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 potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.
A microcontroller is a small computer on a single integrated circuit. In modern terminology, it is similar to, but less sophisticated than, a system on a chip (SoC); an SoC may include a microcontroller as one of its components. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of ferroelectric RAM, NOR flash or OTP ROM is also often included on chip, as well as a small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications consisting of various discrete chips.
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.[ citation needed ] 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.
A resistor ladder is an electrical circuit made from repeating units of resistors. Two configurations are discussed below, a string resistor ladder and an R–2R ladder.
An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, cheaper, and faster than those constructed of discrete electronic components. The IC's mass production capability, reliability and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.
In electronics, a digital-to-analog converter is a system that converts a digital signal into an analog signal. An analog-to-digital converter (ADC) performs the reverse function.
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 midpoint 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.[ citation needed ]
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 a 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.
Another constraint is that special logic is often required to check for zero crossing of an analog AC signal to allow the resistance value to be changed without causing an audible click in the output for audio amplifiers.
Volatile digital potentiometers also differ from electro-mechanical ones in that on power up, the resistance will default to (possibly) a different value after a power cycle. Similarly, their resistance is only valid when the correct DC supply voltage is present. When voltage is removed, the resistance between the two end points and the (nominal) wiper are undefined. In an operational amplifier circuit, the off-state impedance of a real potentiometer can help stabilize the DC operating point of the circuit during the power-up stage. This may not be the case when a digital potentiometer is used.
Both electro-mechanical and digital potentiometers generally have poor tolerances (typically ±20%), poor temperature coefficients (many hundreds of ppm per degree C), and a stop resistance that is typically about 0.5-1% of the full scale resistance. Note that stop resistance is the residual resistance when the terminal to wiper resistance is set to the minimum value.[ citation needed ]
A multiplying DAC used as a digital potentiometer can eliminate most of these limitations. Typically a signal span of +15V to -15V is possible, with 16 bit control, i.e. 65535 discrete set points, and drift and non-linearity are negligible. However a DAC has to be initialised each time the system is powered on, which is typically done by software in an embedded microcontroller. A multiplying DAC can not be directly used as a rheostat (2 wire connection), but in that mode a digipot performs badly anyway, due to its temperature coefficient and resistance tolerance.
A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.
In electronics, an analog-to-digital converter is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an input analog voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities.
A preamplifier is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of noise and interference.
In electronics, an analog multiplier is a device which takes two analog signals and produces an output which is their product. Such circuits can be used to implement related functions such as squares, and square roots.
In electronics, a voltage divider is a passive linear circuit that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). Voltage division is the result of distributing the input voltage among the components of the divider. A simple example of a voltage divider is two resistors connected in series, with the input voltage applied across the resistor pair and the output voltage emerging from the connection between them.
In electronics, a sample and hold circuit is an analog device that samples the voltage of a continuously varying analog signal and holds its value at a constant level for a specified minimum period of time. Sample and hold circuits and related peak detectors are the elementary analog memory devices. They are typically used in analog-to-digital converters to eliminate variations in input signal that can corrupt the conversion process. They are also used in electronic music, for instance to impart a random quality to successively-played notes
A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage.
Delta-sigma modulation is a method for encoding analog signals into digital signals as found in an analog-to-digital converter (ADC). It is also used to convert high bit-count, low-frequency digital signals into lower bit-count, higher-frequency digital signals as part of the process to convert digital signals into analog as part of a digital-to-analog converter (DAC).
A flash ADC is a type of analog-to-digital converter that uses a linear voltage ladder with a comparator at each "rung" of the ladder to compare the input voltage to successive reference voltages. Often these reference ladders are constructed of many resistors; however, modern implementations show that capacitive voltage division is also possible. The output of these comparators is generally fed into a digital encoder, which converts the inputs into a binary value.
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. To be referred to as electronic, rather than electrical, generally at least one active component must be present. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another.
Analog device is usually a combination of both analog machine and analog media that can together measure, record, reproduce, or broadcast continuous information, for example, the almost infinite number of grades of transparency, voltage, resistance, rotation, or pressure. In theory, the continuous information has an infinite number of possible values with the only limitation on resolution being the accuracy of the analog device.
In electronics, a plate detector is a vacuum tube circuit in which an amplifying tube having a control grid is operated in a non-linear region of its grid voltage versus plate current transfer characteristic near plate current cutoff in order to demodulate an amplitude modulated carrier signal. This differs from the grid leak detector, which utilizes non-linearity of the grid voltage versus grid current characteristic for demodulation. It also differs from the diode detector, which is a two terminal device.
The Kelvin-Varley voltage divider, named after its inventors William Thomson, 1st Baron Kelvin and Cromwell Fleetwood Varley, is an electronic circuit used to divide voltages, i.e. to generate an output voltage as a precision ratio of an input voltage, with several decades of resolution. In effect, the Kelvin–Varley divider is an electromechanical precision digital-to-analog converter.
A logarithmic resistor ladder is an electronic circuit composed of a series of resistors and switches, designed to create an attenuation from an input to an output signal, where the logarithm of the attenuation ratio is proportional to a digital code word that represents the state of the switches.
The following outline is provided as an overview of and topical guide to electronics:
A voltage-controlled resistor (VCR) is a three-terminal active device with one input port and two output ports. The input-port voltage controls the value of the resistor between the output ports. VCRs are most often built with field-effect transistors (FETs). Two types of FETs are often used: the JFET and the MOSFET. There are both floating-voltage controlled resistors and grounded floating resistors. Floating VCRs can be placed between two passive or active components. Grounded VCRs, the more common and less complicated design, require that one port of the voltage controlled resistor be grounded.