Liquid crystal driving circuit, semiconductor integrated circuit device, reference voltage buffering circuit, and method for controlling the same

• US 6,982,706 B1
• Filed: 08/31/2000
• Issued: 01/03/2006
• Est. Priority Date: 12/16/1999
• Status: Expired due to Fees

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Nishi, Kazuyoshi, Doi, Yasuyuki, Oomori, Tetsuro
• Primary Examiner(s): Lefkowitz, Sumati
• Assistant Examiner(s): ENGLISH, ALECIA DIANE
• Application Number:
  US10/019,437
• Time in Patent Office: 1,951 Days
• Field of Search: 345/87, 345/519, 345/204, 345/214, 345/206, 345/55
• US Class Current: 345/206
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3688 suitable for active matrices only
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

A source driver 4A arranged on a liquid crystal panel includes therein in-chip reference voltage wires 17 extending from one end to the other end of an LSI chip. The source driver 4A includes therein: branch reference voltage wires 17a branching off from in-chip reference voltage wires 17; reference voltage production buffers 31; a control circuit 30 for controlling the reference voltage production buffers 31; a reference voltage production resistor section 32 for subdividing the reference voltage into values of n steps; voltage level selection circuits 34 each for selecting one of the subdivided voltages; and output buffers 35. Since the reference voltages are supplied to each source driver 4 via wiring for connecting the in-chip reference voltage wires 17 in series with one another, the wiring structure for supplying the reference voltages can be simplified.

Claims

1. A reference voltage buffering circuit provided in a source driver circuit for driving a liquid crystal element of a liquid crystal module, wherein:

the reference voltage buffering circuit comprises two buffering circuits arranged in parallel to each other between an input-side node for receiving an externally produced reference voltage as an input voltage and an output-side node for sending out an output voltage; and

each buffering circuit of the two buffering circuits includes;

an operator for receiving the input voltage at one terminal and an output voltage of the operator itself at the other terminal, and operating so that the output voltage of the operator is substantially equal to the input voltage;

a capacitor including a first electrode and a second electrode and capable of storing a charge corresponding to a voltage difference between the input voltage and the output voltage of the operator;

a first node connected to the first electrode of the capacitor;

a second node connected to the second electrode of the capacitor;

a third node for receiving an output signal from the operator;

a first switching element provided between the second node and the third node;

a second switching element provided between the first node and the input-side node input side of the operator;

a third switching element provided between the first node and the output-side node; and

a fourth switching element provided between the third node and the output-side node.

2. The reference voltage buffering circuit of claim 1, each buffering circuit of the two buffering circuits further comprising a closed circuit added to the second node, the closed circuit including therein a fifth switching element for compensating an electric change in the second node due to switching of the first switching element.

3. A method for controlling a reference voltage buffering circuit, including two buffering circuits arranged in parallel to each other, each buffering circuit of the two buffering circuits including:

an operator provided between an input-side node and an output-side node for operating so that an output voltage of the operator is substantially equal to an input voltage provided via the input-side node;

a capacitor including a first electrode and a second electrode;

a first node connected to the first electrode of the capacitor;

a second node connected to the second electrode of the capacitor;

a third node for receiving an output signal from the operator;

a first switching element provided between the second node and the third node;

a second switching element provided between the first node and the input-side node of the operator;

a third switching element provided between the first node and the output-side node; and

a fourth switching element provided between the third node and the output-side node, wherein;

in each buffering circuit of the two buffering circuits, in an output mode in which a reference voltage is output from the buffering circuit, the third and fourth switching elements are placed in a conductive state while the first and second switching elements are placed in a non-conductive state; and

in a charge storing mode in which the capacitor of the buffering circuit stores a charge, the third and fourth switching elements are placed in a non-conductive state while the first and second switching elements are placed in a conductive state.

4. The method for controlling a reference voltage buffering circuit of claim 3, wherein:

each buffering circuit of the two buffering circuits of the reference voltage buffering circuit further includes a closed circuit added to the second node, the closed circuit including therein a fifth switching element for canceling out an electric change in the second node due to switching of the first switching element; and

when the first switching element is switched between a conductive state and a non-conductive state from one to another, the fifth switching element is switched reversely in an interlocking manner.

5. The method for controlling a reference voltage buffering circuit of claim 3 or 4, wherein:

when switching from a state where one of the two buffering circuits is in the output mode while the other buffering circuit is in the charge storing mode to another state where the one buffering circuit is in the charge storing mode while the other buffering circuit is in the output mode,

the third and fourth switching elements of the other buffering circuit are switched to a conductive state after the third and fourth switching elements of the one buffering circuit are switched to a non-conductive state.

