[sdiy] Nice info on decoupling caps

[jays at aracnet.com]

I've been looking at some of the high end op-amps from National Semi.
Most of them require each chip to be decoupled. Also if I remember right
they require caps in the feed back loops to prevent oscillations.

Jay S.

On Thu, 19 Jan 2012 22:01:32 +0100, ASSI <Stromeko at nexgo.de> wrote:
> On Thursday 19 January 2012, 11:54:04, David G Dixon wrote:
>> I found this article to be frustratingly terse.  "Many ICs have internal
>> circuitry which generates HF noise on the power rails" doesn't really tell
>> me anything!  Am I to believe that an opamp generates HF, just because?
> 
> Surprisingly many of them do, especially if they are set to provide unity 
> gain, but are not compensated for it.  You might not even notice...  Also, 
> the PSRR of an opamp at RF frequencies is essentially zero, any RF present 
> at the supply will propagate to the output.  Conversely, any RF present on 
> the output (if you plug in an "antenna") will propagate to the supply.
> 
> The bypass does two things: short RF coming from the IC to the supply and RF 
> coming from the supply to the IC (try putting a cellphone next to the 
> circuit).
> 
> 
> Regards,
> Achim.