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# week_2 - 8 As you know increase V DS off your channel...

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8 As you know increase Æ your channel narrows down close to drain until it pinches off. DS V Set V in equation (I) th GS DS V V = Æ current saturates. n + n + n G D S Depleted Æ 2 ) ( 2 th GS ox n D V V L W C I = µ independent of . DS V Condition for pinch off: th GS DS V V V > . 9 mA 4 mA 1 mA quadratic increase in current D I DS V v V V tn GS 1 = v V V tn GS 2 = v V V tn GS 3 = Secondary effects 1. Channel length modulation By changing the V you effectively shorten the channel length Æ current increases. DS G n + n +

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9 [] () ) ( 1 ) ( 2 2 th GS DS th GS ox n D V V V V V L W C I + = λ µ ( ) 1 V Æ Channel length modulation coefficient D I DS V Æ D out D D D out I R I V I R 1 1 = = = 2. Body effect Change in the threshold voltage as you bias the substrate. ( ) F F SB th th V V V Φ Φ + + = 2 2 0 γ : Body effect constant increases as you increase the source-body voltage th V
10 3. Velocity saturation Æ present in the short channel devices. Take triode region equation and substitute

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## This note was uploaded on 02/19/2012 for the course ECE 455 taught by Professor Mohammadi during the Fall '10 term at Purdue.

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week_2 - 8 As you know increase V DS off your channel...

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