Circuit arrangement for generating a synchronizable sawtooth voltage

A circuit arrangement for generating a sawtooth-shaped voltage across a capacitor comprising:

• charging current means connected to said capacitor for charging said capacitor until a first threshold voltage is reached and discharging current means connected to said capacitor for subsequently discharging said capacitor until a second threshold voltage is reached,
• means connected to said charging and discharging means for measuring and controlling the capacitor voltage,
• means connected to said capacitor for switching said charging and discharging current means, respectively, at the instant a threshold voltage is reached, the free-running frequency of the sawtooth voltage thus produced being determined by the difference between said first and second threshold voltage at a constant charging and discharging current and by the intensity of said charging and discharging current, respectively, at a constant difference between said first and second threshold voltage,
• the circuit arrangement comprising further a source of synchronizing pulses connected to said circuit, and
• a synchronizing signal detector connected to said current charging and discharging means for establishing the presence and the frequency of synchronizing pulses having a substantially constant nominal repetition frequency, whereby at least one of the two switching instants of the capacitor charging operation can be determined by means of said synchronizing pulses, the sawtooth voltage being thus synchronizable by means of said synchronizing pulses, and whereby it is established by means of said synchronizing signal detector whether the repetition frequency of said synchronizing pulses corresponds with a first lower or a second higher value, at which second frequency value the charging current and/or the discharging current of said capacitor is increased in such a way that the amplitude of the sawtooth voltage is substantially the same for both frequencies.