Maker Pro
Maker Pro

Wideband Amplifier help

sr36

Jan 25, 2014
4
Joined
Jan 25, 2014
Messages
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.

Thanks for your help.
 

Attachments

  • Capture.JPG
    Capture.JPG
    90.3 KB · Views: 126

Laplace

Apr 4, 2010
1,252
Joined
Apr 4, 2010
Messages
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

  • Mathcad - Mathcad-EP45.pdf
    25.7 KB · Views: 239

sr36

Jan 25, 2014
4
Joined
Jan 25, 2014
Messages
4
Hey,

Thank you for your help.
I'm going to look into your calculations right now.
 

sr36

Jan 25, 2014
4
Joined
Jan 25, 2014
Messages
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
Joined
Apr 4, 2010
Messages
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

  • Mathcad - Mathcad-EP45-1.pdf
    25.9 KB · Views: 186

sr36

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