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Simulators >> RF Simulators >> How to measure NF of Mixer without using port
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Message started by jhadroit on Jul 26th, 2004, 1:12pm

Title: How to measure NF of Mixer without using port
Post by jhadroit on Jul 26th, 2004, 1:12pm

Hi~
I am working on the simulation of Mixers. Until now, I have used the "port" as a RF input source for measuring NF of mixer. If I use voltage source(vsin), not port, can I measure NF??? If possible, could you explain how I can do that..

Thanks,


Title: Re: How to measure NF of Mixer without using port
Post by Andrew Beckett on Jul 27th, 2004, 3:08pm

Since noise figure is defined to be the ratio of the signal-to-noise at the input, to the signal-to-noise at the output, clearly you must have some noise at the input of the circuit.

Spectre implements this by looking at the contribution of the inpit noise source at the output of the circuit, and dividing this into the total noise at the output of the circuit (less the noise in the load). The exact definition depends on whether it is SSB, DSB, or IEEE SSB noise figure, but broadly speaking they are similar. Essentially in the formulation used, the signal cancels out, so you only need to look at the noise contributions.

Using a vsin won't give you any noise input, and so you can't then measure the noise contribution from the input (also, the signal-to-noise at the input would be infinite). A port component has a built-in resistor and so generates thermal noise at (by default) 290K.

So the answer is no. You need a port.

Andrew.

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