[sdiy] Replacing CA3080 with CA3046 ??

[Tim Ressel]

Yo,

Don't forget the oft overlooked pin 13 requirement.
The substrate of the IC (pin 13) needs to be at the
lowest voltage the part is likely to see. Otherwise
some internal dides conduct and spoil the party. Keep
this in mind when designing Q5 into your circuit.

--Tim Ressel (rubbing the scar where he was bit...)


--- srnovak at ncsu.edu wrote:
> Hi group.
> I'm somewhat new to the list so sorry if this
> suggestion has been made
> before....
> 
> Has anyone tried to build an OTA out of a CA3046? I
> was looking at the
> schematic on the 3080 datasheet and if seems like if
> one were to replace
> the bias transistors with the appropriate resistors
> it would be possible.
> So here's my idea:
> 
> Q1 & Q2 make a the differential input stage
> Q3 collector connects to Q1 & Q2 emitters and
> provides bias current to
> adjust gain.
> Q4 common source amplification stage
> Q5 commons drain voltage follower.
> 
> This of course omits external resistors for bias
> current, but these could
> be tailored to each individual circuit and furhter
> control over the gain
> of each stage.
> 
> If this works one advantage would be the ability to
> omit another opamp
> stage to change the current from the OTA to a
> voltage. I guess this is
> idea isn't so much an OTA as a OPAMP with gain
> programmable by a current.
> 
> Any thoughts??
> 
> 


		
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