> Any CMOS experts that can help me with a SSB mixer. I managed to design a
> gilbert cell mixer (MOS level design) but it generates double side bands,
I
> only need one of them. Filtering tends to eliminate both as the two
> frequencies are too close. Please suggest a URL or something from
> experience. I have tried to do net searches, found many hits, but none
> helpful.

No circuits or URLs I'm afraid but the following may assist-

You are going to have to try one of the several traditional approaches to
eliminate the other sideband.

These are filtering (which does work if done correctly), phasing (where you
generate two sideband sets in such a manner that the desired ones add and
the unwanted ones subtract) or "folding" (Weaver) which is probably another
version of phasing but implemented differently.

The ARRL (American Radio Relay League) annual amateur handbook always has a
large section on SSB techniques. In my 1990! version it is in section 18
under "Voice communications". Also see the UK based RSGB manual.

The normal method with filtering is to generate SSB at a fixed frequency and
then heterodyne it to the desired output frequency. This is because it is
MUCH easier to make a filter of required sharpness and shape factor at a
fixed frequency. Such filters can be bought commercially and are available
surplus at lowish cost..

With phasing (which can be done at output frequency if desired) audio input
is shifted 90 degrees (not a trivial task for a band of frequencies) and RF
is shifted 90 degrees (much easier as single frequency) and components of
each are combined in balanced modulators (DSB out of each) and then summed
when the undesired sideband components cancel. Swapping the AF component
which is mixed with a given RF component changes the sideband which is
nulled.
For phasing you are going to need TWO of your Gilbert cells plus some extra
equipment.
The ARRL book has a circuit for audio phase shifting using "ordinary loos
tolerance components". This takes a bank of 24 capacitors and 24 resistors
to produce both phase shifted audio channels.
I could scan and send a diagram if of interest.
Search for "SSB" and "Phasing".

The Weaver / 3rd method doesn't seem to have got into the 1990 ARRL manual.
Search for "SSB" and "Weaver" on web.

You MAY be able to produce baseband SSB with a faaaast PIC with A2D (but
I've not heard of it being done) :-).



        Russell McMahon

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