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Active_Notch_Filter.php   11748 Bytes    16-07-2014 00:19:22


Active Twin - T - Notch Filter Calculator



• Suiteable to attenuate a 50 Hz ( 60 Hz ) noise
• Select parts with low tolerance / equal value !
• Design of this calculator was inspired by : Ferdl
• Maybe helpful : FIND PARALLEL RESITORS

With passive networks, the Q is fixed to 0.25 - introducing a variable Feedback 'k' allows the Q to be adjusted. Changing the Q will also change the notch-depth. For numerical reasons, we limited the range of k : 1 < k < 99 [%].




Circuit Diagram :



Twin - T - Notch Filter

Calculations :



Center Frequency

[Hz]

Feedback

[%], 1.0 < k < 99.0

Bandwidth

[Hz]

Q

 

C1, C2

[nF]

C3

[nF]

R1, R2

[kΩ]

R3

[kΩ]

R4

[kΩ]

R5

[kΩ]






Transfer Function :




Active Notch Filter



Simulations :



Simulations were done using TARGET 3001. Center Frequency : 50 Hz

NOTE: Even the Simulations suggest Attenuations of 100 dB and more, real - life values are in the range of 40 ... 60 dB !

Parts used in Simulation :

R1 = R2 = 318.3 kΩ
R3 = 159.2 kΩ
C1 = C2 = 10 nF
C3 = 20 nF
R4, R5 : various values
OPAMP: LM358

Target 3001 FileActive_Notch_Filter_2.T3001




 

 k = 99 %
 R4 = 1 kΩ
 R5 = 99 kΩ
 B = 2 Hz
 Depth : 78.2 dB
 122.9 mV








 

 k = 90 %
 R4 = 10 kΩ
 R5 = 90 kΩ
 B = 20 Hz
 Depth : 97.2 dB
 13.8 mV








 

 k = 80 %
 R4 = 20 kΩ
 R5 = 80 kΩ
 B = 40 Hz
 Depth : 103 dB
 7.16 mV








 

 k = 70 %
 R4 = 30 kΩ
 R5 = 70 kΩ
 B = 60 Hz
 Depth : 106 dB
 4.79 mV








 

 k = 60 %
 R4 = 40 kΩ
 R5 = 60 kΩ
 B = 80 Hz
 Depth : 109 dB
 3.58 mV












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t1 = 3876 d

t2 = 689 ms

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