Can´t find diskrete 3V3 OTA

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speeedbug

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Hello,

I need a discrete OTA for a project that works best with a minimum supply voltage of
at least 3.3V. So far I have only the LM13700 (min 9.5V) and the CA3280 (Vsup +-2V).

I could still manage to install the CA3280 (with 5V instead of 3V3, but
of course I would prefer 3V3). However, it is no longer available, which is why it has been dropped.

It would also be good if it has high gain and is rail-to-rail, but first of all I need one that fits the basic specifications.

Does anyone have any ideas what to use?

Many thanks in advance!
 

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If you have the CA3280 use it. Otherwise https://www.digikey.ca/en/products/detail/onsemi/NE5517DR2G/1484314
It seems the topology of the current sources needs the 4V span min. which limits the range to nearly 0V differential. at (V+ -V-)/2
Vcc=5 will yield 1 V CM range.
--- Updated ---

Both of these devices have current mirrors, top and bottom.

 
Last edited:

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My idea would be to use a higher supply, creating it if
need be. Maybe get yourself split rails while you're at it.
 

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Where do you get minimal LM13700 supply of 9.5 V. The basic OTA can definitely work at +/- 2V, or even 3.3V (with very low CM range and output swing).

No BJT OTA with similar performance (linearity, output resistance) will achieve lower supply range, it's constraint by Wilson current mirror characteristic. Original CA3080 has one diode drop increased input CM range by using a non-cascaded current mirror for Iabc.

It makes sense to check the feasibility of your requirements beyond IC availibility. And check OTA behaviour with transistor level simulation.
 

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These devices share identical schematics.
The LM13700 guarantees the Common-mode range ±12V from a ±15V supply using 0.5mA bias. This suggests there is no sense in trying to use a 6V supply span and the recommended single supply range is 9.5V.

 

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D.A.(Tony)Stewart said:
This suggests there is no sense in trying to use a 6V supply span and the recommended single supply range is 9.5V.
Click to expand...
As stated, simulation with transistor level model gives a different picture. Definitely working with +/- 2V supply. Output swing is only a small fraction of supply span, but the problem is common to standard OTA topology.
 

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