Magic layout extraction

[rohinisan]

I designed a low pass filter using Differential difference amplifier for cutoff frequency 150Hz.When i simulate in ngspice i got correct cutoff frequency,but when i extract the magic layout and simulate using spice i'mgetting very low cutoff frquency around 40Hz.What may be the reason?............

 

[srizbf]

if extracted spice model works otherwise , but only cutoff frequency is reduced then you may have to relayout the leyers with reduced capacitance effect.

 

[crutschow]

For such a low frequency, layout capacitance is likely not a factor. I suspect there is in error in how it extracts the layout. Compare the two spice files to see what the difference might be. Perhaps there's an error in your layout.

 

[rohinisan]

how can we reduce the capacitance effect while drawing the layout.I tried by redraw but no effect,amplification of differential difference amplifier is very low.What may b the reason.................

 

[srizbf]

I tried by redraw but no effect,amplification of differential difference amplifier is very low.What may b the reason.................

if diff amplifier amplification is low , then parameters do not match to your designed value. one is , layout according to your requirement and dipending on thechnology files params will vary.
(assuming that your circuit designed is according to your spec)