Neville Michie wrote: > 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 > Neville
If there was an easier method it would probably have been used. It is probably simpler to use a different structure than the R-2R ladder. For example the R, 2R, 4R, 8R connected to a summing bus followed by a 4.8R interstage resistor connecting to the summing bus of the next decade etc works well. See attached partial circuit for details. Bruce
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