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Design >> RF Design >> mixer conversion gain different by pxf and pss?
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Message started by dot13 on Dec 1^st, 2005, 3:28am

Title: mixer conversion gain different by pxf and pss?
Post by dot13 on Dec 1^st, 2005, 3:28am

hi,
i simulate a single-in balance-out mixer using pxf according to the spectreRF user guide, and get a conversion gain -9dB, while when i use only pss,and plot the voltage gain, it's -15dB, exactly -6dB discrepancy! what's the reason?

Regards

Title: Re: mixer conversion gain different by pxf and pss
Post by Andrew Beckett on Dec 1^st, 2005, 5:08am

I suspect you have used a port at the input, and the input is completely unmatched? Perhaps you have a high input impedance with your mixer, and so pxf is giving you the gain from the internal source. Since there is an implicit gain of 2 from the voltage source, which would then be divided by 2 if the gain matched - but if driving a high impedance you'd get an extra gain factor of 2 with pxf. With pss you're measuring the voltage gain from net to net, so the mismatch doesn't matter any more.

If your mixer does in fact have high impedance input, use a voltage source as the input instead of a port.

Note, the above is a bit of a guess - without more info on the circuit, it's hard to be sure.

Regards,

Andrew.

Title: Re: mixer conversion gain different by pxf and pss
Post by dot13 on Dec 1^st, 2005, 8:05pm

You are quite right! That's the reason.
I also find some informations on the "spectreRF user guide".
thanks a lot