1EE105 - Fall 2005Microelectronic Devices and CircuitsLecture 16Common-Drain AmplifierReview of Phasors425Common-Drain Amplifier21()2DS ox GS TWICVVLµ=−2DSGS ToxIVVWCLµ=+Weak IDSdependence6CD Voltage GainNote vgs= vt–vout||outm gs mb outoc ovgv g vrr=−()||outm t out mb outoc ovgvv gvrr=−−37CD Voltage Gain (Cont.)KCL at source node:Voltage gain (for vSBnot zero):()||outm t out mb outoc ovgvv gvrr=−−1||mb m out m toc oggvgvrr⎛⎞++ =⎜⎟⎝⎠1||out minmb moc ovgvggrr=++1out min mb mvgvgg≈≈+8CD Output ResistanceSum currents at output (source) node:|| ||tout o octvRrri=tmtmbtigvgv=+1outmmbRgg≈+49CD Output Resistance (Cont.)ro|| roc is much larger than the inverses of the transconductances Æ ignore1outmmbRgg≈+Function: a voltage buffer• High Input Impedance• Low Output Impedance1051112613Review of LTI SystemsSince 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:Any linear circuit With L,C,R,Mand dep. sources AmpScalePhase Shift14Sinusoidal Function Reviewvt()vωtφ+()cos=amplitudefrequencyphase (degrees(rad/s) ... ω= 2πf = 2π(1/T)(half ofpeak-to-peak)or radians)715Graphical Descriptionv1t()vωt()cos=v2t()vωt 45–()cos=ω2πT------=T16Why 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 ω, leads to insights into the behavior of the circuit.817Linear CircuitsTheorem: 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:18RC Circuit with Sinusoidal Input R vc(t) C iR iC vs(t) + - vs(t)= Vs cos(ωt) : set phase of source to zero (use as the reference) vc(t)= Vc cos(ωt + φ) : solution is a sinusoidal signal with the same frequency, but with a different amplitude and phase-shifted with respect to the
View Full Document