Testable cascode circuit and method for testing the same

摘要

The cascode circuit comprises a plurality of switching transistors ( 11 ) to be protected from high voltage and a plurality of cascode transistors ( 13 ) connected to the switching transistors ( 11 ). A test node (B') is arranged between each switching transistor ( 11 ) and its cascode transistor ( 13 ), and a test transistor ( 30.1 - 30. n) is allocated to each test node (B'), its gate being connected to the test node (B'). The sources of the test transistors ( 30.1 - 30. n) are connected to a first test point ( 31 ) and the drains of the test transistors ( 30.1 - 30. n) are connected to a second test point ( 32 ). A first voltage (U 1 ) is applied to the first test point ( 31 ) and a second, slightly lower voltage (U 2 ) is applied to the second test point ( 32 ). A current flow detected between the first ( 31 ) and the second ( 32 ) test point indicates that at least one of the cascode transistors ( 13 ) does not work correctly. Thus, the cascode circuit is testable. The high-density IC manufacturing process becomes applicable also for devices with a high number of high-voltage outputs. Internal potentials may be observed in a fast parallel way.