Power-Detection System Covers UWB Spectrum

Many wireless coMMunications systems must be able to measure received signal strength. To provide sufficient bandwidth to cover the Ultra Wideband (UWB) spectrum, a pair of researchers has expanded on the capabilities of a previously introduced system comprising an integrated CMOS broadband detector that uses the nonlinear behavior of a CMOS transistor in deep triode mode. The detector is now incorporated into a feedback loop for gain and filter control of an impulse-UWB receiver by Kenneth A. Townsend and James W. Haslett from the University of Calgary and TRLabs (Calgary, Canada).

The wideband RF power-detection system uses NMOS devices operating in the triode regime to generate an average current that is proportional to RF input power. Using a piecewise linear logarithmic approximation, the current is converted to voltage and then amplified. The power detector occupies an active area of 0.36 mm2 in a 0.18-m process. It consumes 10.8 mW from the power supply. When measured at discrete frequencies, error between the output and a linear-in-decibel best-fit curve is 2.4 dB for a 20-dB input range. It achieves 2.9 dB accuracy when dynamic range is defined to include all of the frequencies within the UWB spectrum.

The measured power metric is applied to an algorithm that tunes a notch filter to remove narrowband interferers from the UWB spectrum. For the algorithm to operate correctly, the power detector must produce a frequency-independent output within the band of interest. The output response varies by less than 1.8 dB for fixed input power as frequency is swept across the UWB spectrum. See "A Wideband Power Detection System Optimized for the UWB Spectrum," IEEE Journal Of Solid- State Circuits, February 2009, p. 371.

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