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9/14 Music for your ears

9/14 Musique 101

9/14 Audio Spectrum 4

9/14 5 Figure 1.21 Typical magnitude response of an amplifier. |T( v )| is the magnitude of the amplifier transfer function— that is, the ratio of the output V o ( v ) to the input V i ( v ). Amplifiers have limited bandwidth  frequency response of Amplifiers Constant gain between w1 & w2 (Bandwidth) ; otherwise lower gain. Amp chosen so its BW coincides with required spectrum to be amplified … otherwise signals distorted

9/14 6 Figure 1.11 (a) A voltage amplifier fed with a signal v I (t) and connected to a load resistance R L. (b) Transfer characteristic of a linear voltage amplifier with voltage gain A v. Voltage Amplifier - Transfer characteristic Can also have circuit Amps input output

9/14 7 Figure 4.26 (a) Basic structure of the common-source amplifier. (b) Graphical construction to determine the transfer characteristic of the amplifier in (a). MOSFET AMP common source Graphical method Using load line :: slope is 1/R D For any value of V I = V GS Locate corresponding I D – V DS curve Find v o

9/14 8 Figure 4.26 (Continued) (c) Transfer characteristic showing operation as an amplifier biased at point Q. MOSFET Amp. Biased at Q Xfer characteristic  inverting Similar to switch characteristic Biased at point Q V i superimposed on V IQ Vi small  linear amp operation  V O proportional to Vi

9/14 9 Figure 4.27 Two load lines and corresponding bias points. Bias point Q 1 does not leave sufficient room for positive signal swing at the drain (too close to V DD ). Bias point Q 2 is too close to the boundary of the triode region and might not allow for sufficient negative signal swing. MOSFET as linear Amp – use saturation seg. How to select Bias point Q1 bias point Not enough +ve swing Too close to Vdd Q2 bias point Too close to triode Insufficient –ve swing

9/14 10 Figure 1.12 An amplifier that requires two dc supplies (shown as batteries) for operation. Some Amplifiers Require 2 supplies Eg 2 supply +ve & -ve swings

9/14 11 Figure 1.13 An amplifier transfer characteristic that is linear except for output saturation. Amplifier transfer characteristics Amps have limitations.. may saturate..signal (2) Amp linearity desired Vout(t) = A * Vin(t) input output Two power supplies used L + >= A*v i

9/14 Amplifier Biasing – ensures linearity 12 Figure 1.14 (a) An amplifier transfer characteristic that shows considerable nonlinearity. (b) To obtain linear operation the amplifier is biased as shown, and the signal amplitude is kept small. Observe that this amplifier is operated from a single power supply, V DD. Nonlinear response

9/14 13 Figure 1.15 A sketch of the transfer characteristic of the amplifier of Example 1.2. Note that this amplifier is inverting (i.e., with a gain that is negative). Inverting Amplifier biasing example Top limit = 10v, lower limit = 0.3v Output 180 degrees out of phase with input L- = 0.3v Vt = L+ =~ Vt = 0 For 5 V Vo = 5v Vt = 0.673

9/14 14 Figure 1.17 (a) Circuit model for the voltage amplifier. (b) The voltage amplifier with input signal source and load. Voltage Amplifier Circuit Model used for simulation, circuit analysis Gain = A w ; input resistance = R i, Output resistance = R o v o = A w * v i * R L /(R L + R o ); effect of output resistance R o v o / v i = A w * R L /(R L + R o ); voltage gain v i = v s * R i / (R i + R s ); effect of R i v o / v s = A w * R i / (R i + R s ) * R L /(R L + R o ); overall voltage gain accounting for input / output impedances Inp. resistanceOut. resistance Inp. source, / R s Load R L

9/14 15 Figure 1.18 Three-stage amplifier for Example 1.3. More Gain ? Use Cascaded stages Ex 1.3 Input stage needs high input impedance Output stage needs low output impedance Input resistance of a stage = load resistance of previous stage Vi 1 / V s = 1 M / ( 1M + 100k) = ; effect of 1 st Rin Av 1 = Vi 2 / Vi 1 = 10 * 100k / (100k + 1k) = 9.9 ; gain 1 st stage, A = 10 Av 2 = Vi 3 / Vi 2 = 100 * 10k / (10k + 1k) = 90.9 ; gain 2 nd stage, A = 100 Av 3 = V L / Vi 3 = 1 * 100 / ( ) = ; gain 3 rd stage, A = 1 Av = V L / Vi 1 = 9.9 * 90.9 * = 818 ; 3 stage gain V L / V s = 818 * = ; from source to load Ideal Gain = 10 * 100 = 1000

9/14 16 Figure 1.21 Typical magnitude response of an amplifier. |T( v )| is the magnitude of the amplifier transfer function— that is, the ratio of the output V o ( v ) to the input V i ( v ). Amplifiers have limited bandwidth  frequency response of Amplifiers Constant gain between w1 & w2 (Bandwidth) ; otherwise lower gain. Amp chosen so its BW coincides with required spectrum to be amplified … otherwise signals distorted

9/14 17 Figure 1.27 Use of a capacitor to couple amplifier stages. Capacitively Coupled Amplifier Stages

9/14 An NMOS Common Source Amplifier 18 Figure 4.26 (a) Basic structure of the common-source amplifier. (b) Graphical construction to determine the transfer characteristic of the amplifier in (a). Amp. Circuit Xfer Characteristic

9/14 NMOS common source Amp. Cont’d Xfer Characteristic 19 Figure 4.26 (Continued) (c) Transfer characteristic showing operation as an amplifier biased at point Q. Biased at point Q

9/14 20 Figure 4.63 Capture schematic of the CS amplifier in Example Pspice Amplifier Example