Sensing evoked compound action potential (ECAP)
A system for providing therapy to a patient includes stimulation generation circuitry, sensing circuitry, and processing circuitry. The processing circuitry is configured to cause storage of a first voltage at a first terminal at a first calibration capacitor and storage of a second voltage at a second terminal at a second calibration capacitor. The processing circuitry is configured to switch out a first calibration switch to prevent the first voltage stored at the first calibration capacitor from changing and switch out a second calibration switch to prevent the second voltage stored at the second calibration capacitor from changing and determine, with the sensing circuitry, a sensing signal based on the first voltage offset by a first calibration voltage stored by the first capacitor and based on the second voltage offset by a second calibration voltage stored by the second capacitor.
1 . A system for providing therapy to a patient, the system comprising:
stimulation generation circuitry configured to provide electrical stimulation to the patient;
sensing circuitry configured to sense a first voltage at a first terminal and to sense a second voltage at a second terminal; and
processing circuitry electrically connected to the sensing circuitry and the stimulation generation circuitry, the processing circuitry being configured to:
in a first time, when the stimulation generation circuitry does not provide the electrical stimulation, cause storage of the first voltage at the first terminal at a first calibration capacitor and storage of the second voltage at the second terminal at a second calibration capacitor, wherein, in the first time, the first voltage stored at the first calibration capacitor is a first calibration voltage and the second voltage stored at the second calibration capacitor is a second calibration voltage;
in a second time, after the first calibration capacitor stores the first calibration voltage in the first time and the second calibration capacitor stores the second calibration voltage in the first time and when the stimulation generation circuitry provides the electrical stimulation, switch out a first calibration switch to prevent the first calibration voltage stored at the first calibration capacitor from changing and switch out a second calibration switch to prevent the second calibration voltage stored at the second calibration capacitor from changing;
in a third time after the second time, while the first calibration switch is switched out and the second calibration switch is switched out and when the stimulation generation circuitry does not provide the electrical stimulation, determine, with the sensing circuitry, a sensing signal based on a first signal acquisition voltage offset by a first offset voltage and based on a second signal acquisition voltage offset by a second offset voltage, wherein the first offset voltage is based on the first calibration voltage, and wherein the second offset voltage is based on the second calibration voltage; and
cause the stimulation generation circuitry to deliver the therapy to the patient based on the sensing signal.
2 . The system of claim 1 , further comprising amplifier circuitry configured to:
receive the sensing signal;
amplify, using a first stage amplifier and at least a second stage amplifier, the sensing signal to generate an amplified sensing signal; and
wherein the processing circuitry is configured to cause the stimulation generation circuitry to deliver the therapy based on the amplified sensing signal.
3 . The system of claim 2 , wherein to amplify, the first stage amplifier amplifies the sensing signal to a first amplified sensing signal for output to the second stage amplifier and wherein the amplifier circuitry further comprises a set of blanking switches configured to:
when the stimulation generation circuitry provides the electrical stimulation, block the first amplified sensing signal from being received at an input of the second stage amplifier; and
when the stimulation generation circuitry does not provide the electrical stimulation, allow the first amplified sensing signal to be received at the input of the second stage amplifier.
4 . The system of claim 3 , further comprising a set of switches configured to:
when the stimulation generation circuitry provides the electrical stimulation, block the sensing signal from being received at an input of the first stage amplifier; and
when the stimulation generation circuitry does not provide the electrical stimulation, allow the first amplified sensing signal to be received at the input of the first stage amplifier.
5 . The system of claim 4 ,
wherein, to block the sensing signal from being received at the input of the first stage amplifier, the set of switches is configured to block the sensing signal after a first time delay from when the stimulation generation circuitry no longer provides the electrical stimulation; and
wherein, to block the first amplified sensing signal from being received at the input of the second stage amplifier, the set of blanking switches is configured to block the sensing signal after a second time delay from when the stimulation generation circuitry no longer provides the electrical stimulation, wherein the second time delay is different from the first time delay.
6 . The system of claim 5 , wherein the second time delay is longer than the first time delay.
7 . The system of claim 3 , further comprising a set of blanking switches configured to clamp a voltage of the sensing signal to a threshold voltage range.
8 . The system of claim 7 , wherein the threshold voltage range comprises a component safe voltage range.
9 . The system of claim 2 , wherein the first stage amplifier comprises a transconductance amplifier.
10 . The system of claim 2 , wherein the second amplifier stage is configured to auto-zero at input and comprises a direct transconductance amplifier.
11 . The system of claim 10 , wherein the amplifier circuitry comprises a third amplifier stage configured to receive an output of the second amplifier stage and to auto-zero at input, wherein the third amplifier stage comprises a linearized transconductance amplifier.
