Different results of noise analysis in BSIM3v3

[tia_design]

Noise analysis

Hi, you guys,

I try to design low noise CMOS Op AMp. The input referred noise of simulation is bigger than my hand calculation results. The hand calculation results can be 0.8nVolts/rtHz for thermal noise, but the simulation results is 1.3nVolts/rtHz. What introduce such big difference? My model is BSIM3v3.

 

[flatulent]

Re: Noise analysis

Something is wrong with your hand calculations. It is difficult to design a circuit with below 1 nv/rt -hz )which is the noise from a 70 ohm resistor.) Yet your hand calculations have beat that by over three orders of magnitude.

 

[tia_design]

Re: Noise analysis

I'm sorry, my calculation is 0.8nV/rtHz, not 0.8pV/rtHz. I correct my typo. Thanks for replying

 

[flatulent]

Re: Noise analysis

The simulator takes the effects of every component in the circuit. Hand calculations just do the major noise sources. Another possibility is the active device models in the program are more accurate than your hand calculation model.