Ramp voltage generating apparatus and active matrix drive-type display apparatus
A ramp voltage generating apparatus according to the present invention includes a ramp voltage generating circuit for generating a plurality of ramp voltages out of phase with each other from one ramp voltage, and a control circuit. The ramp voltage generating circuit includes a plurality of voltage generating circuit portions connected in parallel to a voltage input terminal. Each voltage generating circuit portion includes a voltage output terminal, a capacitor, an operational amplifier, a first switch, a second switch and a third switch. The control circuit turns on the third switches while shifting the time point of switching each of the third switches from off to on state, and the control circuit turns off the first switches and, also, turns on the second switches during the period including the fall time point of the ramp voltage input to the voltage input terminal.
1. A ramp voltage generating apparatus comprising:
a voltage output circuit for outputting a ramp voltage;
a ramp voltage generating circuit for generating a plurality of ramp voltages out of phase with each other from the ramp voltage; and
a control circuit for controlling an operation of the ramp voltage generating circuit, wherein
the ramp voltage generating circuit includes a plurality of voltage generating circuit portions connected in parallel to a voltage input terminal to be supplied with the ramp voltage output from the voltage output circuit,
each of the voltage generating circuit portions includes:
a voltage output terminal;
a capacitor arranged on a line extending from the voltage input terminal to the voltage output terminal;
an amplifier arranged on the portion of the line closer to the voltage output terminal than to the capacitor;
a first switching element interposed between the capacitor and the amplifier on the line;
a second switching element arranged on a feedback line connecting a output terminal of the amplifier and a connecting point of the capacitor and the first switching element; and
a third switching element arranged on a power supply line connected to the connecting point,
the control circuit turns on the third switching elements of the plurality of voltage generating circuit portions while shifting the time point of switching each of the third switching elements from off to on state, and
the control circuit turns off the first switching elements and, also, turns on the second switching elements of the plurality of voltage generating circuit portions during the period including the fall time point and the rise time point of the ramp voltage input to the voltage input terminal.
2. The ramp voltage generating apparatus according to claim 1 , wherein
the control circuit can output and supply a first power source voltage or a second power source voltage to each connecting point through the power supply line connected to each third switching element of each voltage generating circuit portion when the third switching element is in an on state, and
the control circuit outputs the first power source voltage during part of the on-period of each third switching element and, also, outputs the second power source voltage during the period including the time point of turning each third switching element from on to off state.
3. The ramp voltage generating apparatus according to claim 1 , wherein
the control circuit controls the on/off operation of the second switching element and the third switching element in such a manner that the on-period of the second switching element and the on-period of the third switching element do not overlap.
4. An active matrix drive-type display apparatus comprising a display panel including a plurality of pixels arranged in a matrix, each pixel of the display panel including a display element for emitting light when supplied with power and a drive circuit for comparing a data voltage supplied from outside the pixel with a ramp voltage and supplying power to the display element in accordance with the result of comparison, wherein
the display apparatus comprises:
a voltage output circuit for outputting the ramp voltage;
a ramp voltage generating circuit for generating ramp voltages for a plurality of horizontal lines constituting one screen based on the ramp voltage output from the voltage output circuit; and
a control circuit for controlling an operation of the ramp voltage generating circuit,
the ramp voltage generating circuit includes a plurality of voltage generating circuit portions connected in parallel to a voltage input terminal to be supplied with the ramp voltage output from the voltage output circuit,
each of the voltage generating circuit portions includes:
a voltage output terminal connected to pixels on one or more horizontal lines;
a capacitor arranged on a line extending from the voltage input terminal to the voltage output terminal;
an amplifier arranged on the portion of the line closer to the voltage output terminal than to the capacitor;
a first switching element interposed between the capacitor and the amplifier on the line;
a second switching element arranged on a feedback line connecting a output terminal of the amplifier and a connecting point of the capacitor and the first switching element; and
a third switching element arranged on a power supply line connected to the connecting point,
the control circuit turns on the third switching elements of the plurality of voltage generating circuit portions while shifting the time point of switching each of the third switching elements from off to on state, and
the control circuit turns off the first switching elements and, also, turns on the second switching elements of the plurality of voltage generating circuit portions during the period including the fall time point and the rise time point of the ramp voltage input to the voltage input terminal.
