Abstract
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.
Highlights
Bluetooth low energy (BLE) is a wireless communication technology for Internet-of-things (IoT)applications that operates in the 2.4 GHz industrial scientific and medical (ISM) band
The low intermediate frequency receiver architecture is widely adopted for CMOS RF receivers in BLE applications because it can cope with flicker noise and dc offset issues more effectively than zero-IF architecture
In [7], we reported preliminary circuit design results of a complex bandpass filter (BPF) for BLE [1] and MedRadio
Summary
Bluetooth low energy (BLE) is a wireless communication technology for Internet-of-things (IoT). Balankutty et al [2] reported a complex BPF with the gain, bandwidth, center bandwidth, center frequency, and Q tuning, as well as a simple reconfigurability to a real-domain LPF. Most previous complex BPFs [2,4,5,6,7,8,9] have not allowed the tuning of passband gain flatness (illustrated in Figure 1d), which is an important performance parameter in the analog baseband flatness (illustrated in Figure 1d), which is an important performance parameter in the analog filter. Gomez-Garcia et al [12] proposed a design method to improve the passband flatness, but it was passive-type real-domain BPFs. limited only to passive-type real-domain BPFs. In [7], we reported preliminary circuit design results of a complex BPF for BLE [1] and.
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