2010.08.13
지능형 마이크로웨이브 시스템 연구실
박 종 훈
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Contents
 Ch.5 Transceiver Architecture
 5.1 General Considerations
 5.2 Receiver Architectures
 5.3 Transmitter Architectures


5.3.1 Direct-Conversion Transmitters
5.3.2 Two-Step Transmitters
 5.4 Transceiver Performance Tests
 5.5 Case Studies
 5.5.1 Motorola’s FM Receiver
 5.5.2 Philips’ Pager Receiver
 5.5.3 Philips’ DECT Transceiver
 5.5.4 Lucent Technologies’ GSM Transceiver
 5.5.5 Philips’ GSM Transceiver
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5.3 Transmitter Architectures
 Transmitter Performances
 Modulation, Upconversion, Power amplification
 Modulation + Upconversion
 Transmitter VS Receiver
 Transmitter : Only a few forms
 Receiver : Variety of approaches invented
 Relaxed in transmitters than in receivers

Noise, interference rejection, band selectivity
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5.3 Transmitter Architectures
 1. Baseband / RF interface
 1) FM System


Baseband signal is conditioned
 By filter and/or a variable-gain stage, compensating for
manufacturing variations in the VCO characteristic
 Because Output spectrum
 Oscillator must be stabilized by feedback loop
 Frequency synthesizer
Baseband signal modulated by VCO
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5.3 Transmitter Architectures
 2) Digital phase modulation system

Data pulses must be shaped
 To minimize intersymbol interference and/or limit the signal
bandwidth
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5.3 Transmitter Architectures

Bandpass pulse shaping
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5.3 Transmitter Architectures

GMSK

h(t) : Impulse response of a Gaussian filter
-> Impacts the channel bandwidth
-> Prove more accurate filter
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5.3 Transmitter Architectures

Phase and gain mismatch

Ideal case

Mismatch case
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5.3 Transmitter Architectures
 2. PA/Antenna Interface
 Transmitter output must pass through a duplexer filter or a
TDD switch


Duplexer filters : 2 to 3dB
 -> Dissipating 30 to 50% of PA output power in the form of heat
 Example
 PA provides 1W of power -> 300mW is wasted in the filter
 PA efficiency rarely exceeds 50%
 600mW drained from the supply to filter
TDD switch : 0.5 and 1dB loss -> higher overall efficiency
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5.3.1 Direct-Conversion Transmitters
 1. Direct conversion
 Transmitted carrier frequency = Local oscillator frequency
 Modulation and upconversion occur in the same circuit
 Matching Network
 Provide maximum power transfer to the antenna and filter outof-band components
 Noise of the mixers is much less critical
 Signal is sufficiently strong
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5.3.1 Direct-Conversion Transmitters
 Drawback

Disturbance of the transmit local oscillator by the power amplifier
 PA output is a modulated waveform with high power and a
spectrum centered around the LO frequency
 Injection pulling or injection locking
 Worsens if the PA is turned on and off ( to save power)
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5.3.1 Direct-Conversion Transmitters

Solution

Offsetting the LO frequency
 Adding or subtracting the output frequency of another
oscillator
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5.3.2 Two-Step Transmitters
 Circumventing the problem of LO pulling
 Baseband modulate W1 ( Intermediate Frequency)
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5.3.2 Two-Step Transmitters
 Advantage

Quadrature modulation is performed at lower frequencies
 I and Q matching is superior
 Less cross-talk
 Limit the transmitted noise and spurs in adjacent channels
 Difficulty


Second upconversion must reject the unwanted sideband by a
large factor (50 to 60dB)
 Wanted and unwanted sidebands with equal magnitudes
Because of higher center frequency, filter is typically a passive,
relatively expensive off-chip device
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5.4 Transceiver Performance tests
 1. Sensitivity and Dynamic Range
 In most systems, a minimum detectable signal level is
specified

•In-band intermodulation test
•Output carrier-to(noise+intermodulation)
•[C/N+I)] must not far below 9dB
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5.4 Transceiver Performance tests
•Out-of-band and second-order
intermodulation test
•C/(N+I) of the IF signal must exceed 9dB
•Out-of-band cross modulation
•C/(N+I) of greater than 9dB
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5.4 Transceiver Performance tests
 2. Unwanted Emission
 Modulation Mask


