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Design >> RF Design >> RF mixer
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Message started by delinqfour on May 11^th, 2010, 11:27pm

Title: RF mixer
Post by delinqfour on May 11^th, 2010, 11:27pm

hi.

my question is pretty basic. i need to know what will happen to the mixer output

1) if i ground the RF input. will i be getting my LO at the output.
2) if i ground my LO input. will my output simply be the RF input.

thanks

Title: Re: RF mixer
Post by pancho_hideboo on May 12^th, 2010, 5:00am

I assume actual RF mixer which is not ideal four quadrant multiplier and does have mismatch.

delinqfour wrote on May 11^th, 2010, 11:27pm:

1) if i ground the RF input. will i be getting my LO at the output.

Yes.

delinqfour wrote on May 11^th, 2010, 11:27pm:

2) if i ground my LO input. will my output simply be the RF input.

Yes.

Title: Re: RF mixer
Post by aaron_do on May 12^th, 2010, 5:17am

It depends on the design. In a balanced design (Gilbert Cell), ideally you will get nothing for both cases, but in practice there will be some unwanted feed-through.

Title: Re: RF mixer
Post by sabawat on May 13^th, 2010, 5:27am

hi..

@aaron_do

i agree with aaron_do, as far as the active mixers are concerned, if we do not supply any input to LO or RF ports, ideally we will get nothing at the output. i think that is the definition of a doubly balanced mixer. this is not the case in singly balanced types.

correct me if am wrong..

thank you...

Title: Re: RF mixer
Post by pancho_hideboo on May 13^th, 2010, 5:39am

A Kumar R wrote on May 13^th, 2010, 5:27am:

correct me if am wrong..

Observe output of actual mixer by actual instruments not by EDA-Tool-Play.

We can use Gilbert-Cell as Voltage-Controled-Gain-Amplifier, but we can never make output zero in actual circuits.
At most, -40dB~-60dB.

Title: Re: RF mixer
Post by delinqfour on May 13^th, 2010, 6:54pm

hi all
my question is if we only put only one of them on (either RF or LO), and the other grounded (either LO or RF). Just wondering what the output will be

a gilbert cell mixer needs to be driven by LO, am i right? so if i ground the LO input, i will be turning off a couple of transistors in the circuit which makes the output port open, so ideally i get nothing at the output, correct?
but if i ground the RF input, same thing happens

am in the right track?

Title: Re: RF mixer
Post by pancho_hideboo on May 14^th, 2010, 2:18am

Gilbert Cell Mixer is a "four quadrant multiplier" for small input level ideally.

delinqfour wrote on May 13^th, 2010, 6:54pm:

a gilbert cell mixer needs to be driven by LO, am i right?

Right.

delinqfour wrote on May 13^th, 2010, 6:54pm:

so if i ground the LO input, i will be turning off a couple of transistors in the circuit which makes the output port open, so ideally i get nothing at the output, correct?

Correct if it could be very ideal, although the output ports are not open state.

delinqfour wrote on May 13^th, 2010, 6:54pm:

but if i ground the RF input, same thing happens

Yes, if it could be very ideal.

Again, observe output of actual mixer by actual instruments not by EDA-Tool-Play.