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Help me to find out cut-off frequency and gain of Op-Amp LPF

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gary_choo

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My problem: Can anybody help me to find out the Cut-Off frequency and th Gain of the Op-Amp LPF as shown below? Thanks for your help.



Thanks everybody, thanks for your contribution on solving my problem. As suggested, i think i better work it out by using PSpice..

For the unit of the resistor and capacitor, please refer to the schematic drawing:
Resistot:
R1=122= 1200 ohm
R2=R4=682=6800 ohm
R3=223=22000ohm
R5=101=100ohm

Ceramic capacitor:
C1=331=330pF
C2=681=680pF

Electrolytic capacitor:
C3=100/16 means 10uF / 16V
C4=4R7/16 means 4.7uF / 16V

Dear cbsirio,
Can pls send me the calculation of the wo and Gain? Thanks.
 

op amp lpf

CutOff = 52557 Hz
Gain =~ 1 (in passband)

I have obtained this values by simulating it in PSpice.

Your circuit is a bit strange, but for me it is a VCVS 2° order lowpass filter with an attenuator in input (R1/R3).

C3 and C4 are for single alimentation of the op-amp: in op amps, its normal to have a dual alimentation and the signal referred to gnd: here you have an adaptation for a single alimentation where the signal is translated across vcc/2; I think R3 is also for this, to polarize the op-amp: its value is very higher than R1-R2-R4, and the attenuation is very low...

R5 is to compensate the bias current of op-amp.

If you want I can write you the formula to determine w0 and gain.

Ciao!

Sirio.
 

amp lpf?

Try to sweep in frequency from 0 to 100kHz and obtain both gain and cut-off frequency. Cut-off frequency is no magic number. We agreed it is 3dB.

You can try in Spice or you can try to sweep in frequency in hardware.

I in school have a VI (in LabVIEW) which I can sweep in frequency the function generator any kind of wave. Makes things easier in sweeps.

Same VI is one collecting data from Oscilloscope and ouputing frequency response (for the sweep performed) all because Agilent scope and function generator are GBIP capable and I can access their functions via LabVIEW instrumentation.

The easiest one for you is to go with Spice.



What are the units for caps and resistors in your schematic?
djalli
 

lpf op amp frequency

You can use an ac source for your input with a proper dc voltage. by running th ac simulation you can consider the spectrum of output voltage. the frequency where your gain falls about 3db is your cutt-off frequency. you can obtain the magnitude of output voltage easily.
 

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