Operational Amplifier or OpAmp is a DC coupled amplifier with differential inputs and usually with a single output. An OpAmp can deliver an output voltage hundreds or thousand times greater than the voltage difference between its inputs. OpAmps may be single, dual, quad etc. In single OpAmps only one OpAmp is present while in dual type two OpAmps with separate inputs and outputs are present. In quad OpAmp, four OpAmps are present in the single package. Some of the OpAmps like CA3130, CA3140, TL0 71, LM311 etc have excellent performance with very low input current and voltage.
CA 3130 and CA 3140 are excellent Operational Amplifiers for Signal detection circuits. The most important characteristics of these Op Amps are low input current requirements and the zero output in the off state. Some of the general purpose Op Amps will not give a zero output in the off state which will affect the working of the remaining circuitry. More over the input current requirement is also high in most Op Amps so that these devices cannot be used in circuits based on Photo diodes and Infrared sensors.
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This circuit is useful to detect microwaves sources like microwave oven satellite communication devices, Mobile phones etc. It gives audio visual indications when it detects the Microwaves in the Gigahertz band.