Schottky transistor

Schottky TTL ( S -TTL) is a logic family, which specifies a certain semiconductor technology for Integrated Circuits ( ICs). It is called " Schottky transistors " to the switching times and cycle times through logic gates compared to the traditional transistor-transistor logic (TTL ) on bipolar transistors to reduce based.

Description

Basis of the Schottky -TTL technology, the use of a Schottky diode, said base and collector of a bipolar transistor bridge, which is then referred to as " Schottky transistor." With a positive base-emitter voltage and the diode is conducting transistor in the forward direction, and prevents a decrease of the collector-emitter voltage is less than about 0.3-0.4 volts. The transistor does not reach fully into saturation, whereby a faster switching time than with TTL is achieved. To distinguish these transistors in the circuit diagram and not constantly draw this additional Schottky diode having to own circuit symbol for those transistors is used, the base-collector plug is bridged with a Schottky diode.

S- TTL devices were the first TTL components that could compete with the rate of the ECL technology.

Application

ICs of the series LS -TTL were reasonably priced and widely available, but are hardly used any more. They had a five-fold improved speed - power product and an 80 percent reduction in its power consumption compared with standard TTL. The development as TTL is about 30 % faster than LS- TTL. AS- TTL is the fastest TTL series. Named after the manufacturer Fairchild F- TTL series is optimized for the lowest possible power consumption. Series in standard TTL technology usually have the family name 74

The Schottky series are characterized by appending the letter "S". There are the following families of Schottky series:

  • Schottky TTL ( S -TTL), designation 74S
  • Low-power Schottky TTL ( LS -TTL), name 74LS
  • Advanced low-power Schottky TTL (ALS -TTL), name 74ALS
  • Advanced Schottky TTL ( AS- TTL), name 74AS
  • Fairchild Advanced Schottky TTL ( F -TTL), designation 74F

ICs same semiconductor technology can easily interconnect with each other. That is why one speaks of series, if ICs are manufactured with different functions in the same technology.

History

In 1956, Richard H. Baker describes a circuit called Baker clamp circuit, so as not to drive the bipolar transistor in a switching application using two additional diodes in saturation. Baker 's objective by avoiding saturation of the two diodes, and a negative feedback to reduce the switching times of the bipolar transistors. Baker clamp circuit relies on two different types of diodes, a germanium diode ( Ge) in the feedback branch, and a diode silicon (Si ) having different forward voltages. Schottky diodes were not available at that time.

In 1964, James Robert Biard published a patent on the circuit of the " Schottky transistor ", at that time employed by Texas Instruments, which is based on the Baker clamp circuit. Schottky transistors can be, as opposed to the Baker - circuit easily in integrated circuits (ICs ) realize what created the possibilities for the development of the S -TTL logic gates.

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