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Adaptive noise cancellation for IS95 transmitters. Tom ás O’Sullivan and Peter Asbeck University of California, San Diego. Motivation. Antenna. Modern modulation schemes can result in significant noise in the receive band Degrades performance of FDD systems
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Adaptive noise cancellation for IS95 transmitters Tomás O’Sullivan and Peter Asbeck University of California, San Diego
Motivation Antenna • Modern modulation schemes can result in significant noise in the receive band • Degrades performance of FDD systems • Goal of this project is an electrically quiet receive band Noise Canceller Receiver LNA PA Duplexer
Presentation Outline • Feedforward architecture for noise cancellation • Design topology for low insertion loss and low power dissipation • System simulation, implementation and measurements • Techniques for adaptive operation • Conclusions
Feedforward for noise cancellation • Part of signal coupled off • Correct phase and amplitude adjustments are made • Signals merge to cause cancellation • Can achieve deep cancellation over a wide bandwidth Delay Gain and Phase adjust LNA
Improved Topology • System enhances performance of duplexer • Allows for low insertion loss and low power dissipation • Extra component, the TX band filter, is required ANT RX TX TXbandfilter LNA Gain and Phase adjust
Design Issues • Accurate gain and phase match required for good cancellation • 50dB cancellation requires 0.027dB gain match and 0.180 phase match 50dB
Delay mismatch issues • TX band filter introduces delay mismatch between the paths • 30dB cancellation over 25 MHz requires 400ps delay match 600ps 1ns 400ps
System Simulation • Entire system simulated in ADS • Expected narrowband operation was observed with an adjustable null • Optimization tool was used to achieve cancellation at different frequencies by adjusting phase and gain
Simulation Results • Performanceof duplexer is enhanced by feedforward action
Implemented System • Low noise, low power and linear class A amplifiers were used in the design, in conjunction with a voltage variable phase shifter and attenuator Epcos B4224 3rd order Notch filter Gain and Phase adjust Agilent AT-41511
Measurement Results • Measurement agrees well with simulation
Noise Canceller Characteristics • Added Attenuation = 20dB • Attenuation bandwidth = 2MHz • Insertion Loss = 0.27 dB • Power Dissipation = 9.75mW
Adaptation methodology • System provides cancellation for single channel only • System is calibrated and lookup table is populated with required gain and phase for each channel • Table can then be indexed to get optimum performance for particular channel • Periodic updating of table can combat drift and ageing of system
Algorithm Comparison Setup • Equipment centrally controlled by PC • Phase and gain varied by DC power supplies • Algorithms implemented in C++ and tested directly on system
Calibration Algorithms • Several optimization algorithms investigated to find best • Univariant search and pattern search techniques compared Variable 2 Variable 1
Performance of Algorithms • Univariant search outperforms pattern method in speed of convergence, otherwise they are similar
Conclusions • Feedforward techniques have been shown to be viable for noise cancellation in transmitters relaxing requirements on duplexer • Hardware for adaptive noise cancellation has been implemented • Optimization algorithms have been investigated to find best calibration routine