Patent ID: 6114848
Filing Date: 2000-09-05
Classification: G01R

Abstract:
An automatic circuit tester that includes:A) a plurality of backdrive-capable digital driver circuits, each backdrive-capable digital driver circuit including an output port and being adapted for application thereto of a code signal representing a sequence of choices of whether to drive a load coupled to the output port thereof and, if so, between two voltage levels to which the digital driver circuit can drive the load, the digital driver circuit being operable in a backdrive-enabled mode, in which the digital driver circuit drives the load in accordance with the code signal when doing so requires driving a load current within a backdrive current range, the digital driver circuit also being operable in a backdrive-disabled mode, in which the digital driver circuit refrains from driving the load to the voltage level selected by the code signal when doing so requires a load current within the backdrive current range; andB) a plurality of backdrive-limiting circuits, each backdrive-limiting circuit being associated with a respective different one of the digital driver circuits and adapted for application thereto of a time-value signal, each backdrive-limiting circuit sensing the load current driven by its associated driver circuit and operating its associated driver circuit in the backdrive-enabled mode when the load current thus sensed has not exceeded the backdrive-current range or occupied it for more than a continuous-backdrive duration that depends on the time-value signal, and operating its associated digital driver circuit in its backdrive-disabled mode when the current thus sensed has continuously occupied the backdrive-current range for the continuous-backdrive duration.