Overview on Microwave Circuits Design Prof. Yongchae Jeong

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Overview on Microwave Circuits Design

• Prof. Yongchae Jeong
• (E-mail ycjeong_at_chonbuk.ac.kr)

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Overview on Microwave Circuits Design
1. Electronics 2. Radio Wave 3. Comparison
between Analog, Digital and
Microwave, 4. Microwave Applications 5.
Measurement Systems for Microwave Circuits 6.
Curriculum for Microwave Engineering 7. Basic
Concepts in Microwave Circuit Design 8. RF
Transceiver Architectures
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1. Electronics
-?? Electronics Electron (??)ics (???
???) -?? 1 ?? ??? ??, ?? ???? ??? ??? ???? ?? ?
??? ???? ?? -?? 2 ????? ???? ?? ??? ? ????
????? ?? ?? ???? ???? ?? ?? ?? ??? ????? ?? ???
??? ???? ?? ?????, 1948? ?? ? ????? ??? ??????
??? ???? ???? ????? ??? ??? ???? ??? ??? ?????
??? ?? -??? ?? ?, ?, ?, ??? ?? ?? ????? ????
?? -?? ????(???)? ?? ??
Diode(??? ????, ??? ????) Transistor(?????) IC(Int
egrated Circuit ????) VLSI(Very Large Scale
Intefration???? ????)
Digital IC Analog IC, RFIC(Radio Frequency IC),
MMIC(Monolithic Microwave IC) OEIC
(Optoelectronic IC)
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1. Electronics
?? 1. ?? ??? ???
5
2. Radio Wave
-Radio Wave -???? ???? ?? ??? ???? 3THz ?? ??
???? ??? -????? ???? ?? ???? ???? ???, ????, ???,
X?, ??? ?? ?? -??? ?? ??? ??? 3kHz 3THz ? ????
?? ??? -????, ??? ??, TV ??, ?? ??, ??? ?? ?? ???
???? ???, ??? ???? ??? ??? ?? ?? ???? ?? ????
???? ??? ???, ?? ?? ?? ?? ??? ???? ?? ??, ???? ??
?? ???? ??
?? 2. ???? ?
6
2. Radio Wave
??? ?? 1)??? ?? ?? ???? ??? ??? ?????
???? ???? ???? ?? 2) ??? ?? ? ?? ?? ???
??? ??? ?? ?? ?? ??? ??? ???? ??? ???? ? ???
????? ??? ???? ??? ????? ??? ????? ?? 3) ???
?? ???? ?? ????? ?? ???? ?? ?? ?? ?? ??
???? ?? ??, ? ???? ??? ??? ??? ??
4) ??? ?? ? ???? ?? ?? ?? ?????
??? ??? ???? ?? ??? ???? ??? ?? ??? ??? ?? ??
??? ?? ?? ?? ?? ??????? ???? ???
???? ?? ???? ?? ??? ?? ?? ??
???? ??? ????? ?? ?? ??? ???? ???, ?? ????? ?? ??
7
2. Radio Wave
?? 3. ??? ?? ??
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2. Radio Wave
RF? ?? -RF (Radio Frequency) ?? ( ?? ) ???

• ???? ??? ????? ?? ? ???
• RF 1GHz
• ??? ??
• Microwave 300MHz
  300GHz

- ?? 100 300MHz ??? ??? ???? ? ???? ???? ??,
??, ???, ?? ?? ??.
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2. Radio Wave
???(Frequency)? ??
???? ???? ??? ?? ?(??? ???? ??? ??? ??) ? ??
? ???? ???? ? ?? 1? ??? ??? ??? ???? ?? Hz

