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.