Today’s ADC chips usually have such a high input sensitivity that rather than signal amplification an attenuation is needed beforehand. However, the usually active input amplifier circuits, which also take over a first analog anti-aliasing filtering, want to amplify – as the term amplifier says – and work optimally only then. At this point, we came up with the idea of a purely passive design with input transformers. The impedance ratios allow for this. The transformer takes over the down-conversion (12dB attenuation for 21dBu input level) and at the same time a first anti-aliasing filtering due to the limited bandwidth of the transformer. – By the way, we were the first with this idea in 2013. At best, there were designs with transformers in combination with active stages. In the meantime, however, there are also imitators.
This design thus provides a high suppression of interference, in contrast to many electronic solutions, even in case of asymmetry on the line. And there are no additional active circuits between the input and the ADC chip. It doesn’t get any purer than this.
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