The general utility of the operational amplifier is derived from the fact that it is intended for use in a feedback loop whose feedback properties determine the feed-forward characteristics of the amplifier and loop combination. To suit it for this usage， the ideal operational amplifier would have infinite input impedance， zero output impedance， infinite gain and an open-loop 3 dB point at infinite frequency rolling off at 6 dB per octave. Unfortunately， the unit cost–in quantity- –would also be infinite. Intensive development of the operational amplifier， particularly in integrated form， has yielded circuits which are quite good engineering approximations of the ideal for finite cost. Quantity prices for the best contemporary integrated amplifiers are low compared with transistor prices of five years ago. The low cost and high quality of these amplifiers allows the implementation of equipment and systems functions impractical with discrete components. An example is the low frequency function generator which may use 15 to 20 operational amplifiers in generation， wave shaping， triggering and phase-locking.