Reference noise rejection improvement based on sample and hold circuitry
A touch controller may include a measurement circuit, configured to receive a signal from an active channel in a proximity sensor, and to sample and hold the signal to measure the signal. The touch controller may include a driven shield buffer. The touch controller may include a voltage reference circuit configured to generate a divided voltage reference, provide the divided voltage reference to the measurement circuit, and drive the divided voltage reference through a switched circuit to the driven shield buffer to hold channels in the proximity sensor during measurement of the active channel.
1. A touch controller comprising:
a measurement circuit, configured to:
receive a signal from an active channel in a proximity sensor; and
sample and hold the signal to measure the signal;
a driven shield buffer; and
a voltage reference circuit, configured to:
generate a divided voltage reference;
provide the divided voltage reference to the measurement circuit; and
drive the divided voltage reference through a switched circuit to the driven shield buffer to hold channels in the proximity sensor during measurement of the active channel, wherein:
the switched circuit includes a first switch, a second switch, a first capacitor, and a second capacitor; and
the switched circuit is configured to, in a second phase of operation:
alternatively activate the first switch and the second switch to drive the divided voltage reference through the first capacitor and the second capacitor to generate a channel voltage reference to hold the channels in the proximity sensor; and
during each successive cycle, drive an equivalent amount of total charge from the first capacitor and the second capacitor to the held channels.
2. The touch controller of claim 1 , wherein the switched circuit is configured to, in a first phase of operation, activate the first switch and the second switch to charge the second capacitor according to the divided voltage reference.
3. The touch controller of claim 1 , wherein the switched circuit is configured to, in a second phase of operation, alternatively activate the first switch and the second switch to drive the divided voltage reference through the first capacitor and the second capacitor to generate a channel voltage reference to hold the channels in the proximity sensor.
4. The touch controller of claim 1 , wherein driving the divided voltage reference through the switched circuit is configured to reduce noise originating from a voltage supply powering the divided voltage reference.
5. The touch controller of claim 1 , wherein the divided voltage reference is a mid-analog supply voltage.
6. A voltage reference circuit, comprising:
a power supply input connected to a resistive network;
a first switch;
a second switch connected to the first switch and to a midpoint of the resistive network;
a first capacitor connected to a point between the first switch and the second switch;
a second capacitor connected to the first capacitor and to the first switch; and
a switch control signal configured to drive a divided voltage reference from the midpoint of the resistive network through the first switch, second switch, first capacitor, and second capacitor to hold channels of a proximity sensor during measurement of an active channel of the proximity sensor;
wherein the switch control signal is configured to, in a second phase of operation:
alternatively activate the first switch and the second switch to drive the divided voltage reference through the first capacitor and the second capacitor to generate a channel voltage reference to hold the channels in the proximity sensor; and
during each successive cycle, drive an equivalent amount of total charge from the first capacitor and the second capacitor to the held channels.
7. The voltage reference circuit of claim 6 , further comprising an output for the divided voltage reference to a measurement circuit.
8. The voltage reference circuit of claim 6 , wherein the switch control signal is configured to, in a first phase of operation, activate the first switch and the second switch to charge the second capacitor according to the divided voltage reference.
9. The voltage reference circuit of claim 6 , wherein the switch control signal is configured to, in a second phase of operation, alternatively activate the first switch and the second switch to drive the divided voltage reference through the first capacitor and the second capacitor to generate a channel voltage reference to hold the channels in the proximity sensor.
10. The voltage reference circuit of claim 6 , wherein driving the divided voltage reference through the switched circuit is configured to reduce noise originating from a voltage supply powering the resistive network.
11. The voltage reference circuit of claim 6 , wherein the midpoint of the resistive network is a mid-analog supply voltage.
12. A method, comprising:
receiving a signal from an active channel in a proximity sensor;
sampling and holding the signal to measure the signal;
generating a divided voltage reference;
providing the divided voltage reference to a measurement circuit configured to perform the steps of sampling and holding the signal to measure the signal;
driving the divided voltage reference through a switched circuit to a driven shield buffer to hold channels in the proximity sensor during measurement of the active channel;
in a second phase of operation of the switched circuit, alternatively activating the first switch and the second switch to drive the divided voltage reference through a first capacitor and the second capacitor to generate a channel voltage reference to hold the channels in the proximity sensor; and
in the second phase of operation of the switched circuit, during each successive cycle, driving an equivalent amount of total charge from the first capacitor and the second capacitor to the held channels.
13. The method of claim 12 , further comprising, in a first phase of operation of the switched circuit, activating a first switch and the second switch to charge a second capacitor according to the divided voltage reference.
14. The method of claim 12 , wherein driving the divided voltage reference through the switched circuit reduces noise originating from a voltage supply powering the divided voltage reference.