Richard Moore wrote: > On Dec 2, 2008, at 12:25 AM, Bruce and PHK wrote: > > >>> <clip> >>> There was a recent Design Idea in EDN or Electronic Design (don't >>> remember >>> which one) where someone claimed 32 bit resolution out of two 16 >>> bit dacs. That >>> claim is ridiculous of course due to noise and matching etc, but >>> you can >>> probably get 20 - 24 bits resolution and accuracy out of a >>> cascaded system with >>> some care. >>> >>> bye, >>> Said >>> >>> >> If you build this circuit using the values shown in the schematic you >> won't actually achieve 20 bits performance. >> One of the resistor values is incorrect. >> The resistor matching requirements aren't anywhere near as >> stringent as >> one may think on first glance. >> With some subtle alterations to the operating mode the resistor ratio >> matching tolerances can be relaxed considerably. >> In closed loop digital control systems the circuit noise should be at >> least 1LSB or so to maximise performance. >> The trick is to increase the DAC resolution until this condition is >> achieved and not increase the noise to meet the condition. >> 20 bit resolution performance is easy to achieve, 24 bit performance >> requires 2 a little more work. >> >> Actually monotonicity to about 26 bits was claimed with noise a bit >> below 1ppm. >> However since the noise varies with the DAC output such claims are >> perhaps a little too simplistic. >> The noise can be reduced when required by using a better reference. >> Any drift in DAC gain and offset could be compensated by a Kalman >> filter >> should they become significant. >> >> The major advantage of such a DAC is the inherent monotonicity which >> cannot be achieved and maintained (around coarse DAC transitions) >> without frequent calibration when the outputs of 2 16 bit DACs are >> combined. >> >> Bruce >> > > Bruce, is there a way for non-subscribers to see this article? > > Dick Moore > > It should be publicly available by now, just use google with search terms like: EDN PWM 32 bit DAC. However there are some design errors some of which are relatively benign others which may result in component destruction.
Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
