[sdiy] Interpreting four-pole-w-feedback circuits

[Aaron Lanterman]

On Mar 6, 2008, at 2:53 PM, Ian Fritz wrote:

> At 11:22 AM 3/6/2008, René Schmitz wrote:
>
>> It doesn't really matter if they are, if you have an even number of  
>> them.
>
> I count the input transistor 64 as one of them, so I count five total.
>
> But, maybe I'm really missing something. Are we looking at the same  
> patent? (4,011,466).

We're looking a different patents. ;)

The you refer to is the one with the Norton amps, and as far as I can  
tell the patent does match up with the actual real ARP circuits that  
it covers.

The one ARP patent I was referring to is 3,924,199 - and I can't find  
any ARP products which actually use it. It's nearly identical to the  
equivalent Rossum patent about OTA-C filter circuits. As far as I can  
tell, the only difference is that Rossum runs the OTA output current  
through a cap to ground, and then buffers the resulting voltage,  
whereas the ARP patent runs the OTA output current through a cap in an  
output feedback loop - which I wouldn't call very much of a  
difference. ;)

- Aaron