PMOS logic

In the late 1960s and early 1970s, PMOS logic was the dominant semiconductor technology for large-scale integrated circuits before being superseded by NMOS and CMOS devices.

[6] Other companies continued to manufacture PMOS circuits such as large shift registers (General Instrument)[7] or the analogue multiplexer 3705 (Fairchild Semiconductor)[8] which were not feasible in bipolar technologies of the day.

[9] Tom Klein and Federico Faggin at Fairchild Semiconductor improved the self-aligned gate process to make it commercially viable, resulting in the release of the analogue multiplexer 3708 as the first silicon-gate integrated circuit.

[3]: 89 For various reasons Fairchild Semiconductor did not proceed with the development of PMOS integrated circuits as intensively as the involved managers wanted.

Most early microprocessors were manufactured in PMOS technology: 4040 and 8008 from Intel; IMP-16, PACE and SC/MP from National Semiconductor; TMS1000 from Texas Instruments; PPS-4[13] and PPS-8[14] from Rockwell International.

[16] PMOS logic remained in use for a while due to its low cost and relatively high level of integration for applications such as simple calculators and clocks.

PMOS circuits have a number of disadvantages compared to the NMOS and CMOS alternatives, including the need for several different supply voltages (both positive and negative), high-power dissipation in the conducting state, and relatively large features.

PMOS uses p-channel (+) metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits.

The worst problem is that there is a direct current (DC) through a PMOS logic gate when the so-called "pull-up network" (PUN) is active, that is, whenever the output is high, which leads to static power dissipation even when the circuit sits idle.

Additionally, the asymmetric input logic levels make PMOS circuits susceptible to noise.