miller effect in HSPICE

i have a doubt that whether HSPICE takes care of miller effect during it's AC analysis......this is because capacitances of 2 nodes between which a miller capacitance is connected are not shown by HSPICE of value what they should be after taking miller effect in account.


So accordingly does HSPICE calculates correct pole-zeros and what is then the reliability of stability analyis done ????

Normally, each SPICE model for a BJT contains the base-collector capacity CJC and, hence, the ac analysis will take care of the MILLER effect.
Was this your question ?

i have the same problem.

For circuit simulations I use PSpice.
I have checked the influence of the Miller capacitance as follows.

1.) To be sure that the capacitance between base and collector solely determines the frequency behaviour of a transistor stage I have increased the value of CjC from 7pF to 700 pF (BJT 2N2222). This was possible because PSpice allows editing of the model.

2.) Performing an ac analysis I have simulated the input impedance (real at low frequencies) and I have noticed the frequency where the impedance drops down by 3 dB.

3.) Assuming that this impedance decrease is caused by the capacitance CjC I have calculated 1/(ω*CjC*A) and - as a result - this value was indeed roughly identical to the impedance from point 2) under the condition that ω is the corner frequency as found in 2) and A is the maximum voltage gain -1 (as stated by the Miller theorem)..

4.) Fazit: The test has proved that SPICE calculates the Miller effect correctly.
If you are in doubt, first make sure that the frequency dependence really is dominated by the Miller capacitance.

LvW

Hi

I'm sure that Hspice ac analysis take cares of the MILLER effect.

If you use Hspice, then it is probably to use LX19(mn) to get information of miller effect.
http://www.ece.uci.edu/docs/hspice/hspice_2001_2-150.html