Measurement Computing WBK Options - Manual (Page 23)

Programmable Low-Pass Filter Cards 988396 WBK12A and WBK13A, pg. 5
Predicting Amplitude Loss
The following equations can be used to predict the amplitude loss when passing a signal through either the
anti-alias or clock suppression filter.
Definition of equation terms:
Fin is the signal to be measured.
Falias is the cutoff frequency of the anti-alias filter.
Fclock is the cutoff frequency of the clock suppression filter.
Err 20 log
1
1
Fin
Falias
.
Err 20 log
1
1
Fin
Fclock
.
Total error, in dB, due to both filters is :
Etot 20 log
1
1
Fin
Falias
1
1
Fin
Fclock
. .
As an example, with the switched capacitor filter set to 10,000 Hz. and the input frequency set to 6000 Hz.
Fin = 6000
Falias = 33554
Fclock = 14848
Total amplitude loss = sum of both errors = -2.188 dB.
E1 20 log
1
1
6000
33554
.
E1 0.71446 =
E2 20 log
1
1
6000
14848
.
E2 1.47396 =
E1 E2 2.18843 =
Etot 20 log
1
1
6000
33554
1
1
6000
14848
. .
Etot 2.18843 =
Fx 1 2 , 8000 ..
Fp 33554
Fc 14848
E Fx ( ) 20 log
1
1
Fx
Fp
1
1
Fx
Fc
. .