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What types of noise affect an op-amp?

The following noises occur in the op amp as shown in the figure below:

• 1/f noise dependent on frequency

• White noise independent of frequency

Figure 1 Frequency-vs-noise curve of an op-amp
Figure 1 Frequency-vs-noise curve of an op-amp

Figure 2 Comparison of noise between  general-purpose and low-noise op-amps
Figure 2 Comparison of noise between general-purpose and low-noise op-amps

The following compares Toshiba’s TC75S51FU CMOS general-purpose op-amp and TC75S67TU CMOS low-noise op-amp.

The low-noise op-amp has less white noise and exhibits lower corner frequency than the general-purpose op-amp.

General-purpose TC75S51F/FU: White noise ≈ 30 nV/√Hz at f=10 kHz, corner frequency (fc) ≈ 300 Hz

Low-noise TC75S67TU: White noise ≈ 6 nV/√Hz at f=10 kHz, corner frequency (fc) ≈ 100Hz

Both 1/f noise and white noise are generated in the op-amp and defined as Equivalent input Noise Voltage. The equivalent input noise voltage is amplified by a gain and appears at the output. Particular care is required as to low-frequency noise because low frequency noise is frequency dependent.

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