English
Language : 

AKD4628A-B Datasheet, PDF (7/44 Pages) Asahi Kasei Microsystems – single chip CODEC that includes two channels of ADC and eight channels of DAC.
[AKD4628A-B]
c) Frequency response of filter
Frequency response of the 1st-order filter
| Amplitude |2 = K*{1+(f/fc2)2}/{1+(f/fc1)2};
K = 1+4.7k/4.7k = 2,
fc1 = 1/2πRC = 102.7kHz@R=4.7k,C=330p,
fc2 = K*fc1 = 205.3kHz
Frequency response referenced to output level of this board is as following table:
fin
DC
20kHz
40kHz
80kHz
Frequency Response
0dB
-0.121dB -0.452dB -1.448dB
145kHz
-3dB
∞
-6dB
If the frequency response of filter influences the system, 1st-order LPF is also available as the following figure:
3.0Vpp
AK4628A
ROUT1 28
LOUT1 27 Same circuit
22u
10k
ROUT2 26 Same circuit
LOUT2 25 Same circuit
ROUT3 24 Same circuit
LOUT3 23 Same circuit
OP275GPZ
+
-
4.7k
4.7k
LPF
220
3300p
6.0Vpp
Signal
ROUT4 22 Same circuit
LOUT4 21 Same circuit
Example of LPF with flat response.
Frequency response of this LPF
| Amplitude |2 = 1/{1+(f/fc)2};
fc = 1/2πRC = 219kHz@R=220,C=3300p
Frequency response referenced to output level of this board is as following table:
fin
DC
20kHz
40kHz
80kHz
Frequency Response
0dB
-0.036dB -0.142dB -0.543dB
219kHz
-3dB
∞
-∞dB
The total frequency response of this board is sum of the external filter and internal LPF of AK4628A.
These filters are effective to attenuate the high frequency noise since some measurement units is sensitive for out-of-band noise.
<KM084901>
-7-
2007/07