In the passive mixer section of the CMOS RF Receiver front-end, I am unable to obtain the expected voltage conversion gain, which is coming in negative dB. In simulating a mixer, which operational region should it represent, and can anyone make suggestions?
Neerarja Pasupuleti negative conversion gain would make sense in a passive mixer as the premise is for the devices to not consume power as they would in an amplifier type circuit like the gilbert cell. What topology are you using?
https://people.engr.tamu.edu/s-sanchez/665%20MixersII.pdf
Conference Paper Comparison of active and passive mixers
Adam Weidling Thank you sir for responding.
I am am using a double balanced passive mixer after the LNA stage. For the combination of two blocks, I obtain a gain of 29 dB. But, for mixer it is roughly -163 dB. (Voltage conversion gain versus LO signal power). But is not within the acceptable ranges. I am including the result page here.
I think you might expect -10 dB or -20 dB conversion loss at worst. The LO should be about 10 dB more than the input signal, and the signal levels should be no more than a few mW. Have you put the signals in the wrong ports?
Some practical, although rather low loss mixer is e.g. here https://www.minicircuits.com/pdfs/ADE-30+.pdf
Note the passive mixer has loss at least -3dB because output power is shared between two frequency products (of sum and diff frequencies).
@Malcolm White Thank you sir, Problem addressed; I was incorrectly connected the ports. Now I am getting a positive conversion gain in dB
You can get positive voltage gain in passive circuit - just use series resonant circuit with L and C and get output signal from either L or C. Just remember that power gain will be always negative for passive circuit…
I think that the definition of dB is always a power ratio, and if so, then saying a positive voltage gain doesn't make sense for a passive circuit, because it implies that the gain is being expressed in dB so must be for a power ratio which can never be positive dB for a passive circuit. Even if the voltage does increase, this will be in a higher impedance, with the same (or less) power as the input, i.e. 0 dB (or less).
dBVolt only means anything if it refers to an impedance that the voltage is across, or if it is compared to another voltage across the same impedance.
If the signal is 1 volt before a transformer and 10 V after the transformer, it is 0 dBV before and 20 dBV after, but the gain of the transformer is not 20 dB.
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