Analog multiplexers have sets of switches that connect several analog inputs to a common analog output, allowing a single analog-to-digital converter (ADC) to sample data from multiple inputs. Often, analog multiplexers are designed for routing pulse height analysis (PHA) data from multiple amplifier/detector circuits through a single ADC. Some analog multiplexers accept a serial input or can operate with only one power supply. Others can be enabled or disabled by applying a logic signal to the chip enable (CE) pin. Analog multiplexers with bilateral switching, fault-tolerant protection, on-chip electrostatic discharge (ESD) protection, and over-current protection are also available. There are two main European Union (EU) standards or certifications for analog multiplexers: End of Life Vehicles (ELV) and Restriction of Hazardous Substances (RoHS).
Selecting analog multiplexers requires an analysis of performance specifications. Examples include supply voltage, max Ron, power bandwidth, CON, COFF, propagation delay and power dissipation. Supply voltage (VS) refers to the source voltage range. Max Ron is the maximum resistance across the contact when the switch is ON. The power bandwidth or large-signal bandwidth of an amplifier refers to its ability to provide a maximum output voltage swing with increasing frequency. CON is the maximum capacitance when the multiplexer switch is ON. COFF is the maximum capacitance when the multiplexer switch is OFF. Propagation delay is the time interval between the application of an input signal and the occurrence of the corresponding output. For analog multiplexers, power dissipation is the total power consumption of the device. It is generally expressed in watts or milliwatt.
General specifications for analog multiplexers can be divided into three categories: configuration, normal condition, and application. There are five basic choices for configuration: 2x1, 3x1, 4x1, 8x1, and 16x1. In each, the first number refers to the number of inputs while the second indicates the number of outputs. With regard to normal condition, analog multiplexers are either normally open (NO) or normally closed (NC) when the switch is not energized. There are many different applications for analog multiplexers. Some products support a temperature range and meet mechanical and electrical specifications for audio, automotive, avionics, commercial, communications, computer, or data acquisition applications. Others are designed for industrial, medical and military applications. Analog multiplexers for portable devices such as personal digital assistants (PDA) are also available.
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