Design of an ASK RF Transceiver for ETCs with Hybrid ASK Modulator and Ultra Low Power Wake-Up Receiver

Abstract

This article presents a CMOS RF transceiver architecture employing Amplitude-Shift-Keying (ASK) modulation for Electrical Toll Collection (ETC) applications. To meet both Korean and Chinese ETC communication standards, the transmitter adopts a hybrid modulation approach. The Korean and Chinese OBU operates at 1024 kbps and 512 kbps, respectively, and the RSU communicates at 256 kbps. By combining digital and analog features, the hybrid structure offers advantages over conventional analog modulators in area, energy efficiency, design portability, voltage scalability, and robustness against process–voltage–temperature (PVT) variation.
Since Chinese OBUs rely on batteries, minimizing power is a primary concern. The RF transceiver remains in sleep mode until activated by a wake-up receiver (WuRx). To achieve ultra-low-power operation, the WuRx employs an envelope detector with MOSFETs working in the sub-threshold region, allowing continuous operation at extremely low current levels. Digital filtering further improves wake-up detection reliability and prevents false triggers. The WuRx achieves total power consumption of only 3.6 μA.
Unlike conventional receivers with automatic gain control (AGC), ETC receivers must operate reliably without AGC under high-speed vehicle conditions. Therefore, the proposed receiver is designed with a fixed gain yet provides an extended dynamic range of 70 dB. The RX front-end integrates a low-noise amplifier (LNA), a mixer, and a received-signal-strength indicator (RSSI) to achieve robust ASK demodulation while maintaining linearity and compliance with the highest P1dB specification.
The full transceiver is fabricated in 130-nm 1P8M CMOS process with an active area of 3.5 mm × 3.5 mm, including ESD protection.