?? 4. ???? ??
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2. Radio Wave
???? RF ??
? 1. ?? ??? ??
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2. Radio Wave
Microwave ??
? 2. Microwave ??
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3. Comparison between Analog, Microwave, Digital
?? 5. Analog ? Digital
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4. Microwave Applications
?? ? ?? ????? RF Super Heterodyne ??
?? 6. Super heterodyne ??? AM ???? ???? ??
Super Heterodyne ?? ???? ??? ??? ??? ??? ????
??? ?? ??? ?? ??? ????, ??? ??? ?? ???? ?? ??
???? ???? ??? ??? ?? ???? ??? ??? ?? ???? ???
???? ??? ????, ??? ???? ???? ???? ?? ??? ????
?? Direct Conversion (Zero IF) ?? IF? ???? ????
??? ???? ??? ???? ???, IF?? ???? ?? ??? ?????
???? ??? ??? ? ???? ?? ???. IF (Intermediate
Frequency) ??????? ?? ?? ??? ???? ?? ??? ??? ??
???? ???(???), ????? ?? ???? ?? ????? ?? ?? ????
?? ??? ? ???? ?? ?? ?
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4. Microwave Applications
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4. Microwave Applications
???? ??? ??
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4. Microwave Applications
Direct Conversion ??
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4. Microwave Applications
Super Heterodyne ??
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4. Microwave Applications
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4. Microwave Applications

• RF ? Microwave? ???? ??
• ????? ? ?? ???? ?? (?? ?? ??)
• ???? ???? ??? ??? ?? ??
• ??? ?? ?? ??? ??
• ??? ??? ???? ???? ??? ??
• ?? ??? ?? ???? ?? ?? ??
• ??? ????? ?? ???? ??? ???? ??? ??

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4. Microwave Applications
RF ????
? 3. RF ????
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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4. Microwave Applications
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• 5. Measurement Systems for Microwave Engineering

Network Analyzer ??? ?? ?? ???Source?
Spectrum Analyzer? ?????, ??? ??? ??? ??????? ??
????? S ????? ???? ??
??7. 8510C Network Analyzer Systems, 45 MHz to
110 GHz
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5. Measurement Systems for Microwave Engineering
Scalar Network Analyzer magnitude Vector
Network Analyzer magnitude, phase
time domain frequency domain Linear
Device? ?? ??(Frequency Doubler, Mixer?? ?? ???)
Delay Reflection ?? (1 port device) SWR S-paramet
er(S11, S22) Reflection Coefficient Impedance
Return Loss
Transmission ?? (2 port device) Gain or
Insertion Loss S-parameter(S11, S22) Transmission
Coefficient Insertion Phase Group Delay
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5. Measurement Systems for Microwave Engineering
Spectrum Analyzer 1-port ?? ??? ???
????? ?? ??? ??? ?????? ??????, Phase Noise? ??.
??8. 8563EC Portable Spectrum Analyzer, 9 kHz to
25.6 GHz
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5. Measurement Systems for Microwave Engineering

• Noise Figure Meter (or Analyzer)
• ??? ??? ????? Noise Source? ????? ????
  Noise Figure meter ? ??, ??? ??? ???? ????? ??,
  Tuner? ???? Noise Figure Parameter? ?? ??, ???
  ???? ???? ??? ???? ???? ??????? ??

??9. N8975A Series Noise Figure Analyzer
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5. Measurement Systems for Microwave Engineering
Power Meter Power ??
??10. E4418B Single-Channel Power Meter
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5. Measurement Systems for Microwave Engineering

• Probe Station
• Wafer ? Chip sample? ?? ???? ??, ??? ?? ?
  ?? ??? ?? ???? ?? ??? ??. ?? I-V, C-V, ?? ???? ?
  Wafer? ???? ???

