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Free Analog Circuit Simulation

Noise Analysis (Simple Example)

Operating point

noise example
noise v(2) v1 lin 8 100kHz 1MegHz 2
v1 1 0 dc 700mV ac 1V
i1 1 2 dc 10mA ac 50mA
r1 1 2 1
d1 2 0 diode
.model diode d rs=10m tt=5us kf=1f

Linearised ac circuit

Note, that ac magnitude of the input source has to be one. Thermal noise of the resistors r1 and rs given by:

Shot and flicker noise of the diode d1 given by:

All independent sources eliminated (set to zero), noise generators added

Noise analysis creates two plots named noise1 and noise2. The first one contains the information about noise spectral densities, and the second about total noises. The vectors in noise1 are:


onoise_d1_rs =

onoise_d1_id =

onoise_d1_1overf =

onoise_d1 = onoise_d1_rs + onoise_d1_id + onoise_d1_1overf
onoise_spectrum = onoise_r1 + onoise_d1
inoise_spectrum = onoise_spectrum / |A|2

The vectors in noise2 are:

onoise_total_r1 =

onoise_total_d1_rs =

onoise_total_d1_id =

onoise_total_d1_1overf =

onoise_total_d1 =onoise_total_d1_rs + onoise_total_d1_id + onoise_total_d1_1overf
onoise_total = onoise_total_r1 + onoise_total_d1

inoise_total_r1 =

inoise_total_d1_rs =

inoise_total_d1_id =

inoise_total_d1_1overf =

inoise_total_d1 =inoise_total_d1_rs + inoise_total_d1_id + inoise_total_d1_1overf
inoise_total = inoise_total_r1 + inoise_total_d1