[sdiy] using a dac as a digitally controlled amplifier

[Mike Bryant]

The high speed DACs we used in the 70s were of R-2R-4R-8R-16R-32R-64R-128R topology.  TRW, Analog Devices and I think Burr-Brown all made them using ceramic packages and laser trimming.  There was even a 10 bit one from TRW but it was horrendously expensive.

But I agree nowadays R-2R ladders are far more common so I was showing my age :-)

________________________________
From: Roman Sowa <modular at go2.pl>
Sent: 06 August 2024 10:15
To: Mike Bryant <mbryant at futurehorizons.com>; Mattias Rickardsson <mr at analogue.org>
Cc: Synth DIY <synth-diy at synth-diy.org>
Subject: Re: [sdiy] using a dac as a digitally controlled amplifier

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
>
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