[sdiy] using a dac as a digitally controlled amplifier

[Roman Sowa]

I have never seen in my life a DAC with R-2R-4R-8R-16R-32R-128R 
topology. It would be very difficult to make resistors with 128 ratio in 
required tolerance. It's either R-2R ladder or resistor string. Making 
same value resistors is much easier. They make resistor string DACs even 
up to 16 bits, that's a lot of tiny resistors. Sometimes it's split 
topology with part of the bits done in R-2R and part of bits with small 
resistor string.
There used to be DACs with capacitors instead of resistors, possibly 
because it's easier to achieve good precision and repeatability in 
making small cap than a resistor inside IC. But I think they are now 
relict of the past.
BTW, I don't know what technology is used in those modern multi GHz DACs 
used so widely today. Switching resistors at that speed sounds like 
technology stolen from aliens.

Roman

W dniu 2024-08-05 o 20:45, Mike Bryant pisze:
> 
> I think the digital pots are 256 resistors in a string with a MOSFET 
> selecting each position, whereas the DAC use R-2R-4R-8R-16R-32R-128R 
> feeding a summing amp.
> 
> 
> ------------------------------------------------------------------------
> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Mattias 
> Rickardsson <mr at analogue.org>
> *Sent:* 05 August 2024 19:38
> *To:* Roman Sowa <modular at go2.pl>
> *Cc:* Synth DIY <synth-diy at synth-diy.org>
> *Subject:* Re: [sdiy] using a dac as a digitally controlled amplifier
> Is this MDAC "trick" more or less equivalent to using a "digital 
> potentiometer", or are those ICs significantly different?
> 
> /mr
>