A HIGH-SPEED 4-GSAMPLE S 2-BIT ADC SYSTEM FOR RADIO ASTRONOMY/

In recent years, the use of very long baseline interferometer (VLBI) d evices has increased in the geodesy and radio astronomy communities. T o enable these devices to pick out very small variations, it is desira ble to increase the sensitivity of the detection of the VLBI. For obse rving quasars, it is beneficial to increase the observation bandwidth and improve the sensitivity of detection. However, for such wide bandw idth systems, gigahertz-order sampling high-speed AID converters are n ecessary and the technology for achieving these devices is not yet dev eloped. In this work, we developed, using Si-bipolar LSI processes (SS T-LB), a 4-Gsample/s 2-bit ADC LSI and created a high-speed ADC system . We evaluated the loss in this system due to phase stability, samplin g jitter, and the uncertainty region of the comparator of the LSI to e valuate the coherence of the VLBI. We used a frequency transformer dev ice and a picosecond phase comparator as the measurement device for me asuring the phase stability of the gigahertz-order ADC system. From th e measurement results, we determined that the Alien standard deviation over 1-s of integration time was 3.6 x 10(-13), the sampling jitter w as 13.4 ps, and the comparator uncertainty was 20 mV. For a wide bandw idth burst mode VLBI observation system with an observation frequency of 230 GHz, a coherence loss of 7.6 percent was observed. We then demo nstrated the operation of the ADC system by detecting real radio astro nomical observation spectra using this device.