A logic probe is a low-cost hand-held test probe used for analyzing and troubleshooting the logical states (boolean 0 or 1) of a digital circuit. When many signals need to be observed or recorded simultaneously, a logic analyzer is used instead.
A logic probe is a low-cost hand-held test probe used for analyzing and troubleshooting the logical states (boolean 0 or 1) of a digital circuit. When many signals need to be observed or recorded simultaneously, a logic analyzer is used instead.
While most logic probes are powered by the circuit under test, some devices use batteries. They can be used on either TTL (transistor-transistor logic) or CMOS (complementary metal-oxide semiconductor) logic integrated circuit devices, such as 7400-series, 4000 series, and newer logic families that support similar voltages.
Most modern logic probes typically have one or more LEDs on the body of the probe:
A control on the logic probe allows either the capture and storage of a single event or continuous running.
When the logic probe is either connected to an invalid logic level (a fault condition or a tri-stated output) or not connected at all, none of the LEDs light up.
Another control on the logic probe allow selection of either TTL or CMOS family logic. This is required as these families have different thresholds for the logic-high (VIH) and logic-low (VIL) circuit voltages.
Some logic probes have an audible tone, of which vary across models. A model may 1) emit a tone for high logic state otherwise no tone, or 2) emit a higher frequency tone for a high logic state, lower frequency tone for a low logic state, and no tone for no connection or tri-state. An oscillating signal causes the probe to alternate between high-state and low-state tones.
The Logic Probe was invented by Gary Gordon in 1968 while he was employed by Hewlett-Packard. [2] [3]
A logic gate is an idealized model of computation or physical electronic device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device.
A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. Transistors are one of the basic building blocks of modern electronics. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
In electronics, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals and and one binary digital output . The output is ideally
Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors. Its name signifies that transistors perform both the logic function and the amplifying function, as opposed to resistor–transistor logic (RTL) or diode–transistor logic (DTL).
Complementary metal–oxide–semiconductor (CMOS), also known as complementary-symmetry metal–oxide–semiconductor (COS-MOS), is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. CMOS technology is used for constructing integrated circuit (IC) chips, including microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors, data converters, RF circuits, and highly integrated transceivers for many types of communication.
In digital logic, an inverter or NOT gate is a logic gate which implements logical negation. The truth table is shown on the right.
A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch.
In electronics, emitter-coupled logic (ECL) is a high-speed integrated circuit bipolar transistor logic family. ECL uses an overdriven BJT differential amplifier with single-ended input and limited emitter current to avoid the saturated region of operation and its slow turn-off behavior. As the current is steered between two legs of an emitter-coupled pair, ECL is sometimes called current-steering logic (CSL), current-mode logic (CML) or current-switch emitter-follower (CSEF) logic.
The 7400 series of integrated circuits (ICs) were one of the most popular logic families of transistor–transistor logic (TTL) logic chips. In 1964, Texas Instruments introduced the first members of their ceramic semiconductor package series, the SN5400s. A low-cost plastic package SN7400 series was introduced in 1966 which quickly gained over 50% of the logic chip market, and eventually becoming de facto standardized electronic components. Over the decades, many generations of pin-compatible descendant families evolved to include support for low power CMOS technology, lower supply voltages, and surface mount packages.
Resistor–transistor logic (RTL) is a class of digital circuits built using resistors as the input network and bipolar junction transistors (BJTs) as switching devices. RTL is the earliest class of transistorized digital logic circuit used; other classes include diode–transistor logic (DTL) and transistor–transistor logic (TTL). RTL circuits were first constructed with discrete components, but in 1961 it became the first digital logic family to be produced as a monolithic integrated circuit. RTL integrated circuits were used in the Apollo Guidance Computer, whose design was begun in 1961 and which first flew in 1966.
A push–pull amplifier is a type of electronic circuit that uses a pair of active devices that alternately supply current to, or absorb current from, a connected load. This kind of amplifier can enhance both the load capacity and switching speed.
