BFSK MICS direct-DCO transmitter with adaptive background frequency regulation

A frequency-adaptive BFSK MICS band (402-405 MHz) transmitter for use with a flexible loop antenna is presented. The transmitter uses interleaved frequency-locked loops (FLL) that allow simultaneous fast frequency modulation at a maximum bit rate of 2Mbps and slow background frequency adaptation with a time constant of 4.8μs which preserves frequency tuning between burst data transmissions. Frequency tuning is implemented with a digitally controlled oscillator (DCO) tuned with a 16×16 MIM capacitor array. The circuit occupies an area of 285×270μm on a 1.91×1.91mm test chip fabricated in 90nm CMOS and consumes 333μW.