Question:
A very useful way to characterize the stability of the bias current ID is to evaluate the sensitivity of ID relative to a particular transistor parameter whose variability might be large. The sensitivity of ID relative to the MOSFET parameter K ≡ 1 2 kΩ (W/L) is defined as
and its value, when multiplied by the variability (or tolerance) of K, provides the corresponding expected variability of id
The purpose of this problem is to investigate the use of the sensitivity function in the design of the bias circuit of
Fig. 7.48(e).
Show that for Vt constant,
For a MOSFET having K = 100 μA/V2 with a variability of ± 10% and Vt = 1 V, find the value of RS that would result in ID = 100 μA with a variability of ± 1%. Also, find VGS and the required value of VSS
(c) If the available supply VSS = 5 V, find the value of RS for ID = 100 μA. Evaluate the sensitivity function, and give the expected variability of ID in this case.