High Threshold Logic is a variant of DTL which is used in such environments where noise is very high.

Operation

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 1V and 3V). 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.

Disadvantage

• slow speed due to increased supply voltage resulting in use of high value resistors.

Usage

It is used extensively in industrial environments. e.g.

• Logic Controllers with heavy noise
• Heavy Process Machinery

See also

• Diode logic
  Diode logic
  Diode logic or diode-resistor logic constructs Boolean logic gates from diodes acting as electrically operated switches. While diode logic has the advantage of simplicity, the lack of an amplifying stage in each gate limits its application...
  
   (DL)
• Emitter-coupled logic
  Emitter-coupled logic
  In electronics, emitter-coupled logic , is a logic family that achieves high speed by using an overdriven BJT differential amplifier with single-ended input, whose emitter current is limited to avoid the slow saturation region of transistor operation....
  
   (ECL)
• Integrated injection logic
  Integrated injection logic
  Integrated injection logic is a class of digital circuits built with multiple collector bipolar junction transistors . When introduced it had speed comparable to TTL yet was almost as low power as CMOS, making it ideal for use in VLSI integrated circuits...
  
   (I2L)
• Resistor–transistor logic (RTL)
• Transistor–transistor logic (TTL)