The RFID system is attracting attentions in the field of automatic identification. Especially, they need a system that can identify a thousand of tags at a time in practical use. We proposed a communication scheme in combination of time hopping CDMA, CRC error-detecting, and repetition of transmission for error recovery to resolve collision problems by simple circuits. The scheme realizes identification of a thousand in 300 msec with low error rate of 1.214 /spl times/ 10/sup -11/. This paper presents an experimental tag circuit which achieves low power operation of 23.4 /spl mu/W with the core area of 12520 /spl mu/m/sup 2/.