??11. Cascade Microtech Probe System
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6. Curriculum for Microwave Engineering
????(Electromagnetics) Vector ?scalar,
???, ???? ????, ???? ????, ???? ??? ??? ?????
Maxwell ???? ?? ???? ???? ??? ?? ????(Circuit
Theory) ???????, RLC ??, Laplace ??,
Fourier?? ?? ???? ???? ?? ?? ????(Solid State
Electronic Device) ??? ??? ??? ??? ??,
????? ?????? ?? ????(Electronic Circuit)
????, ???? ?????, FET? ?? ????? ????? ????, ???
??? ??? ??? ????? ??? ?? ??? ?? ??????(Microwave
Engineering) ?????, ???? ?????, ???? ?
?? ???? ?? ? ?????? ?? ?????? ? ??(Wireless
Communication Circuits and Experiments)
???????? ???? ?? ?? ??? ?? ? ?? ??? ?? ????(Wave
Propagation Engineering) ?? ???? ??? ?? ???
???? ???? ??
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7. Basic Concepts in Microwave Circuit Design

• ? Memoryless system
• ? A system is called memoryless if its
  output does not depend on the past values of its
  input.
• ? For memoryless linear system,
• y(t)?x(t)
• where ? is a function of time if the system
  is time variant
• ? For a memoryless nonlinear system, the
  input-output relationship can be approximated
  with a polynomial,
• where ?j are in general functions of
  time if the system is time invariant
• ? For memoryless and time-variant systems,
  
  

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7. Basic Concepts in Microwave Circuit Design

• Harmonics
• ? If a sinusoid is applied to a nonlinear
  system, the output generally exhibits
• frequency components that are integer
  multiples of the input frequency.
• ? if x(t)Acos?t, then
• 
  
  
• where the input frequency (?) fundamental
• the higher-order terms(n?,
  ninteger) harmonics.
• ? Even-order harmonics result from ?j with
  even j and vanish if the system has
• odd symmetry, i.e., if it is fully
  differential.
• ? The amplitude of the nth harmonic consists
  of a term proportional to An and
• other terms proportional to higher powers
  of A.

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7. Basic Concepts in Microwave Circuit Design

• ? Gain Compression
• ? The small signal gain (?1)of circuit is
  usually obtained with the assumption that
  harmonics are negligible.
• ? In most circuits of interest, the output
  is a compressive or saturating function of
  input. At high input level, gain is a decreasing
  function of A.

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7. Basic Concepts in Microwave Circuit Design

• ? 1-dB compression point(P1dB) The input
  signal level that causes the small signal gain to
  drop by 1dB.
• Fig. 7 Definition of 1dB compression point
• ? To calculate the 1-dB compression point,
  

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7. Basic Concepts in Microwave Circuit Design

• ? Desensitization and blocking
• ? When the desired signal is fed to circuit
  with a strong interferer, the average gain of
  the circuit is reduced because of a large
  interferer desensitization

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7. Basic Concepts in Microwave Circuit Design

• ? For A1 ltlt A2,
• ? For ?3lt0 and sufficiently large A2, the
  overall gain drops zero, and we
• say the signal is blocked in RF design.
• ? Many RF receivers must be able to withstand
  blocking signals 60 to 70dB
• greater than the wanted signal.? Filter,
  Matching circuits, etc.

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7. Basic Concepts in Microwave Circuit Design

• ? Cross Modulation
• ? When a weak signal and a strong interferer
  pass through a nonlinear system, the transfer of
  modulation on the amplitude of the the interferer
  to the amplitude of the weak signal is occurred.
• ? The desired signal at the output contains
  amplitude modulation at ?m and 2?m.

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7. Basic Concepts in Microwave Circuit Design

• ? Intermodulaton
• ? When two signals with different frequencies
  are applied to a nonlinear system, the output in
  general exhibits some components that are not
  harmonics of the input frequencies. ?
  Intermodulation distortion(IMD)
• ? Fundamental components
• ? Intermodulation products

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7. Basic Concepts in Microwave Circuit Design

• ? The interest IM products are the third-order IM
  products at 2?2-?1 and 2?1-?2.
• ? If the difference between ?1 and ?2 is small,
  the components at 2?1-?2 and
• 2?2-?1 appear in the vicinity of ?1 and ?2 .
• Fig. 8 Intermodulation in a nonlinear system
• ? If a weak signal accompanied by two strong
  interferers experiences third-
• order nonlinearity, then one of the IM
  products falls in the band of interest,
• corrupting the desired component.
• Fig. 9 Corruption of a signal due to
  intermodulation between two interferers

