Diamond buffer

The diamond buffer or diamond follower is a four-transistor, two-stage, push-pull, translinear emitter follower, or less commonly source follower, in which the input transistors are folded, or placed upside-down with respect to the output transistors. Like any unity buffer, the diamond buffer does not alter the phase and magnitude of input voltage signal; its primary purpose is to interface a high-impedance voltage source with a low-impedance, high-current load. Unlike the more common compound emitter follower (a "double" in audio engineering terms), where each input transistor drives the output transistor of the same polarity, each input transistor of a diamond buffer drives the output transistor of the opposite polarity. When the transistors operate in close thermal contact, the input transistors stabilize the idle current of the output pair, eliminating the need for a bias spreader. The diamond buffer is used primarily in the input and output stages of high-speed current-feedback operational amplifiers. The circuit is also the essential building block of bipolar current conveyors, and has seen limited use in line-level audio preamplifiers and in the output stages of audio power amplifiers.