passive mixer help needed (I dont have conversion loss)

[YooCanFly]

Hello

I designed a LNA - passive mixer driven by a VCO.

I used a simple NMOS switch as passive mixer.
the LNA output is 900 MHz, has an amplitude of 5 mV.

The gate of the passive mixer is driven by VCO signal at 901MHz, with rail-to-rail amplitude.

Now, the output (IF signal) is a 1 MHz signal with an amplitude of 4 mV.
That is approx. -2 dB loss, isn't it?

From the books I read, it says -3 dB is the minimum loss I can have... and typically it will be -6 to -9 dB loss. Is my simulation incorrect?

Also, if I mix the LNA output with a differential VCO signals, I get a differential output with an amplitude of ~8mV

Since I started with 5 mV, that is actually a gain...

Am I missing something?
Let me know!

 

[davenn]

for a start use the same level definitions throughout...
you are mixing up mV and dB (dBm) convention would to preferably use
dBm level readings so that gains and losses would be easier to calculate

cheers
Dave