First off, I'd not mess with building DACs. DAC ICs are cheap and come in wide varieties. I'd change to a binary counter and use a 10 to 16 bit commercial DAC.
If you are determined to go the decade BCD route, use the summing junction of an op-amp in an inverting configuration. If the decades are voltage output, connect each to the summing junction through scaling resistors in decade steps: like 1K; 10K; 100K; 1M. If the DACs are current output, you'll have to use two-resistor current dividers. FWIW, -John ================= > Hi, > I am constructing a phase meter to monitor the phase creep of clocks. > It consists of a BCD counter counting say microseconds that has its > count strobed into a latch by a pulse from the clock. > The Latch drives a DAC which drives a pen recorder and an analogue > data logger. > Now I am familiar with R - 2R networks, and that method is used on > each decade > but the resistors that combine the decades in a 10:1 ratio are the > problem. > I have an approximate value, and I will probably have to trim them to > eliminate > digital errors later. > But I can not find a reference anywhere to how to calculate the correct > resistors or even a working example except for an old Analog Devices > data sheet which seems to use a different structure, by reducing the > supply voltage of each decade. > Can anyone Help? > > Cheers, Neville Michie > > _______________________________________________ > 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. > > _______________________________________________ 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.
