Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site tekig.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!whuxl!whuxlm!harpo!decvax!tektronix!tekig!bruceh
From: bruceh@tekig.UUCP (Bruce Harrington)
Newsgroups: net.audio
Subject: Re: Carver CD Player & Technology
Message-ID: <2515@tekig.UUCP>
Date: Wed, 20-Mar-85 13:29:20 EST
Article-I.D.: tekig.2515
Posted: Wed Mar 20 13:29:20 1985
Date-Received: Sat, 23-Mar-85 00:27:43 EST
References: <14700008@hpfcms.UUCP> <5000001@hplsle.UUCP> <474@harvard.ARPA>
Organization: Tektronix, Beaverton OR
Lines: 46

> > 
> > Using 4x oversampling and 16 bit DACs is overkill since there is no
> > information available in the LSB's (unless one wants to manufacture it as
> > noise somewhere in the system).
> 
> You are right about the main reason for oversampling being to reduce the
> demands on the analog filter.  But you still should use 16 bit DAC's.
> Suppose your input signal is 17,18,17,18,17,18,...
> Whether your extra samples inserted before the digital averaging are
> 0's or repeats of the last sample makes no difference.  You still can
> get out a signal 17,17,17,17,18,18,18,18,17,17,17,17,... from this process,
> UNLESS you drop the lower two bits, in which case it will look flat.
> 
> 	John M. Sullivan
> 	sullivan@harvard

*** REPLACE THIS MESSAGE WITH YOUR LINE ***

     I'm not sure this is exactly what is going on in a 4x 14 bit oversampling
     system, but we are currently using the following system in an
     instrument to get 14 bit resolution from a 12 bit DAC.


     4 "time slices" of a 12 bit DAC are integrated over time to get
     voltages between the steps on the DAC.


		 DAC Output

     2 LSBs    | T1 | T2 | T3 | T4 |
     --------------------------------

       11      /--------------\____/      The low and high levels here are
                                          output voltage level N, and
       10      /---------\_________/      output voltage level N + 1,
                                          respectively, where N is the
       01      /----\______________/      12 bit result of dividing the
                                          intended 14 bit value by 4.
       00      \___________________/

     


     Bruce Harrington

     Tektronix, Beaverton