High precision signal measurement in wireless charging system
A wireless charging system is configured to charge one or more receiver devices simultaneously. The wireless charging system includes multiple coils that may be driven independently based on a feedback system with one or more feedback channels. One of the feedback channels may be a voltage and/or current measurement of coil driving signals from the coils that are indicative of receiver device presences on the wireless charging system. A coil driving signal may be sampled and processed using discrete Fourier transform to determine amplitude and phase information of the signal.
1. A non-transitory computer readable storage medium comprising stored instructions to measure an amplitude and a phase of a signal of a coil driven at an operating frequency in a wireless charging system, the instructions when executed causing a microcontroller to:
select a first integer value and a second integer value, wherein the first integer value and the second integer value are coprime integers;
determine a ratio between the first integer value and the second integer value;
select a sampling frequency for sampling the signal, wherein a ratio between the sampling frequency and the operating frequency is same as the ratio between the first integer value and the second integer value;
sample the signal based on the selected sampling frequency to collect a plurality of signal samples;
calculate a value representative of the plurality of signal samples using a discrete Fourier transform (DFT) performed based in part on the first integer value and the second integer value; and
determine the amplitude and the phase of the signal based on the Fourier value.
2. The computer readable storage medium of claim 1 , wherein the signal is a voltage across the coil or a current through the coil.
3. The computer readable storage medium of claim 1 , further comprising instructions to transmit the signal to an op-amp circuit, the op-amp circuit configured to modify the signal to be in a predetermined range compatible with an analog-to-digital converter used to sample the signal.
4. The computer readable storage medium of claim 1 , wherein a number of samples in the plurality of signal samples corresponds to a multiple of the first integer.
5. The computer readable storage medium of claim 1 , wherein a number of samples in the plurality of signal samples is less than the first integer.
6. The computer readable storage medium of claim 1 , wherein the amplitude is a root mean square of a magnitude of the value.
7. The computer readable storage medium of claim 1 , further comprising instructions to modify an amplitude of the signal to be within a predetermined range for the sampling prior to sampling the signal based on the selected sampling frequency.
8. A wireless charging system comprising:
a coil driven by a signal at an operating frequency to wirelessly transfer power to a receiver device;
a coil measurement circuit configured to measure an amplitude and a phase of the signal of the coil; and
a microcontroller configured to:
select a first integer value and a second integer value, wherein the first integer value and the second integer value are coprime integers;
determine a ratio between the first integer value and the second integer value;
select a sampling frequency of the coil measurement circuit for sampling the signal, wherein a ratio between the sampling frequency and the operating frequency is same as the ratio between the first integer value and the second integer value;
receive, from the coil measurement circuit, a plurality of signal samples collected by sampling the signal at the selected sampling frequency;
calculate a value representative of the plurality of signal samples using a discrete Fourier transform (DFT) performed based in part on the first integer value and the second integer value; and
determine the amplitude and the phase of the signal based on the Fourier value.
9. The wireless charging system of claim 8 , wherein the signal is a voltage across the coil or a current through the coil.
10. The wireless charging system of claim 8 , wherein the signal is received by an op-amp circuit, the op-amp circuit configured to modify the signal to be in a predetermined range compatible with an analog-to-digital converter used to sample the signal.
11. The wireless charging system of claim 8 , wherein a number of samples in the plurality of signal samples corresponds to a multiple of the first integer.
12. The wireless charging system of claim 8 , wherein a number of samples in the plurality of signal samples is less than the first integer.
13. The wireless charging system of claim 8 , wherein the amplitude is a root mean square of a magnitude of the value.