I've been trying to replicate the following circuit in LTspice but I'm not getting any frequency response in the pink or white noise output. This is the circuit taken from the “Electronic Devices and Circuit Theory” book (by Boylestad, Nashelsky): Circuit

Here is the circuit in LTspice: Simulation

And this is the output of the circuit: Output

I don't know if I need to use an AC voltage source or if I'm measuring the outputs wrong, I hope someone can help me with this, thank you.

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    \$\begingroup\$ There are more than a few papers on the topic of modeling both zener and avalanche behaviors (and delineating them, as well.) The physics is complex and the models equally so: PDEs and ODEs, both. Most people pick something simple, sufficiently good for testing the circuit itself but not sufficient to test many other facets. For example, one might build a device and look at the actual peak to peak voltage for some BJT and then plug that back into Spice. A 2N2222 might exhibit 4 times as much as a BC547, for example. Quite a range of difference. So you test then simulate, then test again. \$\endgroup\$
    – jonk
    Commented Jan 21, 2022 at 4:58
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    \$\begingroup\$ If you only want to see the effect of the 3 dB/oct filter then use a behavioural source with V=white(time*x), where x should cover (twice) your bandwidth. That will generate the white noise. \$\endgroup\$ Commented Jan 21, 2022 at 9:39

1 Answer 1


You're not going to get the expected output because the Zener noise in reverse Vbe breakdown of Q1 is not modeled. You can try putting an AC source in series with the base of Q1.

You might also want to choose real transistor models eg. 2N4401.

It's also probably not a great idea to leave those capacitor ends hanging (maybe put a 10 meg resistor to ground) though it's not hurting you in this case.


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