6. The method for controlling a reference voltage buffering circuit of claim 5, wherein:

when the third and fourth switching elements of the one buffering circuit are switched to a non-conductive state, the third switching element is switched to a non-conductive state after the fourth switching element is switched to a non-conductive state; and

when the third and fourth switching elements of the other buffering circuit are switched to a conductive state, the fourth switching element is switched to a conductive state after the third switching element is switched to a conductive state.

7. A liquid crystal driving circuit for driving a liquid crystal element on a liquid crystal panel, the liquid crystal driving circuit comprising:

a plurality of source driver circuit devices on the liquid crystal panel, each source driver circuit device including;

a plurality of input-side pads, each input-side pad receiving a reference voltage;

a plurality of output-side pads, each output-side pad outputting the reference voltage;

a plurality of in-chip reference voltage wires, each in-chip reference voltage wire directly connecting each input-side pad to each output-side pad to transmit the reference voltage;

a plurality of branch reference voltage wires, each branch reference voltage wire branching off from each in-chip reference voltage wire and transmitting the reference voltage in parallel with each in-chip reference voltage wire;

a plurality of buffers, each buffer coupled to each branch reference voltage wire and outputting an output voltage in response to the reference voltage transmitted by each branch reference voltage wire and capable of preventing an electric current from flowing via each branch reference voltage wire; and

a selection circuit selecting a voltage for driving the liquid crystal element in response to output voltages of the plurality of buffers,

a plurality of inter-chip reference voltage wire units, each inter-chip reference voltage wire unit interposed between any two adjacent source driver circuit devices of the plurality of source driver circuit devices and including a plurality of inter-chip reference voltage wires, each inter-chip reference voltage wire connecting each output-side pad of one source driver circuit device of the two adjacent source driver circuit devices to each input-side pad of the other source driver circuit device of the two adjacent source driver circuit devices;

a reference voltage production circuit capable of producing a plurality of reference voltages to drive the plurality of source driver circuit devices; and

a reference voltage providing wire unit capable of receiving the plurality of reference voltages and providing the plurality of reference voltages to one of the plurality of source driver circuit devices and including a plurality of reference voltage providing wires, each reference voltage providing wire coupled to each in-chip reference voltage wire via each input-side pad of the one of the plurality of source driver circuit devices to provide a reference voltage.

8. The liquid crystal driving circuit of claim 7, each source driver circuit device of the plurality of source driver circuit devices further comprising a subdivided voltage production circuit, the subdivided voltage production circuit receiving the output voltages of the plurality of buffers and capable of producing subdivided voltages in response to the output voltages of the plurality of buffers and outputting the subdivided voltages to the selection circuit,

wherein the selection circuit selects one of the subdivided voltages as the voltage for driving the liquid crystal element.

9. The liquid crystal driving circuit of claim 7, wherein the plurality of buffers include a first buffer receiving a positive-side reference voltage having a higher voltage than a predetermined voltage and a second buffer receiving a negative-side reference voltage having a lower voltage than the predetermined voltage,

each source driver circuit device of the plurality of source driver circuit devices further includes:

a positive-side voltage production circuit receiving an output voltage of the first buffer so as to produce positive subdivided voltages and outputting the positive subdivided voltages to the selection circuit; and

a negative-side voltage production circuit receiving an output voltage of the second buffer so as to produce negative subdivided voltages and outputting the negative subdivided voltages to the selection circuit, and

the selection circuit of each source driver circuit device selects a positive output and a negative output from the positive subdivided voltages and the negative subdivided voltages such that any two adjacent wires each coupled to a liquid crystal element alternately receive the positive output and the negative output at regular time intervals.

10. The liquid crystal driving circuit of claim 7, wherein each buffer of the plurality of buffers of each source driver circuit device of the plurality of source driver circuit devices has an offset canceling function capable of reducing a potential difference between an input voltage and an output voltage.

11. The liquid crystal driving circuit of claim 10, wherein each buffer of the plurality of buffers of each source driver circuit device of the plurality of source driver circuit devices includes:

an operator capable of receiving an input voltage of the buffer at one terminal and an output voltage of the operator at the other terminal, so as to operate such that the output voltage is substantially equal to the input voltage;

a capacitor including a first electrode and a second electrode and capable of storing a charge corresponding to a voltage difference between the input voltage and the output voltage;

a first node connected to the first electrode of the capacitor;

a second node connected to the second electrode of the capacitor;

a third node for receiving the output voltage from the operator;

a first switching element provided between the second node and the third node;

a second switching element provided between the first node and the one terminal of the operator;

a third switching element provided between the first node and the third node.

