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Help with electronics, Op-amps and so on.

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sarah90

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(b) For the active filter circuit in (a) sketch the circuit. Then given that Ri = 10 kΩ, Ci = 10 nF, the feedback resistor Rf = 500 kΩ and the op-amp is a 741, determine the values of;
(i) The -3-dB frequency.
(ii) The time constant τ (in milliseconds)
(iii) The maximum voltage gain of this circuit in dB.
(iv) The voltage gain in dB at a frequency of f = 1 kHz.
 
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crutschow

Well-Known Member
Most Helpful Member
So is there anything you understand about the questions?

We need a post of the circuit sketch.
 

sarah90

New Member
Op-amps second part




(b) For the active filter circuit in (a) sketch the circuit. Then given that Ri = 10 kΩ, Ci = 10 nF, the feedback resistor Rf = 500 kΩ and the op-amp is a 741, determine the values of;
(i) The -3-dB frequency.
(ii) The time constant τ (in milliseconds)
(iii) The maximum voltage gain of this circuit in dB.
(iv) The voltage gain in dB at a frequency of f = 1 kHz.

I need help as I find it too difficult to do.
 

crutschow

Well-Known Member
Most Helpful Member
Where is C1 connected on your schematic?

So you have no understanding of a simple RC filter or how an op amp works?
 

crutschow

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You didn't answer my first question about C1.
 

crutschow

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Please don't double post.
 

SneaKSz

Member
H(z)= -Z2/Z1 ,

Z2=Rf
Z1=R1+1/jwC1 = (1+jwR1C1)/(jwC1)
H(z)= -Z2/Z1 =- s*Rf*C1/(1+sR1C1)
t=R1C1
-3dB = w=1/t => f= 1/(2*pi*t) = 1591.55 Hz

max voltage gain is when XC1 ~ 0 ohm => Gain = 20log*(rf/ri)=33.97dB

at last voltage gain at 1kHz =

Zi = R1+1/jwC1 = R1-j/wC1 = 10K-j15915.5 = 18822,9<-9,04
H(Z)=Zf/Zi = 500k<0 / 18822,9<-9,04 = 26.56 => dB = 20log(26.56 ) = 28.48 dB

Simulated and the values are correct :)
 
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