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ADG749: SPICE Noise Analysis

Question asked by MatF on Mar 20, 2018
Latest reply on Mar 28, 2018 by mayp

Hi,

 

I'm perfoming a noise analysis in LTSpice. My circuit includes the ADG749, therefore I downloded the provided Spice model (.cir), and created an appropriate symbol in LTSpice (which I have already done several times).

 

By performing my noise analysis in LTSpice, the results are "terrible" large. It seems, the used switch (ADG749) causes the additional noise. 

 

I attached the simulation result obtained in LTSpice for a single switch. The integrated RMS voltage noise from 1 Hz to 100 MHz is about 540µV. As can be seen, Rin and R1 are noiseless, so the whole noise is added by the switch. Comparing this result with my theoretical resullt of v_n = sqrt(4 x k x R x T x B * pi/2) = 4.26 µV (k = Boltzmann constant; R = 7 Ohm, worst case value according to the datasheet; T = 300 °K; B = 100 MHz), the simulatuion result is way to large.

 

I had a lock in the .cir file. I wasn't able to identify any noise-values. So I think the switch doesn't include a noise model. But I'm still curiose why the switch has this strange noise behaviour.

 

Has anyone experience with noise simulations including switch models?

 

BR

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