Broadband Photonic Down-Conversion Preprocessor for ADC With Arcsine Equalization

It is a challenge to convert broadband millimeter-wave signals directly with electronic analog-to-digital converters (ADCs). The photonic down-conversion preprocessor is a promising solution. The arcsine equalization originated from the photonic sampled ADC is applied in the photonic down-conversion preprocessor to leverage the performance. We derive the working principle of the photonic down-conversion system with the arcsine equalization for the first time, and comprehensively investigate the evolution of signal-to-noise ratio (SNR) and signal-to-noise and distortion ratio (SINAD) after the equalization. It shows that the equalization works quite differently in the proposed system, effectively suppressing the nonlinearity from large modulation depth within a periodic frequency range. The common-mode noise is canceled and additional gain of SNR is achieved for any frequency. Factors affecting the performance are discussed in detail, guiding the optimal configuration to exploit the potential of the proposed system under different scenarios. Signals ranging from 31 GHz to 48.9 GHz are digitized via the proposed system with a bandwidth of 10 GHz and an effective number of bits (ENOB) of 5.9. A newly-defined figure of merit (FOM) is proposed to comprehensively and flexibly evaluate bandpass sampling systems and the proposed system displays a favourable performance.