CD4051 Analog MUX Symbol
Definition: The CD4051 Analog MUX symbol represents an 8-to-1 analog multiplexer/demultiplexer integrated circuit that uses three binary select inputs to route one of eight analog or digital channels to a single common input/output pin, as defined in IEC 60617 and referenced in ANSI/IEEE 315 for multiplexer function blocks.
Also known as: analog mux, CD4051, 8:1 multiplexer, analog switch, channel selector.
What the CD4051 Analog MUX symbol means
The CD4051 Analog MUX symbol represents a bidirectional analog switch array that can connect any one of eight independent channels (CH0–CH7) to a single common node (COM). The three address/select inputs (typically A, B, C) plus an active-low enable (EN) determine which channel is active, and the direction of signal flow is determined by external circuit context.
In schematic diagrams, the analog multiplexer symbol is drawn as a rectangular block with numbered channel pins on one side and the common pin on the other, reflecting the IC's function as a configurable switch fabric. The CD4051 operates with both analog and digital signals up to the supply rail, making it a key component in data-acquisition systems, audio routing, and sensor-scanning circuits.
How to identify the CD4051 Analog MUX symbol
The CD4051 Analog MUX symbol appears as a rectangular block labelled 'AMUX', 'MUX 8:1', or 'CD4051'. Multiple channel input pins (CH0 through CH7, or a subset) enter the left side, and a single COM (common) pin exits the right side. Control pins for channel selection (A, B, C address lines) and an active-low enable (EN) are shown entering the bottom or top of the block. Some schematic tools draw a funnel or trapezoid shape inside the rectangle to emphasize the many-to-one routing function.
Function in a circuit
The CD4051 analog multiplexer routes one of up to eight analog or digital input signals to a single output (or vice versa in demultiplexer mode) under the control of three binary address lines. When the EN pin is low (enabled), the addressed channel is connected to COM with a low ON-resistance (typically 50–300 Ω depending on supply voltage). When EN is high, all channels are disconnected. This allows a single ADC or measurement instrument to sample multiple signal sources sequentially without additional discrete switches.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-12 (binary logic elements) depicts multiplexers as rectangular logic blocks with a funnel-like trapezoid, labelled with the MUX function and channel count. The CD4051 is also covered under IEC 60747-17 for analog switches. |
|---|---|
| ANSI/IEEE 315 | ANSI/IEEE 315-1975 and IEEE 91-1984 show multiplexers as rectangular blocks with an encoded selection input; the trapezoid body convention is common in ANSI gate-level schematics and mirrors the IEC rectangular-logic-block style. |
| Key difference | IEC and ANSI/IEEE use nearly identical rectangular-block representations for multiplexer function blocks; IEC 60617-12 strictly uses the rectangle with a funnel while ANSI/IEEE 315 allows both the trapezoid and rectangular forms. Pin labelling conventions (EN vs. INH, COM vs. OUT/IN) may differ between datasheets. |
Terminals / pins
| Pin | Name |
|---|---|
| ch0 | CH0 |
| ch1 | CH1 |
| ch2 | CH2 |
| en | EN |
| com | COM |
| vcc | VCC |
Typical values
Supply voltage VDD: 3 V to 15 V (CD4051B CMOS); ON-resistance RON: 50–300 Ω (VDD-dependent); channel count: 8 (CH0–CH7); address lines: 3 (A, B, C); bandwidth: typically DC to several MHz; maximum analog input range: 0 V to VDD.
Where the CD4051 Analog MUX symbol is used
- Multiplexing multiple analog sensor outputs (temperature, pressure, current) to a single ADC channel in microcontroller systems
- Audio signal routing and matrix mixing in embedded audio projects
- Sequential battery-cell voltage scanning in battery management systems (BMS)
- Automated test equipment (ATE) channel switching for measurement instruments
- Digital-to-analog signal routing in modular synthesizer and audio equipment designs
- Reducing pin count when interfacing multiple I2C or SPI peripherals sharing a bus
- LED matrix row/column scanning and display multiplexing circuits
Example
In a four-channel thermocouple data logger, four type-K thermocouple amplifier outputs connect to CH0–CH3 of a CD4051, with CH4–CH7 unused. A microcontroller drives address pins A, B, C to select each channel in turn, then triggers its onboard ADC to read the COM pin voltage. This lets one ADC port measure all four thermocouples without additional hardware.
