A low-noise-amplifier with selectable internal or external impedance matching

A low-noise-amplifier with selectable internal or external impedance matching A multiband low noise amplifier may be adapted into either inductively-degenerated or resistive-feedback configurations. When switches 400,402 and 410 are off the transistors 200,202 are inductively degenerated and external series matching inductors (230,232 in figure 2) may be provided to produce passive voltage gain and hence a very low noise figure. No external impedance matching inductors are required when the switches are turned on to short-circuit the centre-tapped inductor 250 and bring the feedback resistors 300 and 302 into circuit; input impedance matching is provided by the amplifier in conjunction with the feedback resistors. Although shorted, the inductor 250 improves common-mode rejection and increases power-supply rejection with respect to Earth in the resistive-feedback configuration.