Amplifier configured to provide substantially constant gain for wide input common mode range

An amplifier, comprising:

• an output circuit;
• a current source p-channel field effect transistor (PFET) including a gate coupled to the output circuit and configured to receive a first bias voltage;
• a pair of input differential PFETs including sources coupled to a drain of the current source PFET, drains coupled to the output circuit, and gates configured to receive positive and negative components of an input differential signal, respectively;
• a first pair of current source PFETs;
• a pair of input differential n-channel field effect transistors (NFETs) including drains coupled to the output circuit and to drains of the first pair of current source PFETs, respectively, and gates configured to receive the positive and negative components of the input differential signal, respectively;
• a current source NFET including a gate configured to receive a second bias voltage, and a drain coupled to sources of the pair of input differential NFETs, respectively;
• and
• a control circuit including an input coupled to the current source NFET and an output coupled to gates of the first pair of current source PFETs, respectively.

A method, comprising:

• amplifying an input differential signal using a first pair of input differential field effect transistor (FETs) to generate an output signal at an output circuit;
• amplifying the input differential signal using a second pair of input differential FETs to generate the output signal at the output circuit;
• sensing a current flowing into or out of the second pair of input differential FETs from or to a first current source, respectively;
• and
• controlling a pair of currents flowing out of or into the first pair of input differential FETs and into or out of a first pair of current sources based on the sensed current, respectively, to reduce currents flowing through the output circuit to or from the first pair of current sources.