AN501 Datasheet, PDF (5/11 Pages) Vishay Siliconix – The DG535/536 Wideband Multiplexers Suit a Wide Variety of Applications

AN501
Vishay Siliconix
A general-purpose 16-channel wideband multiplexer is shown in
Figure 7. Dc biasing is achieved with the divider network R₁ and
R₂. A wideband op-amp (CLC410) is configured to give an
inverting unity gain, while removing the +3 V dc by setting the
voltage on the non-inverting input to +1.5 V dc. The use of trimpot
R₇ and precision resistors allows accurate elimination of any dc
bias. This arrangement results in faster multiplexing rates than
capacitive decoupling while providing black-level clamping,
impedance matching for 75 W loads, and greater drive for
transmission stages, with no major compromise on signal quality
(distortion, frequency response, etc.)
Alternatively, the device supplies can be offset to eliminate the
need for 16 separate bias circuits. Such an arrangement, shown
in Figure 8, could be used in a security system or in a remote
industrial monitoring system. The DG535/536 positive supply and
ground pins (at –3 V) should be heavily decoupled to the video
camera ground connections.
The switching threshold of the device at a supply voltage of +15 V
is approximately between +6 V and +8.5 V above the substrate
potential (Figure 9). Since the substrate is held at –3 V, the
effective switching threshold referenced to ground is between
+3 V and +5.5 V. Thus, the device can still be controlled from
CMOS logic signals (provided that the logic 0 (V_AL) is less than
3 V and logic 1 (V_AH) is greater than +5.5 V).
+
Video
Input
0.1 mF
R₁
39 kW
S₂
R₂
10 kW
S₁₆
+15 V
R₅
470 W
CS
S₁
V+
D
DG535/536
CS
+15 V
A₀, A₁,
A₂, A₃
All GNDs
EN ST
R₃
470 W
R₄
18 kW
R₆
1.2 kW
–
CLC410
+
R₇ (1 kW l_in)
75 W
Video
Output
Control Logic
Address Bus
Video Cameras
FIGURE 7. General-Purpose 16-Channel Wideband Multiplexer
+12 V
1
2
EN CS ST V+
S₁
75 W
3
4
S₂
D
S₃
S_{4 DG535/536}
CLC111
1 kW
Video
Monitor
S₁₆
A₀, A₁, A₂, A₃
CS
All
GND
pins
–3 V
16
Address
Logic
Document Number: 70608
03-Aug-99
FIGURE 8. A Closed-Circuit Monitoring System
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