AK8857VQ Datasheet, PDF (19/105 Pages) Asahi Kasei Microsystems – Dual Channel Digital Video Decoder

[AK8857VQ]
Analog band limiting filter and analog clamp circuit
ç Analog band limiting filter
The characteristics of the AK8857 internal analog band limiting filter (anti-aliasing), which is in front
of the AD converter input, are as follows:
±1dB (~6MHz )
−35dB (27MHz)….Typical value
Filte_フr C_ィh_ルara_タc_ーter_特ist_性ic
10
0
-10
-20
-30
-40
-50
-60
-70
-80
0.1
1
10
100
Frequency[MHz]
Analog clamp circuit
ç In AK8857, the input video signal is clamping with analog circuit.
The clamping method is show as follows.
[CVBS signal decoding]
AK8857 clamps the input signal to sync tip. (analog sync tip clamp)
The clamp timing pulse, with its origin at the falling edge of the internally synchronized and
separated sync signal, is generated at approximately the central position of the sync signal.
[S-video signal decoding]
(Y signal)
AK8857 clamps the Y signal to sync tip. (analog sync tip clamp)
The clamp timing pulse, with its origin at the falling edge of the internally synchronized and
separated sync signal, is generated at approximately the central position of the sync signal.
(C signal)
AK8857 clamps the C signal to the middle level. (analog middle clamp)
The clamp timing pulse is generated at same timing with Y signal.
CVBS
analog sync tip clamp
Y
analog sync tip clamp
C
analog middle clamp
MS1189-E-01
-19-
2010/12