample and hold circuit having a switch  414  which stores the value of the tank waveform, after having been buffered by buffer  412 , and stored in capacitor  416 . The switch  414  in the sample and hold circuit is controlled by the output of the 300 ns pulse generator  430  having a fixed phase delay of 60°. This circuit  430  is driven, in turn, by the excitation signal  426  used to excite the tank circuit in the transmitter via buffer inverter  428 . Therefore, the sample of the tank waveform is taken at fixed phase delay of 60° from the excitation signal for the tank waveform. The sample value is stored in capacitor  416  which is coupled between the switch and ground. Voltage across capacitor  416  is filtered by a low pass filter  418 , here in a fifth order Butterworth low pass filter. The output of the low pass filter  418  is coupled to the inverting input of an auto zero or low offset comparator  424 . The output of the low pass filter  418  is also coupled through RC filter  420 ,  422  to the non-inverting input of auto zero comparator  424 . The resistor  420  is coupled in series between the output of the low pass filter  418  and the non-inverting input of auto zero comparator  424 . The capacitor is connected between the non-inverting input of the auto zero comparator  424  and ground. The output of auto zero comparator  424  is the data or command signal. It should be noted that the fixed phase delay can range at least between 15° and 75° without departing from the principles of the present disclosure. 
     In operation, the coil voltage from the transmit coil in the transmit tank circuit can be sensed directly. This voltage, which can be as high as 70 V peak to peak the varying DC level, is AC coupled to the demodulator signal chain through a resistor divider  402 ,  404  which reduces the voltage to level it can be handled by an integrated circuit. Depending upon the voltage reduction of the resistor divider  402 ,  404 , the signal to be detected can be 100 mV or lower riding on top of the 10-70 V peak to peak carrier amplitude. Thus it has a very low signal-to-noise ratio (SNR). In addition, the carrier has both positive and negative swings with respect to ground. Therefore, the present invention maximizes the signal amplitude by setting the DC setpoint at the input of amplifier  412  very close to ground, for example 200 mV. This, along with a higher voltage (for example for 4 V) supply for the amplifier  412  allows for a signal swing of almost 4 V. 
     The input voltage to the non-inverting terminal of buffer amplifier  412  is shown in  FIG. 6 , generally as  600 . 
     As can be seen, it is an amplitude (or phase) modulated sine wave of frequency between 110 kHz-205 kHz. The amplitude modulation frequency is 2 kHz. The  600  shows two periods; one just before the modulation and one after the modulation. 
     The output of buffer amplifier  412  is shown in  FIG. 7  as a half wave rectified sine wave  700 .  FIG. 8  shows the square wave excitation signal  800  is used to excite the tank circuit in the transmitter side of the power transmission device. This signal is sometimes referred to as a “PWM” signal although it is normally a square wave having a 50% duty cycle. However, under extreme light load conditions, the cycle would be cut back from the 50% level to 10% level in order to reduce the power generated when the need for power at the receiver side is low.  FIG. 9  shows the output pulse from the 300 ns pulse generator having a fixed phase delay of 60° generally as  900 . Pulse  900  is coupled to the switch  414  of the sample and hold circuit and used to operate the switch to take samples of the output of buffer  412 . The samples are held in capacitor  416 . 
     The sampled voltage is shown in  FIG. 10  generally as  1000 . In order to remove high-frequency noise from the signal, it is passed through a low pass filter, here a fifth order Butterworth low pass filter  418 . The output of the Butterworth low pass filter is shown in  FIG. 11  generally as  1100 . In order to determine the threshold utilized to extract data or commands from signal stream, an RC filter comprising resistor  420  coupled in series between the output of the fifth order Butterworth low pass filter and the non-inverting input of auto zero comparator  424  and a capacitor  422  coupled from the non-inverting input of amplifier  424  to ground is utilized. The threshold  1102  generated by the low pass filter  420 ,  422  is utilized to extract the data which appears at the output of the auto zero comparator  424 . The signal  1106  represents a digital zero and the signal  1104  represents a digital one. The signal  1200  is the output of auto-zero comparator  424 , with a digital one output being shown at  1202 . 
       FIG. 5  shows an alternative embodiment of a solution to this problem generally as  500 . In  FIG. 5 , the tank waveform from the transmitter side tank circuit is coupled via resistor divider  502 ,  504  to a capacitor  506 . The resistor divider  502 ,  504  divides the voltage across the tank circuit, which may be as much as 70 V peak to peak, to a level that can be handled by an integrated circuit. Capacitor  506  blocks the DC level of the input waveform from affecting the setpoint of a buffer circuit  512 , the non-inverting input of which is coupled to the capacitor  506 . This allows the setpoint of the buffer  512  to be set via the resistor divider  508 ,  510  between a reference voltage and ground. The inventors have found it to be advantageous to utilize the voltage just slightly above 0 V, for example, 100 or 200 mV as the setpoint for the buffer  512 . In addition, this circuit is operated at a higher voltage than may be used for other portions of the transmitter circuit, for example 4 V rather than 3.3 V. The combination of these two features allows for an increased voltage swing of the measured data or commands in the signal stream. Buffer  512  has its output coupled to the inverting input thereof so that it has a gain of unity. The output of buffer  512  is coupled to a switch of sample and hold circuit  514 . The sample and hold circuit  514  is operated by a pulse from pulse generator  530  at a fixed time delay, here shows 1.2 μs. Other time delays can be utilize such as 250 ns to 1.2 μs. Pulse generator  530  is operated by the excitation signal for the tank circuit  526  passing through buffer inverter  528 . This signal is sometimes referred to as a “PWM” signal although it is normally a square wave having a 50% duty cycle. However, under extreme light load conditions, the cycle would be cut back from the 50% level to the 10% level in order to reduce the power generated when the need for power at the receiver side is low. A sample value is stored in capacitor  516  which is coupled between the switch and ground. 
     The voltage across capacitor  516  is filtered by a low pass filter  518 . In this embodiment a fifth order Butterworth low pass filter is utilized. The output of the Butterworth low pass filter is shown in  FIG. 11  generally as  1100 . In order to determine the threshold utilized to extract data or commands from signal stream, an RC filter comprising resistor  520  coupled in series between the output of the fifth order Butterworth low pass filter and the non-inverting input of auto zero comparator  524  and a capacitor  522  coupled from the non-inverting input of amplifier  524  to ground is utilized. The threshold  1102  generated by the low pass filter  520 ,  522  is utilized to extract the data which appears that the output of the auto-zero comparator  524 . The signal  1106  represents a digital zero and the signal  1104  represents a digital one. The signal  1200  is the output of auto-zero comparator  524 , with a digital one output being shown at  1202 . 
     The fixed time delay could be 250 ns to 1.2 μs, for example. The pulse generated by the time delay circuits may be 300 ns wide, for example. These circuits are somewhat simpler in construction than a phase delayed pulse generator circuit. Circuits capable of generating such time delayed pulses are well known in the art and need not be discussed further herein. A circuit for the generation of the phase delayed signals can be found in commonly-own application Ser. No. 14/502,048 filed on even date and incorporated herein by reference in its entirety for all purposes. Details on an alternate threshold detection circuit to replace the RC circuit  420 , 422  or  520 , 522  can be found in commonly-owned applications Ser. No. 14/501,850 or 14/502,048 filed on even date and incorporated herein by reference in their entirety for all purposes. 
     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.