A low-power and fast-response FSK transmitter

A low-power, fast-response transmitter based on frequency-shift keying (FSK) is presented and used in the Sub-GHz band. This transmitter uses the closed-loop modulation structure of a phase-locked loop (PLL) and maintains the constant loop bandwidth of a PLL to ensure a consistent data rate at each frequency point of Sub-GHz. A fast and accurate VCO frequency sub-band selection technology is proposed to reduce the selection time of the optimal variable capacitor array control bits of VCO, thus improving the response speed of PLL and transmitter. This transmitter is implemented in the SMIC 0.18 μm CMOS process. The measured results showed that the selection time of the optimal VCO frequency sub-band is only 3.04 us, and the Error Vector Magnitude (EVM) of the whole transmitter is 4.17% at 115 kHz data rate, meeting the wireless transmission requirements of the nodes of Internet of things.