Circuit arrangement for the generation of a sawtooth voltage

Circuit arrangement for the generation of a sawtooth voltage at a capacitor, which is charged by a first current, until a first threshold voltage is reached, and is discharged by a second current, until a second threshold voltage is reached comprising:

• a source of synchronization signals,
• means for changing the direction and/or the intensity of the direct current supplied to the capacitor at the instant the threshold voltage is reached, whereby the differences between the first and the second threshold voltage as well as the charge and the discharge current determine the natural frequency of the sawtooth voltage generated, and
• a synchronization signal detector and means for switching said circuit from said natural frequency under the influence of said synchronization signal detector for establishing the presence of said synchronization signal, whereby at least one of the two capacitor charge switching instants can be determined by synchronization signals supplied having a substantially constant nominal repetition frequency, the sawtooth voltage being thus synchronizable by said synchronization signals, and whereby said natural frequency is given substantially the nominal value in the absence of synchronization signals, said synchronization signal detector being implemented as a coincidence circuit to which a signal corresponding to a determined time interval, of the sawtooth voltage and a signal corresponding to a determined time interval of the incoming synchronous signal are supplied and which on coincidence of these two signals supplies a signal to a switching stage for switching the natural frequency of the sawtooth circuit arrangement from a value corresponding at least substantially to the nominal frequency to a lower value.