| 摘要 |
A bidirectional transistor switch for large signal voltages comprises a first (T1) and a second (T2) transistor arranged in series, which are supplied with base current under command of a control signal in order to short-circuit a signal terminal (ST) to a reference terminal (RT) which is connected to the substrate of the circuit. When the transistor switch is open large negative voltage excursions of the signal (U) on the signal terminal (ST) will fire a thyristor formed by the first transistor (T1) and a parasitic transistor (TP) and thus cause an undesired short-circuit between the signal terminal and the reference terminal (RT). This is prevented in that under these conditions the node (N) between the two transistors is short-circuited to the reference terminal (RT), as a result of which the loop gain in the thyristor becomes so small that this thyristor is no longer fired. The node (N) is short-circuited with the second transistor (T2) or a separate MOS transistor, which is controlled by a comparator (A1), which compares the signal (U) with a threshold value (UR1). |
