Lecture 36DC Bias: Find Operating PointsFinding RREFDC Operating PointSmall-Signal Device ParametersTwo-Port ModelOutput Voltage SwingLimits to Output VoltageOutput Current SwingOutput Current LimitsTransfer Curves (for RL = 25 k?)1R. T. HoweEECS 105 Spring 2002 Lecture 36Dept. of EECSUniversity of California at BerkeleyOutput Voltage SwingTransistors M2and M6will limit the output swingR. T. HoweEECS 105 Spring 2002 Lecture 36Dept. of EECSUniversity of California at BerkeleyLimits to Output VoltageM6will leave saturation when vOUTdrops to:()66,6,/25.2LWCIVVvoxnDsatDSMINOUTµ+−=+=−M2will leave saturation when vOUTrises to:()22,2,/)(25.2LWCIVVvoxpDsatSDMAXOUTµ−−=−=+What about M4?vOUT,MIN= -2.5 + 0.28 = - 2.22 V vOUT,MAX= 2.5 - 0.32 = 2.18 V R. T. HoweEECS 105 Spring 2002 Lecture 36Dept. of EECSUniversity of California at BerkeleyOutput Current SwingLoad resistor: pick RL= 25 kΩOutput current:LOUTOUTRvi /−= iOUT vOUT Limits: asymmetricalM2: can increase - iD2M6: can’t increase iD6()26 DDOUTiii−−=R. T. HoweEECS 105 Spring 2002 Lecture 36Dept. of EECSUniversity of California at BerkeleyOutput Current Limits• Positive output current (negative vOUT) ()LMINOUTDMAXOUTRvAii /500,6,−==−=µ• Negative output current (positive vOUT) VkAvMINOUT25.1)25)(50(,−=Ω−=µ(less negative than limit set by saturation of M6)No limit on current from M2, so voltage swing setscurrent limitAkVRviLMAXOUTMINOUTµ2.87)25/18.2(/,,−=Ω−=−=2R. T. HoweEECS 105 Spring 2002 Lecture 36Dept. of EECSUniversity of California at BerkeleyTransfer Curves (for RL= 25 kΩ)vOUT vIN 1 2 -1 -2 0 -1 -2 1 2 iOUT [µA]vIN 50 100 -50 -100 0 -1 -2 12Loaded voltage gain = vout/vin= (gm1Rout1)(gm2Rout||RL) = 490Loaded transconductance = iout/vin= (-gm1Rout1)(gm2)(Rout/(Rout+ RL) = -19.5
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