Part Number Search

Cross Reference Search

About information presented in this cross reference

The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.
Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.
TOSHIBA is not responsible for any incorrect or incomplete information. Information is subject to change at any time without notice.

Keyword Search

Parametric Search

Stock Check & Purchase

What is the purpose of using a differential amplifier? (Common-mode rejection ratio: CMRR)

Figure  Noise superimposed on the amplifier’s ground
Figure Noise superimposed on the amplifier’s ground

Differential amplifiers are used mainly to suppress noise.
Noise consists of typical differential noise and common-mode noise, of which the latter can easily be suppressed with an op-amp.
There are two main causes of common-mode noise:

  1. Noise is generated in the wires and cables, due to electromagnetic induction, etc., and it causes a difference in potential (i.e., noise) between the signal source ground and the circuit ground.
  2. Current flowing into the ground of a circuit from another circuit causes a ground potential rise (noise).

In either case, the ground potential, a reference for a circuit, fluctuates because of noise. It is difficult to remove common-mode noise with typical filters. Differential amplifiers are used as a means of suppressing common-mode noise.
The op-amp configures this differential amplifier as the main circuit. The symbol shown below represents a differential amplifier. It has two inputs: VIN(+) and VIN(-). The output voltage is equal to a difference in voltage between the two inputs multiplied by the amp’s gain (AV):
VOUT=AV{VIN(+) - VIN(-)}
Suppose that common-mode noise (vnoise) is superimposed on the differential inputs. Then,
VIN(+)‘=VIN(+) + Vnoise
VIN(-)‘=VIN(-) + Vnoise
Hence, the output is expressed as follows. This indicates that the differential amplifier
cancels out common-mode noise:
VOUT=AV[{VIN(+) + Vnoise} - {VIN(-) + Vnoise}]
=AV{VIN(+) - VIN(-)}

The common-mode rejection ratio (CMRR) is specified as one of the electrical characteristics of an op-amp.

Example of an electrical characteristics table in a datasheet
Example of an electrical characteristics table in a datasheet

Also see the application notes on op-amps:
Link to application notes

A new window will open