Depletion-load NMOS logic

In <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuits</a>, depletion-load NMOS is a form of digital <a href="/facts/Logic_family/QlEgIecX">logic family</a> that uses only a single power supply voltage, unlike earlier <a href="/facts/NMOS_logic/6hup3T21">NMOS</a> (n-type <a href="/facts/Metal-oxide_semiconductor/eTDJT2Km">metal-oxide semiconductor</a>) logic families that needed multiple power supply voltages. Although manufacturing these integrated circuits required additional processing steps, improved switching speed and the elimination of the extra power supply made this logic family the preferred choice for many <a href="/facts/Microprocessor/Fx9CaQht">microprocessors</a> and other logic elements. 
<a href="/facts/Depletion_and_enhancement_modes/KB0o8lya">Depletion-mode</a> n-type <a href="/facts/MOSFET/eTDJT2Km">MOSFETs</a> as load transistors allow single voltage operation and achieve greater speed than possible with enhancement-load devices alone. This is partly because the depletion-mode MOSFETs can be a better <a href="/facts/Current_source/1UkYH0aG">current source</a> approximation than the simpler enhancement-mode transistor can, especially when no extra voltage is available (one of the reasons early PMOS and NMOS chips demanded several voltages).
The inclusion of depletion-mode NMOS transistors in the <a href="/facts/Semiconductor_device_fabrication/Jd23Mu1z">manufacturing process</a> demanded additional manufacturing steps compared to the simpler enhancement-load circuits; this is because depletion-load devices are formed by increasing the amount of <a href="/facts/Dopant/DvChmeRL">dopant</a> in the load transistors channel region, in order to adjust their <a href="/facts/Threshold_voltage/IparzT9A">threshold voltage</a>. This is normally performed using <a href="/facts/Ion_implantation/PHMokNUf">ion implantation</a>.
Although the <a href="/facts/CMOS/7g2EwHGA">CMOS</a> process replaced most NMOS designs during the 1980s, some depletion-load NMOS designs are still produced, typically in parallel with newer CMOS counterparts. One example of this is the <a href="/facts/Zilog_Z80/Jeqe2h55">Z84015</a> and Z84C15.

Depletion-load NMOS logic open-in-new

Depletion-load NMOS logic