[sdiy] Op-amps CA3140 v. TL074

[Oren Leavitt]

Ian Fritz wrote:
> At 01:58 PM 7/29/2010, Tim Daugard wrote:
>> Has any one used the CA3140 or more, compared it to the TL074? The 
>> data sheet says the CA3140 has a MOSFET input. Is that input anything 
>> special?
> 
> Yes it is. A MOSFET input is over 10^14 Ohms. You cannot come close to 
> this input performance in any other opamp without paying a huge price.  
> The CA3140 is still in production and currently available for ~ $2. I 
> use it for my TGTSH module and it easily outperforms high-performance 
> JFET opamps such as the OPA602, which costs over $9.
> 
> Replace it with a TL074 ?!?!?!  No way.
> 
> Ian

Agreed - with that high input impedance, the CA3140 is an unbeatable 
buffer for sample and hold, or integrators for filter stages and 
oscillators.
They work great off of single-ended 5V power supplies - the output can 
swing all the way down to the negative rail. Handy for analog<->logic 
interfacing.
The CA3140 has a special niche that it does very well - no surprise they 
are still in production.
The only "gotchas" are ESD sensitivity*, and the fact that the output 
can only source 10mA and sink 1mA.
*I think I've killed maybe 10 CA3140s in the past 30 years.

Long live the CA3140! (And bring back the CA3080 and CA3280!!)
- Oren