Design of 13.56 MHz ASK transmitter for near field communication using a DLL architecture

This paper presents a high efficient 13.56 MHz near field communication (NFC) transmitter in 0.18 µm CMOS process. A pulse width modulation (PWM) technique is employed to generate the ASK modulated output and to improve the transmitter efficiency. The proposed NFC transmitter can provide 0 ∼ 100% modulation depth in digital 6-bit accuracy. The multi-ASK modulation depth is realized by employing a delay locked loop (DLL), in which the modulation depth is controlled by the up and down charge pumping current ratio of the charge pump And the output current in the power stages is controlled by 6-bit digital codes for efficiency optimization.