An integrated LMS adaptive filter of TX leakage for CDMA receiver front ends

The theory and practical implementation of a continuous-time LMS adaptive filter of the TX leakage in CDMA receivers are described. The filter works by injecting a matched out-of-phase copy of the TX leakage into the LNA output. It requires a reference signal coupled from the TX chain, whose I and Q...

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Bibliographic Details
Published in:IEEE journal of solid-state circuits 2006-05, Vol.41 (5), p.1171-1182
Main Authors: Aparin, V., Ballantyne, G.J., Persico, C.J., Cicalini, A.
Format: Article
Language:English
Subjects:
Adaptive filters
Amplifiers
analog multipliers
Applied sciences
Circuit properties
circuit stability
continuous time filters
Correlation
Correlators
cross modulation distortion
Degradation
Delay
delay effects
Design. Technologies. Operation analysis. Testing
Electric, optical and optoelectronic circuits
Electronic circuits
Electronics
Exact sciences and technology
filter noise
Frequency filters
Group delay
Hardware
Input-output equipment
Integrated circuits
intermodulation distortion
Leakage
least mean square methods
Least squares approximation
Matched filters
Multiaccess communication
Noise levels
notch filters
Receivers
Reference signals
Reproduction
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Signal generators
Stability
Studies
Surface acoustic waves
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Description
Summary:The theory and practical implementation of a continuous-time LMS adaptive filter of the TX leakage in CDMA receivers are described. The filter works by injecting a matched out-of-phase copy of the TX leakage into the LNA output. It requires a reference signal coupled from the TX chain, whose I and Q components are appropriately scaled to generate the matched copy. The scale factors are the results of the correlation between the filter output signal and the I/Q components of the reference signal. The filter was designed as part of a 0.25-/spl mu/m CMOS cellular-band receiver. The effect of the DC offsets in the correlators on the TX leakage rejection ratio (TXRR) was minimized by using the sign-data variant of the LMS algorithm and by increasing the gain of the correlating multipliers. The loop stability margin was improved by swapping the I and Q reference inputs of the scaling multipliers. Without a significant group delay of the TX leakage relative to the reference signal, the filter achieved the maximum TXRR of 28 dB, which was limited by the reference signal coupling. The group delay introduced by the SAW duplexer reduced the minimum TXRR to 10.8 dB. The filter degraded the LNA noise factor and gain by 1.3 dB and 1.7 dB, respectively.
ISSN:0018-9200
1558-173X
DOI:10.1109/JSSC.2006.872738