12 . The system of claim 11 , wherein the amplifier circuitry comprises a fourth amplifier stage configured to receive an output of the third amplifier stage and to auto-zero at input.
13 . The system of claim 9 , wherein the processing circuitry is further configured to:
when the stimulation generation circuitry provides the electrical stimulation, block the first amplified sensing signal from being received at an input of the second stage amplifier; and
when the stimulation generation circuitry does not provide the electrical stimulation, allow the first amplified sensing signal to be received at the input of the second stage amplifier.
14 . The system of claim 2 , further comprising injection circuitry configured to inject a cancelling offset between the first stage amplifier and the second stage of amplifier.
15 . The system of claim 14 , wherein the injection circuitry is further configured to generate the cancelling offset based on a weighted set of digital historical offsets of waveforms.
16 . The system of claim 15 , wherein the processing circuitry is configured to determine the weighted set of digital historical offsets of waveforms based on one or more previous sensing signals that occur before the sensing signal.
17 . The system of claim 15 , wherein the injection circuitry is further configured to generate the cancelling offset by applying an integral controller on the weighted set of digital historical offsets of waveforms.
18 . The system of claim 1 , wherein the processing circuitry is configured to:
generate a waveform based on the sensing signal;
perform a derivative operation on the waveform;
after performing the derivative operation, apply a peak minus trough operation to the waveform to determine an amplitude value; and
cause the stimulation generation circuitry to deliver the therapy based on the amplitude value.
19 . A method comprising:
in a first time, when stimulation generation circuitry does not provide electrical stimulation, causing, by processing circuitry, storage of a first voltage at a first terminal of sensing circuitry at a first calibration capacitor and causing, by the processing circuitry, storage of a second voltage at a second terminal of the sensing circuitry at a second calibration capacitor, wherein, in the first time, the first voltage stored at the first calibration capacitor is a first calibration voltage and the second voltage stored at the second calibration capacitor is a second calibration voltage;
in a second time, after the first calibration capacitor stores the first calibration voltage in the first time and the second calibration capacitor stores the second calibration voltage in the first time and when the stimulation generation circuitry provides the electrical stimulation, switching out, by the processing circuitry, a first calibration switch to prevent the first calibration voltage stored at the first calibration capacitor from changing and switching out, by the processing circuitry, a second calibration switch to prevent the second calibration voltage stored at the second calibration capacitor from changing;
in a third time after the second time, while the first calibration switch is switched out and the second calibration switch is switched out and when the stimulation generation circuitry does not provide the electrical stimulation, determining, by the processing circuitry, a sensing signal based on a first signal acquisition voltage offset by a first offset voltage and based on a second signal acquisition voltage offset by a second offset voltage, wherein the first offset voltage is based on the first calibration voltage, and wherein the second offset voltage is based on the second calibration voltage; and
causing, by the processing circuitry, the stimulation generation circuitry to deliver therapy to a patient based on the sensing signal.
20 . A medical device comprising:
stimulation generation circuitry configured to provide electrical stimulation to a patient;
sensing circuitry configured to sense a first voltage at a first terminal and to sense a second voltage at a second terminal; and
processing circuitry electrically connected to the sensing circuitry and the stimulation generation circuitry, the processing circuitry being configured to:
in a first time, when the stimulation generation circuitry does not provide the electrical stimulation, cause storage of the first voltage at the first terminal at a first calibration capacitor and cause storage of the second voltage at the second terminal at a second calibration capacitor, wherein, in the first time, the first voltage stored at the first calibration capacitor is a first calibration voltage and the second voltage stored at the second calibration capacitor is a second calibration voltage;
in a second time, after the first calibration capacitor stores the first calibration voltage in the first time and the second calibration capacitor stores the second calibration voltage in the first time and when the stimulation generation circuitry provides the electrical stimulation, switch out a first calibration switch to prevent the first calibration voltage stored at the first calibration capacitor from changing and switch out a second calibration switch to prevent the second calibration voltage stored at the second calibration capacitor from changing;
in a third time after the second time, while the first calibration switch is switched out and the second calibration switch is switched out and when the stimulation generation circuitry does not provide the electrical stimulation, determine, with the sensing circuitry, a sensing signal based on a first signal acquisition voltage offset by a first offset voltage and based on a second signal acquisition voltage offset by a second offset voltage, wherein the first offset voltage is based on the first calibration voltage, and wherein the second offset voltage is based on the second calibration voltage; and
cause the stimulation generation circuitry to deliver therapy to the patient based on the sensing signal.