ECE4273/6273 spice checkoff exercise #5 pnj device params version 1.3
In order to assess circuit performance it is often necessary to address the parameters within the device model file. This can be accomplished fairly readily by the same parametric techniques used for circuit analysis.
In this case you will exercise a circuit used in another of your famous exercises, the parallel-configured diode charge pump, as represented by figure pCP4D-1. In this case we desire to investigate the effect of the junction parameter Cjo on circuit performance.
Figure pCP4D-1 . Four-stage voltage-multiplying circuit.
Although it might seem advantageous to merely make changes to the circuit used in exercise CPP4, you would do better by starting again from scratch, as follows:
First call up one of the 1n914 diodes. Save your file under whatever name suits you and call up the
Edit>Model>Edit model instance file which gives you access to the parameters for this diode. In this case, change the value of 4pf given to parameter Cjo to a parametric value { Cx }.
Likewise do the same for a capacitance, giving it a value of { Cp }.
Now construct a ‘subcircuit’ of form as indicated by figure pCP4D-2.
Figure pCP4D-2 . subcircuit for copy/paste tesselation.
Notice that now when you copy/paste this circuit to tessellate the four-stage construct, most of your components will be configured in exactly the form and content that you wish to test. This technique will serve you well in future expeditions.

(a) Your requirement is (therefore) to construct the circuit indicated by figure pCP4D-1 with values as indicated for input source and load. This circuit will then become your figure pCP4D-1 .
(b) Execute a time sweep for (0 < t < 1.5ms). Your step ceiling should be smaller than the period of the input frequency by at least a factor of two (this is also called the sampling theorem). Step the diode junction capacitance Cjo from 1 pF to 10 pF in steps of 1pF (Analysis>setup>Parametric) with Cx as a global parameter. Show the Vo(t) response as your figure pCP4D-2 . You should see an appreciable change in the
Vo(MAX) as result of your choice of Cjo as result of charge-splitting between Cjo and the (relatively small) pump capacitance {Cp}.
(c) Call up a goal function ( Performance Analysis option) that will give you Vo(MAX) vs Cjo . Hint: consider
YatX( , ). Show your result as your figure pCP4D-3 . Your result will probably be an approximately straight line with negative slope if you have done everything correctly.
(d) Capture the points (highlight and use Ctrl-C) generated by step (c) and drop them into the Excel spreadsheet. Using the spreadsheet X-Y (scatter) plot function plot Max(Vout) vs Cjo, just like was done in part (c) but include an extra y-axis that fits the data to the empirical equation
Max ( Vout )

V o
 mC
Jo
 bC
2
Jo for which you should find the best fit of parameters Vo , m and b to the data and show your results as a spreadsheet plot (snapshot) as your figure pCP4D-4. List the values of the fitted parameters in the figure title.
Part (d) is your first ‘real’ model of a device construct. (There will be more).