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參數(shù)資料
| 型號： | GS4981-CKA |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Monolithic Video Sync Separators |
| 中文描述： | 單片視頻同步分離器 |
| 文件頁數(shù)： | 12/14頁 |
| 文件大?。?/td> | 279K |
| 代理商： | GS4981-CKA |
12
520 - 23 - 03
I
CLAMP
C
C
2
C
75
VIDEO
INPUT
4
8
R
S
CLIP
- V
680k
0.1μ
6
(2) FIltering
In order to keep the input to output delay small and temperature
stable, no chrominance filtering is done within the device.
External filtering may be necessary if the input signal contains
large chrominance components (less than 77 mV from sync
tip) or has significant amounts of high frequency noise. This
filter can be a simple low pass RC network constructed by a
resistance (R
S
) in series with the source and a capacitor (C
)
to ground. A single pole low pass filter having a corner
frequency of approximately 500 kHz will provide ample
bandwidth for passing sync pulses with almost 18 dB
attenuation at 3.58 MHz. Care should be taken in choosing
the value of the series resistor in the filter since the source
resistance seen by the sync separator affects its performance.
As the source resistance rises, the video input sync tip starts
to be clipped due to the clamping current during the sync.
This clamping current is relatively large due to the
non-symmetric duty cycle of video. To a good approximation
the amount of sync clamp current can be calculated as
follows:
(
I
CLAMPAVG
) (T
SYNC
) = (
I
DIS
) (T
LINE
- T
SYNC
)
I
CLAMPAVG
(4.7
μ
s) = (11
μ
A) (63. 5
μ
s - 4.7
μ
s)
.
.
.
I
CLAMP
= 137.6
μ
A
AVG
This clamp current flows in the source resistance causing a
voltage drop equal to :
V
CLIP
= (
I
CLAMAVG
) (R
S
)
= (137.6
μ
) (R
S
)
The interfering hum component is defined by:
v
HUM
(t) = V
P
cos(2
π
HUM
t)
where: V
P
= Peak voltage of AC hum
HUM
= Frequency of hum (50 Hz or 60 Hz)
The maximum rate of change of this hum signal occurs at the
zero crossing points and is:
=
±
V
P
2
π
HUM
t =
2 2
dv
HUM
dt
π
3
π
Since the horizontal scan period is much faster than the period
of the interference ( 63.5
μ
s << 1/
)
a good approximation
is to assume that the maximum line to line voltage change
resulting from the interfering hum is:
V
HUM
=
±
V
P
2
π
HUM
T
LINE
where: T
LINE
= 63.5
μ
s
The total line to line voltage change (
V
T
) can then be calculated
by adding the hum component (
V
) and the droop
component (V
DROOP
). This calculation results in two cases:
To correct for
V
T
in case A, the input stage must be able to
charge the input capacitor
V
T
volts in 4.7
μ
s.
This is not a
constraint as the typical clamping current of 650
μ
A can
accomplish this for practical values of coupling capacitor.
58.8 mV
( )
4.7
μ
verifying that there is enough clamping current
V
t
= 29.4 mV + 29.4 mV = 58.8 mV
.
.
. i = 0.022
μ
μ
A
which is less than 650
μ
A.
Fig. 22 Simple Chrominance Filtering
Case A
Case B
V
T
V
T
V
T
=
V
HUM
+ V
DROOP
.
.
. V
DROOP
= 11
μ
- 4.7
μ
) = 29.4 mV
0.022
the maximum amount of 60 Hz hum that could be rejected
would be when:
The only way to compensate for
V
T
in case B is to make
V
DROOP
>
V
HUM
. V
DROOP
is increased by decreasing the input
coupling capacitor value. Therefore the video designer can
increase hum rejection by decreasing the value of this capacitor.
The following is a numerical example:
choosing C
c
= 0.022
μ
F
V
DROOP
=
V
HUM
= V
P
2
π
HUM
T
LINE
V
DROOP
.
.
. V
P
=
PEAK
HUM
2
π
HUM
T
LINE
2
π
(60) (63.5
μ
)
29.4mV
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| GS4981-CTA | Monolithic Video Sync Separators |
| GS4981-IDA | Monolithic Video Sync Separators |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| GS4981-CKAE3 | 制造商:Gennum Corporation 功能描述:Video Sync Separator 8-Pin SOIC |
| GS4981CTA | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog IC |
| GS4981-CTA | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Monolithic Video Sync Separators |
| GS4981-CTAE3 | 制造商:Semtech Corporation 功能描述:TAPE & REEL Sync Separators |
| GS4981-IDA | 制造商:Rochester Electronics LLC 功能描述: 制造商:Gennum Corporation 功能描述: |
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