radio_rookie wrote:

Hello,
I want to know the importance of intermediate frequency in any
receivers. IF was used in Superhet transceivers. My question is why
doesn't anyone use zero IF now a days. What is the problem of brining
the RF signal directly to baseband? Does the IF stage conditions the
incoming signal? What are the advantages of the IF stage?

Just confused. Can anyone throw some light on this?

Thanks.

Direct conversion is used in nearly all modern mobile phones, because it is
cheaper (no IF filters), and because the baseband amplifiers use less
current than the old IF amplifiers used to. The RF performance is not
necessarily as good as a well designed superhet.

It is difficult to make the receiver immune to "AM detection" which is a
problem caused by receiving a strong interfering signal with amplitude
modulation on it, at a frequency other than the one that you are trying to
receive, but which somehow gets turned into a baseband frequency signal
coming out of the mixer, even though it shouldn't. There are plenty of
reasons why this can happen, such as second-order nonlinearity in the
mixer, meaning that a strong interferer coming into the RF port of the
receiver can mix with itself in your mixer and end up on top of the wanted
signal. Another cause could be if there is coupling between the LO
generation circuit and the RF input (in either direction, both are bad.)
Also it is common to get large DC offsets coming out of direct conversion
receivers, and for some modulation formats where you're interested in
frequencies down to DC, that can be a pain. People have pretty much solved
these problems in phones, after a lot of work.

Chris