X-Ray Characteristics of Four-Level Pulse Amplitude Modulation for X-Ray Communication Based on Carbon Nanotube Cold Cathode X-Ray Source

In this work, a pulse amplitude modulation with four-level (PAM-4) signal loading scheme based on carbon nanotube (CNT) cold cathode X-ray source is designed for X-ray communication (XCOM). The relationship between the X-ray waveforms and amplitude characteristics under this scheme is studied, and the XCOM performance is obtained. Results show that the amplitude difference of each level of X-ray waveforms is obvious, and it is corresponding well with the input signal amplitude. The X-ray amplitude difference of each level is 0.7–0.8 V when the ratio of the four pulse voltage signal amplitudes is 1:0.42: −0.12: −1. About 70% of the signal waveforms of each level is relatively concentrated under different frequencies, and this proves the stability and feasibility of the PAM-4 loading scheme. According to the 26-letter American standard code for information interchange (ASCII) code signal transmission experiment, the bit error rate (BER) is increased from 0 to $4.7\times 10^{-{2}}$ when the pulse frequency increases from 1 to 1000 kHz. This work designs a PAM-4 signal loading scheme for XCOM with a CNT cold cathode X-ray source, which can promote the development of XCOM technology in the future.