Patent ID: 8269477

Claim:
A reference voltage generation circuit comprising: an operational amplifier configured to output a substantially constant voltage in accordance with first and second voltages respectively input into first and second terminals of the operational amplifier; a start-up circuit configured to initiate operation of the operational amplifier when the start-up circuit switches from an idle mode to an active mode, the start-up circuit comprising: (i) a first transistor having a gate connected to an output of the operational amplifier, a source connected to a supply voltage, and a drain connected to a first resistor, to supply a substantially constant reference current to the first resistor in accordance with the output voltage from the operational amplifier, thereby generating the reference voltage; (ii) a second transistor having the first conductivity type and a source connected to the supply voltage, the second transistor turning on when the start-up circuit switches from the idle mode to the active mode; (iii) a third transistor having a second conductivity type and a drain connected to the drain of the second transistor, the third transistor having a gate controlled by the reference voltage; (iv) a fourth transistor having the second conductivity type, a gate connected to the drain of the second transistor and the drain of the third transistor, and a drain connected to the output of the operational amplifier; and (v) fifth and sixth transistors each having the second conductivity type, the fifth and sixth transistors being turned on in the active mode.