Architectural Overview
The A20-Nexus takes a brand new approach to professional audio receiver design. The A20-Nexus combines several technologies
resulting in a very powerful and versatile product.The diagram below illustrates the architecture of the A20-Nexus.
The first thing to note about the architecture is that there are two entire signal paths. This performs the True Diversity reception
inherent in the design. This is a lavish proposition, as it doubles the circuitry, but it is absolutely the best way to perform spatial
diversity - superior to any type of antenna or phase diversity.
The first section that comes right after the receive antennas is the first SAW filter array. This pre-select filter is a key element of our
unique SpectraBand technology. It allows for a tuning range from 470 MHz - 1525 MHz which is divided into multiple, tightly-filtered
tuning bands. The extremely sharp attenuation at either end of a tuning band’s range significantly reduces unwanted interference
outside the selected tuning band resulting in excellent range performance. Tuning bands vary in width, but tend to be around 24
MHz wide.
Next is the Low-Noise Amplifier (LNA), which is one of the most important stages in the design. This section has been specially
designed for very low noise and high dynamic range, which results in long-range reception and high overload capability. This LNA
stage exhibits a noise figure of only 0.35 dB, one of the very best on the market currently.
This is followed by yet another SAW filter array. This array further attenuates out-of-band signals, ensuring reliable reception, and
greatly suppressing any image frequencies.
The Local Oscillator and Mixer perform the traditional function of a single downconversion superheterodyne radio. This section has
been meticulously designed and is the other key element of our unique SpectraBand technology. This section exhibits extremely low
phase noise and wide dynamic range to accurately downconvert the RF to a lower Intermediate Frequency (IF) for conversion into
the digital domain.
Before conversion into the digital domain, the signal passes through its final array of SAW filters, rejecting any extraneous energy
not wanted in the downconversion, as well as providing anti-aliasing before the Analog-to-Digital (A/D) converter. The A/D converter
is a wideband, extremely high dynamic range part which accurately captures 24 MHz of IF energy into a digital version of that signal.
The real magic of the entire A20-Nexus happens within the Field-Programmable Gate Array (FPGA). An FPGA is essentially a giant
custom, massively-parallel processor programmed in house. The FPGA can perform filtering, frequency conversion, and
demodulation in the digital domain which far exceeds anything that can be done via analog or traditional digital circuitry. The FPGA
can perform demodulation of 16 channels simultaneously. The FPGA also performs the True Diversity operation which not only
selects the best digital word from the two antennas but actually works at the bit level for additional range. The resultant audio signals
are then fed out of the FPGA to the various audio outputs.
A20-Nexus
User Guide
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