A passive UHF-RFID tag with inkjet-printed electrochromic paper display

In this paper, an inkjet-printed electrochromic (EC) paper display integrated with passive UHF-RFID tag is introduced as a solution for passive electronic shelf labels (ESL). To address the system challenges of the limited power budget of passive UHF-RFID tags and the material aging of EC display, a feedback comparator integrated digital display driver is proposed based on the study of electrochromic, bi-stable and aging features of the EC display. Modularized baseband with different enable conditions and clock domains is implemented in the system design level. Moreover, to maintain the system functions when the input power is lower than the display refresh power, a duty-cycled power management unit (PMU) is activated to reduce the load current during energy scavenging and drive the display in short intervals, enabling the fast charging of the voltage rectifier and the correct output of the regulated supply for the core circuit. The design is fabricated in a 0.18-um CMOS process with an area of 2.25 mm². Fed with EPC C1G2 protocol write command, experiments demonstrate correct refresh of EC display with 4 cm² effective area. System sensitivity at the antenna reference point is basically immune to the display load. Further improvements can be achieved after careful chip-to-antenna impedance matching and PMU efficiency optimization.