1 / 22

ANALOGUE ELECTRONICS I

ANALOGUE ELECTRONICS I. EMT 112/4 Basic BJT Amplifiers (Part 1). Analog Signals & Linear Amplifiers. Analog signals Natural analog signals: physical sense (hearing, touch, vision)

brody
Download Presentation

ANALOGUE ELECTRONICS I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ANALOGUE ELECTRONICS I EMT 112/4 Basic BJT Amplifiers (Part 1)

  2. Analog Signals & Linear Amplifiers • Analog signals • Natural analog signals: physical sense (hearing, touch, vision) • Electrical analog signals: e.g. output from microphone, output signal from compact disc – form of time-varying currents & voltages • Magnitude: any value which vary continuously with time • Analog circuits • Electronic circuits which produce analog signals • E.g. linear amplifier • Linear amplifier • Magnifies input signal & produce output signal that is larger & directly proportional to input signal DC voltage source • Low signal power • High signal power DC power Block diagram of a compact disc player system (a) (b) Signal source Amplifier Load

  3. The Bipolar Linear Amplifier • To use circuit as an amplifier, transistor needs to be biased with DC voltage at quiescent point (Q-point) transistor is biased in forward active region • Time-varying output voltage is directly proportional to & larger than time-varying input voltage  linear amplifier (a) Bipolar transistor inverter circuit; (b) inverter transfer characteristics

  4. The Bipolar Linear Amplifier • Summary of notation

  5. VCC RC vO RB vs VBB Graphical Analysis & AC Equivalent Circuit Fig. D Fig. C iC vCE vBE iB (C) Common-emitter circuit with time varying signal source in series with base dc source (D) Common-emitter transistor characteristics, dc load line, and sinusoidal variation in base current, collector current, and collector-emitter voltage

  6. Graphical Analysis & AC Equivalent Circuit • Base on Fig. C & D (time-varying signals linearly related & superimposed on dc values) • If signal source, vs = 0:

  7. Graphical Analysis & AC Equivalent Circuit • For B-E loop, considering time varying signals: Rearrange: Base on (5), left side of (7) is 0. So: • For C-E loop, considering time varying signals: • Base on (6), left side of (11) is 0. So:

  8. Graphical Analysis & AC Equivalent Circuit • Definition of small signal • Small signal : ac input signal voltages and currents are in the order of ±10 percent of Q-point voltages and currents. e.g. If dc current is 10 mA, the ac current (peak-to-peak) < 0.1 mA.

  9. Graphical Analysis & AC Equivalent Circuit • Rules for ac analysis • Replacing all capacitors by short circuits • Replacing all inductors by open circuits • Replacing dc voltage sources by ground connections • Replacing dc current sources by open circuits

  10. RC ic vO RB + vce + ib - vbe vs - Graphical Analysis & AC Equivalent Circuit • Equations • Input loop • Output loop 0.026 V AC equivalent circuit of C-E with npn transistor

  11. gm=ICQ/VT r=VT/ICQ Small-signal hybrid- equivalent circuit vbe = ibrπ rπ = diffusion resistance / base-emitter input resistance 1/rπ = slope of iB – VBE curve Using transconductance (gm) parameter

  12. Small-signal hybrid- equivalent circuit Using common-emitter current gain (β) parameter

  13. VCC RC vO RB vs VBB B C B C βib E E How to construct Small-signal hybrid- • We know that • i across B  ib • i across C βib • i across E  (β+1)ib • rπ between B -E • Place a terminal for the transistor • Common Terminal as ground rπ

  14. Small-signal hybrid- equivalent circuit Ic RB Vo + + Ib Vbe r gmVbe Vce Vs RC - - Small-signal equivalent circuit Output signal voltage Input signal voltage

  15. VCC RC vO RB vs VBB Small-signal hybrid- equivalent circuit Example Given :  = 100, VCC = 12V VBE = 0.7V, RC = 6k, RB = 50k, and VBB = 1.2V Calculate the small-signal voltage gain.

  16. Solutions 1. 2. 3. 4. 5. 6.

  17. Hybrid- Model and Early Effect transconductance parameter ro=VA/ICQ current gain parameter ro = small-signal transistor output resistance VA = early voltage

  18. Hybrid- Model and Early Effect Early Voltage (pg 299) Early Voltage (VA)

  19. VCC R1 RC vO CC RS vs R2 Basic Common-Emitter Amplifier Circuit Example Given :  = 100, VCC = 12V VBE(on) = 0.7V, RS = 0.5k, RC = 6k, R1 = 93.7k, R2 = 6.3k and VA = 100V. Calculate the small-signal voltage gain.

  20. Ri Ro RS Vo Vs R1 \\ R2 r gmV rO RC Solution Small-signal equivalent circuit

  21. Self-Reading Textbook: Donald A. Neamen, ‘MICROELECTRONICS Circuit Analysis & Design’,3rd Edition’, McGraw Hill International Edition, 2007 Chapter 5:The Bipolar Junction Transistor Page: 334-339 Chapter 6: Basic BJT Amplifiers Page: 370-388.

  22. Exercise The circuit parameters in Figure are changed to VCC = 5V, R1=35.2kΩ, R2=5.83kΩ, RC=10kΩ and RS =0, β =100, VBE(on) =0.7V and VA =100V. Determine thequiescent collector current andcollector-emitter voltageand find thesmall-signal voltage gain. Ans: ICQ = 0.21mA, VCEQ =2.9V, Av =-79.1)

More Related