Signal direction in analog multiplexers/demultiplexers For analog MUX/DEMUX devices, are the channel and common terminals inherently uni-directional or bi-directional for analog signals?

Introduction / Context:
Analog multiplexers/demultiplexers (e.g., 74HC4051/4052/4053, CD4051 family) are built from CMOS transmission gates that act as electronically controlled analog switches. Understanding whether signals can flow in both directions is crucial when routing audio, sensor voltages, or DAC/ADC channels through a single IC.

Given Data / Assumptions:

• Device type: analog MUX/DEMUX using transmission gates.
• Channels and common terminal connect through low-resistance CMOS switches.
• Operation within voltage ranges specified by the datasheet.

Concept / Approach:

Transmission gates are symmetrical pass elements; when enabled, they pass analog voltages/currents in either direction with approximately the same on-resistance and bandwidth (within limits). Therefore, analog multiplexer channels are bidirectional; a device used as a mux can often be used as a demux and vice versa.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets specify I/O as bidirectional with an equivalent on-resistance R_on and leakage in both directions; functional diagrams show bilateral gates.

Why Other Options Are Wrong:

Unidirectional applies to many digital buffers, not these analog pass elements.

Parity and BCD are unrelated to analog routing.

Common Pitfalls:

Driving signals outside supply rails or violating current limits; forgetting that on-resistance and charge injection can distort high-precision signals though direction itself is bidirectional.

Final Answer:

bidirectional