Semiconductor integrated circuit with voltage generation circuit, liquid crystal display controller and mobile electric equipment
View Patent ↗There is to be provided a liquid crystal drive controller with a built-in power supply circuit wherein latch-up is made difficult to arise even if one amplitude level of the segment line drive voltage is set to the ground potential and the levels of other liquid crystal drive voltages are determined accordingly. A semiconductor integrated circuit with a built-in power supply circuit, wherein a negative voltage generated in a power supply circuit is applied to a substrate or a well region as a bias voltage, is provided with a switch for temporarily applying the ground potential to the substrate or well region to be biased with the negative voltage at the time of starting up the power supply circuit.
1. A liquid crystal display controller on a semiconductor substrate and for use with a liquid crystal panel having first electrodes and a common electrode, the liquid crystal display controller comprising:
a power supply circuit coupled to receive an external source voltage and for generating a voltage to be applied to the first electrodes of the liquid crystal panel and for generating a positive voltage higher than the external source voltage or a negative voltage lower than a ground potential, to be applied to the common electrode of the liquid crystal panel;
a switch element coupled between a first wiring for feeding the negative voltage as a bias voltage for a substrate and a second wiring for supplying the ground potential; and
a circuit which generates a first control signal to make the switch element conduct temporarily in accordance with a second control signal for starting up the power supply circuit.
2. A liquid crystal display controller according to claim 1 ,
wherein the switch element is temporarily made to conduct at the time of starting up the power supply circuit to set a potential of the semiconductor substrate, to which the negative voltage is to be applied, temporarily to the ground potential.
3. A liquid crystal display controller according to claims 1 ,
wherein the switch element is comprised of a high voltage withstand MOSFET.
4. A liquid crystal display controller according to claim 3 , further comprising:
a first drive circuit which supplies signals for driving the first electrodes of the liquid crystal panel on the basis of a voltage generated by the power supply circuit; and
a second drive circuit which supplies signals for driving second electrodes of the liquid crystal panel on the basis of a voltage generated by said power supply circuit,
wherein elements constituting the second drive circuit are comprised of MOSFETs higher in voltage withstand than the elements constituting the power supply circuit for liquid crystal display driver, and
wherein the switch element is comprised of a voltage withstand MOSFET having the same structure as the elements constituting the second drive circuit.
5. A liquid crystal display controller according to claim 1 ,
wherein the liquid crystal display controller has:
a first operating mode in which a display operation is performed in a state of a source voltage being supplied from an outside of the liquid crystal display controller, and
a second operating mode in which a display operation is not performed in a state of a source voltage being supplied from the outside of the liquid crystal display controller,
wherein, when changing from the second operating mode to the first operating mode, the switch element is temporarily made to conduct to temporarily apply the ground potential to the substrate, to which the negative voltage should be applied.
6. A liquid crystal display controller according to claim 1 , further comprising:
an oscillating circuit,
wherein the liquid crystal display controller has:
a first operating mode in which the oscillating circuit is operated to perform a displaying operation in a state of a source voltage being supplied from an outside of the liquid crystal display controller, and
a second operating mode in which the operation of the oscillating circuit is stopped not to perform the displaying operation in a state of a source voltage being supplied from the outside of the liquid crystal display controller,
wherein, when changing from the second operating mode to the first operating mode, the switch element is temporarily made conduct to set the potential of the semiconductor substrate, to which the negative voltage is to be applied, temporarily to the ground potential.
7. A liquid crystal display controller according to claim 1 , further comprising:
an external terminal to which a signal for an on/off control of the switch element is inputted.