Could some electronics guru please explain the difference between delta-sigma and continuous
-time delta sigma modulator. In my humble opinion, a modulator is inherently analog and continuous time - so why the different names ?
The actual signal is analog and continuous, but the sampled signal is digital and discrete. That why you get all the digital artifacts and Mr. Nyquist.
Well, your opinion may be humble but it flies in the face of convention. There are many modulation schemes (PCM comes to mind) that are 'modulated' by devices that have a mix of continuous time and sampling.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From what I gather reading through some articles on the subject, most sigma-delta converters use a switched-capacitor low-pass filter inside the modulator loop.
A CT sigma-delta modulator contains a continuous-time low-pass filter instead, basically one or more analog integrators chained together. Nothing new, in fact: The oldest (1962) implementations of the sigma-delta modulator already did it like that.
I imagine that switched-capacitor filters were introduced because they were easier to make in CMOS processes. When the technology had advanced to the point that analog integrators with sufficient specs could be made on the same chip, the architecture reverted to the --in fact superior-- CT style.
Comments, anyone?
Jeroen Belleman
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