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Analog switch vs Digital switch | Difference between Analog switch and Digital switch

This page compares Analog switch vs Digital switch and mentions difference between Analog switch and Digital switch. It covers basics of analog switch vs digital switch including their definitions and working in order to derive difference between analog switch and digital switch.

Introduction:  As we know there are two types of signals viz. analog and digital. Both of these signals are used to carry information from one place to the other. Analog signal is continous in nature which changes over time. Digital signal is discrete in nature and changes in particular shape to represent digital information in the form of zeros and ones. Typically analog signal is represented by sine waves whereas digital signal is represented by square waves.

Analog Switch


analog switch
Figure-1 : Analog Switch, Image Courtesy: Texas Instruments

• Analog switch operates on analog signals.
• Function: It is designed to pass or to isolate analog signals. In other words, it is a switching device which helps in switching or routing analog signals based on control signal.
• Analog switch Examples: CD4066B (CMOS Quad Bilateral Switch), SN74HC4066 (quadruple bilateral analog switch) from Texas Instruments.
• It also often exhibits good digital signal performance.
• Analog switches operate similar to relays but they do not consist of any moving parts.
• They are also known as bilateral switches as they pass signals in both the directions.
• Analog switches are available in different packets such as through-hole technology and surface mount technology.

How does analog switch work ?

Analog switch usually consists of pair of MOSFET transistors one N-channel device and the other P-channel device. The device shown in the figure-1 can pass signals in either directions during ON state and isolates terminals during OFF state. Control input with positive and negative voltages are used to make device ON and OFF respectively. The device is called parallel n-channel/p-Channel FET Switch.

Ideal switch
Figure-2: Ideal switch working, Image Courtesy: Texas Instruments

As shown in figure-2, in an ideal switch, applied input signal at "left I/O pin" produces identical output signal at "right I/O pin". Practically there will be loss incurred to the signal when it traverses from input to output port. Analog switches are mainly of two types viz. mechanical and solid state. Solid state switches are made of CMOS or FET devices.

Typical specifications to be considered while selection of analog switch are as follows.
• On-resistance: The resistance between input and output terminal when switch is ON. It is in few hundred ohms range.
• Off-resistance: The resistance between input and output terminal when switch is OFF. It is in megaohms or gigaohms range.
• Signal Range: The range of voltages from minimum to maximum which are passed through the analog switch are called its range.
• Charge injection : The effect results into injection of small electric charge into the signal when switch is switched ON. This causes small spike or glitch.
• Feedthrough: It is related to ability of switch to block signals when it is off. Parasitic capacitance allows higher frequencies to pass through the switch and hence switch appears to be in ON state.
• Crosstalk : There are two types viz. control (enable) to output crosstalk and crosstalk between switches. The first one refers to how much control signal input is decoupled from the output of the switch.

Digital Switch


digital switch
Figure-3 : Digital Switch, Image Courtesy: Texas Instruments

• Digital switch operates on digital signals.
• Function: It is designed to pass or to isolate digital signal signals.
• Examples: CBT and CBTLV are digital switches from Texas Instruments.
• It also exhibits capability to pass analog signals satisfactorily.
• Digital switches are used in computing applications for multibit switching.
• There are wide applications of digital switches which include multiplexing of USB peripherals, ethernet multiplexing etc.

The figure-3 depicts digital switch logic diagram. As shown multiple digital switches are incorporated between input lines (A1 to A8) and output lines (B1 to B8). OE' signal is used to enable switch in different states i.e. ON or OFF.

Analog switch vs Digital switch | Difference between Analog switch and Digital switch

Following table compares analog switch vs digital switch and mentions tabular difference between analog switch and digital switch.

Analog switch Digital switch
It operates mainly on analog signal. It operates mainly on digital signal.
High power consumption Low power consumption
Lower performance Higher performance
Lower speed of operation due to analog components Higher speed of operation
Can not be stored. Can be stored in digital form with minimum space requirements.
More expensive Less expensive

Conclusion: In order to understand basics of Analog switch vs digital switch i.e. difference between analog switch and digital switch, also refer Analog switching vs Digital switching >>.

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