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Just checking, I'm doing some experimenting of small signal RF design in LTspice.

joeh100
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    When you say "RF" do you mean 100 kHz, 100 MHz, or 10 GHz? – The Photon Oct 13 '14 at 18:36
  • It also depends on which devices you are using. – Leon Heller Oct 13 '14 at 18:38
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    What about 10.7 Mhz for an IF amp for the lowest frequency in question? – joeh100 Oct 13 '14 at 18:52
  • As far as devices; Are any of the stock models accurate at RF? – joeh100 Oct 13 '14 at 18:54
  • My feeling is, if a vendor designs a transistor to run at 10 MHz or 100 MHz or whatever, they should either provide a model that is accurate at those frequencies, or not provide any model at all. Whether (or which) vendors actually work this way or not, I can't say. – The Photon Oct 13 '14 at 19:09
  • What means "accurate"? Of course, the answer is NO because no model can be "accurate". Hence, in each case you must live with tolerances and deviations - and the only question you can ask is "how good is the model" and/or "to what extent does it reflect the real properties of the device"? – LvW Oct 14 '14 at 06:46

2 Answers2

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I use microcap (which uses standard transistor spice files) and there's plenty of times I'm simulating in the low hundreds of MHz for analogue and digital signals. If I don't pick the correct transistor it doesn't work (and neither would it in the real world).

I've pretty much designed radio front ends at 400MHz and got reasonable results when implementing the circuits - sure, component values need tweaking and the odd decoupler adding but you have to remember that spice simulators are not really a guarantee of performance but they are reasonable guarantor of functionality.

If something appears to functionally work in spice then you will likely get it to function in real life but, at high frequencies the PCB layout/grounding is something that you need to know a lot about. Spice doesn't help you with this.

Andy aka
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In general, I would say no. In order to properly model components in RF, you should use a tool specifically designed to simulate at RF frequencies like Genesys for instance.

Awm0121
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