FPGA-based FSK/PSK modulation

Ahmed Asim Ghouri, Embedded Strings Inc.
EDN (December 11, 2014)

Binary FSK(Frequency Shift Keying) and PSK(Phase Shift keying) are extensively used in telecommunication for digital data transmission. FSK/PSK modulator circuits usually employ analogue components such as VCO (voltage control oscillator), RF Mixer, and Level-shifter, with limited frequency range and whose performance drifts with variation in environmental temperature and duty cycle. An FPGA-based all-digital implementation ensures constant optimum performance and reconfigurability.

This article discusses practical application of a combined Binary FSK and PSK modulator. It highlights how embedded resources can be used to implement an all-digital FSK / PSK modulator, which modulates serial data transmission of a UART (Universal Asynchronous Receiver and Transmitter). In this application the modulation scheme targets Altera’s Cyclone-IV FPGA populated on a DE2-115 development board from Terasic and an HSMC (High Speed Mezzanine Card). A system block diagram shows how a LUT based NCO is used to generate the sine wave with varying frequency and then with varying phase. Extensive testing and its results are discussed to verify the modulation.

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