Lecture_18_first_posting - Lecture 18-19 Basic BJT Analog...

Info iconThis preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
Basic BJT Analog Circuits Difference between MOSFET and BJT as a circuit component The BJT DC operations and biasing circuits The BJT single-stage amplifiers Textbook reading: Sedra Chap 5 Lecture 18-19
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Two Choices: NPN and PNP Fig. 5.2
Background image of page 2
Physical Mechanisms Inside NPN in the Active Mode Fig. 5.3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Minority Carrier Concentration Inside NPN in the Active Mode p n not important here due to reverse bias N E >> N B : gain N B > N C : base width modulation W B << L B : gain base p emitter n n p << base p emitter n n p 0 0 sustaining large output voltage depletion region into base: base width modulation Fig. 5.4
Background image of page 4
Physical realization of the diode. Note that V BE junction area and V CB junction areas are not equal. This is taken into account in the Ebers-Moll model
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Four Modes in BJT Mode Base junction Collector junction V BE V BC V CE Forward Active Forward bias Reverse bias npn: small + large + large + pnp: small - large - large - Inverted Active Reverse bias Forward bias npn: large + small + large - pnp: large - small - large + Saturation Forward bias Forward bias npn: small + small + small + pnp: small - small - small - Cutoff Reverse bias Reverse bias npn: large - large + unsure pnp: large + large - unsure Words of caution: in MOSFET, when both S and D junctions are forward biased: linear, S forward and D reverse: saturation!!
Background image of page 6
i C vs v CB Minority carrier concentration in saturation region i C vs v BE Operation in saturation mode Common base characteristic
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Ebers-Moll BJT Model of NPN (Large Signal) ( 29 ( 29 ( 29 ( 29 1 1 1 1 / / / / - - - = + - = - - - = - = kT qV R S kT qV S F F R C kT qV S kT qV F S R R F E BC BE BC BE e I e I I I I e I e I I I I α E B C I F I R R I R F I F Main current path in active mode Main current path in inverted mode I B = I E - I C I FO and I RO are the individual diode sat currents Two components in I B : back injection from base to emitter ( R I R ), and recombination in base ( I F F I F ). Junction laws: F I F0 = R I R0 I S Table 5.3
Background image of page 8
NPN Common-Emitter Gummel Plot V BE V CE V BE log( I B , I C ) Limited by series resistance Slope: η× 60mV/decade of current I B I C current gain β BJT can maintain exponential increase of current only limited by the series resistance. Input characteristics Input characteristics (in term of r π ) Transfer characteristics (in term of g m )
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
NPN Common-Emitter IV Characteristics Output characteristics (in term of r o ) Transfer characteristics (in term of g m ) Early Voltage C A I V r ' 0 =
Background image of page 10
NPN Common-Emitter Current Gain Increasing I B I B V CE Output characteristics o Transfer characteristics (in term of β ) B CEsat forced I I =
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Forward Active npn: Large Signal This is the similar mode to the MOSFET saturation , where a large g m or current gain can be obtained: the main output current ( I C ) is mainly a function of the input voltage V BE , less for V CE .
Background image of page 12
Image of page 13
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 42

Lecture_18_first_posting - Lecture 18-19 Basic BJT Analog...

This preview shows document pages 1 - 13. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online