Synth patents, and the SSM 2040

[Joachim Verghese]

On Mon, 8 Jul 1996, Sean Costello wrote:

> I was wondering if anyone out there could point me towards some useful
> patent numbers for synthesizer circuits.

3,444,362   Exponential Converter (ARP/Teledyne)
3,475,623   Ladder Filter (Moog)
3,805,091   Multi-mode filter (ARP)
3,924,199   Resonant filter
4,011,466   4-pole Low-Pass Filter (ARP 4075/4072)

I've got some more numbers at home. Copies of patents can be ordered
from the US Patent Office at $3 each plus shipping. The URL is

http://www.uspto.gov/

> BTW, I found the patent that the SSM 2040 filter supposedly falls under:
> U.S Patent number 3,969,682. 

> I have no idea if these are the actual circuits that are
> used within the 2040, or just example circuits for the sake of explanation;
> maybe someone who knows more about electronics could take a look at the
> patent and figure something out.

I'm under the impression that the gain stage is pretty much what's
in the patent - a PNP current mirror on top of an NPN diff pair,
but the buffer is an NPN darlington. I've build a few discrete
2040 "clones" using the above configuration, and they work well.
Too bad I haven't been able to compare them to a real 2040.

I'll dig out more patent numbers tonight when I get home. Doug Curtis'
gain cell patent is especially interesting as it differs from most
other designs.

-joachim