EL4332
Expanding the Multiplexer
In Figure 29, a 3:1 multiplexer circuit is shown. The
expansion to more inputs is very straight forward. Since the
EL4332 has a fixed gain of 2, interstage attenuators may be
required as shown in Figure 28. The truth table for the 3:1
multiplexer select lines is:
TABLE 1.
X
Y
MUX OUTPUT
0
0
R3, G3, B3
0
1
R2, G2, B2
1
X
R1, G1, B1
When interstage attenuators are used, the values should be
kept down in the region of 50Ω–300Ω. This is to prevent a
combination of circuit board stray capacitance and the
EL4332’s input capacitance forming a significant pole. For
example, if instead of 100Ω as shown, resistors of 1kΩ had
been used, and assuming 3pF of stray and 3pF of input
capacitance, a pole would be formed at about 53MHz.
FIGURE 29. TYPICAL CONNECTION FOR A 3:1 COMPONENT VIDEO MULTIPLEXER
10