5. The active matrix drive-type display apparatus according to claim 4 , wherein
the control circuit includes a scanning driver and a data driver connected to the display panel,
each pixel of the display panel includes a write element turned on upon application thereto of a scanning voltage from the scanning driver, and a voltage holding unit for holding the data voltage applied thereto from the data driver when the write element is in an on state,
the drive circuit compares the output voltage of the voltage holding unit with the ramp voltage generated by the ramp voltage generating circuit, and
the third switching element of each of the voltage generating circuit portions is turned on/off in accordance with the scanning voltage from the scanning driver.
6. The active matrix drive-type display apparatus according to claim 4 , wherein
the control circuit includes a scanning driver and a data driver connected to the display panel,
each pixel of the display panel includes a write element turned on upon application thereto of a scanning voltage from the scanning driver, and a voltage holding unit for holding a data voltage applied thereto from the data driver when the write element is in an on state,
the drive circuit compares the output voltage of the voltage holding unit with the ramp voltage generated by the ramp voltage generating circuit,
the third switching element of each of the voltage generating circuit portions is turned on/off in accordance with an on/off control signal, and
the ramp voltage generating circuit generates the on/off control signal for the third switching element of each of the voltage generating circuit portions based on the scanning voltage from the scanning driver.
7. The active matrix drive-type display apparatus according to claim 4 , wherein
the ramp voltage output from the voltage output circuit falls or rises during a blanking period with a cycle equal to an integer multiple of one horizontal scanning period or one vertical scanning period.
8. The active matrix drive-type display apparatus according to claim 5 , wherein
the ramp voltage output from the voltage output circuit falls or rises during a blanking period with a cycle equal to an integer multiple of one horizontal scanning period or one vertical scanning period.
9. An active matrix drive-type display apparatus comprising a display panel including a plurality of pixels arranged in a matrix, each pixel of the display panel including a display element for emitting light when supplied with power and a drive circuit for supplying power to the display element in accordance with a data voltage supplied from outside the pixel, wherein
the display apparatus comprises:
a voltage output circuit for outputting a ramp voltage;
a ramp voltage generating circuit for generating ramp voltages for a plurality of horizontal lines constituting one screen based on the ramp voltage output from the voltage output circuit; and
a control circuit for controlling an operation of the ramp voltage generating circuit,
the ramp voltage generating circuit includes a plurality of voltage generating circuit portions connected in parallel to a voltage input terminal to be supplied with the ramp voltage output from the voltage output circuit,
each of the voltage generating circuit portions includes:
a voltage output terminal connected to pixels on one or more horizontal lines;
a capacitor arranged on a line extending from the voltage input terminal to the voltage output terminal;
an amplifier arranged on the portion of the line closer to the voltage output terminal than to the capacitor;
a first switching element interposed between the capacitor and the amplifier on the line;
a second switching element arranged on a feedback line connecting a output terminal of the amplifier and a connecting point of the capacitor and the first switching element; and
a third switching element arranged on a power supply line connected to the connecting point,
the control circuit turns on the third switching elements of the plurality of voltage generating circuit portions while shifting the time point of switching each of the third switching elements from off to on state, and
the control circuit turns off the first switching elements and, also, turns on the second switching elements of the plurality of voltage generating circuit portions during the period including the fall time point and the rise time point of the ramp voltage input to the voltage input terminal.
10. The active matrix drive-type display apparatus according to claim 9 , wherein
the control circuit includes a scanning driver and a data driver connected to the display panel,
each pixel of the display panel includes a write element turned on upon application thereto of a scanning voltage from the scanning driver, and a voltage holding unit for holding the data voltage applied thereto from the data driver when the write element is in an on state,
the drive circuit supplies power to the display element in accordance with the data voltage held by the voltage holding unit and the ramp voltage generated, when the write element is in an off state, by the ramp voltage generating circuit, and
the control circuit can output and supply a first power source voltage or a second power source voltage to each connecting point through the power supply line connected to each third switching element of each voltage generating circuit portion when the third switching element is turned on; turns on the third switching element of the voltage generating circuit portion having the voltage output terminal connected to the pixel having the write element in the on state and, also, outputs the first power source voltage when the write element of the pixel is in the on state; and after the write element is turned from on to off state, keeps the third switching element on for a predetermined period of time and switches the output voltage from the first power source voltage to the second power source voltage during the predetermined period of time.
11. The active matrix drive-type display apparatus according to claim 10 , wherein
a difference voltage between the first power source voltage and the second power source voltage is adjustable.