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.