Edge-Combining for QPSK and FSK Modulation Using a Single Delay-Line
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Proceedings 2020 Austrochip Workshop on Microelectronics
This work introduces a method to use edge-combining to obtain Quadrature Phase Shift Keying (QPSK) as well as Frequency Shift Keying (FSK) signals in a power efficient way to be used in low-power integrated transmitters for Internet of Things applications. Therefore, 16 time-delayed (phase-shifted) signals are produced by one 8-stage differential delay line. The signals are applied in combination with edge-combining for both, 4-times frequency multiplication and quadrature signal generation. Moreover, a phase selector is assigned to perform QPSK as well as FSK by adapting the selector stepping values according to the desired frequency deviation. In order to get better spectral purity, additional phase values (as needed for 12-PSK) for frequency modulation are generated by additional phase shifts. For this work, the concept is proven by simulation and targets a phase locked ring oscillator with a constant in-band phase noise of -80 dBc/Hz in the loop bandwidth of 1MHz and a out of band phase noise with a slope of -20 dB/dec from a carrier frequency of 864 MHz. The proposed method intends to reduce the power demand of integrated transmitters by keeping the frequency and amount of power-hungry components low. Moreover, compared to other work in the area of edge-combining transmitters, a method for complex modulation by one delay line is introduced.