Chopper-stabilized amplifier

1. A chopper-stabilized amplifier comprising:

a main amplifier including a primary input configured to receive an inner input signal from a first path and an auxiliary input configured to receive a compensation signal from a second path;

a first mux-interface circuit in the first path configured to limit the inner input signal received at the primary input of the main amplifier;

a chopper amplifier circuit in the second path configured to receive the inner input signal from the first path and to output the compensation signal to the auxiliary input;

a second mux-interface circuit in the second path configured to couple and decouple the chopper amplifier circuit to and from the first path; and

a slew-detector circuit coupled to the first path and configured to:

detect that the inner input signal is in a slew condition; and

transmit, in response to the detection, a slew signal to configure the second mux-interface circuit to decouple the second path from the first path while the inner input signal is in the slew condition.

2. The chopper-stabilized amplifier according to claim 1 , wherein the first mux-interface circuit is configured to:

receive an input signal at an input to the chopper-stabilized amplifier and output the inner input signal to the primary input of the main amplifier; and

limit an input voltage of the input signal without increasing an input current at the input.

3. The chopper-stabilized amplifier according to claim 2 , wherein the input signal received at the input is in a high-voltage domain.

4. The chopper-stabilized amplifier according to claim 1 , wherein the second mux-interface circuit blocks a low-impedance path between an inner input of the chopper-stabilized amplifier and the chopper amplifier circuit while the inner input signal is in the slew condition.

5. The chopper-stabilized amplifier according to claim 1 , wherein the slew-detector circuit is configured to:

output a slew signal (SLEW) at a first level when the inner input signal is outside a window of a window floating comparator, the first level indicating the slew condition, wherein the slew signal at the first level controls the second mux-interface circuit to decouple the chopper amplifier circuit from the first path; and

output the slew signal (SLEW) at a second level when the inner input signal is within the window of the window floating comparator, the second level indicating a non-slew condition, wherein the slew signal at the second level controls the second mux-interface circuit to couple the chopper amplifier circuit to the first path.

6. The chopper-stabilized amplifier according to claim 5 , wherein the slew-detector circuit is configured to:

sense a positive inner node voltage (VINTP) and a negative inner node voltage (VINTN) of the inner input signal to generate a lower-supply voltage (VSL) of the window floating comparator, the first level being the lower-supply voltage (VSL); and

generate a higher-supply voltage (VSH) relative to the lower-supply voltage (VSL) so that the higher-supply voltage (VSH) is greater than the lower-supply voltage (VSL) by a fixed voltage, the second level being the higher-supply voltage (VSH).

7. The chopper-stabilized amplifier according to claim 6 , wherein the lower-supply voltage (VSL) is a minimum voltage of the positive inner node voltage (VINTP) and the negative inner node voltage (VINTN) of the inner input signal.

8. The chopper-stabilized amplifier according to claim 1 , wherein the chopper amplifier circuit includes:

a first chopper coupled to the second mux-interface circuit, the first chopper configured to receive the inner input signal and to output a modulated signal;

a null amplifier coupled to the first chopper, the null amplifier configured to receive the modulated signal and to output an amplified-modulated signal;

a second chopper coupled to the null amplifier, the second chopper configured to receive the amplified-modulated signal and output a demodulated signal; and

a notch filter coupled to the second chopper, the notch filter configured to receive the demodulated signal and to output a filtered demodulated signal as the compensation signal.

9. The chopper-stabilized amplifier according to claim 8 , wherein the second mux-interface circuit blocks an input current from being conducted by the first chopper while the inner input signal is in the slew condition.

10. The chopper-stabilized amplifier according to claim 1 , wherein the slew-detector circuit includes:

a minimum voltage selector circuit coupled to the first path, the minimum voltage selector circuit configured to:

receive the inner input signal from the first path; and

output a lower-supply voltage (VSL) based on a minimum of a positive inner node voltage (VINTP) and a negative inner node voltage (VINTN) of the inner input signal;

a floating-supply circuit coupled to the minimum voltage selector circuit, the floating-supply circuit configured to:

generate a higher-supply voltage (VSH) at a fixed voltage above the lower-supply voltage (VSL); and

output the higher-supply voltage (VSH) and the lower-supply voltage (VSL); and

a window floating comparator coupled to the floating-supply circuit and the first path, the window floating comparator configured to:

compare the inner input signal from the first path to a voltage window; and

output a slew signal based on the comparison, the slew signal controlling the second mux-interface circuit.

