7.5 A TCXO-less 100Hz-minimum-bandwidth transceiver for ultra-narrow-band sub-GHz IoT cellular networks

Ultra-narrow-band (UNB) signaling is an enabling technology for low-power wide-area (LPWA) networks for the “Internet-of-Things”. Indeed, UNB signaling, based on spectrally efficient modulations such as DBPSK, simultaneously optimizes network capacity while maximizing the communication link budget. However, UNB signaling poses many technical challenges. In the receiver, carrier frequency offsets (CFO) can shift the desired signal from the expected channel. In the transmitter, the difficulty resides in generating the modulated signal with the required spectral purity. This work presents an 850-to-920 MHz RF transceiver dedicated to UNB communication systems employing the DBPSK/GFSK modulations. The receiver is resistant to CFO offsets and drifts of ±75Hz (i.e. 150% of the 100Hz channel) and 35Hz/s, respectively, with only 1dB sensitivity loss, thus allowing the circuit to function without a TCXO. In DBPSK 100b/s transmission mode, an error vector magnitude (EVM) better than 5% is measured for output powers up to 10dBm.