Glossary Terms and Definitions Beginning with the Letter R

R See Resistance
R-2R 1. Short for R-2R ladder: A method for D/A conversion which employs a ladder-shaped resistor array composed of two resistor values: R and 2R. Each bit in the digital input switches a ladder's rungs in and out of the network to change the output voltage by an amount proportional to the significance of the bit.

2. Rail-to-rail

RAC Remaining absolute capacity (mA-hr)
Radio Frequency Identification See RFID
Radio Frequency Interference See RFI
RAID Redundant Array of Independent Disks: A redundant array of inexpensive disks. RAID is a performance-enhancing method of storing the same data in different places on multiple hard disks to achieve speed and/or data redundancy.
rail-switching See Class G
Rail-to-Rail Input The allowable input signal range includes the supply voltages.
Rail-to-Rail Input or Output The allowable input and output voltage ranges include the power-supply rails.
RAM Random access memory
Random Jitter Random jitter (RJ) includes all jitter components not defined as deterministic jitter (i.e., the jitter that is not related to the signal and known noise sources).


RAR Remaining active runtime (min)
RC Resistance-capacitance; resistor-capacitor. In particular, an RC network is a network composed of resistors and capacitors in a series-parallel combination, usually to filter or delay a signal.
rcvr See Receiver
RE Remaining energy (joules)
Real Time Clock See RTCs
Received Signal Strength Indication See RSSI
Received Signal Strength Indicator See RSSI
Receiver A circuit that accepts signals from a transmission medium (which can be wireless or wired) and decodes or translates them into a form that can drive local circuits.


  • A radio receiver that detects and demodulates the signal from the airwaves
  • An ultrasonic receiver that turns ultrasound signals into electrical signals
  • A line receiver that receives signals from a wire or backplane
  • A standard interface receiver (e.g., USB, serial, LVDS)
  • A fiber optic device that translates light pulses into electrical signals
Recording Industry Association Of America See RIAA
Recovery Time The time for a sensor to return to baseline value after the step removal of the measured variable. Usually specified as time to fall to 10% of final value after step removal of measured variable.
Redundant Array Of Independent Disks See RAID
REF REF is a term that appears on IC package drawings in reference to dimensions. It stands for REFERENCE and indicates that this is a reference dimension, calculated or based on another dimension.

For example, the dimension from the first pin to the last pin in the row of a DIP (dual inline package) usually is tagged as REF because it is a multiple of the distance from pin-to-pin. In the case of a 16-pin DIP, the first pin to last pin dimension is 7 times the pin-to-pin dimension (7 spaces between 8 pins).

Regulator See Voltage Regulator
Relay A relay is an electromagnetic switching device consisting of an armature which is moved by an electromagnet to operate one or more switch contacts.

Some advantages of relays are that they provide amplification and isolation and are straightforward. They can switch difficult voltages (e.g. RF or high-powered AC) with complete isolation and no worries about level translation.

Relay disadvantages, compared to solid-state switching, include power efficiency, noise (both mechanical and electrical, including "contact bounce"), size, speed, and reliability. Analog switches are commonly used instead of relays in signal switching applications.

Driving a relay can be tricky because it's an inductive load. Special relay drivers are often used. Contact bounce is another issue. Search the Maxim site for the term "relay" to see application notes on relay driving and for relay driving products.

Remote Diode A diode or diode-connected bipolar transistor used as a temperature-sensing element, often integrated onto an integrated circuit whose temperature is to be measured.
Remote Temp Sensor See Remote Diode
Remote Temperature Temperature at a location other than at the die of the temperature-measuring integrated circuit.
Remote Temperature Sensor A remotely located PN junction used as a temperature sensing device, usually located on an integrated circuit other than the one doing the measurement.
Request To Send See RTS
Resistance Resistance, represented by the symbol R and measured in ohms, is a measure of the opposition to electrical flow in DC systems. Resistance is the voltage across an element divided by the current (R = V/I).
Resistance Temperature Detector See RTD
Resonant Circuit A resonant, or tuned, circuit combines an inductor and capacitor (or mechanical equivalents such as a crystal or MEMS oscillator) to make a circuit that is responsive to a frequency. Depending on the configuration, the circuit can have a high or low impedance at the resonant frequency and operate as bandpass or band stop filter, or an oscillator.

It may be called an LC or LRC circuit because of the inductive (L), resistive (R), and capacitive (C) components used.

An older name is "tank circuit," because its operation is analogous to a tank in a fluid system, in which the dimensions of the tank define the natural frequency observed when fluid is pulsed through the tank.

