Switching circuit comprising a plurality of input channels and an output channel

Claim 1

A switching circuit comprising a plurality of input channels and an output channel, an associated switching device having been provided between the output channel and each input channel, each switching device comprising an emitter-coupled pair of transistors having a switchable transistorized current source in the emitter lead, the emitter of said transistorized current source being connected to a supply voltage through a resistance and the collector thereof connected to the emitter of said switching device, the first and the second transistor, respectively, of each pair having its base connected to the associated input channel and to the output channel, respectively, the collectors of said second transistors of each pair being interconnected, the output channel comprising a transistor the emitter of which is connected to the output of the output channel and the base to the interconnected collectors of the said second transistors in the switching devices, the junction point of said output transistor and said collectors of said second transistor of each pair being connected via a resistor to a voltage-carrying terminal which is further connected to the interconnected collectors of said first transistors in the switching devices, the switching circuit furthermore comprising a selection switch by means of which at all times only one of said transistorized current sources can be switched to the current-carrying state, said bases of said transistors which are arranged as switchable transistorized current sources are connectable via the selection switch to a terminal, for carrying a d.c. voltage having a value at which the transistorized current source can be driven to the saturated state but can, however, not carry current because the signal voltages present at the base of said first and second transistors in the switching devices always cut-off these two transistors.