Help designing a filter for a DAC

1. May 5, 2010

cuallito

Okay, I want to add a filter onto the end of this circuit with the transfer function:

$$\frac{1 - 3e^{-sT} + 3e^{-2sT} - e^{-3sT}}{s^{3}T^{3}}$$
(T is the sampling period)

I'm using PSPICE. The denominator seems simple enough to implement, just 3 op-amp integrators in series (right?), but I'm not sure about the top. Seems like you could implement it as 1 - 3z^-1 + 3z^-2 - z^-3 when the signal's digital, but I'm not sure how to do that without getting lost in a mess of wires and I wouldn't know what parts to use. Seems like there should be an easy way to do it. I'm new to PSPICE so if anyone could help I'd be really thankful.

2. May 5, 2010

mohsenman

Ok, your right about the Z-transform equivalent and recognizing that z^-1 means a unit time delay, you could realize it with a clock controlled D-Flip Flop. However Im not really sure about your mixed analog/discrete view so let me know about the results.