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7. Basic Concepts in Microwave Circuit Design

• ? IP3
• ? This parameter is measured by a two-tone
  test in which A is chosen to be sufficiently
  small so that higher-order nonlinear terms are
  negligible and the gain is relatively constant
  and equal to ?1.
• ? As A increases, the fundamentals increase
  in proportion to A, whereas the third-order IM
  products increase in proportion to A3.
• Fig. 10 Growth of output components in an
  intermodulation test
• ? Horizontal coordinate Input IP3(IIP3)
• ? Vertical coordinate Output IP3(OIP3)
• ? IP3 is used as a measure of linearity and
  a unique quantity that by itself can serves as a
  means of comparing the linearity of different
  circuits.

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7. Basic Concepts in Microwave Circuit Design

• Fig. 11 (a)Calculation of IP3 without
  extrapolation, (b)graphical interpretation of
  (a)
• ? The actual value of IP3, however, must
  still be obtained through accurate extrapolation
  to ensure that all nonlinear and
  frequency-dependent effects are taken into
  account.

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7. Basic Concepts in Microwave Circuit Design

• ? Calculation of an overall input third intercept
  point in terms of the IP3 and gain of the
  individual stage.
• ? Two nonlinear stages in cascade
• Fig. 12 Cascaded nonlinear stages
• ? The overall OIP3

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7. Basic Concepts in Microwave Circuit Design

• ? The alternate overall OIP3
• where AIP3,1 and AIP3,2 represent the
  input IP3 points of the 1st and 2nd stages.
• ? From the result, ?1 increases, the overall
  IP3 decreases. This is because with higher gain
  in the first stage, the second stage senses
  larger input levels producing greater IM3
  products.

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7. Basic Concepts in Microwave Circuit Design

• ? Noise
• ? Thermal noise (or Johnson noise, Nyquist
  noise)
• - The agitated charge carrier random motion
  noise being caused by thermal
• vibration of bound charge
• - White noise up to 1013 Hz
• - Noise power PkTB
• where k
  Boltzman constant (1.38?10-23 J/ºK)
• T
  Absolute temperature
• B
  System bandwidth
• Ex.The available power in a 1Hz
  bandwidth from a thermal noise source
• PkT4?10-23 W/Hz-174dBm/Hz
  _at_room temperature
• ? Shot noise (or Schottky noise)
• - The transfer noise of charge across an
  energy barrier (ex. A PN junction,
• IDS in MOSFET)
• -
• where q1.6 ?10-19C (electron
  charge), Idcdc current through the device

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7. Basic Concepts in Microwave Circuit Design

• ? Flicker noise
• - Random trapping noise of charge at the
  oxide-silicon interface of MOSFETs
• - Dominant at low frequencies in the
  semiconductor devices
• - Must be considered in the design ultra
  wideband amplifiers (dc10GHz) and
• microwave oscillator
• ? Plasma noise
• - Random motion noise of charges in an
  ionized gas as a plasma, the
• ionosphere, or sparking electrical
  contacts
• ? Quantum noise
• - The quantized nature of charge carriers
  and photons
• - Often insignificant relative to other
  noise sources

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7. Basic Concepts in Microwave Circuit Design

• ? Input-Referred Noise
• ? The noise of a two-port system can be
  modeled by two input noise generators a series
  voltage source and a parallel current source. In
  general, the correlation between the two sources
  must be taken into account.
• Fig. 13 Representation of noise by input noise
  generators
• Fig. 14 (a)MOS amplifier, (b) equivalent input
  noise generators

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7. Basic Concepts in Microwave Circuit Design

• ? Noise Figure
• ? Signal-to-noise ratio(SNR) The ratio of
  the signal power to the total noise
• 
  power.
• ?
• where SNRin The SNR measured at the input
• SNRout The SNR measured at the
  output
• ? Friis equation
• ? The noise contributed by each stage
  decreases as the gain preceding the
• stage increases, implying that the
  the first few stages in a cascade are the
• most critical.

