Download Parameters Reflector biased at 10 mA Is

Conventional amplifier
Vcc
Rb1
Rc
Collector
Vout
Base
Vin
RL
Emitter
Rb2
Re
Ce
Av = Vout/Vin = - (Rc//RL) / re
re = ac resistance of the emitter
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High-frequency transformercoupled amplifier
Vcc
L
C1
Vout
RL
Rb1
Collector
Base
Vin
Emitter
Rb2
Ce
Re
f = 1 / (2 pi sqrt(L C1)
Q=f/B
2
Example 2.1
Practical common emitter amplifier
with better impedance matching
Vcc
Rd
L
C1
Vout
RL
Rb1
Collector
Cd
Base
Vin
Emitter
Rb2
Ce
Re
Better impedance matching
Higher Q
3
Common base RF amplifier
Vcc
L
L
Vout
Vin
RL
Cb
Re
4
Wideband amplifier- Class A
Vcc
Vout
L
RL
Rb1
Collector
Base
Vin
Emitter
Rb2
Ce
Re
Linear amplifier
Generally used as single-ended audio amplifiers
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Wideband amplifier- Class B
Vcc
Rb1
Vout
RL
Vin
Compared to Class A:
Greater efficiency
Larger distortion
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Amplifier- Class C
Vcc
Vout
L
RL
Collector
Base
Vin
Emitter
High efficiency
Larger distortion
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Operating condition
Class C amplifiers would improve the
efficiency by operating in nonlinear regime,
however the input has to be a sinusoidal wave
Some means are needed to remove the
distortion and restore the signal to its original
sine shape
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Operation principle
The active device conducts for less than 180
degrees of the input cycle
The output resembles a series of pulses more
than it does the original signal
The pulses can be converted back to sine waves
by an output tuned circuit
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Circuit configuration
Vcc
Vout
L
Output
RL
Input
Collector
Base
Vin
Emitter
Nonlinear
amplifier
Sine input -> nonlinear current output -> sine output
Fig. 2.12
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Pros and Cons of the Class C
amplifiers
Pros:
• High efficiency, no current in absence of signal
Cons:
• The output tuned circuit must be adjusted fairly
close to the operating frequency
• The amplification is nonlinear
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Comparison of three amplifiers
Class
A
B
C
Conduction 360
angle
180
< 180
Maximum
efficiency
50%
78.5%
100%
Likely
practical
efficiency
25%
60%
75%
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Neutralization
Vcc
Rd
L
Vout
Cd
RL
Rb1
Collector
Base
Vin
Emitter
Rb2
Ce
Re
Cn
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Neutralization
capacitor
Oscillator
A
Barkhausen criteria:
•Ax B =1
B
• Phase shift must total
0 or integer multiple of
360 degrees
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Using non-inverting amplifier
N2
N1
Hartley oscillator
B = N1 / (N1 + N2)
f = 1/2pi sqrt(LC)
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Using inverting amplifier
(Hartley oscillator)
N2
N2
N1
N1
B = -N1 / N2
B = (N1 + N2) / N1
Example 2.2
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Colpitts oscillator (non-inverting
amplifier)
C2
C1
B = Xc1 / Xct = C2 / (C1 + C2)
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Colpitts oscillator (inverting
amplifier)
C2
C1
B = -Xc1/Xc2 = - C2/C1
Example 2.3
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Clapp oscillator
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Varactor tuned oscillator
C=C0/sqrt(1+2V)
Example 2.5
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Oscillation frequency of LC
circuit
See MIT open course ware
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Another application of high Q
filter
Clock recovery by strong filtering effect
Before
After
PTL Oct
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Crystal
Crystal oscillators achieve greater stability by using a small
slab of quartz as a mechanical resonator, in place of an LC
tuned circuit
Cs
Two resonance frequency related to Cs and Cp,
respectively
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Cp
Temperature dependence
fT = f0 + k f0(T-T0)
Example 2.6
A portable radio transmitter has to operate at
temperatures from –5 to 35 degrees. If the frequency
is derived from a crystal oscillator with a
temperature coefficient of +1ppm/degree C and it
transmits at exactly 146 MHz at 20 degree, find the
transmitting frequencies at the two extremes of the
operating range
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Mixers
A mixer is a nonlinear circuit that combines two signals in such
a way as to produce the sum and difference of the two input
frequencies at the output
Any nonlinear device can operate as a mixer
Vout = A Vi + B Vi2 + C Vi3 + …
Second order effects
f1- f2
f1
f1+f2
f2
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Square law mixers
Vout = A Vi + B Vi2
If inputs are two frequencies,
the outputs will be:
Original frequencies, double frequencies,
sum frequencies, and differential
frequencies
Example 2.7
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Diode mixers
