Digital potentiometer

A digital potentiometer (also called a resistive digital-to-analog converter, or informally a digipot) is a digitally-controlled electronic component that mimics the analog functions of a potentiometer. It is often used for trimming and scaling analog signals by microcontrollers.

A digital potentiometer is built either from a resistor ladder integrated circuit or a digital-to-analog converter although a resistor ladder construction is the more common. Every step on the resistor ladder has its own switch which can connect this step to the output terminal of the potentiometer. The selected step on the ladder determines the resistance ratio of the digital potentiometer. The number of steps is normally indicated with a bit value e.g. 8 bits equals 256 steps; 8 bits is the most common, but resolutions between 5 and 10 bits (32 to 1024 steps) are available. A digital potentiometer uses digital protocols like I²C or Serial Peripheral Interface Bus for signalling; some use simpler up/down protocols. Some typical uses of digital potentiometers are in circuits requiring gain control of amplifiers (frequently instrumentation amplifiers), small-signal audio-balancing, and offset adjustment.

Most digital potentiometers use only volatile memory, which means they forget their position when they are powered down (on power up they will report a default value, often their mid-point value) - when these are used, their last position may be stored by the microcontroller or FPGA to which they are interfaced. Some digipots do include their own non-volatile storage, so their default reading on power up will be the same as they showed before they were powered down.

While quite similar to normal potentiometers, digital potentiometers are constrained by current limit in the range of tens of milliamperes. Also, most digital potentiometers limit the voltage range on the two input terminals (of the resistor) to the digital supply range (0–5 VDC), so additional circuitry is required to replace conventional potentiometer. Further, instead of the seemingly continuous control that can be obtained from a multiturn resistive potentiometer, digital potentiometers have discrete steps in resistance.

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