Advanced synchronization schemes for NFC card emulation mode, peer-to-peer mode and RFID tag design

摘要

A start-up control for a transmitter (TX) output driver is implemented to prevent the stick state problem when the TX driver is not toggling. TX output driver is set in a high impedance (HZ) mode when data zero is delivered from the digital base band (DBB) and set in an enhanced mode to deliver a stronger signal when data one is delivered from the DBB. The transmitter comprises a dual-loop PLL to synchronize the TX output pulse and the carrier. The dual-loop PLL is composed of a relaxation oscillator, a 1^st Loop, and a 2^nd Loop. The 1^st loop is a voltage-controlled oscillator comprising the relaxation oscillator and an operational transconductance amplifier. The 2^nd loop is a loop comprising a phase frequency detector, a charge pump, a loop filter and the VCO of the 1^st loop.