Key facts
- The CD4051 Analog MUX is an 8-to-1 single-pole analog multiplexer/demultiplexer IC compatible with CMOS logic, defined under IEC 60747-17 and manufactured to JEDEC standard.
- The symbol has six functional pins in the hobbyist schematic block: CH0, CH1, CH2 (channel inputs), EN (active-low enable), COM (common I/O), and VCC; a full 28-pin DIP version additionally includes CH3–CH7, address lines A/B/C, VEE, and GND.
- Channel selection is controlled by three binary address inputs (A, B, C); the binary value 000 selects CH0, 001 selects CH1, up to 111 selects CH7.
- The device is bidirectional: it can function as a multiplexer (many-to-one) or demultiplexer (one-to-many) depending on which port is driven.
- ON-resistance is typically 80 Ω at VDD = 10 V and increases as supply voltage decreases, an important consideration for low-voltage 3.3 V microcontroller designs.
- The CD4051 passes analog signals up to the supply rails (rail-to-rail), unlike many CMOS switches that limit the input range to VDD−2 V.
- In schematics, the designator prefix is typically U or SW (e.g., U3 or SW1) and the component is labelled CD4051 or its equivalent (MC14051, HEF4051, TC4051).
- The active-low enable pin (EN/INH) must be held LOW for any channel to conduct; floating EN may cause undefined channel states and must always be driven.
Frequently asked questions
What does the CD4051 Analog MUX symbol look like in a schematic?
The CD4051 Analog MUX symbol is drawn as a rectangle or trapezoid block labelled 'MUX 8:1' or 'CD4051'. Channel input pins (CH0–CH7) enter the left side, the common COM pin exits the right side, and control pins (address lines A, B, C plus active-low EN) enter from the top or bottom.
What does the analog multiplexer symbol mean in a circuit diagram?
The analog multiplexer symbol means the circuit can select one of several analog signal paths and route it to a single output node. The three binary address pins determine which channel is active, allowing one ADC or instrument to read multiple sources by switching electronically.
What is the difference between IEC and ANSI representations of a multiplexer?
Both IEC 60617-12 and ANSI/IEEE 315 use rectangular logic blocks for multiplexers. IEC strictly uses the rectangle with an internal funnel label; ANSI/IEEE additionally permits a trapezoid body. Pin label conventions (EN vs. INH, COM vs. IN/OUT) may differ but the functional meaning is identical.
How many channels does the CD4051 analog multiplexer have?
The CD4051 has eight analog channels (CH0 through CH7) controlled by three binary address lines (A, B, C). Only one channel is connected to the common COM pin at any time. Cascading two CD4051 ICs can create a 16:1 multiplexer.
What is the designator letter for an analog multiplexer?
Analog multiplexers and switches are typically assigned the designator prefix U (integrated circuit) in ANSI/IEEE 315 schematics, for example U3 or U7. Some older schematics use SW for switch-type MUX ICs. The CD4051 part number appears beside the designator.
What standard defines the CD4051 analog multiplexer?
The CD4051 is a CMOS analog switch defined in JEDEC standards and covered by IEC 60747-17 (discrete semiconductor devices — analog switches). Its logic-block schematic symbol follows IEC 60617-12 and ANSI/IEEE 315 rectangular logic element conventions.
What happens if the EN pin on a CD4051 is left floating?
Leaving the EN (enable/inhibit) pin floating on a CD4051 is undefined behaviour. The pin has no internal pull-up or pull-down, so the switch state is unpredictable. EN must always be driven LOW to enable the selected channel or HIGH to inhibit all channels.
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