11. The chopper-stabilized amplifier according to claim 10 , wherein the minimum voltage selector circuit includes:

a first Schottky diode coupled at a first cathode to a positive inner voltage (VINTP) of the first path; and

a second Schottky diode coupled at a second cathode to a negative inner voltage (VINTN) of the first path, a first anode of the first Schottky diode coupled to a second anode of the second Schottky diode to output a lower supply voltage (VSL) based on a minimum of the positive inner voltage (VINTP) and the negative inner voltage (VINTN).

12. The chopper-stabilized amplifier according to claim 1 , further including a settling-enhancer circuit that is controlled by the slew-detector circuit, the settling-enhancer circuit enabled by the slew-detector circuit to prevent a voltage in the chopper amplifier circuit from changing while the inner input signal is in the slew condition.

13. The chopper-stabilized amplifier according to claim 12 , wherein the settling-enhancer circuit is coupled to an input of a notch filter of the chopper amplifier circuit and to an output of the notch filter of the chopper amplifier circuit, the settling-enhancer circuit configured by a slew signal generated by the slew-detector circuit to hold the input of the notch filter and the output of the notch filter at a reference voltage.

14. The chopper-stabilized amplifier according to claim 13 , further including an analog-level shifter coupled between the slew-detector circuit and the settling-enhancer circuit, the analog-level shifter configured to convert the slew signal from a floating voltage domain to a fixed voltage domain.

15. A multiplexed measurement system comprising:

a multiplexer configured to couple a plurality of measurements to an output; and

a chopper-stabilized amplifier configured to receive an input signal from the output of the multiplexer, the chopper-stabilized amplifier including:

a first mux-friendly interface circuit configured to receive the input signal and to output an inner input signal to a first path, the first mux-friendly interface circuit further configured to limit an input voltage of the input signal without increasing an input current of the input signal;

a main amplifier including a primary input configured to receive the inner input signal from the first path and an auxiliary input configured to receive a compensation signal from a second path;

a chopper amplifier circuit in the second path configured to receive the inner input signal from the first path and to output the compensation signal to the auxiliary input;

a second mux-friendly interface circuit in the second path configured to couple and decouple the chopper amplifier circuit to and from the first path; and

a slew-detector circuit coupled to the first path and configured to detect that the inner input signal is in a slew condition and transmit, in response to the detection, a slew signal to configure the second mux-friendly interface circuit to decouple the second path from the first path while the input signal is in the slew condition.

16. The multiplexed measurement system according to claim 15 , wherein the second mux-friendly interface circuit blocks a low-impedance path between an input of the chopper-stabilized amplifier and the chopper amplifier circuit to reduce an in-rush of input current to the chopper-stabilized amplifier during the slew condition.

17. The multiplexed measurement system according to claim 15 , wherein the slew-detector circuit includes a window floating comparator configured to determine if an inner-input signal is within a voltage window to detect the slew condition.

18. The multiplexed measurement system according to claim 17 , wherein the slew-detector circuit includes:

a minimum voltage selector circuit coupled to the first path, the minimum voltage selector circuit configured to:

output a lower-supply voltage (VSL);

a floating-supply circuit coupled to the minimum voltage selector circuit, the floating-supply circuit configured to:

generate a higher-supply voltage (VSH) at a fixed voltage above the lower-supply voltage (VSL); and

the window floating comparator coupled to the floating-supply circuit.

19. The multiplexed measurement system according to claim 15 ,

wherein the chopper amplifier circuit includes:

a first chopper coupled to the second mux-friendly interface circuit;

a null amplifier coupled to the first chopper;

a second chopper coupled to the null amplifier; and

a notch filter coupled to the second chopper.

20. The multiplexed measurement system according to claim 19 ,

wherein the slew signal configures the second mux-friendly interface circuit to block the input current from being conducted by the first chopper.