In computer engineering, a logic family may refer to one of two related concepts. A logic family of monolithic digital integrated circuit devices is a group of electronic logic gates constructed using one of several different designs, usually with compatible logic levels and power supply characteristics within a family. Many logic families were produced as individual components, each containing one or a few related basic logical functions, which could be used as "building-blocks" to create systems or as so-called "glue" to interconnect more complex integrated circuits. A "logic family" may also refer to a set of techniques used to implement logic within VLSI integrated circuits such as central processors, memories, or other complex functions. Some such logic families use static techniques to minimize design complexity. Other such logic families, such as domino logic, use clocked dynamic techniques to minimize size, power consumption and delay.
In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC. When the switch is closed, it creates a direct connection to ground or VCC, but when the switch is open, the rest of the circuit would be left floating. For a switch that connects to ground, a pull-up resistor ensures a well-defined voltage across the remainder of the circuit when the switch is open. Conversely, for a switch that connects to VCC, a pull-down resistor ensures a well-defined ground voltage when the switch is open.
Integrated injection logic (IIL, I2L, or I2L) is a class of digital circuits built with multiple collector bipolar junction transistors (BJT). When introduced it had speed comparable to TTL yet was almost as low power as CMOS, making it ideal for use in VLSI (and larger) integrated circuits. The gates can be made smaller with this logic family than with CMOS because complementary transistors are not needed. Although the logic voltage levels are very close (High: 0.7V, Low: 0.2V), I2L has high noise immunity because it operates by current instead of voltage. I2L was developed in 1971 by Siegfried K. Wiedmann and Horst H. Berger who originally called it merged-transistor logic (MTL). A disadvantage of this logic family is that the gates draw power when not switching unlike with CMOS.
In integrated circuit design, dynamic logic is a design methodology in combinatory logic circuits, particularly those implemented in MOS technology. It is distinguished from the so-called static logic by exploiting temporary storage of information in stray and gate capacitances. It was popular in the 1970s and has seen a recent resurgence in the design of high speed digital electronics, particularly computer CPUs. Dynamic logic circuits are usually faster than static counterparts, and require less surface area, but are more difficult to design. Dynamic logic has a higher toggle rate than static logic but the capacitive loads being toggled are smaller so the overall power consumption of dynamic logic may be higher or lower depending on various tradeoffs. When referring to a particular logic family, the dynamic adjective usually suffices to distinguish the design methodology, e.g. dynamic CMOS or dynamic SOI design.
In electronics, high impedance means that a point in a circuit allows a relatively small amount of current through, per unit of applied voltage at that point. High impedance circuits are low current and potentially high voltage, whereas low impedance circuits are the opposite. Numerical definitions of "high impedance" vary by application.
In digital circuits, a logic level is one of a finite number of states that a digital signal can inhabit. Logic levels are usually represented by the voltage difference between the signal and ground, although other standards exist. The range of voltage levels that represent each state depends on the logic family being used.
PMOS or pMOS logic is a family of digital circuits based on p-channel, enhancement mode metal–oxide–semiconductor field-effect transistors (MOSFETs). In the late 1960s and early 1970s, PMOS logic was the dominant semiconductor technology for large-scale integrated circuits before being superseded by NMOS and CMOS devices.
In electronics, pass transistor logic (PTL) describes several logic families used in the design of integrated circuits. It reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. Transistors are used as switches to pass logic levels between nodes of a circuit, instead of as switches connected directly to supply voltages. This reduces the number of active devices, but has the disadvantage that the difference of the voltage between high and low logic levels decreases at each stage. Each transistor in series is less saturated at its output than at its input. If several devices are chained in series in a logic path, a conventionally constructed gate may be required to restore the signal voltage to the full value. By contrast, conventional CMOS logic switches transistors so the output connects to one of the power supply rails, so logic voltage levels in a sequential chain do not decrease. Simulation of circuits may be required to ensure adequate performance.
In electronics, power amplifier classes are letter symbols applied to different power amplifier types. The class gives a broad indication of an amplifier's characteristics and performance. The classes are related to the time period that the active amplifier device is passing current, expressed as a fraction of the period of a signal waveform applied to the input. A class A amplifier is conducting through all the period of the signal; Class B only for one-half the input period, class C for much less than half the input period. A Class D amplifier operates its output device in a switching manner; the fraction of the time that the device is conducting is adjusted so a pulse width modulation output is obtained from the stage.
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