Noise calculation in Op.Amp circuit

Figure 1. Noise model


Figure 2. Example of noise spectrum of an actual Op.Amp

(LT1028/LT1128 datasheet Rev.C, 1992, p1-p6)

Rs : Source resistance	Ω
Rg : Gain resistor	Ω
Rf : Feedback resistor	Ω
Ta : Absolute temparature	K
Vn : Input refered voltage noise density of the Op.Amp.	V/√Hz
In : Input refered current noise density of the Op.Amp.	A/√Hz
fv : 1/f voltage noise corner frequency of the Op.Amp.	Hz
fb : 1/f current noise corner frequency of the Op.Amp.	Hz
fh : Higher frequency  (Bandwidth = fh - fl)	Hz
fl : Lower frequency	Hz
Vr : Jhonson noise of the source resistance Rs at Ta	V/√Hz
Vd : Input refered voltage noise density of the amplifier at flat region.	V/√Hz
En : Input refered voltage noise of the amplifier over the bandwidth.	Vrms
Eo : Output voltage noise of the amplifier over the bandwidth.	Vrms
peak-to-peak (limits of 99.7% of the time; 6×RMS)	Vp-p
Noise power into 50 Ohm	dBm
"Noise calculation in Op.Amp circuit Rev.1.02 (Mar. 7, 2015)", Finetune co., ltd.

APPENDIX

Figure 3. Standard normal distribution

REFERENCE

"Noise Calculation in Op Amp Circuits - Design Note 15", Linear Technology Corporation, 1988
"LT1028/LT1128 - Ultralow Noise Precision High Speed Op Amps", Linear Technology Corporation, 1992

SEE ALSO

vn - noise culculation program for the HP 42s