EMT 112 Analog Electronics I Introduction to Field

EMT 112 Analog Electronics I Introduction to Field Effect Transistor (FET) DC Analysis 10 January 2010 DKP 1

Objectives Understand the DC analysis and design techniques of MOSFETs circuits

Previous lecture We understand that there are 2 types of mode in MOSFET which are enhancement and depletion mode. Basically, the enhancement mode of MOSFET is usually used in IC design. Both of enhancement and depletion mode have the same I-V characteristic and the same equation for drain current, i. D = Kn (v. GS –VTN)² (saturation region)

Test your understanding An n-channel enhancement mode MOSFET has a threshold voltage, VTN = 0. 7 V and gate-to-source voltage, v. GS = 1 V. Determine the region of operation when: a) v. DS = 0. 2 V b) v. DS = 1 V c) v. DS = 3 V

MOSFET DC Circuit Analysis The DC biasing is important part of the design of amplifiers. The resistors are used in MOSFET circuit, however, in a real IC, the resistors are generally replaced by MOSFETs. The used of MOSFETs make the smaller area for overall circuit.

Common Source Circuit An NMOS Common Source Circuit VDD R 1 CC vi R 2 i. D VDD RD v. O R 1 ID VG R 2 RD VDS VGS

DC Analysis – Saturation Region VDD R 1 VG R 2 ID RD 0 + + VDS VGS - - DC equivalent circuit

Practise makes perfect Find drain current, i. D then determine the operation of the MOSFET circuit below: VDD VTN = 1 V K = 0. 1 m. A/V 2 VDD = 5 V R 1 = 20 kΩ CC R 2 = 10 kΩ vi R 2 i. D RD v. O

Load Line of MOSFET i. D Transition point Q-point IDQ VDSQ VDD v. DS