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7. Basic Concepts in Microwave Circuit Design

• ? Noise Sensitivity of RF receiver
• ? The minimum signal level that the system can
  detect with acceptable signal-to-noise ratio.
• where Psig The input signal level
  per unit bandwidth
• PRs The source resistance noise
  power per unit bandwidth
• ? The overall signal power is distributed
  across the channel bandwidth, B
• ? The minimum signal level that the system
  can detect with acceptable SNR
• where Pin,min The minimum input level that
  achieves SNRout,min
• B Bandwidth Hz

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7. Basic Concepts in Microwave Circuit Design

• ? In dB scale,
• ? Dynamic Range
• ? The ratio of the maximum input level that
  the circuit can tolerate to the minimum input
  level at which the circuit provides a reasonable
  signal quality.
• ? DR bases the definition of the upper end of
  the dynamic range on the
• intermodulation behavior and the lower end
  on the sensitivity.
• ? Spurious-free dynamic range(SFDR)
• ?

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8. RF Transceiver Architectures

• ? Primary criteria in selecting transceiver
  architectures
• ? Complexity
  ? Cost
• ? Power dissipation
  ? Number of external components
• ?But IC technologies makes once seemed
  impractical design to return as
• plausible solutions.
• ? RF Transceiver Architecture
• ? Heterodyne ?
  Homodyne
• ? Image-reject
  ? Digital-IF
• ? Subsampling receivers ?
  Direct-conversion and two-step transmitters
• ? Transmitter Narrowband modulation,
• amplification, and filtering to avoid
• leakage to adjacent channels
• ? Receiver Able to process the desired
• channel while sufficiently rejecting
• strong neighboring interferers.
• Fig. 15 a)Transmitter and b)receiver front
  ends
• of a wireless transceiver

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8. RF Transceiver Architectures

• ? Terminology
• ? Band The entire spectrum in which the users
  of a particular standard are allowed to
  communicate (e.g., the GSM receive band spans 935
  MHz to 960 MHz)
• ? Channel The signal bandwidth of only one
  user in the system (e.g. 200KHz in GSM)
• ? Band selection The operations that reject
  out-of-band interferers
• ? Channel selection The operations that
  reject out-of-channel(usually in-band)
  interferers.
• ? Isolation between TX and RX
• ? Finite attenuation of the transmitted
  signal in the receive band
• ? Desensitization of LNA by PA output
  leakage
• ? NADC and GSM systems avoid by offsetting the
• transmit and receive time slots, but analog
  FDD
• standards (e.g., AMPS, CDMA) require high
• isolation.
• Fig. 16 Desensitization of LNA by
  PA output leakage

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8. RF Transceiver Architectures

• ? Heterodyne receiver (or Downconversion mixing,
  Downconversion)
• ? Primary the signal band is translated to
  much lower frequencies
• ? Relax the Q required of the
  channel-select filter.
• ? The translation is carried out by means of
  a mixer.
• ? RF signal Bocos?1t
• ? LO signal Aocos?ot ? ?o?1- ?2
• ? Some of output signals(IF)
• ?1??o?1?(?1-?2)?2 or 2?1-?2
• ? Output of LPF ?2
  
  (a)
• Fig. 17 (a)Simple heterodyne downconversion
• (b)inclusion of an LNA to lower
  the
• noise figure
• 
  (b)

RF
IF
LO
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8. RF Transceiver Architectures

