An ultra low power MICS/ISM band transmitter in 0.18 μm CMOS

In this paper the design of an ultra low power transmitter in MICS/ISM band has been presented. The transmitter uses Frequency Shift Keying (FSK) as the modulation scheme. At the heart of the transmitter is an oscillator whose frequency is periodically calibrated. A ring type oscillator has been considered instead of LC type as it reduces the buffer power consumption immediately following the oscillator. Within the ring-based topology a one-stage ring oscillator (basically an astable multivibrator) with fine frequency resolution has been considered for even lower power consumption. The periodically activated frequency calibration system is based on measuring the fraction when the oscillator frequency is divided by a reference frequency and thereby correcting the oscillator frequency. The power amplifier (PA) used is Class-E type. A switch is present to disconnect the frequency calibration unit and turn on the PA after the channel frequencies have been calibrated. The transmitter can work from a data rate of 250kbps to 1Mbps consuming only the minimum bandwidth required for FSK transmission and allowing for simultaneous transmission in the band. It draws an average current of 180 μA from a 1.6V supply achieving the lowest current consumption for a transmitter designed at the specified band and allowing for multichannel operation.