Seeking A->D converter IC

gstopp at fibermux.com gstopp at fibermux.com
Thu Oct 31 19:41:05 CET 1996


     What converstion time? You could make something with a counter, some 
     1% resistors, a latch, a high-frequency fixed oscillator and a 
     comparator, I'll bet....
     
     Drive the counter with the oscillator so it counts from zero to max 
     and resets. Take the counter outputs and stick them into a latch. Take 
     the counter outputs and also drive a passive R-2R ladder DAC, which 
     goes into one side of the comparator. The other input of the 
     comparator is your analog voltage in. Take the output of the 
     comparator and use it to drive the latch's clock input.
     
     So - x number of times per second (depending on the fixed oscillator 
     frequency) the counter counts from zero to max, so the DAC voltage 
     goes from zero to max. When the DAC voltage passes through the input 
     voltage, the latch takes a snapshot of the counter value at that 
     point. There's your A/D converted byte.
     
     You can add a hold feature by blocking the latch clock from the 
     comparator.
     
     The above is probably good enough for converting slowly moving 
     voltages, up to a few hundred hertz maybe. If you want to convert 
     audio this method will probably not be fast enough.
     
     - Gene


______________________________ Reply Separator _________________________________
Subject: Seeking A->D converter IC
Author:  Christopher_List at Sonymusic.Com at ccrelayout
Date:    10/30/96 9:21 AM


     
     
     
  Hi Guys,
     
  I've looked through the Analog Devices Databook, and poked around on at 
  the Nat Semi web site (though they don't have a selection tree, so I 
  couldn't get a feel for what the chips offered other than the bit count). 
  So far I haven't found what I'm looking for, which is;
     
  8 bit A->D converter IC
  Operation from +15V supply (that's the hard part) 
  Parallel CMOS output
  Relatively cheap (less than $15)
  No clock required
  Preferably with track and hold feature
     
  - Any suggestions?
     
  - Thanks,
  Chris
     
     




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