Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uwm.edu!rpi!image.soe.clarkson.edu!dean
From: dean@image.soe.clarkson.edu (Dean Swan)
Newsgroups: comp.dsp
Subject: Re: 1 Bit D to A Revisited
Message-ID: <1989Nov22.185136.2273@sun.soe.clarkson.edu>
Date: 22 Nov 89 18:51:36 GMT
References: <7070002@hpnmdla.HP.COM>
Sender: dean@sun.soe.clarkson.edu (Dean Swan)
Organization: Clarkson University, Potsdam, NY
Lines: 19

From article <7070002@hpnmdla.HP.COM>, by sheppard@hpnmdla.HP.COM (Roger Sheppard):
 > anouncement that concerns a 1 bit D/A is from Phillips addressing the
 > problem of costly and inaccurate 16/18 + D/A's on low level signals
 > in CD players. They claim that by drastically oversampling at x256 they
 > convert the parallel words to an 11.3MHz bit stream that represents a
 > "pulse density modulation" that is similar to delta modulation in that
 > it pumps up and down a filter. The rf components can be removed by gentle
 > filtering because there is a wide frequency difference between the information
 > and the data rate. Also adverse effects on the phase of inband signals are 
 > minimized. Since only two states are needed to go up or down a simple 1 bit
 > D/A can be used and the filter designed with switched capacitor technology.

 This technique is also not entirely new.  As I posted a while back, when
this thread started, The General Instruments SP0256 speech synthesizer
chip has used this technique of D to A conversion for 5 or 6 years now.

-Dean Swan
dean@sun.soe.clarkson.edu