  Backed by advances in digital electronics, signal processing, computation,
and storage technologies, aperture arrays, which had strongly influenced the
design of telescopes in the early years of radio astronomy, have made a
comeback. Amid all these developments, an international effort to design and
build the world's largest radio telescope, the Square Kilometre Array (SKA), is
ongoing. With its vast collecting area of 1 sq-km, the SKA is envisaged to
provide unsurpassed sensitivity and leverage technological advances to
implement a complex receiver to provide a large field of view through multiple
beams on the sky. Many pathfinders and precursor aperture array telescopes for
the SKA, operating in the frequency range of 10-300 MHz, have been constructed
and operationalized to obtain valuable feedback on scientific, instrumental,
and functional aspects. This review article looks explicitly into the
progression of digital-receiver architecture from the Murchison Widefield Array
(precursor) to the SKA1-Low. It highlights the technological advances in
analog-to-digital converters (ADCs),field-programmable gate arrays (FPGAs), and
central processing unit-graphics processing unit (CPU-GPU) hybrid platforms
around which complex digital signal processing systems implement efficient
channelizers, beamformers, and correlators. The article concludes with a
preview of the design of a new generation signal processing platform based on
radio frequency system-on-chip (RFSoC).