Response Time The time for a sensor to respond from no load to a step change in load. Usually specified as time to rise to 90% of final value, measured from onset of step input change in measured variable.
Return To Zero See RZ
Reverse Breakdown Voltage See Peak Inverse Voltage
Reverse Recovery Time When switching from the conducting to the blocking state, a diode or rectifier has stored charge that must first be discharged before the diode blocks reverse current. This discharge takes a finite amount of time known as the Reverse Recovery Time, or trr. During this time, diode current may flow in the reverse direction.
RF Radio Frequency: An AC signal of high enough frequency to be used for wireless communications.
RFDS Radio frequency design system
RFI Radio Frequency Interference: Unwanted noise from RF sources.
RFID Radio Frequency Identification: A method for uniquely identifying an object using a tag or module that carries a unique ID number, or code. Identification can be made using wireless (RF, or radio-wave) connection, meaning no line-of-sight or physical contact is needed. There are many different ways to achieve RFID and many applications including pet ID, identification of parts on an assembly line, tracking goods in manufacturing or retail settings, etc.

Also see: NFC/RFID Products

RFPF Positive reference
RH Relative humidity
RI Reference input; ring indicate
RIAA Recording Industry Association of America
Ripple Rejection Ripple Rejection is the ability of an amplifier to maintain accurate output voltage despite AC fluctuations in the power supply.
RISC Reduced instruction set computer (RISC): Computer hardware designed to support a short list of simple instructions. This makes the hardware simpler and faster, since it does not need to accommodate complex instructions.

Although more instructions must be executed for some operations, a RISC architecture can be faster, depending on the instruction mix, the design of the instruction set, and how effective the compilers and support software are in translating operations into optimized instructions.

RJ See Random Jitter
RMS Root mean square
RNPF Negative reference
Robbed Bit Signaling See Channel Associated Signaling
ROM Read-only memory
RRC Remaining relative capacity: The percent of the full charge that remains in a power cell.
A serial interface published by the EIA for asynchronous data communication over distances up to a few hundred feet. Characterized by a single-ended (not differential) physical layer, it uses one signal wire for transmission, another for reception, and a common wire (ground), plus some timing and control signals. Its specifications are rooted in electromechanical equipment signaling (Teletype machines). Still a very common interface but largely replaced by USB in recent years.
The term "serial" interface is often used for an RS-232 interface. The usage is not quite accurate—while RS-232 is a serial interface, there are other serial interfaces in addition to RS-232.
When it was introduced in 1987, the MAX232 rapidly became the most common way to implement RS-232 because it required only a single 5-volt supply. On-board DC-DC converters developed the odd voltages required by the official spec.
(Maxim still manufacturers the MAX232 and makes a wide range of newer products as well.)
See Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards to learn about the differences between RS-232, RS-422, and RS-485.
RS-232C See RS-232
RS-422 See RS-422/RS-485
RS-422/RS-485 RS-485 and RS-422 are serial interface standards in which data is sent in a differential pair (two wires, or twisted pair cable), which allows greater distances and higher data rates than non-differential serial schemes such as RS-232. See: Differential Signaling.

RS-485 and RS-422 can be configured for full-duplex or half-duplex bus systems.

See Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards to learn about the differences between RS-232, RS-422, and RS-485.

RS-485 See RS-422/RS-485
RS232 See RS-232
RS422 See RS-422/RS-485
RS485 See RS-422/RS-485
RSA A public key cryptographic algorithm named after its inventors (Rivest, Shamir, and Adelman). It is used for encryption and digital signatures. RSA was developed in 1977 and is today the most commonly used encryption and authentication algorithm.
RSR Remaining standby runtime (min)
RSSI Received Signal Strength Indicator (or Indication): A signal or circuit that indicates the strength of the incoming (received) signal in a receiver. (The signal strength indicator on a cell phone display is a common example).

RSSI is often done in the IF stage before the IF amplifier. In zero-IF systems, it is done in the baseband signal chain, before the baseband amplifier.

RSSI output is often a DC analog level. It can also be sampled by an internal ADC and the resulting codes available directly or via peripheral or internal processor bus.

RTCs Real-time clock: Integrated circuit that contains a timer that supplies the time of day (and often, the date). An RTC generally contains a long-life battery to allow it to keep track of the time even when there is no power applied.

See the Real Time Clocks page for much more information.

RTD A Resistance Temperature Detector (RTD) is a device with a significant temperature coefficient (that is, its resistance varies with temperature). It is used as a temperature measurement device, usually by passing a low-level current through it and measuring the voltage drop. A thermistor is a common type of RTD.
RTS Request to send: A data communications signal (e.g. RS-232)
Rx Receive
RZ Return to Zero: A binary bitstream encoding scheme in which the signal returns to zero voltage in between the data bits. The signal has three valid levels: High, Low, and the return to zero volts after each bit.