Lecture 16

# Ming c wu 8 linear resistance ron 1 ncox w vgs

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ?mes the gate voltage in excess of the threshold voltage. EE105, Fall 2013 Lecture 16 – Slide 13 Prof. Ming C. Wu Charge Density at a Point Q( x) = WCox [VGS − V ( x) − VTH ] §༊  Let x be a point along the channel from source to drain, and V(x) its poten?al; the expression above gives the charge density (per unit length). EE105, Fall 2013 Lecture 16 – Slide 14 Prof. Ming C. Wu 7 Parabolic ID- VDS Rela?onship ID = Q ⋅ v Q ( x ) = WCox #VGS − V ( x ) − VTH % \$ & v = +µ n dV dx dV ( x ) I D = WCox #VGS − V ( x ) − VTH % µ n \$ & dx 1 W# 2 I D = µ nCox \$2(VGS − VTH )VDS − VDS % & 2 L EE105, Fall 2013 §༊  By keeping VG constant and varying VDS, we obtain a parabolic rela?onship. §༊  The maximum current occurs when VDS equals to VGS- VTH. Lecture 16 – Slide 15 Prof. Ming C. Wu ID- VDS for Diﬀerent Values of VGS 2 I D ,max ∝ (VGS − VTH ) EE105, Fall 2013 Lecture 16 – Slide 16 Prof. Ming C. Wu 8 Linear Resistance Ron = 1 µ nCox W (VGS − VTH ) L §༊  At small VDS, the transistor can be viewed as a resistor, with the resistance depending on the gate voltage. §༊  It ﬁnds applica?on as an electronic switch. EE105, Fall 2013 Lecture 16 – Slide 17 Prof. Ming C. Wu Applica?on of Electronic Switches §༊  In a cordless telephone system in which a single antenna is used for both transmission and recep?on, a switch is used to connect either the receiver or transmiJer to the antenna. EE105, Fall 2013 Lecture 16 – Slide 18 Prof. Ming C. Wu 9 Eﬀects of On- Resistance §༊  To minimize signal aJenua?on, Ron of the switch has to be as small as possible. This means larger W/L aspect ra?o and greater VGS...
View Full Document

## This note was uploaded on 01/22/2014 for the course EE 105 taught by Professor King-liu during the Fall '07 term at Berkeley.

Ask a homework question - tutors are online