Q-factor measurement

Patent metadata

Field	Value
Publication number	US-2019109499-A1
Application number	US-201816154665-A
Country	US
Kind code	A1
Filing date	Oct 8, 2018
Priority date	Oct 9, 2017
Publication date	Apr 11, 2019
Grant date	—

Abstract

In accordance with some embodiments of the present invention, a method of determining a Q-factor in a transmit circuit with a resonant circuit includes setting a system voltage; performing a coarse scan to determine a course resonant frequency; performing a fine scan based on the course scan to determine a resonant frequency; performing a final measurement at the resonant frequency to determine an average system voltage and an average peak voltage of the resonant circuit; calculating a Q parameter from the average system voltage and the average peak voltage; and calculating the Q-factor from the Q parameter.

First claim

What is claimed is:

1 . A method of determining a Q-factor in a transmit circuit with a resonant circuit, comprising:
setting a system voltage; performing a coarse scan to determine a course resonant frequency; performing a fine scan based on the course scan to determine a resonant frequency; performing a final measurement at the resonant frequency to determine an average system voltage and an average peak voltage of the resonant circuit; calculating a Q parameter from the average system voltage and the average peak voltage; and calculating the Q-factor from the Q parameter.

2 . The method of claim 1 , wherein setting the system voltage includes adjusting a buck voltage converter to produce the system voltage.

3 . The method of claim 1 , wherein the system voltage is set at a low enough voltage that a receiver in the proximity of the transmit circuit will not be activated.

4 . The method of claim 1 , wherein performing a course scan comprises:
setting a course frequency range and a course step size; sweeping a frequency through the frequency range at the course step size while monitoring a peak voltage of the resonant circuit; and determining the course resonant frequency wherein the peak voltage is at a maximum.

5 . The method of claim 1 , wherein performing a fine scan comprises:
setting a fine frequency range based on the course resonant frequency; setting a fine step size based on the fine frequency range; sweeping a frequency through the fine frequency range at the fine step size while monitoring a peak voltage of the resonant circuit; and determining the resonant frequency where the peak voltage is at a maximum.

6 . The method of claim 5 , wherein the fine frequency range is set from a percentage of the course resonant frequency less than the course resonant frequency to the percentage of the course resonant frequency higher than the course resonant frequency.

7 . The method of claim 6 , wherein the percentage is 25%

8 . The method of claim 6 , wherein the percentage is 10%.

9 . The method of claim 1 , wherein performing a final measurement comprises:
setting a frequency at the resonant frequency; setting a duty cycle; measuring the average system voltage VBRG and the average peak voltage at the frequency and the duty cycle.

10 . The method of claim 1 , wherein calculating the Q parameter as the ratio of the average peak voltage to the average system voltage.

11 . The method of claim 10 , wherein the average peak voltage is adjusted according to an ADC parameter.

12 . The method of claim 1 , wherein calculating the Q-factor from a 2 nd order polynomial or linear piece-wise equation fitting to the Q parameter.

13 . A transmitter that determines a Q-factor, comprises:
a switching bridge circuit; a resonant circuit that includes a transmit coil and a transmit capacitor coupled to the switching bridge circuit; and a controller coupled to the switching bridge circuit to control operation of the resonant circuit and coupled to the resonant circuit to receive a peak voltage from the resonant circuit, wherein the controller executes instructions to set a system voltage, perform a coarse scan to determine a course resonant frequency, perform a fine scan based on the course scan to determine a resonant frequency, perform a final measurement at the resonant frequency to determine an average system voltage and an average peak voltage of the resonant circuit, calculate a Q parameter from the average system voltage and the average peak voltage, and calculate the Q-factor from the Q parameter.

14 . The transmitter of claim 13 , further including a buck voltage converter to provide the system voltage and wherein the controller sets the system voltage by adjusting the buck voltage converter.

15 . The transmitter of claim 14 , wherein the system voltage is set at a low enough voltage that a receiver in the proximity of the transmit circuit will not be activated.

16 . The transmitter of claim 13 , wherein the controller performs a course scan by
setting a course frequency range and a course step size; sweeping a frequency through the frequency range at the course step size while monitoring a peak voltage of the resonant circuit; and determining the course resonant frequency wherein the peak voltage is at a maximum.

17 . The transmitter of claim 13 , wherein the controller performs a fine scan by
setting a fine frequency range based on the course resonant frequency; setting a fine step size based on the fine frequency range; sweeping a frequency through the fine frequency range at the fine step size while monitoring a peak voltage of the resonant circuit; and determining the resonant frequency where the peak voltage is at a maximum.

18 . The transmitter of claim 17 , wherein the fine frequency range is set from a percentage of the course resonant frequency less than the course resonant frequency to the percentage of the course resonant frequency higher than the course resonant frequency.

19 . The transmitter of claim 18 , wherein the percentage is 25%

20 . The transmitter of claim 18 , wherein the percentage is 10%.

21 . The transmitter of claim 13 , wherein the controller performs a final measurement by
setting a frequency at the resonant frequency; setting a duty cycle; measuring the average system voltage VBRG and the average peak voltage at the frequency and the duty cycle.

22 . The transmitter of claim 13 , wherein the controller calculates the Q parameter as the ratio of the average peak voltage to the average system voltage.

23 . The transmitter of claim 22 , further including
a select circuit that provides a divided voltage from the peak voltage, and a scale circuit that receives the divided voltage and provides a coil voltage to an analog-to-digital converter of the controller, wherein the average peak voltage is adjusted according to an ADC parameter.

24 . The transmitter of claim 23 , wherein the controller calculates the Q-factor from a 2 nd order polynomial or linear piece-wise equation fitting to the Q parameter.

Assignees

• Integrated Device Tech

Inventors

• Smith Nicholaus
• Maireanu Stefan
• Jiang Haiwen
• Wilson David

Classifications

• H02M3/1582

  Buck-boost converters (H02M3/1584 takes precedence) · CPC title

• H02J50/12

  of the resonant type · CPC title

• H02J50/60 Primary

  responsive to the presence of foreign objects, e.g. detection of living beings · CPC title

• H02M3/156

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H02J50/70

  involving the reduction of electric, magnetic or electromagnetic leakage fields · CPC title