US Patent 7459975 Baseband filter start-up circuit

An amplifier comprises an input circuit that receives an input to the amplifier. A start-up circuit communicates with the input circuit, generates a start-up signal, and turns off the start-up signal when an output of the amplifier reaches a threshold voltage. The start-up circuit includes a first transistor having first and second terminals and a base terminal and a second transistor having first and second terminals and a base terminal. The base terminals of the first and second transistors receive a bias input, the first terminals of the first and second transistors communicate with each other and with a first current source, and the second terminals of the first and second transistors communicate with the input circuit.