rf microelectronics - basic concepts - nonlinearity
TRANSCRIPT
RF MicroelectronicsCHAPTER- 2: BASIC CONCEPT'S.
BY: AHMED SAKR.
SUPERVISED BY:
PROF. HESHAM HAMED, DR. MAHMOUD A. ABDELGHANY.
Introduction
RF section of Cellphone
RF section of a cellphone
Introduction
Design bottleneck
RF Section is the bottleneck of wireless
communication systems. Because:
- The performance of the RF front end affects the
overall performance of the entire system.- RF design involves many disciplines the designer
should understand.
- There are many trade-offs in RF design.
- Relay on experience even while using design tools.
Trade-offs in RF design
Basic concepts.
Design bottleneck
Nonlinearity
โข Harmonic distortion.
โข Compression.
โข Intermodulation.
โข Dynamic nonlinear systems.
Noise
โข Noise Spectrum.
โข Device Noise.
โข Noise in circuits.
Impedance Transformation
โข Series- Parallel conversion.
โข Matching networks.
โข S-Parameters.
Unites in RF
Logarithmic operations review
๐๐ 10๐ด = ๐ต , ๐กโ๐๐ log ๐ต = ๐ด
log1
๐ฅ= โ log ๐ฅ
log 10๐ฅ = ๐ฅlog ๐ฅ๐ = ๐๐๐๐(๐ฅ)
log ๐ฅ๐ฆ = log ๐ฅ + log ๐ฆ
log๐ฅ
๐ฆ= log ๐ฅ โ log ๐ฆ
Unites in RF
Gain
Rin Rout
Vin Vout
๐ฝ๐๐๐๐๐๐ ๐๐๐๐ ๐จ๐ =๐๐๐ข๐ก
๐๐๐๐ ๐๐
๐ท๐๐๐๐ ๐๐๐๐ ๐จ๐ท =๐๐๐ข๐ก
๐๐๐=
๐๐๐ข๐ก2
๐ ๐๐ข๐ก๐๐๐2
๐ ๐๐
=๐๐๐ข๐ก2
๐๐๐2ร๐ ๐๐ข๐ก
๐ ๐๐= ๐ด๐ฃ2 ร
๐ ๐๐ข๐ก
๐ ๐๐
๐ข๐ ๐๐จ๐ฎ๐ญ = ๐๐ข๐ง โ ๐๐ = ๐๐ฏ๐
Unites in RF
Gain (in dB)
๐ ๐ฉ ๐จ๐ = 20log(๐๐๐ข๐ก
๐๐๐)
๐ ๐ฉ ๐จ๐ท = 10 log๐๐๐ข๐ก
๐๐๐
= 10 log๐๐๐ข๐ก2
๐๐๐2ร๐ ๐๐ข๐ก
๐ ๐๐
๐ ๐๐๐๐๐ ๐๐๐ค๐๐|๐๐ต ๐๐ = 10 log๐๐
1๐๐โ ๐๐ ๐ ๐๐ข๐ก = ๐ ๐๐ โ ๐ ๐ฉ ๐จ๐ = ๐ ๐ฉ(๐จ๐)
๐ฝ๐๐๐๐๐๐ ๐๐๐๐ ๐จ๐ =๐๐๐ข๐ก
๐๐๐๐ ๐๐
๐ท๐๐๐๐ ๐๐๐๐ ๐จ๐ท =๐๐๐ข๐ก
๐๐๐=
๐๐๐ข๐ก2
๐ ๐๐ข๐ก๐๐๐2
๐ ๐๐
=๐๐๐ข๐ก2
๐๐๐2ร๐ ๐๐ข๐ก
๐ ๐๐= ๐ด๐ฃ2 ร
๐ ๐๐ข๐ก
๐ ๐๐
โ ๐ข๐ ๐๐จ๐ฎ๐ญ = ๐๐ข๐ง โ ๐๐ = ๐๐ฏ๐
Unites in RF
Voltage gain Vs. power gain
Rin Rout
Vin Vout
We are interested in calculating the output
voltage rather than the output power
when the input and output impedance are
not equal or contain negligible real parts.
Why?
Because the voltage gain is not equal to
the power gain in this case, which is
common in RF design.
Linearity and time variance
LinearityFor a linear system, if:
X1(t) โ Y1(t) , X2(t) โ Y2(t)
aX1(t) + bX2(t) โ aY1(t) + bY2(t)
Otherwise, the system is nonlinear.
Time Variance
For a time invariant system, if:
X(t) โ Y(t)
Then : X(t-T)โ Y(t-T)
Otherwise, the system is time variant.What about nonzero initial conditions and
dc offsets? - They are linear too.
Linearity and time variance
Switching system
Nonlinear, time variant Linear, time variant
Linearity and time variance
Nonlinear, time variant
Linearity and time variance
Linear , time variant Vin2 delayed by 45 degree
Memory-less systems [outputs donโt depend on past values of
input(s), opposite to Dynamic systems.]
Memory-less linear systems
y(t) = x(t)
Memory-less nonlinear systems y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +โฆ n xn(t)
If j=0 for even j, the system is said to
have odd symmetry, when his
response to โx(t) is negative to that to
x(t).
The circuit having this property is
called differential or balanced.
Nonlinearity effects.
y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +โฆ n xn(t)
DC
component
Total
Gain [compression
@ 1 3 <0]
2nd
harmonic
Suppresse
d for odd
symmetry.
3rd
harmonic
Small
signal
gain
Harmonic distortion.
y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +โฆ n xn(t)
DC
componentfundamental 2nd
Harmonic
3rd
Harmonic
In many RF designs, the harmonics
distortion is unimportant but should be
tested before they are dismissed, usually
harmonics are filtered, but it is a key
parameter to test the performance of
specific circuits such as Mixers
Common
in
MIXERS
&OSC
Gain compression
y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +โฆ n xn(t)
DC
component
Total
Gain [compression
@ 1 3 <0]
2nd
harmonic
Suppresse
d for odd
symmetry.
3rd
harmonicSmall
signal
gain
@ 1 3 <0 the gain is compressed as A rises
1 =500
3 =-0.1
Gain compression [1-dB compression point]
@ 1-dB compression point, the gain is
reduced by 10%
Desensitization: when large
interferer [blocker] causes gain
compression while sensing weak
desired signal.
[lowers the SNR]
Cross modulation.
y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +โฆ n xn(t)
Weak signal + large interferer
large interferer:
Variations in A2 (modulation) affects the
amplitude of the signal (A1) Common
in
AMPLIFIERS
Intermodulation.
Intermodulation
components
Fundamental
components
Intermodulation.
Third order intermodulation products are the most important. If the difference between w1 and
w2 is small they will appear close to the fundamentals, making it hard to design a filter to
discard the effect of them.
This effect is significant in LNA as shown in next figureโฆ
Intermodulation[two-tone test].
Two signals with
small A is chosen to minimize
nonlinearity effect on it
Gain = 1
Fundamental A
IM products A3
Plot in log-log scale,
the intersection is
the third-order
intercept point
IIP3 is beyond the allowable
input range or even higher
than the supply voltage,
because if the input level
reached the AIP3 the gain
drops and higher order IM
products become significant.
Intermodulation[two-tone test].
IIP3 is chosen beyond the allowable
input range or even higher than the
supply voltage, because if the input level reached the AIP3 the gain drops
and higher order IM products
become significant.
AIIP3 is greater than
the 1-dB compression
point with 9.6 dB
IIP3 direct calculation. [two-tone test].
Any Questions?