4/28/2009 1 Mixed Signal Techniques for RF Transceivers Renaldi Winoto EE242 Guest Lecture, Spring 2009 April 29 th , 2009 Outline • RF Receivers: A Mixed‐Signal Perspective • Discrete‐Time RF Receivers • Sigma‐Delta A/D Converters – Intro to Sigma‐Delta Modulation – Sigma‐Delta Converters in RF Receivers Mi d Si lT hi i RF T itt • Mixed‐SignalT echniques in RF T ransmitter
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4/28/2009
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Mixed Signal Techniques for RF Transceivers
Renaldi WinotoEE242 Guest Lecture, Spring 2009
April 29th, 2009
Outline
• RF Receivers: A Mixed‐Signal Perspective
• Discrete‐Time RF Receivers
• Sigma‐Delta A/D Converters– Intro to Sigma‐Delta Modulation
– Sigma‐Delta Converters in RF Receivers
Mi d Si l T h i i RF T itt• Mixed‐Signal Techniques in RF Transmitter
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Wireless Communication System
Dyn
VDD
Retrieve original information
3
namic R
ange
Circuit Noise
Retrieve original information
Challenge:• Maintaining SNR• Large blocker signals
fcarrier freq (Hz)
(dBm)
A Direct‐Conversion Receiver
• Mix – Amplify – Filter→ A/D Conversion
• Virtually all RF receiver today has an A/D− Complex modulation schemes to achieve spectral efficiency− Needs digital circuit to perform complex demodulation
algorithm
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RF Receiver : A Mixed‐Signal Perspective
• A receiver pre‐conditions an RF signal for A/D conversion
Deriving Requirements
Blocker MaskBlocker Mask
A/D SpecificationsA/D Specifications
• System specifications for receiver is derived from the blocking mask and the choice of A/D converters
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UMTS Blocker Mask
GSM Blocker MaskNarrow‐band signals
3MHz
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A/D Converters SpecificationsSufficient Condition
• Nyquist Criterion– F = 2xRFFs = 2xRFBW– Doesn’t have to be at DC !
(Beware of noise folding)
• Dynamic‐range budgeting– SNRmin for successful decodingdecoding
– Peak‐to‐average power ratio– Margin for other ‘stuff’
(intermods, leftover blocker signals, etc)
A/D Converters SpecificationsThe Full Picture
• Desired signal is not in isolation
• Blocker signals will fold down due to a sampling operation (aliasing)
• Adjacent channels are especially hard to filter out
• A 1-bit quantizer and DAC is used to ensure excellent linearity
[3] F. Chen, B. Leung, “A 0.25-mW Low-Pass Passive Sigma-Delta Modulator with Built-in Mixer for a 10-MHz IF Input,” IEEE Journal of Solid State Circuits, vol. 32, No. 6, pp 774-782, June 1997
• Boundary between ‘RF’ and ‘Mixed‐signal’ is diminishing in RF Transceiver design (0 5GHz)diminishing in RF Transceiver design (0‐5GHz)
• Lots of system optimization ‘tricks’ that uses a combination of RF and mixed‐signal techniques– Transceiver design is no longer: RF designer + baseband designer + A/D designerdesigner + A/D designer