Apparatus for converting an analogue input signal of narrow bandwidth to digital form.

摘要

A narrow band signal is converted into digital form using an analogue to digital converter of relatively small capacity. The input signal (1) is compared at (17) with a prediction of it based on previous cycles of the incoming waveform. This produces an error signal which is compared at (3) with a prediction of the error signal to produce at (4) an "error of the error" signal. A relatively small A/D converter converts this into 8 bit digital form and this is applied to a feedback loop consisting of an adder (8) and delay (9) to give a sixteen bit prediction of the error signal which is applied via D/A converter (10) to the subtractor (11). The sixteen bit prediction also provides an input to a further adder (12) forming part of a feedback loop (12, 12, 14) to give an eighteen bit prediction of the input signal. The latter is applied via D/A converter (15) to subtractor (17) and is used as the system output.