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From: jeh@dcs.simpact.com
Newsgroups: sci.electronics
Subject: Re: ..but what about _output_ filtering for D/A's?
Message-ID: <1723.2719ec29@dcs.simpact.com>
Date: 16 Oct 90 00:04:41 GMT
References: <1319@beguine.UUCP>
Organization: Simpact Associates, San Diego CA
Lines: 29

In article <1319@beguine.UUCP>, Jeff.Miller@samba.acs.unc.edu (Jeff Miller)
writes:
> [...] I don't recall any treatment of the need and mathematics of filtering
> the output of a D/A converter. I would imagine at CD or DAT frequencies
> it wouldn't be too critical as any harmonics would be ultrasonic (or would
> they? 

No no no.  The output filter (aka the "reconstruction filter") is an essential
part of the process.  

Also be aware that the input to this filter is NOT a step waveform, but rather
a series of pulses -- one pulse per sample.  Ideally the pulses should be of
zero width. 

> If the requirements are as stringent as the input filtering requirements,
> I may have some trouble. 

yep.  

> Would mathematically interpolating a few output
> levels between each input sample help, and deos that technique have a name
> I should look out for?

yes... I believe it's called oversampling with digital filtering.  

	--- Jamie Hanrahan, Simpact Associates, San Diego CA
Chair, VMSnet [DECUS uucp] and Internals Working Groups, DECUS VAX Systems SIG 
Internet:  jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com
Uucp:  ...{crash,scubed,decwrl}!simpact!jeh