Question

Electronics 2

1. Give two reasons it would be better to use a MOSFET over a BJT and two reasons it would be better to use a BJT over a MOSFET. 2. What are the simplest equivalent models for the input and output side of a MOS circuit? 3. What are the two main reasons for cascoding in a circuit? 4. Using a T model, draw the small signal equivalent model for VOD Ro Vout VG R RSG + V Rs

Answer 1

@ Two reason why mosfet better than BJT © High input Resistance device (71952), which thereby lower the power consumpsion and more power will be delivered. © Majority Carrier devices, No Minority Carrier becausof this FET is less noisy, and no excellent thermal stability leakage current, Two reason why BJT better than MOSFET :: when compare to FET, BJT is a better devices as an Amplifier because of large gain bandwidth product. MOSFET is very expensive compare to BJT.

Small Signal Model of FET It is the requivalent_circuit of & JRET OY MOSFET which is used in analysis of small signal fet FET It is obtained from the following equ. Ios gm Vgs & Vas > Small signal Model egne ros Sot DL IDS. f Vgg gm Tds vgs Vos o oben_circuit blw gate and source implies that telo current flows into gate terminal. gm_and rðş is called small signal parameteng FET gm: Transconductance :-) It is the rate of change q Drain current with respet to VGS. 1 m² 2 @IDs avas

There are two main reason for the use of cascode Circuit. output Resistance qa a cascode circuit is higher than that of an ordinary MOSFET ③ Input Capacitance can be kept low due to an reduced Miller effect @ Т. • Ro Vout RL Rsg vga we Ž Rs Vin

G • Vout ords vgs vos gm (S BRL ERO Rsq Rg Vin! Small signal equivalent Model

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