Question about .TRANNOISE in HSPICE

[MagnetsGT]

Hey Guys.

I need to have a noisy voltage source in the transient simulations of my circuit. I've been reading the HSPICE documentation and I don't understand how to control the amplitude of the noise. How do you set how much noise gets injected into the node?

Thanks

 

[haykding]

There are two parameters which are controlling the energy of noise sources.

FMIN - Sets base frequency for modeling frequency-dependent noise sources. Sets
low-frequency flicker noise limit for contributing noise sources. (Default: 1/TSTOP);
FMAX - Maximum frequency used for modeling frequency-dependent noise sources.
Sets maximum noise-source waveform bandwidth and ensures Nyquist sampling.
Default: 1/TSTEP;

NOTE:
FMAX has a dramatic effect on TRANNOISE, since it controls the amount of energy each noise source can emit. Therefore, huge values of FMAX (like 100G) can result in huge
instantaneous noise levels. FMIN sets the low frequency limit for flicker noise, and therefore controls the energy in flicker noise sources. You can expect some significant differences with FMAX
and FMIN changes: Noise power increases linearly with FMAX; flicker noise power can scale as 1/FMIN. FMAX is a critical parameter for controlling TRANNOISE performance. This keyword sets the noise bandwidth of noise sources which also controls the maximum time step taken. A large FMAX can cause very slow simulation performance. The default value of FMAX is the inverse of the .TRAN tstep value. In some circumstances very small tstep values can causes poor performance. A good setting for FMAX is ~2X the fastest clock frequency in the circuit under test.

 

[FvM]

In a first order, noise denisity in .TRANNOISE is equal to frequency domain .NOISE analysis, determined by the basic component properties, e.g. resistor noise.