Apparatus and methods for amplifier input protection

An amplifier comprising:

• a non-inverting input terminal and an inverting input terminal;
• an amplification circuit comprising a non-inverting input and an inverting input;
• an input protection circuit comprising a first input electrically connected to the non-inverting input terminal, a second input electrically connected to the inverting input terminal, a first output electrically connected to the non-inverting input of the amplification circuit, and a second output electrically connected to the inverting input of the amplification circuit, wherein the input protection circuit comprises:
• a first field effect transistor (FET) including a source electrically connected to the first input and a drain electrically connected to the first output;
• a second FET including a source electrically connected to the second input and a drain electrically connected to the second output;
• a first clamp electrically connected to the first output, wherein the first clamp is configured to activate to generate a first clamp current in response to a first overvoltage condition;
• a first current mirror configured to mirror the first clamp current to generate a first mirrored current;
• a third FET electrically connected between the gate and the source of the first FET, wherein the third FET is configured to receive the first mirrored current;
• a second clamp electrically connected to the second output, wherein the second clamp is configured to activate to generate a second clamp current in response to a second overvoltage condition;
• a second current mirror configured to mirror the second clamp current to generate a second mirrored current;
• and
• a fourth FET electrically connected between the gate and the source of the second FET, wherein the fourth FET is configured to receive the second mirrored current.

A method of protecting an amplification circuit having a first input electrically connected to a first input terminal via a channel of a first FET and having a second input electrically connected to a second input terminal via a channel of a second FET, the method comprising:

• activating a first clamp in response to a first overvoltage condition;
• mirroring a first clamp current through the first clamp to generate a first mirrored current using a first current mirror;
• increasing a channel impedance of the first FET in response to the first mirrored current using a third FET;
• activating a second clamp in response to a second overvoltage condition;
• mirroring a second clamp current through the second clamp to generate a second mirrored current using a second current mirror;
• and
• increasing a channel impedance of the second FET in response to the second mirrored current using a fourth FET.