IFfrequency2

[thejim]

I know that IF frequency is the difference between the incoming signal
and the local oscilator frequency in a frequency synthesizer.
My question is why in a frequency synthesizer we need the IF frequency>

 

[John Popelish]

I know that IF frequency is the difference between the incoming signal
and the local oscilator frequency in a frequency synthesizer.
My question is why in a frequency synthesizer we need the IF frequency>

You need a frequency synthesizer to generate all those different local
oscillator frequencies, so that, no matter what frequency you are
wanting to receive, the IF frequency is the same. The IF gain section
has fixed tuning.

 

[Don Bowey]

I know that IF frequency is the difference between the incoming signal
and the local oscilator frequency in a frequency synthesizer.

The I.F. is at either the _sum_ or the _difference_ frequency; it's up to
the designer.

The mixing (multiplication) of the frequencies that results in the sum and
difference, is not done in the synthesizer; it is done in the Mixer, a.k.a.
Converter stage.

My question is why in a frequency synthesizer we need the IF frequency>

In a receiver using an I.F., a synthesizer is commonly used to generate the
variable (tuning) frequencies, whereas the fixed frequency for the Mixer is
typically generated by a crystal oscillator.

If you elect to design a Direct Conversion receiver, you use only the
variable frequency tuning oscillator (or synthesizer) and demodulate
received signals directly to baseband audio - there is no I.F.

Don

 

[Charles Schuler]

I know that IF frequency is the difference between the incoming signal
and the local oscilator frequency in a frequency synthesizer.
My question is why in a frequency synthesizer we need the IF frequency>

You don't need any mixing and thus any intermediate frequencies in some
synthesizers. Google for "direct digital synthesis" (DDS) to see how this
can work. Also, single-loop phase-locked-loop (PLLs) synthesizers use only
a reference, a divider, a phase comparator and a voltage controlled
oscillator.

 

[Don Bowey]

You don't need any mixing and thus any intermediate frequencies in some
synthesizers. Google for "direct digital synthesis" (DDS) to see how this
can work. Also, single-loop phase-locked-loop (PLLs) synthesizers use only
a reference, a divider, a phase comparator and a voltage controlled
oscillator.

Even a Direct Conversion receiver needs a mixer (demodulator).

Don