Circuits and architectures for the implementation of broadband channelizers




Ho, Wei-Gi

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Broadband spectrum channelizers sub-divide a broadband input spectrum into multiple sub-bands, where each of the sub-bands is down-converted and further processed at baseband. These designs can help to relax baseband design specifications. For example, baseband analog-to-digital converters (ADCs) that process the sub-bands at the channelizer output see only a part of the incident spectrum. The sampling frequency, and potentially the dynamic range of each sub-band ADC can thus be relaxed, compared to the case where a single ADC is used to digitize the full spectrum.

Spectrum channelizers can be used for multiple applications. These designs can be used as general-purpose hybrid frequency-and-time domain ADCs. The designs can also be employed for spectrum analysis, as well as for wireless communication applications.

In this dissertation, two circuit techniques for the implementation of broadband channelizers are proposed. A frequency-translational feedback-based interference canceler for attenuating large interferers at the output of the front-end low-noise amplifier (LNA) of a channelizer is shown. The design uses harmonic rejection mixers (HRMs) with embedded frequency synthesis capability. While channelizers reduce the bandwidth and potentially the dynamic range of the baseband ADCs, the analog signal paths in the channelizer can be broadband. Consequently the dynamic range required of the analog section of a sub-band path can still be limited by the presence of large signals in other, potentially distant parts of the spectrum. The demonstrated design is useful for relaxing the dynamic range requirement of the analog section that follows the front-end LNA in a channelizer. Reduction of the harmonic response and the frequency synthesizer tuning-range is also achieved in this design.

Second, a two-stage HRM is proposed which shares the same bias current between the RF and baseband stages, thus reducing the power consumption. Issues arising from bias-current sharing, such as the 1/f noise of the RF stage and potential degradation of the 2nd harmonic response are identified, and circuit techniques are introduced to mitigate these potential degradation mechanisms.


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