Cascaded active electro-magnetic interference filter

1. A circuit comprising:

a first amplifier having a reference input, an inverting input and an output, the inverting input of the first amplifier coupled to a conductor via alternating current (AC) coupling;

a compensation network coupled between the inverting input and the output of the first amplifier;

a voltage follower having a voltage follower input and a voltage follower output, the voltage follower including a second amplifier, the second amplifier having a non-inverting input, an inverting input, and an output, the inverting input of the second amplifier directly coupled to and tracks the voltage follower output, the output of the second amplifier coupled to the voltage follower output, and the non-inverting input of the second amplifier coupled to the output of the first amplifier via the voltage follower input, in which the voltage follower has a lower gain and a lower output impedance than the first amplifier; and

an injection network including a capacitor and a resistor coupled between the voltage follower output and the conductor.

2. The circuit of claim 1 , wherein the conductor is a first conductor, the compensation network is a first compensation network, and the circuit further comprises a second compensation network coupled between the first conductor and a second conductor.

3. The circuit of claim 2 , wherein the capacitor is a first capacitor, the resistor is a first resistor, and the second compensation network includes a second capacitor coupled in series with a second resistor between the first conductor and the second conductor.

4. The circuit of claim 3 , wherein the second compensation network further includes an inductor coupled in series with the second capacitor and the second resistor between the first and second conductors.

5. The circuit of claim 1 , wherein the compensation network is configured to provide negative feedback to the first amplifier.

6. The circuit of claim 1 , wherein the capacitor is a first capacitor, the resistor is a first resistor, and the compensation network comprises a second resistor and a second capacitor.

7. The circuit of claim 1 , wherein the resistor is a first resistor, and the voltage follower includes a second resistor coupled between the output of the second amplifier and the voltage follower output.

8. The circuit of claim 1 , wherein the resistor of the injection network is coupled between the capacitor and the inverting input of the second amplifier.

9. The circuit of claim 1 , wherein the first amplifier and the voltage follower are integrated on an integrated circuit.

10. A circuit comprising:

a sense amplifier having a reference input, an inverting input, and an output, the inverting input of the sense amplifier coupled to a conductor via AC coupling;

a compensation network coupled between the inverting input and the output of the sense amplifier;

a voltage follower having a voltage follower input and a voltage follower output, the voltage follower including an amplifier, the amplifier having a non-inverting input, an inverting input, and an output, the inverting input of the amplifier directly coupled to and tracks the voltage follower output, the output of the amplifier coupled to the voltage follower output, and the non-inverting input of the amplifier coupled to the output of the sense amplifier via the voltage follower input, in which the voltage follower has a lower gain and a lower output impedance than the sense amplifier, and

an injection network including a capacitor and a resistor coupled between the voltage follower output and the conductor.

11. The circuit of claim 10 , wherein the compensation network is a first compensation network, the conductor is a first conductor, and the circuit further comprises a second compensation network coupled between the first conductor and a second conductor.

12. The circuit of claim 11 , wherein the resistor is a first resistor, the capacitor is a first capacitor, and the second compensation network includes a second capacitor coupled in series with a second resistor between the first and second conductors.

13. The circuit of claim 12 , wherein the second compensation network further includes an inductor coupled in series with the second capacitor and the second resistor between the first and second conductors.

14. The circuit of claim 10 , wherein the resistor is a first resistor, the conductor is a first conductor, the compensation network is a first compensation network, the capacitor is a first capacitor, and the circuit further comprises a second compensation network coupled between the first conductor and a second conductor,

wherein the second compensation network includes a second capacitor coupled in series with a second resistor between the first conductor and the second conductor.

15. The circuit of claim 10 , wherein the compensation network is configured to provide negative feedback to the sense amplifier.

16. The circuit of claim 10 , wherein the sense amplifier and the voltage follower are integrated on an integrated circuit.

17. The circuit of claim 10 , wherein the resistor is a first resistor, and the voltage follower includes a second resistor coupled between the output of the amplifier and the voltage follower output.

18. The circuit of claim 10 , wherein the resistor of the injection network is coupled between the capacitor and the inverting input of the amplifier.

19. A circuit comprising:

a first amplifier having a reference input, an inverting input and an output, the inverting input of the first amplifier coupled to a conductor via AC coupling;

a compensation network coupled between the inverting input and the output of the first amplifier;

a voltage follower having a voltage follower input and a voltage follower output, the voltage follower including a second amplifier, the second amplifier having a non-inverting input, an inverting input, and an output, the inverting input of the second amplifier directly coupled to and tracks the voltage follower output, the output of the second amplifier coupled to the voltage follower output, and the non-inverting input of the second amplifier coupled to the output of the first amplifier via the voltage follower input, in which the voltage follower has a lower gain and a lower output impedance than the first amplifier; and

an injection network including a capacitor and a resistor coupled to the voltage follower output, the injection network configured to provide a cancellation signal.

20. The circuit of claim 19 , wherein the injection network is coupled to the conductor.

21. The circuit of claim 19 , wherein the compensation network is a first compensation network, the conductor is a first conductor, and the circuit further comprises a second compensation network coupled between the first conductor and a second conductor.

22. The circuit of claim 21 , wherein the capacitor is a first capacitor, the resistor is a first resistor, and the second compensation network includes a second capacitor coupled in series with a second resistor between the first and second conductors.

23. The circuit of claim 22 , wherein the second compensation network further includes an inductor coupled in series with the second capacitor and the second resistor between the first and second conductors.

24. The circuit of claim 19 , wherein the resistor is a first resistor, the conductor is a first conductor, the compensation network is a first compensation network, the capacitor is a first capacitor, and the circuit further comprises a second compensation network coupled between the first conductor and a second conductor,

wherein the second compensation network includes a second capacitor coupled in series with a second resistor between the first conductor and the second conductor.

25. The circuit of claim 19 , wherein the resistor is a first resistor, and the voltage follower includes a second resistor coupled between the output of the second amplifier and the voltage follower output.

26. The circuit of claim 19 , wherein the resistor of the injection network is coupled between the capacitor and the inverting input of the second amplifier.