Analog Filter Implementation Using Active Filters - Practical Analog and Digital Filter Design - page 111

the randomly chosen values used when it is assembled. An example of a worst-
case analysis using PSpice is given in Section 4.8.
Another type of statistical test that is less rigorous than a worst-case test, but
probably more typical of what will happen in real life, is the Monte Carlo
simulation. In this test, component values are selected randomly within their
tolerance range and the circuit is tested to see if it meets the required
specifications. In most software packages, the values can be characterized as
having a Gaussian or uniform distribution. A number of Monte Carlo tests are
usually run to simulate the variation of component values that will be seen in the
normal assembly process.
4.8 USING WFILTER IN ANALOG FILTER IMPLEMENTATION
In order to see how WFilter helps in analog filter implementation, we generate the
component values and PSpice data file for the problem given in Example 4.5.
After we enter the filter specifications and design the filter, we can specify the
common component values and frequency specification in the Circuit
Specification dialog box shown in Figure 4.15. This dialog box is displayed by
selecting Options and then Generate Spice File from the menu bar.
Figure 4.15 Circuit specification dialog box.
We have entered a common capacitor value of 0.1 µF and common resistor
value of 10 kΩ. In addition, we have specified the frequency analysis range to be
from 10 Hz to 1 kHz. After pressing the Show File button, the PSpice text file
shown in Listing 4.1 is displayed. Notice that the first stage is first-order with an
R B value of one ohm (most circuit analysis tools do not accept zero ohms), while
the other two stages describe twin-tee notch filters. The original calculated values
are shown in the listing and should be used in a test analysis of the circuit to
determine if the specifications have been met. If the specifications are not met
with these “ideal” values, either the op-amp model is not adequate or an error has
been encountered in the design steps.