hello svante,
Am Freitag, 17. November 2006 18:57 schrieb Svante Hermansson:
Christian Klippel wrote:
Am Freitag, 17. November 2006 17:26 schrieb Steffen:
I read about it in Delton T. Horns Music Synthesizers: A Manual of Design and Construction, if i recall correct, where the author suggested to use a S/H in connection with such a converter to save CPU power (when one wanted to keep a given CV for a period of time (faster then the port)).
this is only usefull if you want to digitize a changing signal. you use the s&h circuit (usually just a capacitor and a switch) to "freeze" the current value, so it stays stable while you digitze it. to digitize a signal, you basically need a dac, s&h and comparator. you load the s&h, set a value at the dac, and compare the two voltages with the comparator. you change the dac value so long until you have a match between the two voltages. then you discharge the s&h, and go ahead with the next sample.
Not only useful for digitizing an analog sample into the digital world, but also useful as a multiplexer. If you build a converter using one single ADC, you could share it to say 8 channels by sending them one at a time. Often (but not always) cheaper and easier than using 8 normal ADC's. Multiplexing with S&H works even on a low pass filtered PWM-signal if thats what someone (?) was planning on using...
you are right. but that also implies that the outputs are updated periodically, even if the value doesnt change. also, you need a buffering op-amp with high input impedance, to keep the voltage stable between the updates (a too high load will discharge the cap in the s&h). that continous update may also cause some ripple on the output, a thing that needs to be considered if you go for high resolution, like 16 bits....
nowdays you can get 8 channel, 12 bit dac's (like the tlv5610) for a low price, so i doubt that it is worth going the s&h way nowdays.
greets,
chris
mvh//Svante - with a homebuilt midi to 8-channel CV somewhere in some drawer...
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