Operational Amplifier GCSE

Op Amp Chip

Operational amplifiers (Op Amps) are the basic building blocks used in analogue electronics. They are basic reading for any GCSE Design and Technology student.

Originally invented to perform mathematical operations such as summation, subtraction, integration, they have two inputs, inverting, and non-inverting. An amplifier such as this can also amplify weak signals, hence the name amplifier. To use this component one must connect additional components. The level of amplification depends upon the feedback resistor and the input resistor.

An eight-pin PDIP package such as this is the most commonly used in electronics. The 741 was the most popular and one of the earliest design to appear in the electronics industry and consequently modern operational amplifier chips such as the CA3140 have the same pin layout as the 741.

Based on a new semiconductor technology called Bi-MOS the CA3140 utilises gate-protected transistors making it a very robust chip.

OP Amp Pinouts


A dual rail power supply requires a positive voltage and a negative voltage. The positive connects to pin 7 and the negative to pin 4. In a single rail design, the positive supply connects to pin 7 whilst pin 4 connects to a common ground.

This is a very efficient little chip and the maximum output voltage can be very close to the power supply voltage. It is not possible for the chip to provide an output greater than the supply voltage. If you amplify to a voltage greater than the power supply, then clipping occurs.

Pins 2 and pin 3 are for signal input and pin 6 for the output, hence, this is a very simple little chip to work with.

Differential Amplifier

Differential Amplifier

An operational amplifier has two inputs so it can compare two input signals. If there is an input signal A in pin 2 and signal B in pin 3, then the amplifier will subtract the two signals such that the output is B-A. Hence, it is termed a comparator because it compares the two input signals by subtracting one from another.

A negative sign at pin 2 signifies inverting input, or subtraction. A positive sign at pin 3 indicates a non-inverting input, or addition. Differential amplifiers utilise both inputs simultaneously to amplify the difference of the two signals.

Negative Feedback

Negative Feedback

A small amount of the output signal feeds back to the inverting input providing negative feedback. Since the feedback signal is in opposite phase to the input signal, the two cancel each other out forming a virtual earth.

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