Doubt regarding considering the value of Slew Rate.

[amit.31]

Hi

While designing a 2-stage opamp, few specifications are to be known beforehand. One of those specifications is "Slew Rate".

For instance for calculating (W/L)1,2 = (wu^2*Cc)/(un*Cox*SR);where wu=unity gain bandwidth, Cc=Coupling capacitor, un=mobility Cox= Oxide cap & SR = Slew rate.

Let the SR = plus minus 5V/us & also all other values are known to us.

Now my doubt is whether we take SR=5V/us or 10 V/us & why?

Thanks & regards.

 

[godfreyl]

Normally, if you say SR=10V/uS, it means 10V/uS either way i.e. plus or minus 10V/uS.

 

[amit.31]

Thanks a lot godfreyl sir

But when i take SR = 10 (instead of 5) in different equations, my results for various (W/L)'s are coming almost same to the given (W/L)'s only with slight variations.
So, that's why i am a bit confused like which SR value should i consider for finding the W/L's.

 

[varunkant2k]

Slew rate is voltage to time slope. That line is as long as linear ( in positive/ negative -axis) will show the same slope (tangent). so if it is 5V/us, it will remain the same 5V/us. +ve or -ve slew rate is defined at separate instances, (for charging and for discharging the output node cap).
Most of the time +/-ve slew rate are of the same value.