EE105 Fall 2005 Microelectronic Devices and Circuits Lecture 16 Common Drain Amplifier Review of Phasors 4 1 Common Drain Amplifier I DS Cox VGS VT 2 I DS W Cox L W 1 VGS VT 2 L 2 Weak IDS dependence 5 CD Voltage Gain Note vgs vt vout vout g m vgs g mb vout roc ro vout g m vt vout g mb vout roc ro 6 2 CD Voltage Gain Cont vout g m vt vout g mb vout roc ro KCL at source node 1 g mb g m vout g m vt roc ro Voltage gain for vSB not zero vout vin gm 1 g mb g m roc ro vout gm 1 vin g mb g m 7 CD Output Resistance Sum currents at output source node Rout ro roc vt it Rout it g m vt g mb vt 1 g m g mb 8 3 CD Output Resistance Cont ro roc is much larger than the inverses of the transconductances ignore Rout 1 g m g mb Function a voltage buffer High Input Impedance Low Output Impedance 9 10 4 11 12 5 Review of LTI Systems Since most periodic non periodic signals can be decomposed into a summation integration of sinusoids via Fourier series Transform the response of a LTI system to virtually any input is characterized by the frequency response of the system Phase Shift Any linear circuit With L C R M and dep sources Amp Scale 13 Sinusoidal Function Review v t v cos t amplitude half of peak to peak phase degrees or radians frequency rad s 2 f 2 1 T 14 6 Graphical Description v 1 t v cos t v2 t v cos t 45 2 T T 15 Why are Sinusoids Important Any periodic signal v t can be expressed as a sum of sinusoidal signals by a Fourier series expansion EECS 20N EE 120 The response of a linear circuit to a sinusoidal input as a function of its frequency leads to insights into the behavior of the circuit 16 7 Linear Circuits Theorem solutions for voltages and currents in a linear circuit i e one consisting of R L C and dependent sources Gm Rm Av and Ai with a sinusoidal signal as the input are 17 RC Circuit with Sinusoidal Input iR vs t vc t R iC C vs t Vs cos t set phase of source to zero use as the reference vc t Vc cos t solution is a sinusoidal signal with the same frequency but with a different amplitude and phase shifted with respect to the source 18 8
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