Patent ID: 6563338
Filing Date: 2003-05-13
Classification: H03K

Abstract:
A control circuit to be used inside an input/output buffer forreplacing a terminal resistor on a motherboard, wherein the input/output buffer has an input/output pad, comprising:a first field effect transistor, wherein a gate terminal of the first field effect transistor is connected to a pull-up enable signal line and a first source/drain terminal of the first field effect transistor is connected to a first voltage source; a second field effect transistor, wherein a gate terminal of the second field effect transistor is connected to the pull-up enable signal line, a first source/drain terminal of the second field effect transistor is connected to a second source/drain terminal of the first field effect transistor, and a second source/drain terminal of the second field effect transistor is connected to a ground; and a third field effect transistor, wherein a gate terminal of the third field effect transistor is connected to the second source/drain terminal of the first field effect transistor, a first source/drain terminal of the third field effect transistor is connected to a second voltage source, and a second source/drain terminal of the third field effect transistor is connected to the input/output pad; wherein when the pull-up enable signal line is activated, the second field effect transistor is cut off while the first field effect transistor is turned on so that an equivalent resistance is set up between the source and the drain terminal of the third field effect transistor and connected in parallel between the input/output pad and the second voltage source.