Diode Circuit Analysis

Diode Circuit Analysis • Goal: find quiescent operating point (Q-point) of the diode (
 ,   ) • Analytical tools: – Kirchhoff’s voltage law (KVL) – Kirchhoff’s current law (KCL) – Element relations • Solution methods (Often can’t solve analytically due to non-linearity) – Graphical methods – Numerical iteration

Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Diode Circuit Analysis • Goal: find quiescent operating point (Q-point) of the diode (ܫ ஽ , ܸ ஽ ) • Analytical tools: – Kirchhoff’s voltage law (KVL) – Kirchhoff’s current law (KCL) – Element relations • Solution methods (Often can’t solve analytically due to non-linearity) – Graphical methods – Numerical iteration Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Diode Circuit Analysis • Example: Given ݒ ஽ , R, and parameters for the diode (ܫ ௌ , ܸ ் ), find Q-point (ܫ ஽ , ܸ ஽ ). + – V S R i D V D + – linear nonlinear • Linear Part (resistor, load) ܸ ௌ ൌ ݅ ஽ ܴ ൅ ݒ ஽ • Nonlinear part (diode) ݅ ஽ ൌ ܫ ௌ ሺ݁ ௩ ವ ௏ ೅ െ 1ሻ • Two equations, two unknowns ܫ ஽ , ܸ ஽ . Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Load Line Analysis (Graphical) • Write the two equations in the form of ݅ ஽ v.s. ݒ ஽ . ݅ ஽ ൌ െ ݒ ஽ ܴ ൅ ܸ ௌ ܴ ,  ݅ ஽ ൌ ܫ ௌ ሺ݁ ௩ ವ ௏ ೅ െ 1ሻ • Plot them on a same graph, find the intersection. + – V S R i D V D + – linear nonlinear ݅ ஽ ൌ ܫ ௌ ሺ݁ ௩ ವ ௏ ೅ െ 1ሻ ݅ ஽ ൌ ܸ ௌ െ ݒ ஽ ܴ ܸ ௌ ܴ ܸ ௌ “Q-point” ݒ ஽ ݅ ஽ Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Numerical Analysis • Combining: ݅ ஽ ൌ െ ݒ ஽ ܴ ൅ ܸ ௌ ܴ ,  ݅ ஽ ൌ ܫ ௌ ሺ݁ ௩ ವ ௏ ೅ െ 1ሻ • We have: െ ௩ ವ ோ ൅ ௏ ೄ ோ ൌ ܫ ௌ ሺ݁ ೡ ವ ೇ ೅ െ 1ሻ => ݒ ஽ ൌ ܸ ் ln 1 ൅ ௏ ೄ ି௩ ವ ூ ೄ ோ • Let ܴ ൌ 1kΩ, ܫ ௌ ൌ 10 ିଵ଴ A, ݒ ் ൌ 26mV, ܸ ௌ ൌ 10V. we have ݒ ஽ ൌ 0.026ln 1 ൅ ଵ଴ି௩ ವ ଵ଴ షళ • Make an initial guess (ݒ ஽ ൌ 0.5V) and solve by iteration: Iteration # 0 1 2 3 ݒ ஽ (V) 0.5 0.4776 0.4777 0.4777 converged ! ݅ ஽ ൌ െ ௩ ವ ோ ൅ ௏ ೄ ோ ൌ 9.522mA Q-point = (9.522 mA, 0.4777 V) Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Numerical Analysis • Now use . Expect diode to be reverse biased. • From graphical analysis, . Thus • Check for : • Q-point = (10 -10 A, -10 V) • Be careful of round-off error: should be 9.999999999 V Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Simplified Diode Models ݒ ஽ ݅ ஽ ݒ ஽ ݅ ஽ “OFF” ݅ ஽ ൌ 0 ݒ ஽ ൑ 0 “ON” ݒ ஽ ൌ 0 ݅ ஽ ൒ 0 ݒ ஽ ݅ ஽ ܸ ୭୬ ON: short circuit OFF: open circuit ON: voltage source OFF: open circuit + – ܸ ୭୬ General diode Ideal diode Constant voltage drop “ON” ݒ ஽ ൌ ܸ ୭୬ ݅ ஽ ൒ 0 “OFF” ݅ ஽ ൌ 0 ݒ ஽ ൑ ܸ ୭୬ Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Diode Circuit Analysis – simplified model • Analysis Method: – Guess a state for the diode, ON or OFF – Replace the diode by its equivalent model for this state – Analyze the circuit using this equivalent model – Verify that the guess was correct Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Diode Circuit Analysis Ideal model + – V S +10 V R 1kΩ i D V D + – Guess ON: + – V S +10 V i D V D =0 Since I D = 10 mA ≥ 0, D = ON correct R 1kΩ “ON” condition: ݒ ஽ ൌ 0, ݅ ஽ ൒ 0 Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Diode Circuit Analysis LVD model + – V S +10 V R 1kΩ i D V D + – Guess ON: + – V S +10 V i D Since I D = 9.4 mA ≥ 0, D = ON correct R 1kΩ + – V on +0.6 V “ON” condition: ݒ ஽ ൌ ܸ ୭୬ , ݅ ஽ ൒ 0 ܸ ୭୬ ൌ 0.6V Guess OFF: + – V S +10 V R 1kΩ V D = V S = 10V Since V D = 10 V ≥ V on , D = OFF wrong! “OFF” condition: ݅ ஽ ൌ 0, ݒ ஽ ൑ ܸ ୭୬ + – Microelectronic Circuit Design © UW EE Chen/DunhamEE 331 Spring 2012 Multiple Diode Circuits R 1 =20kΩ R 2 =10kΩD 2 D 1 V S1 15V V S2 -15V D 1 , D 2 = Ideal diodes R 2 10kΩ D 2 D 1 R 1 20kΩ V S1 15V V S2 -15V Engineering Schematic Textbook Schematic [...]...Multiple Diode Circuits VS1 15V Guess: D1, D2 both ON R1 20kΩ iR1 iD2 0V Check: D2 , both D1 and D2 are ON Correct! iD1 D1 R2 10kΩ VS2 -15V EE 331 Spring 2012 Microelectronic Circuit Design © UW EE Chen/Dunham Multiple Diode Circuits VS1 15V Now: Swap resistors Guess: D1, D2 both ON R1 10kΩ iR1 iD2 0V D2 Check: => Contrary to D1 ON! iD1 D1 R2 20kΩ VS2 -15V EE 331 Spring 2012 Microelectronic Circuit. .. Contrary to D1 ON! iD1 D1 R2 20kΩ VS2 -15V EE 331 Spring 2012 Microelectronic Circuit Design © UW EE Chen/Dunham Multiple Diode Circuits VS1 15V Guess: D1 OFF, D2 ON R1 10kΩ iR1 iD2 VA Check: => D1 off Correct => D2 on Correct D2 vD1 D1 R2 20kΩ VS2 -15V EE 331 Spring 2012 Microelectronic Circuit Design © UW EE Chen/Dunham . biased. • From graphical analysis, . Thus • Check for : • Q-point = (10 -10 A, -10 V) • Be careful of round-off error: should be 9.999999999 V Microelectronic. Diode Circuit Analysis Ideal model + – V S +10 V R 1kΩ i D V D + – Guess ON: + – V S +10 V i D V D =0 Since I D = 10 mA ≥ 0, D = ON correct R 1kΩ “ON” condition: