GB1170448A - Improvements in or relating to Methods of and Apparatus for Testing Encoders and Decoders in P.C.M. Transmission Systems - Google Patents

Abstract

1,170,448. Testing apparatus for P.C.M. systems. MARCONI CO. Ltd. 3 Feb., 1967 [24 May, 1966], No. 23162/66. Heading G4H. A pulse code modulation system including testing apparatus for the encoder (Fig. 1), or the decoder (Fig. 2), comprises a first detector 6 (Fig. 1), 15 (Fig. 2) for detecting in normal transmission the occurrence of signals of a predetermined level applied to the input of the encoder or decoder, a second detector 5 (Fig. 1), 16 (Fig. 2) for detecting the occurrence of encoder or decoder output signals corresponding to input signals of the predetermined level and means 7 (Fig. 1), 17 (Fig. 2) for producing a fault indicating signal in the event of non- correspondence of the detected signals. In the embodiment described the encoder which is of the type in which the input signal is compared in a comparator 2 (Fig. 1) with a signal from a level synthesizer 3, the output from the comparator being fed to logic circuitry 4 controlling the synthesizer 3, the binary coded output from the comparator 2 is fed through an AND gate 9 enabled by a fault code generator 8 when there is coincidence of signals to the comparator 7. If, however, the level detector 6 gives an output when there is no output from the detector 5, the AND gate 9 is disabled and an error signal is transmitted. At the decoder, in which the binary coded signal transmitted on lead 12 is converted into an analogue signal and transmitted by a gate 19, a fault code detector 18 detects incoming signals corresponding to a fault indicating signal to disable the gate 19. The gate 19 is also disabled when there is non- coincidence of signals to the comparator 17. Multiplexing arrangements may be included at the input 1 (Fig. 1) of the encoder and at the output 20 (Fig. 2) of the decoder.