GATE Electronics and Communications (EC) 2020 Solved Papers

Question : 45 of 65

Marks: +1, -0

An enhancement MOSFET of threshold voltage

3 {V}

is being used in the sample and hold circuit given below. Assume that the substrate of MOS device is connected to

-10 {V}

. If the input voltage

V_{1}

lies between

± 10 {V}

, the minimum and the maximum values of

{V}_{6}

required of proper sampling and holding respectively, are

Solution:

During sampling, MOSFET must be as ON switch.

⇒ {\V}_{ {\GS}}> {\V}_{ {\TH}}

⇒( {\V}_{ {\G}}- {\V}_{ {\S}})> {\V}_{ {\TH}}

⇒ {\V}_{ {\G}} > {\V}_{ {\s}}+ {\V}_{\;\text "тн "\;}

⇒ {\V}_{ {\G}}>10+3 {\V}

∵ {\V}_{ {\s}}= {\V}_{ {\I}, \max }=10 {\V}

⇒ {\V}_{ {\G}}>13 {V} \;\; . . .(1)

During hold, MOSFET must be as OFF switch.

⇒ \V_{\GS}< \V_{\TH}

⇒(\V_{\G}-\V_{\S}) < \V_{\T H}

⇒ \V_{\G} < (\V_{\S}+\V_{\TH})

⇒ \V_{\G} < -7 \V

∴ \V_{\S}=\V_{\I,\min}=-10 \V

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