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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.〔Jaume Segura, Charles F. Hawkins ''CMOS electronics: how it works, how it fails'', Wiley-IEEE, 2004 ISBN 0-471-47669-2, page 132〕 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.〔Clive Maxfield ''Bebop to the boolean boogie: an unconventional guide to electronics''Newnes, 2008 ISBN 1-85617-507-3, pp. 423-426〕 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. == Applications == Pass transistor logic often uses fewer transistors, runs faster, and requires less power than the same function implemented with the same transistors in fully complementary CMOS logic.〔 Norimitsu Sako. ("Patent US7171636: Pass-transistor logic circuit and a method of designing thereof" ). 'It is known in the art to employ a "pass-transistor logic circuit" to reduce a number of elements and power consumption, and to improve operating speed.' 〕 XOR has the worst-case Karnaugh map -- if implemented from simple gates, it requires more transistors than any other function. The designers of the Z80 and many other chips save a few transistors by implementing the XOR using pass-transistor logic rather than simple gates.〔 Ken Shirriff. ("Reverse-engineering the Z-80: the silicon for two interesting gates explained" ). 2013. 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pass transistor logic」の詳細全文を読む スポンサード リンク
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