Investigation of two-point modulation to increase the GFSK data rate of PLL-based wireless transceivers of wireless sensor nodes

Gaussian Frequency-shift-keying (GFSK) is a widely used modulation scheme in state-of-the-art wireless transceivers. Most often a phase-locked-loop (PLL) is utilized for carrier generation and GFSK modulation. Using this architecture the maximum applicable data rate is limited by the PLL´s bandwidth. This paper investigates the possibility of using two-point modulation in order to be able to choose the GFSK data rate independently of the bandwidth. The most important aspect of two-point modulation is the mismatch of the gain of the two modulation paths. Two methods which allow close gain matching are presented in this work. Time-domain simulations using Verilog-A models of the analog and RTL models of the digital building blocks of a wireless transceiver have been carried out and confirm the capability of extending its GFSK data rate to 1Mbps while using a PLL closed-loop bandwidth of 44.5 kHz.