CONTINUOUS TIME CORRELATOR ARCHITECTURE

• US 20140152328A1
• Filed: 02/04/2014
• Published: 06/05/2014
• Est. Priority Date: 02/25/2011
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Erdogan, Ozan E., Shen, Guozhong, Anantharaman, Rajesh, Taparia, Ajay, Javid, Behrooz, Mahmud, Syed T.
• Granted Patent: US 9,625,507 B2
• Time in Patent Office: Days
• US Class Current: 324/679
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A system includes a signal generator and a correlator. The signal generator outputs a first signal to a first end of a capacitance to be measured. The correlator is connected to an output of the signal generator that outputs the first signal and to a second end of the capacitance. The correlator receives the first signal from the output of the signal generator and receives a second signal from the second end of the capacitance. The correlator correlates the first signal and the second signal and generates an output signal based on a correlation between the first signal and the second signal. The output signal is proportional to a capacitance value of the capacitance.

Claims

1. A system comprising:

a signal generator that outputs a first signal to a first end of a capacitance to be measured; and

a correlator that is connected to an output of the signal generator that outputs the first signal and to a second end of the capacitance, that receives the first signal from the output of the signal generator, that receives a second signal from the second end of the capacitance, that correlates the first signal and the second signal, and that generates an output signal based on a correlation between the first signal and the second signal,

wherein the output signal is proportional to a capacitance value of the capacitance.

2. The system of claim 1 wherein the capacitance is a capacitance of a touch screen.

3. The system of claim 1 wherein the output signal is a DC voltage that is proportional to the capacitance value of the capacitance, the system further comprising a sampling circuit that samples the output signal to measure the capacitance value of the capacitance.

4. The system of claim 1 wherein the correlator comprises:

a mixer that mixes the first signal and the second signal; and

an integrator that integrates an output of the mixer to generate the output signal.

5. The system of claim 4 wherein the integrator integrates the output of the mixer over a time period that is a multiple of a period the first signal.

6. The system of claim 4 wherein the integrator provides a band-pass filtering function with a peak around a frequency of the first signal and filters noise from the second signal.

7. The system of claim 6 wherein the signal generator is configured to alter a frequency of the first signal so as to alter the band-pass filtering function of the integrator.

8. The system of claim 1 wherein the correlator comprises:

a programmable impedance element that outputs a product of the first signal and the second signal; and

an integrator that integrates the product to generate the output signal.

9. The system of claim 8 wherein the programmable impedance element receives a control signal and includes a plurality of resistors or a plurality of capacitors, and wherein an impedance of the programmable impedance element varies with time in response to the control signal.

10. The system of claim 1 wherein the correlator comprises:

a voltage-to-current converter that converts the second signal to a current;

a programmable impedance element comprising a current digital-to-analog converter that has a programmable gain and that receives the current and a control signal, wherein the control signal varies the programmable gain to change an effective impedance of the current digital-to-analog converter with time to generate a product of the second signal and the first signal; and

an integrator that integrates the product to generate the output signal.

11. A method comprising:

outputting a first signal to a first end of a capacitance to be measured;

receiving a second signal from a second end of the capacitance;

correlating the first signal and the second signal; and

generating an output signal based on the correlating of the first signal and the second signal,

wherein the output signal is proportional to a capacitance value of the capacitance.

12. The method of claim 11 wherein the capacitance is a capacitance of a touch screen.

13. The method of claim 11 wherein the output signal is a DC voltage that is proportional to the capacitance value of the capacitance, the method further comprising sampling the output signal to measure the capacitance value of the capacitance.

14. The method of claim 11 wherein the correlating comprises:

generating a product of the first signal and the second signal by mixing the first signal and the second signal; and

generating the output signal by integrating the product.

15. The method of claim 14 further comprising integrating the product over a time period that is a multiple of a period the first signal.

16. The method of claim 14 wherein the integrating comprises filtering noise from the second signal using a band-pass filtering function with a peak around a frequency of the first signal.

17. The method of claim 16 further comprising altering a frequency of the first signal so as to alter the band-pass filtering function.

18. The method of claim 11 wherein the correlating comprises:

generating a product of the first signal and the second signal using a programmable impedance element; and

generating the output signal by integrating the product.

19. The method of claim 18 wherein the programmable impedance element includes a plurality of resistors or a plurality of capacitors, the method further comprising:

supplying a control signal to the programmable impedance element; and

generating the product of the first signal and the second signal by varying an impedance of the programmable impedance element with time in response to the control signal.

20. The method of claim 11 wherein the correlating comprises:

converting the second signal to a current;

outputting the current and a control signal to a programmable impedance element comprising a current digital-to-analog converter having a programmable gain; and

changing an effective impedance of the current digital-to-analog converter with time by varying the programmable gain using the control signal to generate a product of the second signal and the first signal; and

integrating the product to generate the output signal.

21. A method comprising:

outputting a first signal to a first end of a capacitance of a touch screen, wherein a capacitance value of the capacitance is configured to vary in response to a conductive element being proximate to or in contact with the touch screen;

receiving a second signal from a second end of the capacitance;

correlating the first signal and the second signal;

generating an output signal based on the correlating of the first signal and the second signal, wherein the output signal is proportional to the capacitance value of the capacitance;

sampling the output signal to determine whether the capacitance value of the capacitance changed; and

determining whether the conductive element was proximate to or in contact with the touch screen based on whether the capacitance value of the capacitance changed.

22. The method of claim 21 wherein the correlating comprises:

generating a product of the first signal and the second signal by mixing the first signal and the second signal; and

generating the output signal by integrating the product over a time period that is a multiple of a period the first signal,

wherein the output signal is a DC voltage that is proportional to the capacitance value of the capacitance.

23. The method of claim 22 wherein the integrating comprises filtering noise from the second signal using a band-pass filtering function with a peak around a frequency of the first signal.

24. The method of claim 23 further comprising altering a frequency of the first signal so as to alter the band-pass filtering function.

25. The method of claim 21 wherein the correlating comprises:

generating a product of the first signal and the second signal using a programmable impedance element; and

generating the output signal by integrating the product.

26. The method of claim 25 wherein the programmable impedance element includes a plurality of resistors or a plurality of capacitors, the method further comprising:

supplying a control signal to the programmable impedance element; and

generating the product of the first signal and the second signal by varying an impedance of the programmable impedance element with time in response to the control signal.

27. The method of claim 21 wherein the correlating comprises:

converting the second signal to a current;

outputting the current and a control signal to a programmable impedance element comprising a current digital-to-analog converter having a programmable gain; and

changing an effective impedance of the current digital-to-analog converter with time by varying the programmable gain using the control signal to generate a product of the second signal and the first signal; and

integrating the product to generate the output signal.