0195136047.pdf

7.4 FIELD-EFFECT TRANSISTORS 371

Solution

(a) From Equation (7.4.1),

4 × 10 −^3 =IDSS

(

1 +

− 1

VP

) 2

and

6. 25 × 10 −^3 =IDSS

(

1 +

− 0. 5

VP

) 2

Simultaneous solution yields

IDSS=9 mA and VP=3V

(b) ForIDQ=4 mA,VGS=−1V,

RS=

1

4 × 10 −^3

= 250 

The KVL equation for the drain loop is

−VDD+IDQRD+VDS+IDQRS= 0

or

− 15 + 4 × 10 −^3 RD+ 4 + 4 × 10 −^3 × 250 = 0

or

RD= 2 .5k

G

S

+ VDD

D

+

+

−

vGS −

RS

VDS

RD

RG

IG = 0

ID

VR = IGRG = 0

Figure E7.4.1

MOSFETs

The metal-oxide-semiconductor construction leads to the name MOSFET, which is also known
as insulated-gate FET or IGFET. One type of construction results in thedepletionMOSFET, the
other in theenhancementMOSFET. The names are derived from the way in which channels
are formed and operated. Bothn-channel andp-channel MOSFETs are available in either type.