2.5. Find an approximation for Ap in (2.6.17) as follows. Show that (2.6.12) can be written as

V=20F+ , In{[(VGB - VFB - )²/y² - ]/}. In the argument of the logarithm, replace

, by the approximation = 2F from (2.6.16). This gives an expression in the form of

(2.6.17), with Ao weakly dependent on VGB. Show that, for practical cases, where y is

between 0.2 and 2 V1/2, and VGB - VFB-20F is up to several volts, Ad is several ; an

average value is 6. Thus, a better estimate can be obtained if, in the preceding equation,

in the argument of the logarithm is replaced by 20 + 60. Caution: This expression

totally fails in moderate and weak inversion.

VGB =VFB+Vs+Y√√5 + (¹4₁-20F)/$,

-

Φο = 2φF + Δφ

Po= 20 (a bad choice)

(2.6.12)

(2.6.17)

(2.6.16)