High-threshold logic (HTL), also known as low-speed logic (LSL) or high-level logic (HLL), is a variant of diode–transistor logic used in environments where noise is very high.
Schematic of basic unbuffered three-input HTL NAND gate
The threshold values at the input to a logic gate determine whether a particular input is interpreted as a logic 0 or a logic 1 (e.g. anything less than 1 V is a logic 0, and anything above 3 V is a logic 1; in this example, the threshold values are 1 V and 3 V). HTL incorporates Zener diodes to create a large offset between logic 1 and logic 0 voltage levels. These devices usually ran off a 15 V power supply and were found in industrial control, where the high differential was intended to minimize the effect of noise.
Schematic of a real buffered two-input HTL NAND gate FZH101A; PV = 180 mW; tpd = 175 ns.
Advantages
Increased noise margin
High noise threshold value
Disadvantage
Slow speed due to increased supply voltage resulting in use of high value resistors.
High power drawn
Usage
It is used extensively in industrial environments. e.g.
Logic controllers with heavy noise
Heavy-process machinery
Similar circuits
The buffer in this device is exactly the same of what was used in RGB video output stages in TV circuits in the way that the upper NPN transistor quickly rises a cathode capacitance with a relatively high load resistor on the lower NPN transistor, while the lower NPN transistor controls the turning on of the output voltage.
The principle of improving charge–discharge parasitic capacitances used here is the same as in high-threshold logic circuits.
high, threshold, logic, also, known, speed, logic, high, level, logic, variant, diode, transistor, logic, used, environments, where, noise, very, high, schematic, basic, unbuffered, three, input, nand, gate, fzh251, four, input, contents, operation, advantages. High threshold logic HTL also known as low speed logic LSL or high level logic HLL is a variant of diode transistor logic used in environments where noise is very high Schematic of basic unbuffered three input HTL NAND gate FZH251 four two input HTL AND Contents 1 Operation 2 Advantages 3 Disadvantage 4 Usage 5 Similar circuits 6 See also 7 ReferencesOperation EditThe threshold values at the input to a logic gate determine whether a particular input is interpreted as a logic 0 or a logic 1 e g anything less than 1 V is a logic 0 and anything above 3 V is a logic 1 in this example the threshold values are 1 V and 3 V HTL incorporates Zener diodes to create a large offset between logic 1 and logic 0 voltage levels These devices usually ran off a 15 V power supply and were found in industrial control where the high differential was intended to minimize the effect of noise Schematic of a real buffered two input HTL NAND gate FZH101A PV 180 mW tpd 175 ns Advantages EditIncreased noise margin High noise threshold valueDisadvantage EditSlow speed due to increased supply voltage resulting in use of high value resistors High power drawnUsage EditIt is used extensively in industrial environments e g Logic controllers with heavy noise Heavy process machinerySimilar circuits EditThe buffer in this device is exactly the same of what was used in RGB video output stages in TV circuits in the way that the upper NPN transistor quickly rises a cathode capacitance with a relatively high load resistor on the lower NPN transistor while the lower NPN transistor controls the turning on of the output voltage The principle of improving charge discharge parasitic capacitances used here is the same as in high threshold logic circuits See also EditDiode logic DL Diode transistor logic DTL Emitter coupled logic ECL Integrated injection logic I2L Resistor transistor logic RTL Transistor transistor logic TTL References Edit This electronics related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title High threshold logic amp oldid 1118845319, wikipedia, wiki, book, books, library,
