Arrangement for imaging a useful signal from the frame of a first

Abstract

A circuit arrangement for imaging a useful digital signal from a frame of a first digital signal having a first bit rate into a frame of a second digital signal having a second bit rate, where the useful digital signal had been written into a first elastic memory and then read out of the first elastic memory in the frame of the first digital signal using a pulse stuffing technique, and with the frame of the first digital signal containing data representing the average fill level of the first elastic memory. The arrangement includes a second elastic memory, a frame detector for detecting the frame of the first signal and controlling activation of write-in of the useful digital signal from the frame of the first digital signal to the second elastic memory, and a frame generator which generates the frame of the second digital signal and controls activation of stuffing and of read-out of the useful digital signal from the second elastic memory into the frame of the second digital signal. An integrator determines the average fill level of the second elastic memory and a subtracter determines the difference between the average fill levels of the first and second elastic memories. This digital difference is fed to a digital control circuit, which includes a digital filter and a pulse density modulator that makes a stuffing decision as a function of the output of the digital filter. Each stuffing decision is input to the frame generator.