Amplified charge cancellation in a touch sensor, and related systems, methods, and devices
A charge compensation circuit is disclosed that provides amplified charge cancellation. A touch controller is disclosed that includes such a charge compensation circuit and may realize improved immunity to baseline capacitance signals that are much larger than a change in capacitance due to proximity of an object. Such a charge compensation circuit may include a capacitor, a driver circuit arranged to apply a pulsed voltage signal to the capacitor, and a current conveyor having a programmable gain and arranged to amplify an initial charge generated by the capacitor in response to the pulsed voltage signal and provide an amplified charge to an output of the charge cancellation circuit.
1. A charge cancellation circuit, comprising:
a capacitor;
a driver circuit directly coupled to a first plate of the capacitor to apply a pulsed voltage signal to the capacitor; and
a current conveyor having a programmable gain, the current conveyor directly coupled to a second plate of the capacitor to amplify an initial charge generated by the capacitor in response to the pulsed voltage signal and provide the amplified initial charge to an output of the charge cancellation circuit.
2. The charge cancellation circuit of claim 1 , wherein the current conveyor comprises one of a positive output or a negative output.
3. The charge cancellation circuit of claim 2 , wherein the negative output is configured to invert a polarity of an output signal relative to a polarity of an input signal.
4. The charge cancellation circuit of claim 3 , wherein the positive output is configured to track a polarity of an output signal relative to a polarity of an input signal.
5. The charge cancellation circuit of claim 1 , wherein the output of the charge cancellation circuit is to provide the amplified initial charge to a touch sensor line.
6. A method of reducing charge transfer across a capacitor of a sense line of a touch sensing system, comprising:
pre-charging a touch sensor line to a first voltage rail;
injecting a first measurement charge at the touch sensor line;
amplifying a first cancellation charge;
injecting the amplified first cancellation charge at the touch sensor line;
pre-charging the touch sensor line to a second voltage rail;
injecting a second measurement charge at the touch sensor line;
amplifying a second cancellation charge;
injecting the amplified second cancellation charge at the touch sensor line; and
pre-charging the touch sensor line to the first voltage rail.
7. The method of claim 6 , wherein the injecting the first measurement charge or the second measurement charge at the touch sensor line comprises:
applying a first or a second measurement pulse at the touch sensor line to generate the first measurement charge or the second measurement charge.
8. The method of claim 6 , wherein the injecting the amplified first cancellation charge or the amplified second cancellation charge at the touch sensor line comprises:
applying a first or a second driver pulse at a compensation capacitor to generate the amplified first cancellation charge or the amplified second cancellation charge, respectively.
9. The method of claim 8 , comprising generating the first or the second driver pulse exhibiting voltage changes that track voltage changes exhibited by a measurement pulse generated for injecting the first measurement charge or the second measurement charge at the touch sensor line.
10. The method of claim 8 , comprising generating the first or the second driver pulse exhibiting voltage changes that track voltage changes exhibited by an inverted measurement pulse corresponding to a measurement pulse generated for injecting the first measurement charge or the second measurement charge at the touch sensor line.
11. A touch controller, comprising:
a pad;
a pre-charge circuit;
a measurement circuit; and
a charge cancellation circuit arranged to provide an amplified cancelation charge to a charge transfer path between the pad and the measurement circuit, wherein the charge cancellation circuit comprises:
a capacitor;
a driver circuit arranged to apply a pulsed voltage signal to the capacitor; and
a current conveyor having a programmable gain arranged to amplify an initial charge generated by the capacitor in response to the pulsed voltage signal and provide the amplified initial charge to an output of the charge cancellation circuit,
wherein an output of the charge cancellation circuit is operably coupled to provide the amplified initial charge to a signal path between the pad and the measurement circuit.
12. The touch controller of claim 11 , wherein the driver circuit is configured to generate a driver pulse exhibiting voltage changes that track voltage changes exhibited by a measurement pulse generated by the measurement circuit.
13. The touch controller of claim 11 , wherein the driver circuit is configured to generate a driver pulse exhibiting voltage changes that track voltage changes exhibited by an inverted measurement pulse corresponding to a measurement pulse generated by the measurement circuit.
14. The touch controller of claim 11 , wherein the output of the current conveyor is one of a negative output and a positive output.
15. The touch controller of claim 11 , comprising:
a first switch arranged to selectively couple the pre-charge circuit to the pad; and
a second switch arranged to selectively couple the measurement circuit and the charge cancellation circuit to the pad.