Amplifier having controllable input impedance

A method of amplifying a low noise RF communication signal by applying the signal to an amplifier circuit comprising:

• receiving the signal by a circuit input;
• receiving the signal from the circuit input by a gain stage, the gain stage having an inverter including an inverter input, the gain stage comprising first and second MOS transistors;
• providing first and second supply voltages to the first and second MOS transistors, respectively, the first and second MOS transistors being connected between the first and second supply voltages,
• providing an inverter output current by an inverter output to a load circuit, the inverter output current corresponding to a circuit input voltage, the load circuit comprising a first resistive element, the first resistive element comprising at least a third MOS transistor, connected to the inverter output and to the first supply voltage;
• providing, by the load circuit, a voltage output corresponding to the inverter output current;
• applying a first voltage, by a first voltage source, to a gate of at least a fourth MOS transistor such that the fourth MOS transistor operates in a linear region, the fourth MOS transistor having a drain and source terminals connected between a circuit output and the circuit input, the fourth MOS transistor operating as a second resistive element and being comprised in a feedback circuit;
• determining the active input impedance of the amplifier circuit;
• and
• adjusting a feedback resistance of the feedback circuit such that the active input impedance of the amplifier is set to a required value.