Isolation Amplifier Working and Its Applications

An isolation amplifier or a unity gain amplifier provides isolation from one fraction of the circuit to another fraction. So, the power cannot be drawn, used and wasted within the circuit. The main function of this amplifier is to increase the signal. The same input signal of the op-amp is passed out exactly from the op-amp as an output signal. These amplifiers are used to give an electrical safety battier as well as isolation. These amplifiers protect the patients from the outflow of current. They crack electrical signal’s ohmic continuity among input & output and isolated power supply can be provided for both the input and output. So, the low-level signals can be amplified.

What is an Isolation Amplifier?

An isolation amplifier can be defined as, an amplifier which doesn’t have any conductive contact among input as well as output sections. Consequently, this amplifier gives ohmic isolation among the i/p & o/p terminals of the amplifier. This isolation must have less leakage as well as a high amount of dielectric breakdown voltage. The typical resistor and capacitor values of amplifier among the input & output terminals are resistor should have 10 Tera Ohms and capacitor should have 10 picofarads.


These amplifiers are frequently used when there is extremely huge common-mode voltage disparity among input & output side. In this amplifier, the ohmic circuitry is not there from input ground to output ground.

Isolation Amplifier Design Methods

There are three kinds of design methods are used in isolation amplifiers which include the following.

  • Transformer Isolation
  • Optical Isolation
  • Capacitive Isolation

1). Transformer Isolation

This type of isolation uses two signals like PWM or frequency modulated. Internally, this amplifier includes 20 KHz oscillator, rectifier, filter, and transformer to give supply to every isolated stage.

  • The rectifier is used as an input to the main op-amp.
  • Transformer links the supply.
  • The oscillator is used as an input to the secondary op-amp.
  • An LPF is used for removing the components of other frequency.

The advantages of transformer isolation mainly include high CMRR, linearity, and accuracy.

The applications of transformer isolation mainly include medical, nuclear and industrial.

2). Optical Isolation

In this isolation, the l signal can be changed from biological to light signal with LED for further process. In this, the patient circuit is input circuit whereas the output circuit can be formed by a phototransistor. These circuits are operated with a battery. The i/p circuit changes the signal into the light as well as the o/p circuit changes the light back to the signal.

The advantages of optical isolation mainly include;

  • By using this we can obtain amplitude and original frequency.
  •  It connects optically without the need of modulator otherwise demodulator.
  • It improves the safety of the patient.

The applications of transformer isolation mainly include process control in industries, data acquisition, measurements of biomedical, monitoring of the patient, interface element, test equipment, controlling of SCR, etc.

3). Capacitive Isolation

  •  It uses frequency modulation and the input voltage’s digital encoding.
  •  The input voltage can be changed to relative charge over the switched capacitor.
  • It includes circuits like modulator as well as a demodulator.
  • The signals are sent across a differential capacitive barrier.
  •  For both sides, separate supplied are given.

The advantages of capacitive isolation mainly include;

  • This isolation can be used to remove ripple noises
  • These are used for analog systems
  • It includes linearity and high-gain stability.
  • It gives high immunity to magnetic noises
  • By using this, noise can be avoided.

The applications of capacitive isolation mainly include data acquisition, interface element, monitoring of the patient, EEG, and ECG.


The main features of the isolation amplifier mainly include the following.

  • Voltage Supply
  • Current Supply
  • Operating Temperature

The voltage supply of amplifiers mainly refers to the range of voltage source. The current supply is the amount of current which is taken from the source of power supply as it is allied to an amplifier. The operating temperature of an amplifier is the particular value of ambient temperature.

These amplifiers use different methods to reduce distortion & huge signal non-linearity like using a LOC (linear optocoupler) to enhance the amplifier’s linearity over an exact range of the signal. This LOC includes an input LED connected to 2- photodiodes. These photodiodes feed the input and output circuitry.

When designing this amplifier is the main task to reduce the signal drift and an isolation amplifier heats up frequently throughout working, then the current supply with the circuit will decrease. These amplifiers are normally evaluated by size, performance, and cost with the technical necessities being stability, linearity and high-frequency response of the signal. The main concerns while designing this amplifier include breakdown voltage and managing leakage.

How to Achieve Isolation?

When the input impedance of an op-amp is extremely high then the isolation can be caused. As this circuit includes high input impedance, then minute current can be drawn from the amplifier circuit. According to Ohms law, when the resistance is high, then the current will be drawn less from the power supply.

isolation-amplifier-circuit -diagram
isolation-amplifier-circuit -diagram

Therefore, an op-amp does not draw a significant quantity of current from the power source. So in practice, there is no current will be drawn as well as transferred from one portion to another portion of the circuit. Therefore, this amplifier works as an isolation device.

When the input impedance of an op-amp is low then it draws a vast amount of current. Ohms law states that, if load impedance has less resistance, then it draws huge current by the source of power so that high disturbances can be caused, and this is quite opposite to isolation.  Here, isolation amplifier works like a buffer and they do not strengthen signals although provide to isolate divisions of circuits.

Isolation Amplifier Applications

These amplifiers are normally used in applications like signal conditioning. This may utilize different bipolar, CMOS, & complementary bipolar amplifiers which include chopper, isolation, instrumentation amplifiers.

As several devices work by using low power sources otherwise batteries. Selecting an isolation amplifier for different applications mainly depends on the supply voltage characteristics of an amplifier.

Thus, this is all about Isolation amplifiers which can be used to isolate the signals like input & output electrically with inductive couplings. These amplifiers protect the electrical and electronic components from overvoltages in different applications using numerous channels. Here is a question for you, what is the application of this amplifier in medical devices?