Input boosting for chopped neural recording systems
Described herein is a front-end for a neural recording system that boosts input impedance of the front-end circuit. The front-end includes an amplifier and two choppers. A first input terminal of the first chopper may be coupled to a first output terminal from one or more signal sensors. A first input terminal of the second chopper may be coupled to a second output terminal from the signal sensors. A second input terminal of the first chopper may be coupled to a first output terminal of a feedback subsystem. A second input terminal of the second chopper may be coupled to a second output terminal of the feedback subsystem. The output terminals of each chopper may each be coupled to a different capacitor such that after switching, the voltage of each capacitor remains substantially the same, improving the input impedance of the circuit.
1. A front-end for a neural recording system, the front-end comprising:
a sensor comprising first and second sensor output terminals;
a feedback subsystem comprising first and second feedback output terminals;
a first chopper comprising first and second input terminals, and first and second output terminals, wherein:
the first input terminal of the first chopper is electrically coupled to the first sensor output terminal,
the second input terminal of the first chopper is electrically coupled to the first feedback output terminal,
a second chopper comprising first and second input terminals, and first and second output terminals, wherein:
the first input terminal of the second chopper is configured to be electrically coupled to the second sensor output terminal,
the second input terminal of the second chopper is configured to be electrically coupled to the second feedback output terminal;
an amplifier comprising first and second amplifier input terminals;
a first capacitor coupled to the first output terminal of the first chopper and the first amplifier input terminal;
a second capacitor coupled to the second output terminal of the first chopper and the second amplifier input terminal;
a third capacitor coupled to the first output terminal of the second chopper and the second amplifier input terminal; and
a fourth capacitor coupled to the second output terminal of the second chopper and the first amplifier input terminal;
wherein the first and second choppers are configured to operate in a first phase and a second phase, wherein:
during the first phase:
the first sensor output terminal, the second feedback output terminal, and the first and fourth capacitors are in electrical communication with the first amplifier input terminal, and
the second sensor output terminal, the first feedback output terminal, and the second and third capacitors are in electrical communication with the second amplifier input terminal; and
during the second phase:
the first sensor output terminal, the second feedback output terminal, and the second and third capacitors are in electrical communication with the second amplifier input terminal, and
the second sensor output terminal, the first feedback output terminal, and the first and fourth capacitors are in electrical communication with the first amplifier input terminal.
2. The front-end for the neural recording system of claim 1 , further comprising:
a first coupling capacitor electrically coupled between the first input terminal of the first chopper and the first sensor output terminal; and
a second coupling capacitor electrically coupled between the first input terminal of the second chopper and the second sensor output terminal.
3. The front-end for the neural recording system of claim 1 , wherein at least one of the first capacitor, the second capacitor, the third capacitor, or the fourth capacitor comprises a capacitor array.
4. The front-end for the neural recording system of claim 1 , wherein the first capacitor and the third capacitor form a first capacitor pair, and the second capacitor and the fourth capacitor form a second capacitor pair, and wherein the first and third capacitors each have a first capacitance, the second and fourth capacitors each have a second capacitance, and wherein the first capacitance is different from the second capacitance.
5. The front-end for the neural recording system of claim 1 , wherein the amplifier comprises at least one amplifier output terminal and wherein the at least one amplifier output terminal is electrically coupled to an input terminal of the feedback subsystem.
6. The front-end for the neural recording system of claim 1 , wherein the sensor is configured to measure a response signal from a nerve of a patient.
7. The front-end for the neural recording system of claim 1 , further comprising a common mode (“CM”) sensing circuit having a CM output, and first and second summing circuits, wherein:
a first input of the first summing circuit is coupled to the first feedback output terminal;
a second input of the first summing circuit is coupled to the CM output; and
an output of the first summing circuit is coupled to the second input of the first chopper;
a first input of the second summing circuit is coupled to the second feedback output terminal;
a second input of the second summing circuit is coupled to the CM output; and
an output of the second summing circuit is coupled to the second input of the second chopper.
8. A method comprising:
providing the front-end for the neural recording system according to claim 1 ;
coupling the sensor to a patient; and
measuring a neural response of the patient using the front-end for the neural recording system.
9. The method of claim 8 , wherein the front-end for the neural recording system further comprises:
a first coupling capacitor electrically coupled between the first input terminal of the first chopper and the first sensor output terminal; and
a second coupling capacitor electrically coupled between the first input terminal of the second chopper and the second sensor output terminal.
10. The method of claim 8 , wherein at least one of the first capacitor, the second capacitor, the third capacitor, or the fourth capacitor comprises a capacitor array.
11. The method of claim 8 , wherein the first capacitor and the third capacitor form a first capacitor pair, and the second capacitor and the fourth capacitor form a second capacitor pair, and wherein the first and third capacitors each have a first capacitance, the second and fourth capacitors each have a second capacitance, and wherein the first capacitance is different from the second capacitance.
12. The method of claim 8 , wherein the amplifier comprises at least one amplifier output terminal and wherein the at least one amplifier output terminal is electrically coupled to an input terminal of the feedback subsystem.
13. The method of claim 8 , wherein the sensor is configured to measure a response signal from a nerve of a patient.
14. The method of claim 8 , wherein the front-end for the neural recording system further comprises a common mode (“CM”) sensing circuit having a CM output, and first and second summing circuits, wherein:
a first input of the first summing circuit is coupled to the first feedback output terminal;
a second input of the first summing circuit is coupled to the CM output; and
an output of the first summing circuit is coupled to the second input of the first chopper;
a first input of the second summing circuit is coupled to the second feedback output terminal;
a second input of the second summing circuit is coupled to the CM output; and
an output of the second summing circuit is coupled to the second input of the second chopper.