10 Multistage

Two Stage Amplifier Design

ENGI 242ELEC 222

January 2004 ENGI 242/ELEC 222 2

HYBRID MODEL PI


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



• Parasitic Capacitances• Cje0 = Base-emitter junction (depletion layer) capacitance,

0.1pF ≤ Cje0 ≤ 1pF• C0 = Base-collector junction capacitance, 0.2pF ≤ C0 ≤

1pF• Ccs0 = Collector-substrate capacitance, 1pF ≤ Ccs0 ≤ 3pF• Cje = 2Cje0 (typical) 0 =.55V (typical) F = Forward transit time of minority carriers, average

of lifetime of holes and electrons, 0ps ≤ F ≤ 530ps



• r = rb’e = dynamic emitter resistance – magnitude varies to give correct low frequency value of Vb’e for Ib

• r = 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

• c = Cb’e = dynamic emitter capacitance – due to Vb’e stored charge

• c = Cb’c = collector base transistion capacitance (CTC) plus Diffusion capacitance (Cd) due to base width modulation

• gmV = gmVb’e = Ic – equivalent current generator


Hybrid Pi Relationships

Cm

T

T

Cm

C B

I g =

V k T

V = = 26mV @ 300 Kq

I g =

26mV (26mV) ( ) 26mV

r = = I I

= gm r

πc m π

π

β v i = = g v

r


Hybrid Pi Relationships


Design of a Two Stage Amplifier


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 = 2mARE2A = .4RE2 VC2 = .55VCC IC2 = 2.5mAR2 = .1RE1 R4 = .1RE2 RL = 10kfCL1 = 16Hz fCL2 = 13Hz fCL3 = 12HzfCL4 = 67Hz fCL5 = 8Hz

For both stages: = 140 CB = 150ps VA = 100VC 8pF fT = 150MHz rb = 19


Hybrid Pi Model


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


Hybrid Pi Model Input First Stage

IN1 1 2 b1 π1 E1AZ = R //R // r + r + (β + 1)R


Hybrid Pi Model Output First Stage

O1 C1 O1 E1AZ = R // r + R


Hybrid Pi Model Input Second Stage

IN2 3 4 b2 π2 E2AZ = R //R // r + r + (β + 1)R


Hybrid Pi Model Output Second Stage

O2 C2 O2 E2AZ = R // r + R


Hybrid Pi Model Emitter Bypass First Stage

1 2 b1 π1 TH_IN1 + E1A E1B

R //R + r + rZ = R // R

+ 1


Hybrid Pi Model Emitter Bypass Second Stage

3 4 C1 o1 E1A b2 π2 TH_IN2 + E2A E2B

R //R //R //(r + R ) + r + rZ = R // R

+ 1


fCL1

CL1

IN1 1

1 f =

2 Z C


fCL2

CL2

O1 IN2 2

1 f =

2 Z + Z C

Determine the Thevenin Impedance seen by C2


fCL3

CL3

O2 L 3

1 f =

2 Z + R C

Determine the Thevenin Impedance seen by C3


fCL4

Determine the Thevenin Impedance seen by CE1

CL4

TH_IN1 4

1 f =

2 Z C


fCL5

Determine the Thevenin Impedance seen by CE2

CL5

TH_IN2 5

1 f =

2 Z C


Schematic of Design


Simulation Profile


Probe Plot – Y Axis Settings


Probe Plot – X Axis X Grid Settings


Frequency Response

10 Multistage

Documents

Transcript of 10 Multistage