Glossary Terms and Definitions Beginning with the Letter H

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H Henry(ries): The unit of inductance.
H-Bridge A circuit diagram which resembles the letter "H." The load is the horizontal line, connected between two pairs of intersecting lines. It is very common in DC motor-drive applications where switches are used in the "vertical" branches of the "H" to control the direction of current flow, and thus the rotational direction of the motor.
Half-Duplex Data transmission over a circuit capable of transmitting in either direction, but not simultaneously.
Half-Flash An ADC architecture which uses a bank of comparators first to digitize the upper half bits, then uses a digital-to-analog converter (DAC) to subtract that voltage from the input, and then digitizes what remains of the input signal to get the lower half bits. Also see application note 748, "The ABCs of ADCs."
Handover Switching an on-going call to a different channel or cell in a wireless cellular network. Also known as "handoff."
Harmonic Distortion The presence of frequencies in the output of a device that are not present in the input signal, and are multiples of components of the input signal. Clipping is a common cause but other nonlinearities can also introduce harmonics.
HART Highway Addressable Remote Transducer (HART) communication is a commonly used mode of transmission for digital signals that are superimposed on the analog signal of a 4–20mA current loop.

The HART protocol is based on the phase continuous frequency shift keying (FSK) technique. Bit 0 is modulated to a 2200Hz sinusoidal signal, and bit 1 is modulated to a 1200Hz sinusoidal signal with a baud rate of 1200bps. These two frequencies can easily be superimposed on the analog current-loop signal, which is in the range of DC to 10Hz, without affecting either signal. This unique nature of the HART protocol enables simultaneous analog and digital communication on the same wire.

HAST Highly accelerated stress test; highly accelerated steam and temperature
HB LED High-Brightness LEDs are any of a new generation of LEDs bright enough for illumination applications such as automotive interior, exterior, and display; room and architectural illumination; task and general lighting; projection display; display backlights; and signage.

See: High-Brightness LED Drivers and Solutions

HBT Heterojunction bipolar transistor
HD Harmonic distortion
HD2 See Second Harmonic Distortion
HDLC High Level Data Link Control: An ITU-TSS link layer protocol standard for point-to-point and multi-point communications.
HDLC Controller See HDLC
HDSL High bit-rate Digital Subscriber Line: The oldest of the DSL technologies, it continues to be used by telephone companies deploying T1 lines at 1.5Mbps and requires two twisted pairs.
HDTV High-definition television: an all-digital system for transmitting a TV signal with far greater resolution than the analog standards (PAL, NTSC, and SECAM). A high-definition television set can display several resolutions, (up to two million pixels versus a common television set's 360,000). HDTV offers other advantages such as greatly improved color encoding and the loss-free reproduction inherent in digital technologies.
Heat Sink Mechanical device that is thermally-connected to a heat-producing electronic component, designed to conduct heat away from the device. Most heat sinks are aluminum and employ fins to increase surface area and encourage the transfer of heat to the ambient environment.
Heating-Ventilation-Air Conditioning See HVAC
heatsink See Heat Sink
HEMT High-electron-mobility transistor
Hertz See Hz
HF High frequency
HGLL High gain, low linearity
Hi-Z Hi-Z (or High-Z or high impedance) refers to an output signal state in which the signal is not being driven. The signal is left open, so that another output pin (e.g. elsewhere on a bus) can drive the signal or the signal level can be determined by a passive device (typically, a pull-up resistor).
High Bit-Rate Digital Subscriber Line See HDSL
high impedance See Hi-Z
High-Brightness LED See HB LED
High-Definition Television See HDTV
High-Side An element connected between the supply and the load. High-side current sensing applications measure current by looking at the voltage drop across a resistor placed between the supply and the load.
High-Speed Downlink Packet Access See HSDPA
High-Speed Packet Access See HSPA
High-Speed Serial Interface See HSSI
High-Speed Uplink Packet Access See HSUPA
High-Z See Hi-Z
Home RF Trademarked name for Home Radio Frequency, a networking technology which uses antennae and transmitters to provide wireless home networking via transmitted radio signals.
Home-Rf See Home RF
HomePlug HomePlug (Powerline) is an industry-standard method for transmitting data via the power lines. It can transmit audio, video, control signals, etc. HomePlug is a trademark of the HomePlug Powerline Alliance; Powerline is the generic term for the method.

See our Powerline product page.

PLC is an acronym for Powerline Communications.
HomeRF See Home RF
hot carrier diode See Schottky Diode
Hot-Swap A power supply line controller which allows circuit boards or other devices to be removed and replaced while the system remains powered up. Hotswap devices typically protect against overvoltage, undervoltage, and inrush current that can cause faults, errors, and hardware damage.
HotSwap See Hot-Swap
HP-IB See GPIB
HR High reliability
HSDPA High-Speed Downlink Packet Access (HSDPA) is a 3G radio interface standard in the HSPA family for wireless and cellular handsets or datacards that increase the datarate and improve the traffic handling of existing UMTS standards.
HSPA High-Speed Packet Access (HSPA) is a collection of radio interface standards for wireless and cellular handsets or datacards that increase the datarate and improve the traffic handling of existing UMTS standards.
HSSI High-Speed Serial Interface: A short-distance communications standard for data rates from 2Mbps to 52Mbps.
HSUPA High-Speed Uplink Packet Access (HSUPA) is a 3G radio interface standard in the HSPA family for wireless and cellular handsets or datacards that increase the datarate and improve the traffic handling of existing UMTS standards.
HTML Hyper Text Markup Language: Coding language used to create web pages.
HTS High-temperature semiconductor
HTTP Hyper Text Transport/transfer Protocol
Human Body Model An ESD test method where the ESD generator consists of a 100pF capacitor and a 1.5kohm series resistor.

See the following application notes that describe how ESD is generated, how it damages electronic systems, human body and machine models for testing, IEC compliance levels, and design approaches.

HVAC Heating, Ventilation, and Air Conditioning: Industry term for the systems and technology responsible for the heating, ventilation, and air conditioning in buildings. HVAC systems regulate comfort (temperature and humidity), energy efficiency, and air quality.

See: Maxim Solutions for HVAC designers.

Hz Hertz: A measure of frequency. An older term is cycles per second, or cps.