A 30-MHz-2.4-GHz complementary metal oxide semiconductor (CMOS) receiver with an integrated tunable RF filter and a dynamic-range-scalable energy detector for both white-space and interference-level sensing in cognitive radio systems is reported. The second-order RF filter has only two stacked transistors, and its use, in combination with a subsequent harmonic rejection mixer, results in wideband interference rejection. The energy detector with programmable rectifiers provides dynamic-range (DR) scalability, enabling shared use for white-space/interference-level detection and automatic gain control. A prototype chip, fabricated using 90-nm CMOS technology, achieved over 42-dB harmonic rejection including 7th-order component without any external device, a 67-dB gain, a 5-8-dB noise figure, a $-$11-dBm in-band third-order intercept point, and a $+$38-dBm second-order intercept point while drawing only 25-37 mA from a 1.2-V power supply. Multi-resolution DR-scalable spectrum sensing with a 0.2-30-MHz detection bandwidth, $-$83-dBm minimum sensitivity, and a 29-48-dB DR was demonstrated.
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