simulating a digital control loop

John Larkin · 2010-03-29T16:11:48+00:00

I'm designing a gadget that uses an ARM uP, with 12-bit mux'd ADC anda 10-bit DAC, to essentially make a current and voltage regulatedpower supply. The ADC will measure voltage and current and the DACwill control a fairly soft source-follower series-pass mosfet. Thecustomer load could be most anything.I think it would be time-effective to simulate the control loop whilethe PC board is being fabbed, so we don't have to play with dynamicsas much in the critical delivery path. I can simulate it as an analog loop using LT Spice, as I'm familiarwith that and could get it done quickly. It would be handy if I couldalso use the same model in digital mode, which would add samplingdelays and maybe even quantization.Any thoughts on how to do this?I note here that more and more formerly-analog control loops, thingslike switching power supplies, motor drivers, power amps, will begoing digital in the future. Some of the ARM chips are selling forunder a dollar. Analog parts will, I think, increasingly be used forthings like amplification, and less for computation.John

Mar 29, 2010 45 Replies

Rate this thread:

Jim Thompson 16 years ago

A little over a year ago I made up a behavioral 10-bit DAC, so I could quickly self-check a 10-bit SAR-based (device-level) ADC in simulation.

I know, in developing the ADC, that I used the behavioral DAC along with CMOS-level stuff to develop the SAR timing.

So I'd guess it's be easy enough to make a fully behavioral SAR-based ADC.

What kind of behavioral ADC's would you like to see?

I like a modeling challenge... that's how I keep myself amused (besides lurking here) while long term simulations are churning.

(A behavioral sample-and-hold is trivial ;-) ...Jim Thompson

Vote

JosephKK 16 years ago

Since you asked:

A. 12 bit ADC made with 2 ea 8 bit flash ADC in a coarse-fine conversion,

250 MSPS B. Two slope and 4 slope integrating converters 20-bits or more, as fast as it can go. C. A 14-bit or more SAR ADC >10MSPS D. A 12-bit 50 MSPS CVSD ADC

And realizing any of these in the real world could pay off handsomely.

Vote

John Larkin 16 years ago

Most of those performance points are already available as standard ICs. But the faster ICs are mostly pipeline designs, and the big-bits boys are delta-sigma. SARs are currently peaking out around 2 MHz.

John

Vote