(57) Decoder circuit arrangement for decoding binary coded colour video signals to produce
analogue colour video signals therefrom comprising three inputs (1,2.3) to which the
binary signals are applied these inputs being connected through an analogue level
conversion circuit (5) to a selector circuit (6), both of which are provided in an
8-channel analogue multiplexer demultiplexer (4), the selector circuit (6) selecting
a particular one-out-of-eight outputs (7-14) for application as control signals to
the control inputs of individual switches (15-22) which are also provided in the analogue
multiplexer (4). The control signal so formed renders the appropriate one of the switches
(15-22) conductive. The inputs of the switches are respectively connected to points
(A-H) on a potential divider (24-30) energised from a supply input (31) for a voltage
supply. The one of the switches which is conductive conveys the voltage at the appropriate
point (A-H) to an output terminal (2) of the analogue multiplexer (4) which output
terminal is connected through a buffer amplifier to an output (33). The output (33)
provides an analogue signal for the input binary signal. The arrangement also comprises
two similar analogue multiplex- errdemultiplexer circuits (4',4"), the inputs to these
analogue switches (15-22) also being connected to the voltage reference points (A-H).
If the inputs (1,2,3) to the analogue multiplexer (4) are red binary coded video signals
and inputs (34,35,36 and 37,38,39) for the analogue multiplexer (4',4") are respectively
blue and green binary coded video signals then the output of the three multiplexers
(4,4',4") will track due to the use of the common reference supply arrangement.
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