Electronics
- lectures for Mechanical Engineering
part 4
Dr. Bogusław Boratyński
Faculty of Microsystems Electronics and Photonics,
Wroclaw University of Technology,
2011
From the course syllabus
Basic literature & figure sources:
G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill
R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publ.,
B.G. Streetman, Solid State Electronic Devices, Prentice-Hall,
J. Millman, Microelectronics, McGraw-Hill
Additional literature:
W. Marciniak, Przyrządy półprzewodnikowe i układy scalone, WNT,
A. Świt, J. Pułtorak, Przyrządy półprzewodnikowe, WNT,
B.G. Streetman, Przyrządy półprzewodnikowe, WNT
Semiconductor devices
Chapter 3. Electronic devices.
3.2 Bipolar transistors and applications:
continuation…
Limits of operation
High frequency operation
Switching operation
Class of amplifiers (A, B)
Differential amplifier
Operational amplifiers
Bipolar transistor dc bias in CE amplifier
Constant base potential VB
due to voltage divider (R1, R2)
Problem to solve:
Calculate ICQ
Calculate R1, R2 such that: VCEQ=10V
assume: =100, calculate IB .
Draw the load line and iC swing for sine-wave signal
VB = [R1/(R1 + R2)] VCC
VCC
IC
RC
C2
C
C1
Input
VB
Output
B
VBE
VCE
With CE, the circuit configuration is CE for ac signals
C1, C2 block the dc currents and allow ac signals to go through.
E
CE
RE
Without CE, the circuit configuration is CE+RE
and the voltage gain is Av = RC/RE and does not depend on
the transistor
Bipolar transistor - limits of biasing
Voltage and current limits of a bipolar transistor operation:
- Voltage limit - CB junction breakdown, base region punch-through
- Current limit - rated current - thermal effects
- Power limit - dissipated power P = IU - thermal effects
Q-point
Common emitter – output voltage breakdown BVCBO
Common base – output voltage breakdown BVCEO
BVCBO >> BVCEO
typically: 50V – 100V (800V)
Source: B.C.Streetman Solid State Electronic Devices, Prentice Hall.
Bipolar transistor frequency response
Filtering RC circuits:
high –pass filter
low –pass filter
No high freq. limit,
fH oo
No low freq. limit,
fL =0
fL - low 3-dB frequency
fH - high 3-dB frequency
at fL or fH :
3dB frequency band: Δf = fH – fL
voltage gain: Av = Vo/Vi
Av [dB] = 20 log Av
or 3dB drop in Av
Source J. Millman, Microelectronics, McGraw-Hill
Bipolar transistor frequency response
Resulted transistor frequency response,
transistor - as a low-pass RC filter:
LF model
hfe =h21e - CE current gain
detailed
LF model
CB junction
HF model
includes
capacitances
EB jun.
f - 3dB frequency
3dB drop in h21e
fT - cutt-off frequency
h21e =1 (0 dB)
Δf 3dB = f
Source: J. Millman, Microelectronics, McGraw-Hill
Transistor as a switch or a driver
Transistor - current or voltage activated switch
OFF
example: LED driver
ON
High –low
voltage
signal
Source: R.F. Pierret, Semiconductor Device Fundamentals,
Addison-Wesley Publishing Comp.
ON- OFF
state
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Bipolar transistor switching
Switch ON
Switch OFF
ON – OFF switching
Input
voltage
waveform
Input
current
waveform
saturation
Output
voltage
waveform
Minority
carriers in
the base
cut-off
0.2V
Source: J. Millman, Microelectronics, McGraw-Hill
Transistor as a switch or a driver
Transistor - current or voltage activated switch
Example:
Vcomputer pulse train Vpp=5V, RB = 1kohm
ILED=20mA VLED=1.4V, Veb sat = 0.7V Vcesat =0.2V
Proof that the transistor is in saturation mode
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Transistor circuit configurations
n-p-n
Current relations:
IC + IE + IB =0
IE= -(IB + IC)= - (1+ ) IB
Darlington transistor pair
current gain
Common Base
current gain
R output
R input
Common Emmiter
current gain
R output
R input
Common Collector
(emitter follower)
current gain
V. high input resistance!
R input
R output
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Transistor class A amplifier
The voltage and current swing symmetical with respect to Q-point
- large signal operation limited by a supply bias VCC
iB
iC
Output current
ac signal iC = iB
Vcc
UCEsat =0.2V
class-A
class-B
Max. signal amplitude
Vcc – 0.2V
Output voltage
ac signal vCE
Source: G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill
Transistor class B amplifier
Class B (AB) amplifier operation
Q-point at cut-off (class B) or
in the onset of the active region (class AB)
Complementary (npn and pnp)
transistor pair to amplify
full sine-wave signal
- push-pull amplfier needs a symetrical
power supply ±Vcc
Transistor amplifies one half
of the sine-wave signal only.
Source:J. Millman, Microelectronics, McGraw-Hill
Source: R.F. Pierret, Semiconductor Device Fundamentals,
Addison-Wesley Publishing Comp.
Differential amplifier
Operational amplifier
(basic IC building block chip)
Vo = Avd ( Vs1-Vs2)
Avd – differential voltage gain
Vs1-Vs2 - differential input signal
Source:J. Millman, Microelectronics, McGraw-Hill
vout = - RF/RS ( vs )
Ideal amplifier parameters:
R output
0
R input
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Operational amplifier
Operational amplifier (IC chip)
e.g.: 741 op-amp
Vo = AVd ( v+ - v-) = AVd ( vin)
Open loop gain (no RF):
AV(OL)
oo
With feedback loop:
vout = - RF/RS ( vin )
R out
Vo = Avd ( Vs1-Vs2)
0
R in
Avd – differential voltage gain
Vs1-Vs2 - differential input signal
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Operational amplifier configurations
Summing amplifier
Inverting amplifier
vout = - RF/RS ( vs )
vout = - RF/RS1 ( vs1 ) - RF/RS2 ( vs 2).... - RF/RSN ( vs N)
Source:J. Millman, Microelectronics, McGraw-Hill
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Operational amplifier configurations
Noninverting amplifier
Inverting amplifier
vout = - RF/RS ( vs )
vout = 1+ RF/RS ( vs )
Avd = 1+ [RF/RS ]
Source:J. Millman, Microelectronics, McGraw-Hill
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill