454Lec09_Inv_Delay

454Lec09_Inv_Delay - ECEN 454 Digital Integrated Circuit...

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ECEN 454 Lecture 9 1 ECEN 454 Digital Integrated Circuit Design Lecture 9 CMOS Inverter Delay
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ECEN 454 Lecture 9 2 Inverter Parasitics (1)
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ECEN 454 Lecture 9 3 Inverter Parasitics (2)
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ECEN 454 Lecture 9 4 Delay Definitions (1) 50% voltage point ± V 50% = V OL + ½ ( V OH -V OL ) = ½ (V OL + V OH ) Delay between V 50% of the rising input and the V 50% of the falling output: Delay between V 50% of the falling input and the V 50% of the rising output: PHL τ PLH
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ECEN 454 Lecture 9 5 Delay Definitions (2) Average propagation delay Output rise and fall times ( ) 2 / PHL PLH p τ + = ) ( 1 . 0 % 10 OL OH OL V V V V + = ) ( 9 . 0 % 90 OL OH OL V V V V + =
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ECEN 454 Lecture 9 6 CMOS Inverter Delay – First Glance (1) V DD V out V in = V DD R on C L t pHL = f(R on .C L ) = 0.69 R on C L t V out V DD R on C L 1 0.5 ln(2) 0.36
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ECEN 454 Lecture 9 7 CMOS Inverter Delay – First Glance (2) V DD V out V in = V DD C L I av t pHL = C L V swing /2 I C L k n V ~
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ECEN 454 Lecture 9 8 Delay Calculation (1) Average current method ± A quick estimate [] ) , ( ) , ( 2 1 % 50 , V V V V i V V V V i I out OH in C OH out OH in C HL avg = = + = = = ) , ( ) , ( 2 1 % 50 , V V V V i V V V V i I out OL in C OL out OL in C LH avg = = + = = = avg I V C Δ = τ
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ECEN 454 Lecture 9 9 Delay Calculation (2) Solving the differential equations Integrate both sides ± Need to identify regions of operation out n D load n D out load dV i C dt i dt dV C , , = =
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ECEN 454 Lecture 9 10 Delay Calculation (3) Saturation Linear ∫∫ = = = = = ' 1 0 , , 1 t t t t V V V V V out n D load n T OH out OH out dV i C dt 2 , , 0 ' 1 ) ( 2 n T OH n n T load V V k V C t t = = =− = = 1 ' 1 % 50 , , 1 t t t t V V V V out n D load n T OH out dV i C dt
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This note was uploaded on 04/17/2008 for the course ELEN 454 taught by Professor Jianghu during the Spring '08 term at Texas A&M.

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454Lec09_Inv_Delay - ECEN 454 Digital Integrated Circuit...

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