An operational amplifier, or op-amp, is a differential amplifier with very high differential-mode gain, very high input impedance, and low output impedance. By applying negative feedback, an op-amp differential amplifier (Fig. 4) with predictable and stable gain can be built.[nb 5] Some kinds of differential amplifier usually include several simpler differential amplifiers. For example a fully differential amplifier, an instrumentation amplifier, or an isolation amplifier are often built from several op-amps.