Operational amplifier, line driver, and liquid crystal display device
View Patent ↗An operational amplifier capable of offset cancel in a shorter period, as well as a line driver capable of shortening one horizontal period and a liquid crystal display device are provided. In the operational amplifier of the invention, a time necessary for feed back control can be shortened than usual by a constitution that an output voltage VO in one horizontal period H 1 which is one horizontal period before is defined as a reference voltage in an offset cancel preparatory period HC 2 , thereby changing the output voltage VO( 2 ) only by the offset voltage VO( 2 ) by the feed back control. In the line driver of the invention, the operational amplifier not used for the output of display data D 1 to D 6 conducts offset cancel operation and it is successively shifted on every one horizontal period. Since it is no more necessary to incorporate the offset cancel preparatory period in the output period, one horizontal period can be shortened further.
1. An operational amplifier in which a differential amplifier circuit equipped with a current mirror circuit is incorporated, the operational amplifier comprising:
a first switch connected to a portion between an inverted input terminal and a non-inverted input terminal of the differential amplifier circuit;
a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch;
a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively;
a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state;
a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage;
a fourth switch connected to a portion between a gate of the second transistor and the output terminal of the operational amplifier, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and
a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage,
wherein the operational amplifier has offset cancel function.
2. A line driver for amplifying at least one input signal in an output period that is repeated periodically, the line driver including operational amplifier allocated to respective input signals for amplifying the input signals, the operational amplifier being equipped with a differential amplifier circuit in which a current mirror circuit is incorporated,
wherein the operational amplifier comprises:
a first switch connected to a portion between an inverted input terminal and a non-inverted input terminal of the differential amplifier circuit;
a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch;
a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively;
a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state;
a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage;
a fourth switch connected to a portion between a gate of the second transistor and the output terminal of the operational amplifier, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and
a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage, and
wherein the line driver has offset cancel function.
3. A liquid crystal display device for applying an image data voltage signal in one horizontal period that is repeated periodically, the liquid crystal display device including operational amplifier allocated to respective image data voltage signals for amplifying the input signals, the operational amplifier being equipped with a differential amplifier circuit in which a current mirror circuit is incorporated,
wherein the operational amplifier comprises:
a first switch connected to a portion between an inverted input terminal and non-inverted input terminal of the differential amplifier circuit;
a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch;
a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively;
a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state;
a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage;
a fourth switch connected to a portion between a gate of the second transistor and the output terminal of the operational amplifier, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and
a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage, and
wherein the liquid crystal display device has offset cancel function.
4. An operational amplifier for amplifying an input signal in an output period that is repeated periodically in which a differential amplifier circuit equipped with a current mirror circuit is incorporated, the operational amplifier comprising:
a first switch connected to a portion between an inverted input terminal and a non-inverted input terminal of the differential amplifier circuit;
a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch;
a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively;
a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state;
a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage;
a fourth switch connected to a portion between a gate of the second transistor and the non-inverted input terminal, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and
a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage, the second capacitor being configured to hold the input signal in the output period that is immediately preceding,
wherein the operational amplifier has offset cancel function.
5. A line driver for amplifying at least one input signal in an output period that is repeated periodically, the line driver including operational amplifier allocated to respective input signals for amplifying the input signals, the operational amplifier being equipped with a differential amplifier circuit in which a current mirror circuit is incorporated,
wherein the operational amplifier comprises:
a first switch connected to a portion between an inverted input terminal and a non-inverted input terminal of the differential amplifier circuit;
a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch;
a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively;
a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state;
a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage;
a fourth switch connected to a portion between a gate of the second transistor and the non-inversion input terminal, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and
a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage, the second capacitor being configured to hold the input signal in the output period that is immediately preceding and
wherein the line driver has offset cancel function.
6. A liquid crystal display device for applying an image data voltage signal in a horizontal period that is repeated periodically, the liquid crystal display device including operational amplifier allocated to respective image data voltage signals for amplifying the input signals, the operational amplifier being equipped with a differential amplifier circuit in which a current mirror circuit is incorporated,
wherein the operational amplifier comprises:
a first switch connected to a portion between an inverted input terminal and a non-inverted input terminal of the differential amplifier circuit;
a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch;
a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively;
a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state;
a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage;
a fourth switch connected to a portion between a gate of the second transistor and the non-inverted input terminal, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and
a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage, the second capacitor being configured to hold the image data voltage signal in the horizontal period that is immediately preceding, and
wherein the liquid crystal display device has offset cancel function.