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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.</div>
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But I agree nowadays R-2R ladders are far more common so I was showing my age :-)</div>
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<div id="divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Roman Sowa <modular@go2.pl><br>
<b>Sent:</b> 06 August 2024 10:15<br>
<b>To:</b> Mike Bryant <mbryant@futurehorizons.com>; Mattias Rickardsson <mr@analogue.org><br>
<b>Cc:</b> Synth DIY <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] using a dac as a digitally controlled amplifier</span>
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<div style="font-size: 11pt;">I have never seen in my life a DAC with R-2R-4R-8R-16R-32R-128R<br>
topology. It would be very difficult to make resistors with 128 ratio in<br>
required tolerance. It's either R-2R ladder or resistor string. Making<br>
same value resistors is much easier. They make resistor string DACs even<br>
up to 16 bits, that's a lot of tiny resistors. Sometimes it's split<br>
topology with part of the bits done in R-2R and part of bits with small<br>
resistor string.<br>
There used to be DACs with capacitors instead of resistors, possibly<br>
because it's easier to achieve good precision and repeatability in<br>
making small cap than a resistor inside IC. But I think they are now<br>
relict of the past.<br>
BTW, I don't know what technology is used in those modern multi GHz DACs<br>
used so widely today. Switching resistors at that speed sounds like<br>
technology stolen from aliens.<br>
<br>
Roman<br>
<br>
W dniu 2024-08-05 o 20:45, Mike Bryant pisze:<br>
><br>
> I think the digital pots are 256 resistors in a string with a MOSFET<br>
> selecting each position, whereas the DAC use R-2R-4R-8R-16R-32R-128R<br>
> feeding a summing amp.<br>
><br>
><br>
> ------------------------------------------------------------------------<br>
> *From:* Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Mattias<br>
> Rickardsson <mr@analogue.org><br>
> *Sent:* 05 August 2024 19:38<br>
> *To:* Roman Sowa <modular@go2.pl><br>
> *Cc:* Synth DIY <synth-diy@synth-diy.org><br>
> *Subject:* Re: [sdiy] using a dac as a digitally controlled amplifier<br>
> Is this MDAC "trick" more or less equivalent to using a "digital<br>
> potentiometer", or are those ICs significantly different?<br>
><br>
> /mr<br>
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