Class-ab radio frequency amplifier for envelope detector

A class-AB voltage amplifier comprising:

• complementary first and second transistors to provide a negative radio frequency (RF) output at interconnected drains;
• complementary third and fourth transistors to provide a positive RF output at interconnected drains;
• where a positive RF input is coupled with gates of the first and second transistors and a negative RF input is coupled with gates of the third and fourth transistors;
• a fifth transistor to provide a positive bias voltage to the first and third transistors;
• a sixth transistor to provide a negative bias voltage to the second and fourth transistors;
• and
• a feedback circuit connected to the fifth and sixth transistors and to the differential positive and negative RF outputs, the feedback circuit configured to set a common voltage at the positive and negative RF outputs of approximately half a power supply (Vdd) voltage, such that the positive and negative RF outputs swing through a range approximately as large as the power supply voltage, to drive an envelope detector (ED) core over a full linear range of the ED core.

A feedback circuit of a class-AB voltage amplifier for an envelope detector, comprising:

• a first transistor to provide a positive bias voltage to drive a first pair of differential transistors of the class-AB voltage amplifier;
• second and third transistors connected to each other in series to provide a bias current to the first transistor, the bias current adjusting the positive bias voltage;
• and
• fourth and fifth complementary transistors and having drains interconnected through an impedance, where the drain of the fifth transistor is configured to generate a negative bias voltage to drive a second pair of differential transistors of the class-AB voltage amplifier, and where a gate of the fourth transistor is controlled by an output (Cmref) of a voltage divider between positive and negative power supplies (Vdd and Vss).