When a large number of channels are multiplexed, the outputs of two or more multiplexers can be connected together and each multiplexer sequentially enabled. In the inhibit mode. the multiplexer draws less power and its output and inputs act as open circuits. Theoretically, an infinite number of channels can be accommodated in this way; in practice, the accumulated output capacitance and leakage of many paralleled multiplexers limits the speed and accuracy of the system. A much better method is the two-level multiplex system.
Two-level-multiplexer - schematic

The two-level system has a bank of high-speed switches at the output which sequentially switch between the four DG406s. Each DG406 is able to switch during the time the other three are being interrogated. The DG406s contribute leakage and capacitance at the output only, when they are switched on by the DG411-1/4 of the time. The two-level multiplex system is very useful in communications links, high-speed interfacing with comparators, or wherever a large number of channels must be multiplexed at high speeds.

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