US Patent 9413313 Multimode power amplifier bias circuit with selectable bandwidth

Multimode power amplifier bias circuit with selectable bandwidth. In some embodiments, a bias circuit for a power amplifier can include a first bipolar junction transistor (BJT) configured to pass a reference current. The first BJT can be coupled with a second BJT that performs at least some amplification for the power amplifier. The first and second BJTs can be configured as a current mirror. The bias circuit can further include a coupling circuit that couples the collector and the base of the first BJT. The coupling circuit can include a switchable element to allow the coupling circuit to be in a first state or a second state. The first state can be configured to yield a first bandwidth for the bias circuit, and the second state can be configured to yield a second bandwidth for the bias circuit.