[sdiy] ADc & DAC voltage dividers.. fixed or trimmer adjustables ??

Mike Bryant mbryant at futurehorizons.com
Sat Feb 13 23:02:59 CET 2021

Always GOOD quality metal film fixed resistors.  The noise from trimmers is far more than the LSB of a 16 bit ADC/DAC.  If you need to adjust the gain then change the resistor values.  And always use the lowest values you can use without overloading the driving amplifiers so as to reduce Johnson noise.

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Jean-Pierre Desrochers
Sent: 13 February 2021 20:25
To: Synth-diy at synth-diy.org
Subject: [sdiy] ADc & DAC voltage dividers.. fixed or trimmer adjustables ??

Hi list,

I'm in the process of design for 16 bits ADC/DAC circuits.

This circuit will receive a 0-8vdc CV voltage, drop it down to 0-5vdc, process it through a MAX11100 16 bits ADC (reference voltage  REF02 +5.00v)

Then process the cpu data out to a LTC2641 16 bits DAC (reference voltage  REF02 +5.00v).

The DAC's 0-5vdc will then be amplified back to 0-8vdc.

To keep as much as LSB precision I'm wondering if the voltage dividers

Should be fixed or adjustable..

See the attached schematic. The 5v to 8v amplification on the DAC section

Is made using U19B , R3 & R4 (fixed gain of 1.6)

And the ADC attenuation is made using U19A, R1, P1, R2. (adjustable attenuation of 5/8).

What would you use for a 16 bits ADC/DAC transfer like this ?

Fixed resistor values (shown in DAC) or 2 resistors with a center trimmer (shown in ADC)?

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