US Patent 8928415 Adjustable gain for multi-stacked amplifiers

Techniques for providing adjustable gain in an amplifier. In an aspect, a composite amplifier having adjustable gain includes a plurality of amplifiers coupled in parallel, wherein each of the amplifiers may be turned on or off to adjust the overall gain of the composite amplifier. Each amplifier may include an input transistor and at least two cascode transistors. To turn each amplifier off, the gate voltage of a second or lowermost cascode transistor coupled to the input transistor may be grounded, and the gate voltage of a first cascode transistor coupled to the output voltage may be coupled to a first turn-off voltage to reduce the drain-to-gate voltage drop across the first cascode transistor. Further aspects provide for decoupling a capacitor coupled to the gates of the cascode transistors from AC ground when the amplifier is turned off.