A low noise amplifier with an impedance matching amplifier stage and a bias circuit which compensates process and temperature variations

摘要

A low noise amplifier 605 comprises an input impedance matching stage M1, M3, Rfb in parallel with the main input transistor M2. The matching stage is compensated against process, aging, and temperature variations by a feedback circuit (figure 5) acting on M3 to stabilize the voltage at node A. A common bias voltage for devices M1 and M2 is provided internally through Rfb. No input coupling capacitor or bias resistor is required, which reduces the circuit size and noise factor. The output of the matching stage may be added to the output of the main input transistor M2 at node B, using device M4. The LNA may possess a differential structure 605,610. The LNA is compact, inexpensive, consumes little power, has no external matching or bias components, and is suitable for high volume manufacture.