Implementations for Scattering at 1.8 Volt Between Battery-Less Transponder and Mobile Telephones

Abstract

This work concerns advanced implementations of a battery-less transponder operated by intentionally generated wireless signals in the 2.4 GHz ISM band. The wireless signals consist of a power supplying data stream and of a quasi-continuous Bluetooth RF (radio frequency) signal, which enables the transponder to back-scatter the RF signal to a receiver. Our setup uses two regular, unmodified mobile telephones, one for transmitting the signals, the other for receiving the scattered signals. The transponder modulates the quasi-continuous RF signal according to a subcarrier and a predetermined 1 Mbit/s bit-stream. The present extended study further compares advanced implementation techniques: Micro Controller Unit (MCU), FPGA (Field Programmable Gate Array), CPLD (Complex Programmable Logic Device) and ASIC (Application Specific Integrated Circuit) and implements a CPLD test version. Experimental results suggest that our CPLD is more suitable than MCU or FPGA implementations. The paper further demonstrates the transition from a fully synchronous to a low-power asynchronous CPLD implementation. The measured power consumption for generating the bit-stream is $\mathrm {87\,\mu W}$ , which results in a 6-fold reduction compared to our previous work. Accordingly, the asynchronous CPLD implementation increases total efficiency by 40% and it is expected that this will significantly extend the wireless operational range of the battery-less transponder. Thus, the CPLD technology enables fast, flexible, and cost-effective implementation, particularly in the field of research and development.