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25. What is latchup in CMOS design and ways to prevent it?
To best understand the concept behind the latchup, we need to understand the concept
behind SCR(Silicon Controlled Rectifiers), and how to model the basic transistor in an
SCR structure and on what conditions SCR structures are created in the CMOS design
process and its effects and what are the ways used to prevent it in the design-phase.An
SCR is an acronym for Silicon Controlled Rectifier. It works similar to a typical diode, but is
controlled similar to a bipolar transistor as far as connections go. Connection points are Anode
[A], Cathode [K], and Gate [G]. The SCR is made up of two "P-N" junctions with a "Gate"
attachment between them. The gate is connected between the two P-N junctions with a current
waiting in the forward bias direction [+ to -] and the voltage is above 1-volt. A momentary pulse to
the gate will cause the SCR to conduct and current will flow across the device until the value
changes.