Two Stage Amplifier Design ENGI 242 ELEC 222 HYBRID MODEL PI January 2004 ENGI 242/ELEC 222 2 Multistage Amplifier Design 1
HYBRID MODEL PI PARAMETERS Parasitic Resistances rb = rb b = ohmic resistance voltage drop in base region caused by transverse flow of majority carriers, 50 rb 500 rc = rce = collector emitter resistance change in Ic due to change in Vc, 20 rc 500 rex = emitter lead resistance important if IC very large, 1 rex 3 January 2004 ENGI 242/ELEC 222 3 HYBRID MODEL PI PARAMETERS Parasitic Capacitances Cje0 = Base-emitter junction (depletion layer) capacitance, 0.1pF Cje0 1pF Cµ0 = Base-collector junction capacitance, 0.2pF Cµ0 1pF Ccs0 = Collector-substrate capacitance, 1pF Ccs0 3pF Cje = 2Cje0 (typical) ψ0 =.55V (typical) τf = Forward transit time of minority carriers, average of lifetime of holes and electrons, 0ps τf 530ps January 2004 ENGI 242/ELEC 222 4 Multistage Amplifier Design 2
HYBRID MODEL PI PARAMETERS rπ = rb e = dynamic emitter resistance magnitude varies to give correct low frequency value of Vb e for Ib rµ = rb c = collector base resistance accounts for change in recombination component of Ib due to change in Vc which causes a change in base storage cπ = Cb e = dynamic emitter capacitance due to Vb e stored charge cµ = Cb c = collector base transistion capacitance (CTC) plus Diffusion capacitance (Cd) due to base width modulation gmvπ = gmvb e = Ic equivalent current generator January 2004 ENGI 242/ELEC 222 5 Hybrid Pi Relationships g m = V T = g m = I C VT k T q = 26mV @ 300 K I C 26mV r π = (26mV) ( β) IC = β = gm rπ π c = g mvπ π i = β v r 26mV IB January 2004 ENGI 242/ELEC 222 6 Multistage Amplifier Design 3
Hybrid Pi Relationships January 2004 ENGI 242/ELEC 222 7 Design of a Two Stage Amplifier January 2004 ENGI 242/ELEC 222 8 Multistage Amplifier Design 4
Two Stage Amplifier Design Specifications Design a two stage common emitter amplifier with partial emitter bypass for the following specifications: VCC = 20V VE =.1VCC RE1A =.25RE1 VC1 =.6VCC IC1 = 2mA RE2A =.4RE2 VC2 =.55VCC IC2 = 2.5mA R2 =.1βRE1 R4 =.1βRE2 RL = 10kΩ fcl1 = 16Hz fcl2 = 13Hz fcl3 = 12Hz fcl4 = 67Hz fcl5 = 8Hz For both stages: β = 140 τcb = 150ps VA = 100V Cµ 8pF ft = 150MHz rb = 19Ω January 2004 ENGI 242/ELEC 222 9 Hybrid Pi Model January 2004 ENGI 242/ELEC 222 10 Multistage Amplifier Design 5
Low Critical Frequencies There is one low critical frequency for each coupling and bypass capacitor We start by determining the (Thevenin) impedance seen by each capacitor Then we construct a RC high pass filter (output across Z) We may then calculate the critical frequency by letting XC = Z and solving for either fcl or C f CL = 1 2 π Z C 1 C = 2 π f CL Z and fcl = fcl1 + fcl2 + fcl3 + fcl4 + fcl5 January 2004 ENGI 242/ELEC 222 11 Hybrid Pi Model Input First Stage Z IN1 = R 1//R 2// ( r b1 + r π1+ (β + 1)RE1A) January 2004 ENGI 242/ELEC 222 12 Multistage Amplifier Design 6
Hybrid Pi Model Output First Stage Z O1 = R C1// ( r O1 + RE1A) January 2004 ENGI 242/ELEC 222 13 Hybrid Pi Model Input Second Stage Z IN2 = R 3//R 4// [ r b2 + r π2+ (β + 1)RE2A] January 2004 ENGI 242/ELEC 222 14 Multistage Amplifier Design 7
Hybrid Pi Model Output Second Stage Z O2 = R C2// ( r O2 + RE2A) January 2004 ENGI 242/ELEC 222 15 Hybrid Pi Model Emitter Bypass First Stage ( ) R//R 1 2 + r b1+ rπ1 Z = R // R β + 1 TH_IN1 + E1A E1B January 2004 ENGI 242/ELEC 222 16 Multistage Amplifier Design 8
Hybrid Pi Model Emitter Bypass Second Stage [ R //R //R //(r + R ] 3 4 C1 o1 E1A) + r b2+ rπ2 Z = R // R β + 1 TH_IN2 + E2A E2B January 2004 ENGI 242/ELEC 222 17 fcl1 1 f CL1 = 2 π Z IN1 C 1 January 2004 ENGI 242/ELEC 222 18 Multistage Amplifier Design 9
fcl2 Determine the Thevenin Impedance seen by C2 f CL2 = 2 Z O1 + Z IN2 C 2 1 π ( ) January 2004 ENGI 242/ELEC 222 19 fcl3 Determine the Thevenin Impedance seen by C3 1 f CL3 = 2 Z O2 + R L C 3 π ( ) January 2004 ENGI 242/ELEC 222 20 Multistage Amplifier Design 10
fcl4 Determine the Thevenin Impedance seen by CE1 1 f CL4 = 2 Z TH_IN1 C 4 π ( ) January 2004 ENGI 242/ELEC 222 21 fcl5 Determine the Thevenin Impedance seen by CE2 1 f CL5 = 2 Z TH_IN2 C 5 π ( ) January 2004 ENGI 242/ELEC 222 22 Multistage Amplifier Design 11
Schematic of Design January 2004 ENGI 242/ELEC 222 23 Simulation Profile January 2004 ENGI 242/ELEC 222 24 Multistage Amplifier Design 12
Probe Plot Y Axis Settings January 2004 ENGI 242/ELEC 222 25 Probe Plot X Axis X Grid Settings January 2004 ENGI 242/ELEC 222 26 Multistage Amplifier Design 13
Frequency Response January 2004 ENGI 242/ELEC 222 27 Frequency Response January 2004 ENGI 242/ELEC 222 28 Multistage Amplifier Design 14