PN Junction Reverse Breakdown-Introduction to Microelectronic Circuits-Lecture 20 Slides-Electrical Engineering, Slides of Microelectronic Circuits

Download PN Junction Reverse Breakdown-Introduction to Microelectronic Circuits-Lecture 20 Slides-Electrical Engineering and more Slides Microelectronic Circuits in PDF only on Docsity! 1 Lecture 20, Slide 1EECS40, Fall 2003 Prof. King Lecture #20 OUTLINE • The pn junction (cont’d) – reverse breakdown • Load line analysis method • Diode models • Diode applications Reference Reading • Rabaey et al. (finish Chapter 3.2) • Howe & Sodini – Chapter 6.4.1 - 6.4.2 • Schwarz and Oldham (finish Chapter 13.2) Lecture 20, Slide 2EECS40, Fall 2003 Prof. King pn-Junction Reverse Breakdown • As the reverse bias voltage increases, the peak electric field in the depletion region increases. When the electric field exceeds a critical value (Ecrit ≅ 2x105 V/cm), the reverse current shows a dramatic increase: ID (A) VD (V) reverse (leakage) current forward current breakdown voltage VBD 2 Lecture 20, Slide 3EECS40, Fall 2003 Prof. King Circuit Analysis with a Nonlinear Element Since the pn junction is a nonlinear circuit element, its presence complicates circuit analysis. (Node and loop equations become transcendental.) VTh + − + V – RTh I Lecture 20, Slide 4EECS40, Fall 2003 Prof. King Load Line Analysis Method 1. Graph the I-V relationships for the non-linear element and for the rest of the circuit 2. The operating point of the circuit is found from the intersection of these two curves. VTh + − + V – RTh I I V The I-V characteristic of all of the circuit except the non-linear element is called the load line VTh VTh/RTh operating point 5 Lecture 20, Slide 9EECS40, Fall 2003 Prof. King Application Example #2 (using the Perfect Rectifier model) vs(t) + − + vR(t) – vs(t) t RC vR(t) t Lecture 20, Slide 10EECS40, Fall 2003 Prof. King integrated circuit A Zener diode is designed to operate in the breakdown mode. Zener Diode ID (A) VD (V) reverse (leakage) current forward current breakdown voltage R VBD = 15V VBD + vs(t) – t + vo(t) – Example: 6 Lecture 20, Slide 11EECS40, Fall 2003 Prof. King Light Emitting Diode (LED) • LEDs are made of compound semiconductor materials – Carriers diffuse across a forward-biased junction and recombine in the quasi-neutral regions optical emission Lecture 20, Slide 12EECS40, Fall 2003 Prof. King Diode Logic • Diodes can be used to perform logic functions: AND gate output voltage is high only if both A and B are high A B R Vcc C OR gate output voltage is high if either (or both) A and B are high A B R C Inputs A and B vary between 0 Volts (“low”) and Vcc (“high”) Between what voltage levels does C vary?