Two Stage Amplifier Design using PSpice M2-3
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Two Stage Amplifier Design using PSpice
M2-3
HYBRID MODEL PI
M2-3 Electronics
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
M2-3 Electronics
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
M2-3 Electronics
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
M2-3 Electronics
Hybrid Pi Relationships
Cm
T
T
Cm
C B
I g = V k T V = = 26mV @ 300 K
q I g =
26mV (26mV) ( ) 26mV r = =
I Iπ
°
β
β = gm rπ
πc m π
π
β v i = = g vrM2-3 Electronics
Hybrid Pi Relationships
M2-3 Electronics
Design of a Two Stage Amplifier
M2-3 Electronics
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
M2-3 Electronics
Hybrid Pi Model
M2-3 Electronics
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 and fCL = fCL1 + fCL2 + fCL3 + fCL4 + fCL5
CL
CL
1 f = 2 π Z C
1 C = 2 π f Z
M2-3 Electronics
Hybrid Pi Model Input First Stage
( )IN1 1 2 b1 π1 E1AZ = R //R // r + r + (β + 1)R
M2-3 Electronics
Hybrid Pi Model Output First Stage
( )O1 C1 O1 E1AZ = R // r + R
M2-3 Electronics
Hybrid Pi Model Input Second Stage
[ ]IN2 3 4 b2 π2 E2AZ = R //R // r + r + (β + 1)R
M2-3 Electronics
Hybrid Pi Model Output Second Stage
( )O2 C2 O2 E2AZ = R // r + R
M2-3 Electronics
Hybrid Pi Model Emitter Bypass First Stage
( ) β
1 2 b1 π1 TH_IN1 + E1A E1B
R //R + r + rZ = R // R
+ 1
M2-3 Electronics
Hybrid Pi Model Emitter Bypass Second Stage
[ ] β
3 4 C1 o1 E1A b2 π2 TH_IN2 + E2A E2B
R //R //R //(r + R ) + r + rZ = R // R
+ 1
M2-3 Electronics
fCL1
πCL1
IN1 1
1 f = 2 Z C
M2-3 Electronics
fCL2
( )πCL2
O1 IN2 2
1 f = 2 Z + Z C
Determine the Thevenin Impedance seen by C2
M2-3 Electronics
fCL3
( )πCL3
O2 L 3
1 f = 2 Z + R C
Determine the Thevenin Impedance seen by C3
M2-3 Electronics
fCL4
Determine the Thevenin Impedance seen by CE1
( )πCL4
TH_IN1 4
1 f = 2 Z C
M2-3 Electronics
fCL5
Determine the Thevenin Impedance seen by CE2
( )πCL5
TH_IN2 5
1 f = 2 Z C
M2-3 Electronics
Schematic of Design
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Simulation Profile
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Probe Plot – Y Axis Settings
M2-3 Electronics
Probe Plot – X Axis X Grid Settings
M2-3 Electronics
Frequency Response
M2-3 Electronics
Frequency Response
M2-3 Electronics
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