note5 - Handout 5 MOSFET Large-Signal/ Small-Signal...

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Handout 5 ECE 3150, Cornell University 1 MOSFET Large-Signal/ Small-Signal Single-Stage Amplifiers What you will learn: • Simple MOSFET-resistor DC circuits • Large-signal biasing for small-signal operations • Current mirror biasing in MOS circuits • Common-source amplifier characteristics • Common-gate and common-drain (source follower) Handout 5
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Handout 5 ECE 3150, Cornell University 2 4.1 Large-signal current mirrors for small-signal circuit biasing • Small-signal amplifiers need to set the large-signal Q point • Large-signal DC calculations of single MOSFET circuits. • Small-signal amplification principles • DC biasing for small-signal operations • Current mirrors and steering with MOSFET • Current mirrors with BJT and comparison to MOSFET. Textbook reading: 4.3, 4.5, 5.4, 5.5, 6.3
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Handout 5 ECE 3150, Cornell University 3 Large-Signal Analytical Solution: Ex. 1: Resistor-Transistor Logic (RTL) I D V D Fixed V GS > V th R + + V DD () DD D D th GS n D V V RI V V k L W I = + = 2 ' 2 To obtain I D and V D : 1. Assume NMOS in saturation 2. Solve KVL ignoring the Early effect 3. Check if V D can make NMOS saturate
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Handout 5 ECE 3150, Cornell University 4 Use of Load-Line Plots for Intuition I D V Dsat =V GS –V th V D V DD -1/R Large-signal load-line plot I D V D Fixed V GS > V th R + + V DD •L a r g e R : NMOS out of saturation • Small R : the small-signal gain will reduce ( R is in parallel with r o ). large R small R r o
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Handout 5 ECE 3150, Cornell University 5 Ex. 2: Diode-Connected MOSFET • The MOSFET is diode-connected : V GS =V DS , and always in saturation. • Use KVL to find I D : () 2 ' 2 3 th D n D D D V V k L W I V V RI = = + I D R V DD Diode- connected MOS has a diode IV I D V th V D V DD -1/R Large-signal load-line plot +
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Handout 5 ECE 3150, Cornell University 6 Ex. 3: PMOS Active Load (No Other) • The nMOSFET is diode connected: V GS =V DS , and in saturation. • Assume PMOS in saturation I D (PMOS) from V GS (PMOS) – Check V D –V DD for consistency of PMOS saturation V ref I D V D V DD Diode- connected NMOS + I D V th V D V DD Large-signal load-line plot Fixed V GS +
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Handout 5 ECE 3150, Cornell University 7 Unique Load-Line Solution • Load-line can be exact if there is no input control and output load currents • As long as the top and bottom devices are monotone functions (i.e., no negative differential resistance anywhere), there is always a unique solution from the load-line plot. I D V DD I D V th V D V DD Large-signal load-line plot v I1 v I2
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ECE 3150, Cornell University 8 Ex. 4: Inverter with a Resistive Load Fig. E4.25 v I still control PMOS and NMOS as in the inverter. • In comparison with
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note5 - Handout 5 MOSFET Large-Signal/ Small-Signal...

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