# Amplifier Gain Charactersitics

Discussion in 'Analog & Mixed-Signal Design' started by Nathan Hale, Oct 15, 2016.

1. ### Nathan Hale Thread Starter Member

Oct 28, 2011
125
2
Hello Folks. I am trying to solve an amplifier problem.

I believe the DC gain of the circuit below is ( -10k ÷ 1k). Can you please let me know if that is correct?

I also think the AC gain would be [ (- 10k)(1k - 1000j) / (1k) (-1000j) ].

Did I figure out the DC and AC gains correctly?
Thank You

p.s. I am calculating the closed loop gain here, keeping in mind that this is an inverting amplifier.

Last edited: Oct 19, 2016 at 3:09 AM
2. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,294
482
Why did you leave capacitor out?

3. ### Nathan Hale Thread Starter Member

Oct 28, 2011
125
2
Cause the problem is asking me to find the DC and AC gains. i figured in the DC gain scenario the capacitor is nothing more than an open wire.

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,294
482
I believe your DC is correct. DC will not interrupt, the capacitor will fully charge and, in DC environment, will act as open circuit. Therefore the gain is determine my only R1 and R2, like you have done.

5. ### Nathan Hale Thread Starter Member

Oct 28, 2011
125
2
What about my AC gain? Did i figure out the AC Gain correctly? Can you please comment on my AC gain?

Last edited: Oct 16, 2016 at 11:28 AM
6. ### ramancini8 Member

Jul 18, 2012
438
113
yes you did the ac correct, but it might be better expressed as G = (R1/R2)(s + 1/R2C2) where s = jw.

Nathan Hale likes this.
7. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,294
482
I think w might be giving to OP. They just did not tell us what it is. That would explain the -1000j Ohm value of the capacitor. There is no need to go to s domain because w does not change, it is constant and is known to OP.

8. ### ramancini8 Member

Jul 18, 2012
438
113
In the s domain representation it is simple to graph the result in a Bode plot form so further analysis can be done visually. A matter of preference I think.

9. ### anhnha Active Member

Apr 19, 2012
748
44
No schematic?