Afternoon,

If I have a 2volt input for the below circuit (LM741 opamp), the gain would be 1+586/1000 = 1.586 giving me an output of 3.172 volts

So 20 log (vout/vin) = log(1.586) = 0.2

Therefore 20*0.2 = 4db on the pass band as per the AC analysis.

So for the corner frequency I calculated as

3.172*0.707 = 2.24volts

Therefore 2.24/2 =1.121302 = log(1.121302) = 0.0492

Therefore 20*0.0492 = 1db as per the AC analysis.

But on the transient analysis the output is 2.14v not 2.24v at 1Khz, what causes this voltage drop ?

The same is for at 3Khz, the attenuation is -15.152db on the AC analysis

But when I calculate results from transient analysis I get,

20log (326mv/2) so (326mv/2) = 0.163, therefore log (0.163) = -0.7878

Therefore 20*-0.7878 = -15.75db.

thanks matt.

 

Two things:

1. What is the actual magnitude of the errors?
2. What is the value of VC and VE?

It is well known that the 741 is a very poor performer at lower power supply voltages. The output cannot even begin to approach the supply rails. IMHO, for the signal levels you are using ±10VDC supplies would be the minimum.

 

159Ω would be difficult for a 741 to drive. Try it again with 10nF and 15.9k, and see if that makes a difference. (And check the supply rails).
And if it’s just a SPICE simulation, you can afford a better op-amp!

 

hi matt,
This is what I see in LTS.
E
Look at the box data lower right. 2.41V

Added:
AC Analysis

 

Hi thank you for your replies. So Im using microcap software for my simulation. At fc which is around 1k, theres a 0.1v (2.14 to 2.24) difference from my calculated to the actual on the simulation results.
And at 3KHz the transient simulation shows the output amplitude at 326mV, but to give me the -15.2db as per the AC analysis it should be around 347mV (20log(0.34731/2)=~15.2db.

What is the reason for these differences? Is it due to losses within the opamp its self.
Hope that all makes sense, sorry I'm still learning.

 

Your extremely low resistor values are overloading the opamp. But most simulator programs do not care about overloading.