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This paper presents a field programmable gate array (FPGA) implementation of a digital circuit that measures in real-time first harmonics of voltage and current medium-frequency (25 kHz-70 kHz) induction-heating cooking appliances. The inverter output voltage and load current are sensed using first-order delta-sigma (ΔΣ) analog to digital converters. The coefficients of the Discrete-Time Fourier Series (DTFS) of voltage and current are computed over a half period of the mains. The DTFS coefficients are computed directly from the ΔΣ modulated 1-bit data stream signals. The main advantages are that the digital low-pass filter implementation at the output of the modulator is not needed and the arithmetic complexity is reduced since a bit-stream is processed. The system is simulated using a mixed-signal simulation tool and it is experimentally verified.