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RF MICROELECTRONICSBEHZAD RAZAVI

2010.08.13지능형 마이크로웨이브 시스템 연구실

박 종 훈

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ContentsCh.5 Transceiver Architecture

5.1 General Considerations5.2 Receiver Architectures5.3 Transmitter Architectures

5.3.1 Direct-Conversion Transmitters 5.3.2 Two-Step Transmitters

5.4 Transceiver Performance Tests5.5 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 ArchitecturesTransmitter Performances

Modulation, Upconversion, Power amplificationModulation + Upconversion

Transmitter VS ReceiverTransmitter : Only a few formsReceiver : Variety of approaches inventedRelaxed in transmitters than in receivers

Noise, interference rejection, band selectivity

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5.3 Transmitter Architectures1. Baseband / RF interface

1) FM System

Baseband signal is conditioned By filter and/or a variable-gain stage, compensating for manufac-

turing 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 Architectures2) 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 Architectures2. 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 Transmitters1. Direct conversion

Transmitted carrier frequency = Local oscillator frequencyModulation and upconversion occur in the same circuitMatching Network

Provide maximum power transfer to the antenna and filter out-of-band components

Noise of the mixers is much less critical Signal is sufficiently strong

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5.3.1 Direct-Conversion TransmittersDrawback

Disturbance of the transmit local oscillator by the power amplifier PA output is a modulated waveform with high power and a spec-

trum 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 oscilla-

tor

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5.3.2 Two-Step Transmitters

Circumventing the problem of LO pullingBaseband modulate W1 ( Intermediate Frequency)

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5.3.2 Two-Step TransmittersAdvantage

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 tests1. Sensitivity and Dynamic Range

In most systems, a minimum detectable signal level is speci-fied

•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 inter-modulation 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 tests2. Unwanted Emission

Modulation Mask Below which the transmitter output spectrum must lie Standard to ensure negligible radiation in adjacent channels

ACP IS-54 standards : -26dBc IS-95 standards : -42dBc

Mask

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5.5 Case Studies5.5.1 Motorola’s FM Receiver5.5.2 Philips’ Pager Receiver5.5.3 Philips’ DECT Transceiver5.5.4 Lucent Technologies’ GSM Transceiver5.5.5 Philips’ GSM Transceiver

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5.5.1 Motorola’s FM Receiver

Walkie-talkies or first-generation cordless phone (50MHz)No LNA and Image rejection filterRequired some external components

Re-move some image

50Mhz±10.7MHz

Reject in-terferers Reasonable

noise figure and linearity

Channel Selection

Amplified nonlinearly

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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

Matching,Single-

ended to differential

Spilit RF signal

( LO sim-plicity)

Channel Selection

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5.5.2 Philips’ Pager ReceiverBypolar 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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5.5.3 Philips’ DECT Transceiver

2nd IF is much higher than MC3362 because the DECT channel band-width of 1.7MHz requires a sufficiently high center frequency

1.89GHz

TDD

Matching,Converted to Differen-

tial

Mismatch-limited

SAW filter

110MHz

9.8MHz

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5.5.3 Philips’ DECT TransceiverBlind 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

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5.5.3 Philips’ DECT Transceiver Error Problem

Separation from the feedback loop, the VCO control line experi-ences 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

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5.5.4 Lucent Technologies’ GSM Transceiver

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

900Mhz

Channel Se-lection

To avoid VCO pulling

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5.5.5 Philips’ GSM Transceiver

Philips’ semiconductor offers a pair of RF and IF chips for GSM transceivers

900Mhz

Allow the use of two low-cost,

lossy image-re-ject filter

1.3GHz

Signal : 700MhzImage : 1.7GHz

Integrated fifth-order low-pass

filters-> IF SAW filters has relaxed

1.3GHz Oscillator,Suppressing the un-

wanted sideband-> LC Filter has relaxed

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5.5.3 Philips’ DECT TransceiverOnly two oscillators

Simplifying the prediction of various spurs Because the system is time division(and frequency division) du-

plexed, making it possible to share the oscillators between the two paths