Variable gain amplifiers with output phase invariance

A method of variable gain amplification, the method comprising:

• amplifying a radio frequency (RF) input signal from an input terminal to generate a signal current using a gain transistor of a variable gain amplifier (VGA);
• controlling a gain setting of the VGA by biasing an output cascode transistor of the VGA with a first bias voltage and a shunt cascode transistor of the VGA with a second bias voltage to control a proportion of the signal current that flows through the output cascode transistor relative to the shunt cascode transistor;
• flowing a first portion of the signal current from the gain transistor to a DC voltage through a series combination of a first degeneration resistor of the VGA, the output cascode transistor, and an output matching inductor of the VGA;
• flowing a second portion of the signal current from the gain transistor to the DC voltage through a series combination of a second degeneration resistor of the VGA and the shunt cascode transistor;
• providing an RF output signal at an output terminal between the output cascode transistor and the output matching inductor;
• and
• providing output phase invariance at the output terminal by using the first degeneration resistor and the second degeneration resistor to provide a zero in a transfer function of the VGA to compensate for a pole in the transfer function arising from the output cascode transistor and the shunt cascode transistor.