High Threshold Logic


High Threshold Logic is a variant of Diode–transistor logic 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.. 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.

Advantages

It is used extensively in industrial environments. e.g.
The buffer in this device is exactly the same of what was used in RGB video output stages in TV circuits in this way the upper NPN rises quickly a cathode capacitance with a relatively high load resistor on lower NPN, while lower NPN turn-on controls carefully K voltage
This shows the same improvement in charge-discharge parasitic capacitances in such high voltage logic circuit