• ? Problem of Image
• - For x1(t)A1cos?1t and x2(t)A2cos?2t,
  the low pass filtered product of x1(t) and x2(t)
  is of the form cos(?1-?2)t, no different form
  cos(?2-?1)t
• - In a heterodyne architecture, the bands
  symmetrically located above and below the LO
  frequency are downconverted to the same center
  frequency.
• ? Image frequency
• - If RF signal is centered around ?1 ( ?LO-
  ?IF), the image is around 2?LO- ?1( ?LO ?IF)
  and vice versa.
• ?Image rejection filter in front of mixer is
• designed to have a relatively small loss in
• the desired band and a large attenuation
• in the image band
• Fig. 18 Problem of image in heterodyne
  reception Fig. 19 Image rejection by
  means of a
• 
  
  filter

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8. RF Transceiver Architectures

• ? Two cases corresponding to high and low
  values of ?IF
• 1) High IF ?Leads to substantial rejection of the
  image
• 2) Low IF ? High Q ? Allows great suppression of
  nearby interferers.
• 
  
  ? The trade-offs parameters in choice
  of ?IF
• 
  - Amount of image noise
• 
  - The spacing between the desired
  band
• 
  and the image
• 
  - The loss of the image-reject
  filter
• 
  ? Trade-off between image rejection
  and
• 
  channel selection.
• 
  Fig. 20 Rejection of image
  versus suppression of
• 
  interferers for
  (a)high IF and (b)low IF
• ? An important drawback of the heterodyne
  architecture
• - The image reject filter is realized as a
  passive, external component because
• of high Q.
• - This requires input/output matching of
  LNA to 50?, where LNA is
• inevitable more severe trade offs
  between the gain, noise figure, stability,
• and power dissipation in the amplifier.

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8. RF Transceiver Architectures

• ? Dual IF topology
• ? Multiple downconversion technique
  performs partial channel selection at
  progressively lower center frequencies, thereby
  relaxing the Q required of each filter.
• ? Most of todays RF receivers 2-stages
  of downconversion(Dual-IF)
• 
  Fig.
  21 Dual-IF heterodyne receiver

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8. RF Transceiver Architectures

• ? Homodyne Receivers (or Directconversion, Zero
  IF)
• ? The LO frequency is equal to the input
  carrier frequency. Channel selection requires
  only a low pass filter with relatively sharp
  cutoff characteristics.
• ? Fig. 12(a) operates properly only with
  double-sideband AM signals because it overlaps
  positive and negative parts of the input
  spectrum.
• ? For frequency and phase modulated
  signals, the downconversion must provide
  quadrature output so as to avoid loss of
  information. This is because the two sides of FM
  or QPSK spectra carry different information and
  must be separated into quadrature phases in
  translation to zero frequency.
• 
  Fig.
  22 (a) Simple homodyne receiver,
• 
  
  (b) homodyne receiver with
• 
  
  quadrature downconversion

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8. RF Transceiver Architectures

• ? Two advantages over a heterodyne
  counterpart.
• 1)The image problem is circumvented because
  ?IF0. As a result, no image filter is required,
  And the LNA need not drive a 50-Ohm load.
• 2)The IF SAW filter and subsequent downconversion
  stages are replaced with low pass filters and
  base band amplifiers are amenable to monolithic
  integration.
• ? Direct conversion has number of
  issues do not exist or are not as serious in a
• heterodyne receiver.
• ? Channel selection Rejection of
  out-of-channel interferers by an active low-
• pass filter is more difficult than by a
  passive filter, fundamentally active
• filters exhibit much more severe
  noise-linearity-power trade-offs than do
• their passive counterparts.