The V-I curve for a typical silicon signal
diode is nonlinear
Diode mixers can operate between reverse
and forward biased states
Or they can operate with a small forward bias
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Transistor mixers
Vcc
Vout
L
RL
Rb1
Collector
Base
f2
f1
Emitter
Rb2
Re
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Balanced mixers
A multiplier circuit, where the output amplitude
is proportional to the product of two input
signals, can be used as a balanced mixer
V1 = sinω1t
V2 = sinω2t
Vo = V1 x V2 = 0.5 x [cos(ω1t - ω2t) – cos(ω1t +
ω2t)]
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Applications of balanced mixers
Data (…01101001…)
AM Modulation
Output
Signal
Carrier
Signal
input
AM de-modulation
Filter
Local oscillator
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Output
Signal
Detection schemes
Homodyne and heterodyne detection
One example of heterodyne detection
Self-mixing homodyne detection
Signal
input
Filter
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Output
Signal
Phase detector using mixer
Signal
input
The DC output depends on the phase of the
two paths
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Phase locked loop
Phase
detector
LPF
Amp
VCO
Output
Input
Capture range
Lock range
Example 2.8
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Simple frequency synthesizer
Phase
detector
LPF
Amp
VCO
Output
Input
/N
divider
FM and AM channel spacing
Example 2.9
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A practical example – 29M to
10G synchronization circuit
29MHz / 6 circuit
15V
29MHz
pulse
in
4.7
u
150
4.7u
5V
4K
4.84 M
TTL
Output
200
150
Clk
MRV
901
100 MAV11
MAV11
1K
10
Reset
D1
D0
74F163
Counter
D
Clk
Q
_
Q
74F74
D Flip-Flop
7K
29MHz amplification, digitization and frequency division circuit
(All capacitors are 0.1uF).
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5M to 10G synchronization
circuit
To 10G laser
+15V
2-10 dBm
10 dBm
10GH
VCO
+6V
5
Splitter
2.2V
Zener
UPG506B
14GHz
divide
by 8
Prescalar
8
1
-15~0 dBm
8
2
+17V
100K
3
6
4
10K
2
K
1.5K
5
10K
74F86
XOR
gate
1000UF
7
UPB1502
1.25GHz
divide
by 128
Prescalar
74F74
f/2
4.84 MHz TTL Input
1.5K
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Experimental results
Spectrum of 4.827MHz square signal
wave. Span: 500Hz, RB: 30Hz.
Spectrum of 4.827MHz square signal wave.
Span: 500Hz, RB: 30Hz.
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Pre-scaling
Phase
detector
LPF
Amp
VCO
Output
Input
Fixed
/Q
Fixed
/M
Programmable
/N
Example 2.10
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Frequency translation
The movement of a block of frequencies is
called a frequency translation
Two configurations:
Synthesizer with frequency shifting
Synthesizer with mixer in the loop
Example 2.11
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Transmission lines
Coaxial cables (solid dielectric, air dielectric)
Parallel line cables (television twin-lead, openwire line, shielded twin-lead)
Twisted pair cable
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Two models of short
transmission line section
Balanced line
Unbalanced line
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Step and pulse response of lines
Characteristic impedance: the ratio of voltage
to current through the transmission line with a
step signal
Concept of matched line
Characteristic impedance Z0 = sqrt[(R + jwL) /
(G + jwC)]
Many lines approach Z0 = sqrt(L/C)
Example 14.1, 14.2
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Reflection (step input)
Open end scenario
Short end scenario
Pulse input…
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Some definitions
Γ = Vr/Vi: reflection efficient
Γ = (ZL – Z0) / (ZL + Z0)
Meaning of the above equation:
1. To have zero reflection, ZL has to be equal to Z0
2. By measuring Γ, ZL can be derived to probe the
internal characteristic of the load
Example 14.13
44
An example to know the internal
parameters of a tunable laser
Lp
Transmission
line
Source
Rp
Rs
Cs
Cp
D
Rsub
S11
Parameters
Reflector biased at 10 mA
Is (A)
1.79E10-5
q
4.47
Rp (ohm)
0.1
Rs (ohm)
0.1
Rsub (ohm)
1.0
Cp (pF)
4.58
Cs (pF)
355
Lp (nH)
21.4
Parasitics
PN junction
S11 = (ZL – Z0) / (ZL + Z0)
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Voltage driver is better than
current driver
Y. Su et al, IEEE PTL Sept. 2004
Current response
Optical response
46
Wave propagation
In a matched line, a sine wave moves down the
line and disappear into the load. Such a signal is
called a traveling wave
Example 14.5
RF Phase shifter
47
Standing waves
The interaction between the incident and
reflected waves causes what appears to be a
stationary pattern of waves on the line, which
are called standing waves
SWR = Vmax/Vmin
For a matched line, the SWR = 1
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Relation between Γ and SWR
SWR = (1+ |Γ|) / ( 1 - |Γ|)
If ZL >Z0,
SWR = Z0 / ZL
Example 14.6
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