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Open AccessArticle

Low-Power CMOS Complex Bandpass Filter with Passband Flatness Tunability

Department of Electronics Convergence Engineering, Kwangwoon University, Seoul 01897, Korea
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Author to whom correspondence should be addressed.
Electronics 2020, 9(3), 494; https://doi.org/10.3390/electronics9030494
Received: 25 February 2020 / Revised: 12 March 2020 / Accepted: 14 March 2020 / Published: 17 March 2020
(This article belongs to the Section Circuit and Signal Processing)
We present a low-power CMOS active-resistance-capacitance (active-RC) complex bandpass filter (BPF) with tunable gain, bandwidth, center frequency, quality factor, and passband flatness for Bluetooth applications. A transfer function analysis for a cross-coupled Tow-Thomas biquad structure is presented to prove that the flatness profile of the passband gain can be effectively controlled by independently tuning two cross-coupling resistors. The proposed biquad-based complex BPF was employed to realize a fourth-order baseband analog processor for a low intermediate frequency (low-IF) RF receiver. The baseband analog processor was composed of two complex biquad filters and three first-order variable-gain amplifiers. It was fabricated in a 65-nm RF CMOS and achieved wide tuning capabilities, such as a gain of −15.6 to 50.6 dB, a bandwidth of 1.4–3.9 MHz, a center frequency of 1.5–4.1 MHz, and a passband flatness of −1 to 1 dB. It also achieved an image rejection ratio of 40.3–53.3 dB across the entire gain tuning range. It consumed 1.4 mA from a 1 V supply and occupied an area of 0.19 mm2 on the silicon substrate. The implementation results prove that the proposed complex BPF was able to effectively enhance the signal processing performances through the flexible and wide-range tunability of the passband flatness, as well as that of the gain, bandwidth, center frequency, and quality factor. View Full-Text
Keywords: complex filter; bandpass filter; passband flatness; baseband analog processor; low-IF; RF receiver; bluetooth; CMOS complex filter; bandpass filter; passband flatness; baseband analog processor; low-IF; RF receiver; bluetooth; CMOS
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Kim, J.; Lee, Y.; Chang, S.; Shin, H. Low-Power CMOS Complex Bandpass Filter with Passband Flatness Tunability. Electronics 2020, 9, 494.

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