An Ultra-Low Power, Adaptive All-Digital Frequency-Locked Loop With Gain Estimation and Constant Current DCO
In this paper, an ultra-low power, adaptive all-digital integer frequency-locked loop (FLL) with gain estimation and constant current digitally controlled oscillator (DCO) for Bluetooth low energy (BLE) transceiver in Internet-of-Things (IoT) is presented. For locking DCO frequency closest to the ta...
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| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IEEE
2020-01-01
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| Series: | IEEE Access |
| Subjects: | |
| Online Access: | https://ieeexplore.ieee.org/document/9097205/ |
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| Summary: | In this paper, an ultra-low power, adaptive all-digital integer frequency-locked loop (FLL) with gain estimation and constant current digitally controlled oscillator (DCO) for Bluetooth low energy (BLE) transceiver in Internet-of-Things (IoT) is presented. For locking DCO frequency closest to the target channel, it adaptively controls capacitor banks with binary algorithm. With decrease in frequency resolution, DCO clock counts for each capacitor bank bit evaluation dynamically increases with the proposed technique for accurate frequency tracking. For compensating PVT variations and finding the BLE frequency deviation, the configurable digital DCO gain estimation is incorporated. The low power and constant current DCO operates in sub-threshold region and its power consumption is minimized by <inline-formula> <tex-math notation="LaTeX">$g_{m}/I_{D}$ </tex-math></inline-formula> methodology optimization, constant current source for limiting current in DCO core through adaptive low-dropout regulator (LDO) and lowering the supply voltage. The proposed design is integrated in an ADPLL for BLE transceiver and it is fabricated with 1P6M TSMC 55 nm CMOS technology. The all-digital adaptive FLL is fully synthesizable and its area is <inline-formula> <tex-math notation="LaTeX">$1800~\mu \text{m}^{2}$ </tex-math></inline-formula> with 1.233 K gate count. The RMS current consumption is <inline-formula> <tex-math notation="LaTeX">$103.32~\mu \text{A}$ </tex-math></inline-formula> from 1 V voltage supply with <inline-formula> <tex-math notation="LaTeX">$103.32~\mu \text{W}$ </tex-math></inline-formula> power requirement. The experimental results reveal, DCO draws <inline-formula> <tex-math notation="LaTeX">$480~\mu \text{A}$ </tex-math></inline-formula> current from 0.55 V supply voltage at center frequency. It has frequency resolution of 4.8 kHz. The oscillator PN, FOM and FOM<sub>T</sub> at 1-MHz offset frequency from 2.44 GHz carrier frequency are −122.85 dBc/Hz, 196.38 dBc/Hz and 208.19 dBc/Hz, respectively. |
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| ISSN: | 2169-3536 |