[sdiy] Low voltage synthesis?
modular at go2.pl
Fri Jan 14 08:10:42 CET 2022
Well, obviously I meant "running at MORE than 5V"
W dniu 2022-01-14 o 08:02, Roman Sowa pisze:
> There are lots of R-R opamps running at 5V. Typicaliy at 12V, 16V, 20V
> and even 40V.
> To name a few from my stock:
> TLV93xx - not addvertised as input R-R but has pretty low input
> crossover error
> Most opamp application don't even require input going higher than
> about 1.5V from upper rail where non-R2R opamps start to get dizzy, so
> in fact RRO (as oposed to RRIO) is all we really need in many LV
> applications. Nearly all opamps released during last 20-30 years have
> rail-to-rail outputs, including OPA1678.
> W dniu 2022-01-13 o 22:08, Brian Willoughby pisze:
>> Most op-amps lose a couple of volts near each rail; the input and
>> output voltages can't reach all the way to the rail voltage without
>> lots of distortion. That's one reason to use ±12V to feed op-amps
>> that need to accurately handle ±10V signals (of course, if your
>> circuit regulates a ±12V power source down to ±10V for the supply
>> rails, then the op-amps are good for less than ±8V or so in terms of
>> signal levels). Apart from maximum supply voltage ratings, op-amps
>> generally don't care what voltages are used, but there's always the
>> stipulation that your signal levels will be a few volts less than the
>> rails on either side. When the rails are as low as ±2V, there'd be no
>> room left for (undistorted) signals.
>> I've not seen any rail-to-rail op-amps that work with more than +5V,
>> which can be treated as ±2.5V by using a virtual ground throughout
>> the circuit, as well as capacitive coupling (*). Thus, it seems like
>> there's a gap between the 5V rail-to-rail signal ranges and the
>> typical 20V to 24V or more that normal op-amps can handle. Granted,
>> there are R2R op-amps that work with less than 5V, e.g., 3.3V, but
>> I'd be curious whether anyone knows of an R2R with more than 5V. In
>> particular, I don't think you can manage ±5V - because there don't
>> seem to be any 10V R2R chips - unless you're happy with signal levels
>> within ±3V. At that point, you'd basically be better off with ±2.5V
>> R2R than with standard op-amps operating at ±5V.
>> * You can avoid capacitive coupling of signals by operating with
>> literal bipolar supply, but that can end up with more components than
>> a virtual ground system (like guitar pedals usually are).
>> Brian Willoughby
>> On Jan 13, 2022, at 09:07, Mike Bryant <mbryant at futurehorizons.com>
>>> The other issue you run against is you need to use rail-to-rail
>>> op-amps, but most of these are specified for 5V/+-2.5V operation.
>>> Also these opamps are often CMOS based and have what I term "input
>>> crossover distortion" as they switch from the N to P type devices
>>> conducting. Negative feedback reduces this, but it's always
>>> slightly there. There are a few bipolar R2R opamps without this
>>> problem - Rohm BA2510 is my favourite.
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