How do you simulate a mixed-signal system?

I have a PWM based DAC that I want to simulate.
PWM is digital and I also have an analog low pass filter to make my DAC.
How do I simulate the whole system?
any free software for simulation? Even the student version would work.


Thank you in advance.

you can do a mixed mode simulation, commercial tools have support for that.
you can simulate everything in spice if the circuit is small enough.
you can simulate the digital alone, create a model for it, and then simulate it next to the analog.

all options have caveats.

blacki said:

How do I simulate the whole system?
any free software for simulation?

Click to expand...

LTSpice often gets favorable mention here. It's free and supports many Linear Technology IC's. You can select a large range of oscilloscope views.

Falstad's animated interactive simulator is easy to use. It supports a number of popular generic IC's. Its menu contains a library of all sorts of circuits (including ADC and DAC).
Free to download and use at:

www.falstad.com/circuit

Demo of 50Hz sinewave generator (created in Falstad's). The carrier is 800 Hz so that all waveforms are obvious in one view. However designers commonly choose several kHz for the carrier frequency.

The sine and ramp waves are input to the op amps which create PWM. (Notice this is not exactly the same method DAC. Falstad's does not support micro-controllers.)

Pulses go through LC low-pass filter. The load gets 50VAC sine-like waves.