Physiological sensors with combined signal outputs

1 . A device for measuring voltage signals comprising:

a physiological sensor comprising a plurality of sensing electrodes;

a signal combining chip comprising:

a plurality of input channels configured to receive a plurality of voltage signals from the plurality of sensing electrodes, wherein each input channel of the plurality of input channels is configured to receive a corresponding voltage signal of the plurality of voltage signals from a corresponding sensing electrode of the plurality of sensing electrodes;

a waveform generator configured to generate a set of modulation signals, wherein each of the set of modulation signals is applied to a corresponding voltage signal of the plurality of voltage signals to generate a corresponding encoded voltage signal of a set of encoded voltage signals;

a summing circuit configured to superimpose the set of encoded voltage signals to form a combined voltage signal; and

an output channel configured to output the combined voltage signal; and

a signal processing chip communicably coupled to the signal combining chip, the signal processing comprising:

a receiving channel configured to receive the combined voltage signal as an input; and

an analog-to-digital converter configured to digitize the combined voltage signal.

2 . The device of claim 1 , wherein each of the set of modulation signals alternates between zero amplitude in a first state and a non-zero amplitude in a second state according to a common modulation frequency and a different phase.

3 . The device of claim 1 , wherein:

the plurality of voltage signals comprises a first voltage signal and a second voltage signal;

the set of modulation signals comprises a first modulation signal that is applied to the first voltage signal and a second modulation signal that is applied to the second voltage signal;

the first modulation signal modulates, during a measurement window, the first voltage signal with a first non-zero amplitude at a first state to form a first encoded voltage signal; and

the second modulation signal modulates, during the measurement window, the second voltage signal with a second non-zero amplitude at a second state to form a second encoded voltage signal, such that the combined voltage signal corresponds during the measurement window to a differential voltage signal between the first encoded voltage signal and the second encoded voltage signal.

4 . The device of claim 1 , wherein the signal combining chip further comprises:

a controller configured to select a set of voltage signals from the plurality of voltage signals and control the waveform generator to select the set of modulation signals based on the selected set of voltage signals.

5 . The device of claim 1 , wherein the signal combining chip further comprises: a digital interface driver configured to receive one or more control signals through a control channel.

6 . The device of claim 1 , wherein the signal combining chip further comprises a buffer positioned between the summing circuit and the output channel.

7 . The device of claim 1 , wherein the signal combining chip further comprises an active low pass filter electrically coupled to a respective input channel.

8 . The device of claim 1 , wherein the signal combining chip further comprises a reference clock input configured to receive a timing signal that is used by the waveform generator to generate the set of modulation signals.

9 . A method of processing a plurality of voltage signals received from a plurality of sensing electrodes of a physiological sensor, the method comprising:

receiving, at a signal combining chip, a plurality of voltage signals that are measured by the plurality of sensing electrodes, wherein each voltage signal of the plurality of voltage signals is measured by a corresponding sensing electrode of the plurality of sensing electrodes;

selecting, with a scan controller associated with the signal combining chip, a set of voltage signals from the plurality of voltage signals;

generating, using a waveform generator in the signal combining chip, a set of modulation signals corresponding to the selected set of voltage signals;

applying each modulation signal of the set of modulation signals to a corresponding selected voltage signal to form a corresponding encoded voltage signal of a set of encoded voltage signals;

superimposing the set of encoded voltage signals, using a summing circuit, to form a combined voltage signal;

outputting, at an output channel of the signal combining chip, the combined voltage signal

receiving, through a receiving channel at a signal processing chip communicably coupled to the signal combining chip, the combined voltage signal;

digitizing, using an analog-to-digital converter at the signal processing chip, the combined voltage signal to generate a digital combined signal; and

demodulating the digital combined signal to generate a corresponding digital signal for each of the plurality of voltage signals received from the plurality of sensing electrodes of the physiological sensor.

10 . The method of claim 9 , further comprising:

buffering the combined voltage signal before outputting the combined voltage.

11 . The method of claim 9 , wherein each of the set of modulation signals alternates between zero amplitude in a first state and a non-zero amplitude in a second state according to a common modulation frequency and a different phase.

12 . The method of claim 9 , wherein the combined voltage signal comprises, during a first measurement window, a differential voltage signal between a first selected voltage signal and a second selected voltage signal.

13 . The method of claim 9 , wherein selecting one or more of the plurality of voltage signals further comprises assigning a weighted duty cycle to a respective one of the selected voltage signals.

14 . The method of claim 9 , further comprising:

receiving one or more control signals through a control input channel.

15 . The method of claim 14 , further comprising:

changing a duty cycle of at least one of the set of modulation signals based on the received one or more control signals.

16 . The method of claim 9 , further comprising:

receive a timing signal that is used to generate the set of modulation signals.

17 . The method of claim 9 , further comprising:

generating the set of modulation signals such that set of modulation signals collectively has a 100% duty cycle.

18 . A device for measuring voltage signals comprising:

a physiological sensor comprising a plurality of sensing electrodes; and

a signal combining chip comprising:

a plurality of input channels configured to receive a plurality of voltage signals from the plurality of sensing electrodes, wherein each input channel of the plurality of input channels is configured to receive a corresponding voltage signal of the plurality of voltage signals from a corresponding sensing electrode of the plurality of sensing electrodes;

a waveform generator configured to generate a set of modulation signals, wherein each of the set of modulation signals is applied to a corresponding voltage signal of the plurality of voltage signals to generate a corresponding encoded voltage signal of a set of encoded voltage signals; and

a summing circuit configured to superimpose the set of encoded voltage signals to form a combined voltage signal;

a digital interface driver configured to receive one or more control signals through a control channel; and

an output channel configured to output the combined voltage signal.

19 . The device of claim 18 , wherein the signal combining chip is configured to change a duty cycle of at least one of the set of modulation signals based on the received one or more control signals.

20 . The device of claim 18 , wherein the signal combining chip further comprises:

a controller configured to select a set of voltage signals from the plurality of voltage signals and control the waveform generator to select the set of modulation signals based on the selected set of voltage signals.