An op amp is a (i)high-gain (ii) dc (iii) differential amplifier. The best way for the design of a circuit that uses op amps is to assume that the op amp is ideal. After the initial design, the circuit is checked to determine whether the non-ideal characteristics of the op amp are important. If not, the design is complete; if they are, another check is made, which may require minor modification of the original design. Computer simulation is helpful in prototype design