Op Amp Circuits

- overview of the various op amp circuits that can be designed, developed and used.

Operational amplifiers or op amps can be used in a wide variety of different analogue circuits.

The basic op amp integrated circuit, makes them an almost ideal circuit building block which can be used to provide exceedingly high levels of performance.

A photo showing a selection of op amps in different packages - DIL and SMT

Typically an operational amplifier circuit requires a few external components to make a high performance analogue circuit.

It is the high gain of the basic amplifier combined with the use of feedback (most often negative feedback) that enables the final circuits to provide such a high level of performance.

Op amp circuits

The list below provides links to a variety of commonly used op amp circuits. These circuit range from simple linear amplifiers, to filters, variable gain amplifiers, a-stables and bi-stables and more.

  • Inverting amplifier:   The inverting amplifier is one of the most commonly used. It is simple requiring just a few additional resistors to provide a highly effective amplifier. It can also be used as a virtual earth mixer, combining several audio inputs together. The inverting amplifier has a low input impedance and a low output impedance. Read more about the Inverting op-amp
  • Non-inverting amplifier:   The non-inverting amplifier is another popular circuit. It is often just a little more complicated than the inverting format, but has a very high input impedance while maintaining a low output impedance. Read more about the Non-inverting op-amp
  • High pass filter:   High pass filters can be used in many applications. One instance where a high pass filter may be used is to remove unwanted low frequency noise such as mains hum. Read more about the Op-amp high pass filter
  • Low pass filter:   Low pass filters are very useful and can be used to remove the unwanted high frequency elements of a signal. Read more about the Op-amp low pass filter
  • Bandpass filter:   Band pass filters can be made quite easily using op amps. While the upper frequencies can be limited, they are ideal for audio and many other applications. Read more about the Op-amp bandpass filter
  • Variable gain amplifier:   This op amp circuit enables the gain of the amplifier to be controlled using a single resistor.Read more about the Op-amp variable gain amplifier
  • Notch filter:   Notch filters are widely used in removing a single frequency from a spectrum. For op amp notch filters that will tend to be used more within the audio spectrum, these notch filters could be used for removing mains hum, or for removing or accepting specific tones. Read more about the Op-amp notch filter circuits
  • Multivibrator:   Multivibrators are a commonly used in many areas of electronics. An op amp multibrator may be used where a simple oscillator is needed in an analogue circuit. Read more about the Operational amplifier multivibrator
  • Bistable:   It is sometimes convenient to have a bi-stable made from op amps. This circuit shows how this can be done very easily. Read more about the Op-amp bistable
  • Comparator:   This circuit shows how a comparator can be made using an op amp. Strictly speaking a comparator chip rather than an op-amp should be used as you will find out. Read more about the Op-amp comparator
  • Schmitt trigger:   The Schmitt trigger is a very popular circuit. Introducing some hysteresis into the switching, this reduces the effects of noise and enables solid switching to be achieved. Read more about the Op-amp Schmitt trigger

Op amp circuit design considerations

When designing operational amplifier circuits there are several design considerations that need to be remembered. Various aspects of op amp circuit design are common to most circuits if not all.

  • Basic op amp circuit design:   Some of the basic concepts about basic op-amp design. Read more about Op amp basics
  • Op-amp gain:   Operational amplifiers have very high levels of gain when operated in open loop. The final level of gain is very much less when negative feedback is applied. Knowing about the gain, and how to use it to obtain the best results is a key factor in op-amp circuit design. Read more about Op amp gain

By Ian Poole

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