Current Sources and Voltage References

240

Characteristics of CMOS FETs

Conduction ceases when the V

GS

drops to less than the threshold voltage; otherwise,

the value of V

GS

mostly controls conduction through the MOSFET’s channel. To

ensure that the device is fully conducting, a V

GS

of between +10 volts or higher is rec-

ommended for N-channel or –10 volts or more for P-channel. Most enhancement-

mode MOSFET data sheets show the drain current I

D

vs. V

GS

curves (aka the transfer

characteristic). Manufacturers use a standard drain current of 10 µA (and with V

GS

=

V

DS

) to determine the V

GS(th)

value. Manufacturers typically tie the drain and gate

together to determine the ...