AD8074_15 Datasheet, PDF (11/15 Pages) Analog Devices – Video Buffers with Disable

AD8074/AD8075
Triple Video Multiplexer
The AD8074 and AD8075 each have an output-enable function
that can be used to disable the outputs and put them in a high-
impedance state. Usually, for a unity-gain device, it is relatively
easy to provide high disabled impedance, because the feedback
path is from the output to a high-impedance input. However, for a
non-unity-gain part, the feedback provides a resistive path to
ground. This will usually dominate the disabled output imped-
ance, and make it a much lower value than the unity-gain device.
The AD8075 has an internal buffer that provides a low-impedance,
ground level output that terminates the feedback path during
enabled operation. In the disabled state, both this buffer output
and the amplifier output are disabled to a high impedance to
provide a high-impedance disabled state.
To construct a multiplexer, the outputs from one or more devices
are connected in parallel and only one device is enabled at a
time while all of the others are disabled. The two sets of inputs
are applied individually to each of the separate device inputs.
Figure 4 shows the circuit details for this function. The first RGB
Source 1 is input to the first AD8075. Each of the individual
signals is terminated to ground with 75 Ω to provide proper
termination for the input cables. In a similar fashion, the Source
2 signals are input to the second AD8075.
+5V
+5V
+5V
+
25␮F
0.1␮F
0.1␮F
0.1␮F
R
SOURCE 1 G
B
75⍀
75⍀
75⍀
75⍀
AD8075
75⍀
75⍀
OE
R
G OUTPUT
B
SEL1/SEL2
R
SOURCE 2 G
B
25␮F ₊
0.1␮F
0.1␮F
0.1␮F
–5V
–5V
–5V
+5V
+5V
+5V
+
25␮F
0.1␮F
0.1␮F
0.1␮F
OE
75⍀
75⍀
AD8075
75⍀
75⍀
75⍀
75⍀
Rev. B
25␮F ₊
0.1␮F
0.1␮F
0.1␮F
–5V
–5V
–5V
Figure 4. Mux
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