A Battery-Free Crystal-Less BLE Transmitter Tag With Fully-Integrated RF Harvesting and Multitag TDD and FDD Broadcasting

This article reports a Bluetooth Low-Energy (BLE) transmitter (TX) tag without the battery and crystal (XTAL) while supporting multitag time-division duplex (TDD) and frequency-division duplex (FDD) broadcasting. Such TX tag has a PCB size of 17
$\times$
27
$\times$
3 mm
$^{3}$
, including 1 off-chip antenna and 1 off-chip storage capacitor. It facilitates installation in large-scale deployment in intelligent warehouses, portable devices, or volume-constrained, hard-to-reach locations. The key innovations are threefold: 1) a single antenna that not only features a
trifilar RF harvester
and an RF-reference phase-locked loop (PLL) to extract the energy and reference clock from the wireless access point (AP), but operates with the power amplifier (PA) to transmit packets; 2) a
$V_{\text{DD}}$
-insensitive voltage-controlled oscillator-PA that provides stable output power (
$P_{\text{OUT}}$
) and frequency of the BLE output data packet against the harvester’s output-voltage variation; and 3) multitag TDD and FDD broadcasting that features a frequency-retaining technique to save the power consumption when the TX tag is idle. Prototyped in 28-nm CMOS, our TX tag occupies an active area of 1.4 mm
$^{2}$
, including a fully-on-chip micropower manager. The measured VCO frequency pushing and
$P_{\text{OUT}}$
variation are 1.74 MHz/V and
$<$
0.05 dB against supply voltage from 0.26–0.46 V. The data-package frequency drift is 11 kHz (4.43 ppm). The system-level verification is validated with the over-the-air measurement.