Touch sensor compensation circuit
An apparatus includes an integrator circuit, a compensation circuit, and a sense circuit. The compensation circuit applies a positive charge and a negative charge to the integrator circuit during a first time period and a second time period respectively. The integrator circuit integrates a signal and the positive charge to produce a first sense signal. The signal is based on a charge at an electrode of a touch sensor. The integrator circuit integrates the signal and the negative charge to produce a second sense signal. The sense circuit detects a touch based on the first sense signal and the second sense signal.
1. An apparatus comprising:
an integrator circuit;
a compensation circuit distinct from and coupled to the integrator circuit, the compensation circuit comprising:
a driver;
a resistor coupled in series with the driver;
a capacitor coupled in series with the resistor; and
a demultiplexer coupled in series with the capacitor,
the driver operable to:
drive, during a first time period, a positive charge through the resistor, capacitor, and demultiplexer to the integrator circuit, the integrator circuit operable to integrate a signal and the positive charge to produce a first sense signal, the signal based on a charge at an electrode of a touch sensor; and
drive, during a second time period, a negative charge through the resistor, capacitor, and demultiplexer to the integrator circuit, the integrator circuit further operable to integrate the signal and the negative charge to produce a second sense signal; and
a sense circuit operable to detect a touch based on the first sense signal and the second sense signal.
2. The apparatus of claim 1 , wherein the resistor is a variable resistor.
3. The apparatus of claim 1 , wherein the capacitor is a variable capacitor.
4. The apparatus of claim 1 , wherein the driver uses a ground based reference voltage as a supply to remove an effect of drift in a main supply voltage.
5. The apparatus of claim 1 , wherein an output of the demultiplexer is coupled to the integrator circuit, an input of the demultiplexer is coupled to the capacitor.
6. The apparatus of claim 1 , wherein an output of the demultiplexer is coupled to a current amplifier circuit, an input of the demultiplexer is coupled to the capacitor.
7. The apparatus of claim 1 , wherein an output of the demultiplexer is coupled to a built-in self-test bus, an input of the demultiplexer is coupled to the capacitor.
8. The apparatus of claim 1 further comprising a current amplifier circuit coupled to the integrator circuit and the compensation circuit.
9. The apparatus of claim 1 further comprising a built-in self-test bus coupled to the compensation circuit.
10. A device comprising:
a touch sensor array;
an integrator circuit;
a compensation circuit distinct from and coupled to the integrator circuit, the compensation circuit comprising:
a driver;
a resistor coupled in series with the driver;
a capacitor coupled in series with the resistor; and
a demultiplexer coupled in series with the capacitor,
the driver operable to:
drive, during a first time period, a positive charge through the resistor, capacitor, and demultiplexer to the integrator circuit, the integrator circuit operable to integrate a signal and the positive charge to produce a first sense signal, the signal based on a charge at an electrode of the touch sensor array; and
drive, during a second time period, a negative charge through the resistor, capacitor, and demultiplexer to the integrator circuit, the integrator circuit further operable to integrate the signal and the negative charge to produce a second sense signal; and
a sense circuit operable to detect a touch based on the first sense signal and the second sense signal.
11. The device of claim 10 , wherein the resistor is a variable resistor.
12. The device of claim 10 , wherein the capacitor is a variable capacitor.
13. The device of claim 10 , wherein the driver uses a ground based reference voltage as a supply to remove an effect of drift in a main supply voltage.
14. The device of claim 10 , wherein an output of the demultiplexer is coupled to the integrator circuit, an input of the demultiplexer is coupled to the capacitor.
15. The device of claim 10 , wherein an output of the demultiplexer is coupled to a current amplifier circuit, an input of the demultiplexer is coupled to the capacitor.
16. The device of claim 10 , wherein an output of the demultiplexer is coupled to a built-in self-test bus, an input of the demultiplexer is coupled to the capacitor.
17. The device of claim 10 , further comprising a current amplifier circuit coupled to the integrator circuit and the compensation circuit.
18. The device of claim 10 , further comprising a built-in self-test bus coupled to the compensation circuit.