The analogue-to-digital converter.
Radar experts from the CSIR assisted engineers from the Square Kilometre Array (SKA) project with the characterisation of a wideband analogue-to-digital converter (ADC or A-to-D) for integration into the Karoo Array Telescope (or ‘MeerKAT’) antennae, as a component of the L-band frequency (0.9 - 1.67GHz) upgrade currently underway.
An ADC is a device that converts an analogue signal (current, voltage, or electric charge) to the digital domain usually represented by a binary code. In the digital domain, the data become easier to analyse with commercial off the shelf (COTS) equipment like personal computers (PCs).
The suitability of a particular ADC for an application is determined by a variety of measures including speed and resolution of the conversion that need to be achieved. Considering the sensitivity of the signal of interest (small/weak signal) in the presence of other radio frequency (RF) emissions from space like satellites, the total dynamic range and linearity of the ADC are very important. The standard measure that is used in describing the dynamic range of an ADC is referred to as the spurious free dynamic range (SFDR). It was this figure of merit that was seen by the SKA engineers as a potential risk area.
The CSIR’s published research and expertise on the design and performance of wide-band digital radio frequency memory (DRFM) technology attracted the attention of the SKA’s digital back-end team. An ADC forms part of the DRFM architecture and the one being considered for the MeerKAT development was similar to what the CSIR currently uses in radar and electronic warfare research and technology development. DRFM technology is utilised for the test and evaluation of radars and since the CSIR is involved in the development of radars, the DRFM technology complements this competence. The DRFM technology developed at the CSIR is regarded as world-class.
The role of the CSIR in this project was to perform characterisation of the ADC to provide the team with an evaluation performed at the sampling speed they intended to use to determine the attainable performance levels of the eventual system.
With the measured results in hand, the SKA team had the necessary confidence to go ahead with designing this ADC into the MeerKAT.
The MeerKAT is a mid-frequency radio telescope and seen as forerunner to the SKA technology. It will be the largest and most sensitive radio telescope in the southern hemisphere until the Square Kilometre Array (SKA) is completed by about 2024.
Christa van der Merwe