Patent ID: 6288526
Filing Date: 2001-09-11
Classification: G05F

Abstract:
An adjustable voltage regulator for converting an external supply voltage from an external voltage source to a selected internal supply voltage, the adjustable voltage regulator circuit comprising:a reference voltage generator for converting the external supply voltage to a stable reference voltage; anda variable tuning circuit for adjusting the stable reference voltage to the selected internal supply voltage, wherein the variable tuning circuit comprises:a first op-amp, a non-inverting input terminal of the first op-amp being coupled to receive the stable reference voltage from the reference voltage generator;a first resistive element, the first resistive element being connected between an output terminal of the first op-amp and a negative input terminal of the first op-amp,a second resistive element, the second resistive element being connected between the non-inverting input terminal of the first op-amp and a first voltage source; anda control circuit for regulating the resistance of the second resistive element such that an output voltage at the output terminal of the first op-amp is equal to the selected internal supply voltage,wherein the second resistive element comprises a first plurality of serial resistive elements,wherein the control circuit selectively connects the non-inverting input terminal of the first op-amp to the first voltage source through at least one of the first plurality of serial resistive elements, andwherein the control circuit comprises:a second plurality of MOS transistors, a first signal terminal of each of the second plurality of MOS transistors being connected to a junction of two of the first plurality of serial resistive elements, and a second signal terminal of each of the second plurality of MOS transistors being connected to the first voltage source; anda third plurality of memory cells, an output terminal of each of the third plurality of memory cells being connected to a gate terminal of one of the second plurality of MOS transistors.