ANALOG-TO-DIGITAL CONVERTERS (Syllabus: GS Paper 3 - Sci & Tech)

Context: A newly designed prototypes in the Next-Generation Photonic Analog-to-Digital Converters (NG-PADC) project which can carry out instantaneous frequency measurement, generation and transport of Radio Frequency (RF) through optical methods could revolutionize various sectors, enabling faster digital communication, improved satellite communication, better medical imaging, and Photonic radars.

• An NG-PADC developed by IIT Madras with support from the IMPRINT programme of Science, Engineering, Research Board (SERB), is equipped with a time-stretched photonic ADC whose effective bandwidth is 12 times higher than a corresponding EADC, which enables sampling of higher bandwidth signal with effectively lower bandwidth EADCs.

Key Points

• Analog-to-digital converters (ADCs) are critical components for developing the next generation of advanced digital receivers. 

• The limitation of electronic ADCs (EADCs) is that their vertical resolution is compromised at high bandwidths. There are two possible approaches to solve this problem through Photonics.

• RF, when modulated on a spectrally rich optical pulsed source, can be stretched in the optical domain through a dispersive medium, thus converting high-frequency RF signals into effectively low-frequency signals. 

• This reduces the input bandwidth requirements of the back-end ADC as many times as the stretch factor of the optical pulse. 
• The other Photonic approach is to use an optical clock whose fluctuations in timing (timing jitter) is much smaller an electronic clock; which is possible with a short pulsed laser. High bandwidth RF signals, when sampled with stable optical clocks, can provide a much higher effective number of bits (ENOB) compared to electronic clocks. 
• It has time-stretched photonic ADC with effective bandwidth 12 times higher than EADC, which enables digitisation of signals with a much larger precision.