GS1881_09 Datasheet, PDF (21/29 Pages) Gennum Corporation – Monolithic Video Sync Separators

CH1
CH2
VIDEO
2
0.1μF
75W
4
8
6
680k _0.1μ
Figure 5-2: Test Circuit 1 and Video Waveforms for 0.1μF
CH1
CH2
VIDEO
2
0.01μF
75W
4
8
6
680k _0.1μ
Figure 5-3: Test Circuit 2 and Video Waveforms for 0.01μF
The interfering hum component is defined by:
v_HUM(t) = V_Pcos(2 πƒ_HUMt)
where: V_P = Peak voltage of AC hum
ƒ_HUM = Frequency of hum (50Hz or 60Hz)
The maximum rate of change of this hum signal occurs at the zero crossing points and is:
dv _HUM
dt
π 3π
t= ,
22
= ± V_P2πƒ_HUM
Since the horizontal scan period is much faster than the period of the interference
(63.5ms << 1/ƒ_HUM) a good approximation is to assume that the maximum line to line
voltage change resulting from the interfering hum is:
∆V_HUM = ± V _P2πƒ_HUM T_LINE
where: T_LINE = 63.5μs
GS1881, GS4881, GS4981 Monolithic Video Sync
Separators
Data Sheet
6926 - 5
November 2009
21 of 29
Proprietary & Confidential