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8. RF Transceiver Architectures

• ? DC offsets
• - Since in a homodyne topology the
  downconverted band extends to zero
• frequency, extraneous offset voltages can
  corrupt the signal and saturate the
• following stages.
• - LO leakage From capacitive and substrate
  coupling and, if the LO signal is
• provided externally, bond wire coupling,
  the isolation between the LO port
• and the inputs of the mixer and the LNA
  is not infinite.
• - Self-mixing The leakage signal
• appearing at the inputs of the LNA
• and the mixer from LO signal is
• mixed with LO signal, thus producing
• a DC component at C.
• - A large interferer leaks from the LNA
• or mixer input to the LO port and is
• multiplied by itself.
• 
  Fig. 23 Self mixing of (a) LO signal , (b) a
  strong interferer

65
8. RF Transceiver Architectures

• ? I/Q Mismatch
• - For phase and frequency modulation
  schemes, a homodyne receiver must
• incorporate quadrature mixing.
• - Either the RF signal or the LO output by
  90o phase shifting
• ?The shifting the RF signal generally entails
  severe noise-power-gain trade-offs, making it
  more desirable to use the topology of quadrature
  generation in LO path.
• Fig. 24 Quadrature generation in
• (a) RF path,
• (b) LO path
• Fig. 25 Effect of I/Q mismatch on a demodulated
  QPSK waveform (a)gain error (b)phase error

66
8. RF Transceiver Architectures

• ? Even-Order distortion
• - Two strong interferers close to the
  channel of interest experience nonlinearity
• such as in the LNA.
• - Mixers exhibit a finite direct feedthrough
  from the RF input to the IF output.
• Thus, a fraction of vRF(t) appears at the
  output with no frequency translation. (Ex. 30
  40 dB in typical differential mixers)
• - Even order distortion demodulates AM
  components.
• Fig. 26 Effect of even-order distortion on
  interferers
• - Differential LNAs and mixers can suppress
  even-order distortion.
• ?1) Balun (single ended ant. to
  differential LNA) (difficult!!)
• 2) NF increasing due to insertion
  loss of balun

67
8. RF Transceiver Architectures

• ? Flicker noise
• - Flicker noise arises from random trapping
  of charge at the oxide-silicon
• interface of MOSFETs. Represented as a
  voltage source in series with the
• gate, the noise density is
• where K A process-dependent
  constant and negligible at high
• frequencies.
• - In particular, since the downconverted
  spectrum extends to zero frequency,
• the 1/f noise of devices substantially
  corrupts the signal, a severe problem in
• MOS implementations.
• ? LO leakage
• - Leakage of the LO signal to the antenna and
  radiation creates interference in the band of
  other receivers using the same wireless standard.
• - The design of the wireless standard and the
  regulations of the Federal Communications
  Commission(FCC) impose upper bounds on the amount
  of in-band LO radiation, typically between 50dB
  and 80dBm.

68
8. RF Transceiver Architectures

• ? Hartley Architecture
• ? The RF input is mixed with the quadrature
  phases of the local oscillator (cos?LOt and
  sin?LOt), low-pass filters the resulting signals
  and shifts one by 90o before adding them
  together.
• 
  
  Fig. 27 Hartley image-reject receiver
• ? Key point The signal components at B and
  C have same polarity, whereas the image
  components have opposite polarities.
• ? The input signals x(t)ARFcos?RFt
  Aimcos?imt
• where
  ARFcos?RFt The desired channel signal
• 
  Aimcos?imt The image channel signal

69
8. RF Transceiver Architectures

• ? Signals of at point A and B
• ? Signals of at point C and output port
• ? The RF signal is down-converted with no
  corruption by the image.

70
8. RF Transceiver Architectures

• ? Weaver Architecture
• ? The weaver architecture replaces the 90?
  stage of the Hartley architecture by a second
  quadrature mixing operation.
• ? Assume ?2ltlt ?1
• Fig. 28 Weaver image-reject receiver
• 
  Fig. 29 Graphical
  analysis of Weaver architecture

71
8. RF Transceiver Architectures

• ? Digital-IF Receivers
• ? The 1st IF signal is digitized, and
  mixed with the quadrature phases of a digital
  sinusoid, and low-pass filtered to yield the
  quadrature baseband signals.
• ?Digital processing avoids the problem of I
  and Q mismatch.
• Fig. 30 Digital-IF receiver