Below which the transmitter output spectrum must lie
Standard to ensure negligible radiation in adjacent channels
Mask

ACP
 IS-54 standards : -26dBc
 IS-95 standards : -42dBc
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5.5 Case Studies
 5.5.1 Motorola’s FM Receiver
 5.5.2 Philips’ Pager Receiver
 5.5.3 Philips’ DECT Transceiver
 5.5.4 Lucent Technologies’ GSM Transceiver
 5.5.5 Philips’ GSM Transceiver
18/27
5.5.1 Motorola’s FM Receiver
50Mhz±10.7MHz
Reject
interferers
Reasonable noise
figure and linearity
Remove
some
image
Channel
Selection
Amplified
nonlinearly
 Walkie-talkies or first-generation cordless phone (50MHz)
 No LNA and Image rejection filter
 Required some external components
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Matching,
Single-ended
to differential
Spilit RF
signal ( LO
simplicity)
Channel
Selection
5.5.2 Philips’ Pager Receiver
 UAA2080T is a single-chip bipolar homodyne receiver (FSK)
 Required some external components
 Local Oscillator
 470MHz (frequency doubler : 235MHz X 2)
 Actually operates at the third harmonic of a 78.3MHz crstal
 Received single fixed freq. -> freq. need not be variable -> eliminating synthersizers
 compact, low-power
 But cannot easily generate precise quadrature phases -> Seperation in the RF path
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5.5.2 Philips’ Pager Receiver
 Bypolar Technology




Minimize the I/Q imbalance
Even-order distortion is suppressed (Differential circuits)
LO leakage is reduced by cascode configuration (LNA, mixers)
Limited dynamic range is less serious
 FSK : High frequency -> High SNR
 Bit error rate can be as high as 3%
 Because redundancies are incorporated in the data stream to
correct errors
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Mismatchlimited
5.5.3 Philips’ DECT Transceiver
Matching,
Converted to
Differential
110MHz
SAW
filter
TDD
9.8MHz
1.89GHz
 2nd IF is much higher than MC3362 because the DECT channel
bandwidth of 1.7MHz requires a sufficiently high center frequency
22/27
5.5.3 Philips’ DECT Transceiver
 Blind slot



Receive and transmit modes are separated by blind slot
Stabilize the frequency
Approximately 250μs to settle, a blind slot precedes the signal
transmission to avoid leakage of the spectrum into adjacent
channels
23/27
5.5.3 Philips’ DECT Transceiver

Error Problem
 Separation from the feedback loop, the VCO control line
experiences finite charge injection errors
 PA is turned on, its input impedance varies thereby changin the
load impedance and hence the oscillation frequency of the VCO
 PA active current, about 250mA, drops the battery voltage by a
few hundred millivolts, affecting the VCO output frequency
 The sum of these errors must not exceed 50kHz
24/27
5.5.4 Lucent Technologies’ GSM Transceiver
Channel
Selection
900Mhz
To avoid VCO pulling
 Lucent Microelectronics(formerly AT&T Microelectronics) offers a single-chip solution that,
along with a low-noise amplifier and a power amplifier
 Requires only two external filters
 But the IF SAW device tends to have higher loss(and higher cost) if it must filter adjacent
channels to sufficiently low levels
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Allow the use of
two low-cost, lossy
image-reject filter
5.5.5 Philips’ GSM Transceiver
Signal : 700Mhz
Image : 1.7GHz
900Mhz
1.3GHz
Integrated
fifth-order
low-pass
filters
-> IF SAW
filters has
relaxed
1.3GHz Oscillator,
Suppressing the unwanted
sideband
-> LC Filter has relaxed
 Philips’ semiconductor offers a pair of RF and IF chips for GSM transceivers
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5.5.3 Philips’ DECT Transceiver
 Only two oscillators


Simplifying the prediction of various spurs
Because the system is time division(and frequency division)
duplexed, making it possible to share the oscillators between the
two paths
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