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High flatness log-scale comb-generator using FPGA-based arbitrary waveform generator for sub-30 MHz emission test systems

In this study, we propose a high flatness log-scale comb-generator using FPGA-based arbitrary waveform generator. The proposed comb-generator can cover the frequency range from 9 kHz to 30 MHz and can generate almost-equal-spaced comb-like spectrum in frequency logarithmic scale. In addition, the fine tuning of the output level of each comb can be realized by the use of FPGA architecture. After fine tuning for the flatness of comb spectrum, the output levels of 90 dBuV ±0.02 dB are achieved. The standard deviation of the output spectrum measurements taken over a span of 3 hours is less than 0.01 dB for frequencies less than 30 MHz. Therefore, the output spectrum of the proposed comb-generator is quite stable. The proposed comb-generator can find applications in calibration systems such as a reference signal generator for checking emission test systems or performing round robin tests.