Practice Problem 2 This problem examines a poor alternative to an isolated gate

Question

Practice Problem 2 This problem examines a poor alternative to an isolated gate drive and introduces the phenomenon of leakage current. We will discuss this more in the next lecture, so be sure to attempt this problem before then to be prepared. TA+ When a MOSFET is off, its channel leaks a finite amount of current and can be modeled as a resistance Rds-500RA Assume the diodes are ideal. The value of Rg can be assumed small (-1.10 ). Ves -o 40 V TA- Design RA, R, so that VGS,-0 V when both MOSFETs are off. Protar PRA PRE Should equal 100 mW. What value should Voa1 be during this time? What drain-source current leaks through the MOSFET channels? How much power is lost in each MOSFET due to the leakage current? Now VGG1 is changed to 10 V so that TA-begins to turn on. What happens to Vosz? What happens in the circuit overall? 1. Voss Vesi

Explanation / Answer

Leakage is big problem in recent CMOS technology. A varity of lekage mechanism exist in the DSM transistor. Source and drain junctions are normally reverse biased so they will leak current. When the gate voltage is zero the thickness of the gate - source capacitance is approximately equal to the thickness of the gate oxide layer.As the gate source voltage increases the width of the depletion layer in the p body region also increases . science the depletion layer is a region of immobile charge it infact increases the thickness of the gate source capacitance and hence the value of this capacitance decreases with increasing VGS. As VGS is increased further free electrons generated by thermal ionization get attracted towards the gate oxide semiconductor interface. These free electron screen the depletion layer and gate cource capacitance starts increasing again. When VGS is anove VGS(t) the inversion layer completely screens the depletion layer and the effective thickness of the gate source capacitances became once again equal to the thickness of the oxide layer

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.