| 摘要 |
PURPOSE: To test power lines for the same rated supply voltage by detecting a standard voltage difference when the power lines are normal or generating an error signal when the power lines show a critical deviation by connecting an on-chip test circuit between the power lines. CONSTITUTION: When both power lines are normal, electric currents of, for example, 50mA flow to pins A and B, with the difference between both currents being about 10%, and the voltage drop at an equivalent resistor Ral (3Ω) on an IC 20 is about 15mV. When one of the power lines becomes abnormal, the voltage drop becomes +150mV or -150mV. When the resistor Ral is made of polysilicon, the voltage difference becomes larger. In this case, the voltage difference detected at a comparator circuit 50 can become as high as the power supply voltage. The comparator 50 detects the positive and negative difference voltages with a certain threshold of, for example, 75mV, generates an error signal from its output terminal 52, and supplies the signal to a processing circuit. When such a constitution is used, various kinds of defects of the power lines can be tested without requiring the so-called functional test. |
