ASK Modulator Design for Passive RFID Tags in Backscatter Communication Systems

Passive Radio Frequency Identification (RFID) tags are battery-less transponders, with the power delivered to the output load being the critical factor of the backscatter communication (BackCom) system performance. This paper proposed a novel tag circuit design for amplitude-shift keying (ASK) modulation. Instead of using the conventional resistive modulator, we proposed a reactive modulator for impedance matching and backscattered signal modulation. Besides, we mathematically proved that the output power is maximized with a purely resistive load design for ASK modulation. The closed-form expressions for the modulating reactances required to get the optimal resistive load design are derived. In contrast to the prior art, the proposed design significantly improves the load power delivered to the integrated circuit (IC) chip. The simulation result gives an insight into the load power for different BackCom applications. An overall gain of around 5.7 dB signifies the utility of the proposed circuit design.