# Wideband Amplifier help

#### sr36

Jan 25, 2014
4
Hi,

I have two doubts about the circuit I have attached with this thread. I am testing this circuit to obtain the frequency response on a scope.

I have the option of testing the non-inverting configuration or the inverting configuration. I am testing the non-inverting configuration, so C4,C8 & C10 are not connected.

I calculated the cutoff freq to be 160Hz using 1/(2*pi*R9*C11) and the gain was found to be (1 + (R8/R9)) = 6.6.

Can someone verify if this is correct please? This is because after testing on the scope, I find that the gain is 2.5 at the pass band and the cutoff frequency (which gives a gain of about 0.707*2.5) happens at 500Hz. Not sure if some component is faulty or I have made errors in my calculations.

#### Attachments

• Capture.JPG
90.3 KB · Views: 126

#### Laplace

Apr 4, 2010
1,252
I calculated a gain of 16.4 dB in the passband (same as your 6.6x). But the 3 dB low pass cutoff frequency is 379 Hz. Calculations attached.

#### Attachments

25.7 KB · Views: 239

#### sr36

Jan 25, 2014
4
Hey,

I'm going to look into your calculations right now.

#### sr36

Jan 25, 2014
4
Hi

I was going through the calculations on paper and sure enough if adds up.
But why set Vcc = 0? Wouldn't that have any effects on our actual results because actual Vcc = 5.

Thanks

#### Laplace

Apr 4, 2010
1,252
Vcc should only affect the DC bias point, and if Vcc is held constant it should not affect the small signal analysis. Setting Vcc=0 simplifies the math considerably. I have attached an updated analysis where the result is an expanded polynomial instead of a factored polynomial.

#### Attachments

25.9 KB · Views: 186

#### sr36

Jan 25, 2014
4
thanks for clearing that up and the new attachment.

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