EE 330 Lect 39 Fall 2011

EE 330 Lect 39 Fall 2011 - EE 330 Lecture 39 Digital...

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EE 330 Lecture 39 Digital Circuits Multiple-input gates Propagation Delay – basic characterization Device Sizing
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Transfer characteristics of the static CMOS inverter V DD V DD V IN V OUT -V Tp V Tn V DD +V Tp Case 1 Case 2 Case 3 Case 4 Case 5 (Neglect λ effects) Review from Last Time M 1 M 2 V DD V IN V OUT
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Transfer characteristics of the static CMOS inverter V DD V DD V IN V OUT -V Tp V Tn V DD +V Tp V TRIP 1 1 (Neglect λ effects)     1 p 21 Tn DD Tp n 1 2 IN p n 1 2 μ WL V V +V μ W L V μ μ W L From Case 3 analysis: Review from Last Time
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Inverter Transfer Characteristics of Inverter Pair IN V OUT V What are V H and V L ? Find the points on the inverter pair transfer characteristics where V OUT ’=V IN and the slope is less than 1 V’ OUT V IN V L V H V TRIP Review from Last Time
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Inverter Transfer Characteristics of Inverter Pair for THIS Logic Family IN V OUT V V DD V DD V IN V OUT -V Tp -V Tn V DD +V Tp V TRIP 1 1 V DD V DD V IN V OUT -V Tp -V Tn V DD +V Tp V TRIP 1 1 V DD V DD V IN V’ OUT -V Tp -V Tn V DD +V Tp V L V H V TRIP V H =V DD and V L =0 Note this is independent of device sizing for THIS logic family !! M 1 M 2 V DD V IN V OUT Review from Last Time
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Sizing of the Basic CMOS Inverter M 1 M 2 V DD V IN V OUT How should M 1 and M 2 be sized? How many degrees of freedom are there in the design of the inverter? The characteristic that device sizes do not need to be used to establish V H and V L logic levels is a major advantage of this type of logic
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How should M 1 and M 2 be sized? M 1 M 2 V DD V IN V OUT How many degrees of freedom are there in the design of the inverter? { W 1 ,W 2 ,L 1 ,L 2 } 4 degrees of freedom But in basic device model and in most performance metrics, W 1 /L 1 and W 2 /L 2 appear as ratios { W 1 /L 1 ,W 2 /L 2 } effectively 2 degrees of freedom
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How should M 1 and M 2 be sized? M 1 M 2 V DD V IN V OUT { W 1 ,W 2 ,L 1 ,L 2 } 4 degrees of freedom How are W 1 and W 2 chosen? { W 1 /L 1 ,W 2 /L 2 } effectively 2 degrees of freedom Usually pick L 1 =L 2 =L min Depends upon what performance parameters are most important for a given application!
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How should M 1 and M 2 be sized? M 1 M 2 V DD V IN V OUT One popular sizing strategy: 1. Pick W 1 =W MIN to minimize area of M 1 2. Pick W 2 to set trip-point at V DD /2 { W 1 /L 1 ,W 2 /L 2 } 2 remaining degrees of freedom Usually pick L 1 =L 2 =L min
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How should M 1 and M 2 be sized? M 1 M 2 V DD V IN V OUT One popular sizing strategy: 1. Pick W 1 =W MIN to minimize area of M 1 2. Pick W 2 to set trip-point at V DD /2 pick L 1 =L 2 =L min V DD V DD V IN V OUT -V Tp V Tn V DD +V Tp V TRIP 1 1     1 p 21 Tn DD Tp n 1 2 OUT IN TRIP p n 1 2 μ WL V V +V μ W L V =V V μ μ W L  Observe Case 3 provides expression for V TRIP Thus, at the trip point,
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How should M 1 and M 2 be sized?
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EE 330 Lect 39 Fall 2011 - EE 330 Lecture 39 Digital...

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