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error in op amp layout if using pads

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vashistha

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i am working on the layout of opeartional amplifier it gives the correct output but when i make pads for input, output and power and connect inputs, output and power to their respective pads the gain decreases by 20 dB. Pads consists only of square made of metal layers. If i increases the width of routing metal the gain increases by 1 dB. Please help me its urgent.
 

Is it schematic or post-layout simulations? What is your power consumption for this opamp? If it is a post-layout simulations, are You sure about correctness of the netlist?
 

it is a post layout simulation and power cosumption is between 500 uW to 1 mW

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yes...netlist is correct. when i do a post layout simulation without using input pads the result is correct
 

At least one of your assumptions must be wrong. I'd guess
that

Pads consists only of square made of metal layers.
Click to expand...

is one of them. Maybe you want to eyeball the netlists and
see just what kind of parasitics are thrown down.

But why pad parasitics would make that much of a problem,
is a question. Is amplifier drive extremely weak? Test
bench (input / feedback elements) so high-impedance that
pad parasitics somehow whack the operating point, or
the way you are picking up gain/phase numbers maybe
"works for ideal, not so good for nonideal" (like, assuming
AIN is the source amplitude and not the pin difference
voltage)?
 

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