{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Weak_Inversion_Vittoz_Current_Mirror - page 1 Weak...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
page 1 CSEM, E. Vittoz, 2003 Weak inversion Behaviour and model of MOS transistors in weak inversion [1,2,3] . Examples of analog circuits. Exploratory analysis of weak inversion logic [4,5] . Eric A.Vittoz CSEM , Centre Suisse d'Electronique et de Microtechnique SA Jaquet-Droz 1, CH 2007 Neuchâtel, Switzerland [email protected] WEAK INVERSION IN ANALOG AND DIGITAL CIRCUITS CCCD Workshop 2003, Lund, Oct. 2-3
Background image of page 1

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

View Full Document Right Arrow Icon
page 2 CSEM, E. Vittoz, 2003 Weak inversion W,L width, length of the channel C ox gate capacitance per unit area U T = kT/q ( = 26 mV at 300 ° K) V = local non-equilibrium voltage in channel : channel voltage (quasi-Fermi potential of electrons) at source end of channel: V = V S at drain end of channel: V = V D Q i local mobile inversion charge in channel (electrons) V T0 gate threshold voltage for V =0. V S S D B V D V G V S I D G B S D V D V G I D symbols: p -channel n -channel n -channel MOS TRANSISTOR : DEFINITIONS D G S I D V D V G V S n+ n+ p B local substrate
Background image of page 2
page 3 CSEM, E. Vittoz, 2003 Weak inversion ( µ =mobility) with β = µ C ox W L slope -n - Q i / C ox V S V D I D β V G const. V I D = β - d V V S V D Q i C ox Given by: DRAIN CURRENT Weak inversion already possible for V S =0 if V G < V T0 ("subthreshold") V G -V T0 0 Pinch-off voltage V P V G - V T0 n strong inversion, V P -V U T weak inversion : = 2 nU T exp -Q i C ox exponential slope factor n =1.2 to 1.6
Background image of page 3

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

View Full Document Right Arrow Icon
page 4 CSEM, E. Vittoz, 2003 Weak inversion - Q i /C ox V V P <0 0 slope -n I D / β V D V S - Q i /C ox V V G -V T0 > 0 V P >0 0 slope -n I D / β V D V S DRAIN CURRENT IN WEAK INVERSION (vertical axis magnified) V G -V T0 < 0
Background image of page 4
page 5 CSEM, E. Vittoz, 2003 Weak inversion V V D I R reverse current I R -Q i β /C ox V V S I F forward current I F -Q i β /C ox V I D = Drain current I D V S V D FORWARD AND REVERSE CURRENTS -Q i β /C ox I D (V G , V S , V D ) = F(V G , V S ) - F(V G , V D ) = I F - I R Drain current is the superposition of independent and symmetrical effects of source and drain voltages. basic property of long-channel transistors, independent of current [6] . Transistor saturated if I R « I F , then I D = I F .
Background image of page 5

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

View Full Document Right Arrow Icon
page 6 CSEM, E. Vittoz, 2003 Weak inversion DRAIN CURRENTEXPRESSION IN WEAK INVERSION V D U T - V S U T - nU T V G -V T0 I D = I S e ( e - e ) I F I R for I F and I R « I S thus: I F , R = I S e V P -V S , D U T -Q i /C ox = 2 nU T e V P -V U T « 2 nU T Introducing V P ( V G -V T0 )/ n and I D = I F - I R , this yields: Definition: specific current of the transistor: I S = 2 n β U T 2 (10 to 300 nA for W = L )
Background image of page 6
page 7 CSEM, E. Vittoz, 2003 Weak inversion I D ~ e V S U T - nU T V G I D ~ e ~ 1-e V D -V S U T - I D slope 1 log I D I D0 V S U T - log I D I D0 slope 1/ n V S , V D const. V G U T transfer from gate 1 0 5% V D -V S U T I D / I F saturation 0 1 2 3 4 5 6 output FORWARD CHARACTERISTICS IN WEAK INVERSION V D U T - V S U T - nU T V G I D = I D0 e ( e - e ) transfer from source minimum V DSsat exponential, slope 1/ n exponential, slope 1 where I D0 = I S e - V T0 nU T V G , V D const.
Background image of page 7

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

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}