What is subthreshold current?

Q.  Subthreshold current is basically a drain current that flows only when __________
- Published on 23 Sep 15

a. VGS is slightly greater than VT
b. VGS is slightly less than VT
c. VGS is exactly equal to VT
d. None of the above

ANSWER: VGS is slightly less than VT

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    Discussion

  • Satyawati   -Posted on 06 Oct 15
    The drain current which flows when gate -to-source voltage is slightly less than its threshold value, can be termed as 'Sub-threshold current'. The consequences of sub-threshold current is quite negligible for a single device but has greater impact on maximum number of devices.

    If more number of MOSFETs are biased on an IC in such a way that the biasing level is slightly lower than the threshold voltage, then IC starts drawing large current from the power supply. This is so, because the sub-threshold current gets drawn by each device, which eventually increases the power dissipation of an integrated circuit to the maximum level.

    Hence, in order to avoid the sub-threshold conduction, MOSFET must be biased to a few tenths of a voltage below than the threshold voltage & this also assures the presence of MOSFET in an off state.

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