Hi

We all know that the mixer is just a multiplier that can be modeled mathematically as
V_out = m(t) * cos(wc*t)
where: m(t) is the input modulating signal
wc is the carrier frequency

if we are upconverting from an IF-frequency then
V_out = cos(w_IF*t) * cos(wc*t) = 0.5*(cos((wc+w_IF)t)+cos((wc-w_IF)t)))
And we are interested in only one sideband. So, after filtering the unwanted side band
V_out_filtered = 0.5*cos((wc+w_IF)t)

However, if we are upconverting directly from baseband
V_out = m(t)*cos(wc*t)

From which we can conclude that the conversion gain of direct upconversion mixer = 2*conversion gain of IF upconversion mixer (after filtering)
(Am I right at this point??)

Anyway, I am using spectre to simulate the direct up-conversion gain of a gilbert cell. I am also using PSS+PAC method in which the PSS fundamental = flo and in the PAC,  I am adjusting the input source's AC magnitude =1 so the output voltage is the conversion gain directly.
So, does the resulting conversion gain is that corresponding to DIRECT CASE or the IF CASE????

Thank you pancho_hideboo
I got your point.
I think in both cases of direct up-conversion and IF up-conversion the mixer operation is the same. However, in the direct up-conversion mixer we are interested in the whole up-converted signal. However, in the IF up-conversion case, we are interested in only one side band of the signal (either the upper side band or the lower side band).
This can be shown from the following mathematical relations:

The IF up-conversion
IF signal = m(t)*cos(w_IF*t)
The transmitted signal = IF signal *cos(wc*t) = m(t)*cos(w_IF*t)*cos(wc*t)
                                = 0.5*m(t)*(cos((wc+w_IF)t)+cos((wc-w_IF)t)))
which has a spectrum of --> 0.25*(M(w-(wc+w_IF))+M(w+(wc+w_IF))+M(w-(wc-w_IF))+M(w-(wc-w_IF)))
we are interested in the signal with spectrum (for example): 0.25*((M(w-(wc+w_IF))+M(w+(wc+w_IF))
                                           or in time domain = 0.5*m(t)*cos((wc+w_IF))

The direct up-conversion
Baseband signal = m(t)
The transmitted signal = m(t)*cos(wc*t)
which has a spectrum of --> 0.5*M(w+wc)+0.5*M(w-wc)
However, we are interested in the hole signal which is =m(t)*cos(wc*t)

So,apparently there is a factor of 2.

Please, pancho_hideboo, I am confused could you explain it more to me.

Also, If the spectre is calculating the IF conversion case. How can I calculate the direct up-conversion case??

Thanks for your time inadvance

Thaks for the reply pancho_hideboo

In the double conversion architecture you mentioned. There is basically two mixers, one is to up-convert from baseband to the IF frequency (which behaves identically to the direct up-conversion case) while the other is to up-convert from the IF frequency to the RF frequency.

If we rephrased my previous questionas follow. If I used identical circuit topology for both mixers, will they have the same conversion gain given that the second mixer will generate the output @ ωc+ωIF & ωc+ωIF (and their negative frequency counter parts) and we will take only one sideband and filter the other.

Can you please also refer me to a good book or tutorial that elaborate on this issue.

Thanks for your time