12. The liquid crystal driving circuit of claim 11, each buffer of the plurality of buffers of each source driver circuit device of the plurality of source driver circuit devices further comprising a closed circuit added to the second node, the closed circuit including therein a fourth switching element for compensating an electric change in the second node due to the switching of the first switching element.

13. The liquid crystal driving circuit of claim 10, wherein each buffer of the plurality of buffers of each source driver circuit device of the plurality of source driver circuit devices includes two buffering circuits arranged in parallel to each another between an input-side node for receiving an input voltage of each buffer of the plurality of buffers and an output-side node for sending an output voltage of each buffer of the plurality of buffers, each buffering circuit of the two buffering circuits including:

an operator capable of receiving the input voltage of the buffer at one terminal via the input-side node and an output voltage of the operator at the other terminal, so as to operate such that the output voltage of the operator is substantially equal to the input voltage;

a capacitor including a first electrode and a second electrode and capable of storing a charge corresponding to a voltage difference between the input voltage and the output voltage of the operator;

a first node connected to the first electrode of the capacitor;

a second node connected to the second electrode of the capacitor;

a third node for receiving an output voltage from the operator;

a first switching element provided between the second node and the third node;

a second switching element provided between the first node and the input-side node of the operator;

a third switching element provided between the first node and the output-side node; and

a fourth switching element provided between the third node and the output-side node.

14. The liquid crystal driving circuit of claim 13, each buffering circuit of the two buffering circuits further comprising a closed circuit added to the second node, the closed circuit including therein a fifth switching element for compensating an electric change in the second node due to switching of the first switching element.

15. A semiconductor integrated circuit device provided in a liquid crystal module having a liquid crystal element, the semiconductor integrated circuit comprising:

a plurality of input-side pads, each input-side pad receiving a reference voltage;

a plurality of output-side pads, each output-side pad outputting the reference voltage;

a plurality of in-chip reference voltage wires, each in-chip reference voltage wire directly connecting each input-side pad to each output-side pad to transmit the reference voltage;

a plurality of branch reference voltage wires, each branch reference voltage wire branching off from each in-chip reference voltage wire and transmitting the reference voltage in parallel with each in-chip reference voltage wire;

a plurality of buffers, each buffer coupled to each branch reference voltage wire and outputting an output voltage in response to the reference voltage transmitted by each branch reference voltage wire and capable of preventing an electric current from flowing via each branch reference voltage wire; and

a selection circuit selecting a voltage for driving the liquid crystal element in response to output voltages of the plurality of buffers.

16. The semiconductor integrated circuit device of claim 15, further comprising a subdivided voltage production circuit receiving the output voltages of the plurality of buffers and capable producing subdivided voltages in response to the output voltages of the plurality of buffers and outputting the subdivided voltages to the selection circuit,

wherein the selection circuit selects one of the subdivided voltages as the voltage for driving the liquid crystal element.

17. The semiconductor integrated circuit device of claim 15, further comprising a positive-side voltage production circuit receiving an output voltage of a first buffer of the plurality of buffers so as to produce positive subdivided voltages and outputting the positive subdivided voltages to the selection circuit;

and

a negative-side voltage production circuit receiving an output voltage of a second buffer of the plurality of buffers so as to produce negative subdivided voltages and outputting the negative subdivided voltages to the selection circuit,

wherein the first buffer receives a positive-side reference voltage having a higher voltage than a predetermined voltage, and the second buffer receives a negative-side reference voltage having a lower voltage than the predetermined voltage,

the selection circuit selects a positive output and a negative output from the positive subdivided voltages and the negative subdivided voltages such that any two adjacent wires each coupled to a liquid crystal element alternately receive the positive output and the negative output at regular time intervals.

18. The semiconductor integrated circuit device of claim 15, wherein each input-side pad is configured along one side of the semiconductor integrated circuit device, and

each output-side pad is configured along another side of the semiconductor integrated circuit device.

19. The semiconductor integrated circuit device of claim 15, wherein each buffer of the plurality of buffers has an offset canceling function capable of reducing a potential difference between an input voltage and an output voltage.

20. The semiconductor integrated circuit device of claim 19, wherein each buffer of the plurality of buffers includes:

an operator capable of receiving an input voltage of the buffer at one terminal and an output voltage of the operator at the other terminal, so as to operate such that the output voltage is substantially equal to the input voltage;

a capacitor including a first electrode and a second electrode and capable of storing a charge corresponding to a voltage difference between the input voltage and the output voltage;

a first node connected to the first electrode of the capacitor;

a second node connected to the second electrode of the capacitor;

a third node for receiving the output voltage from the operator;

a first switching element provided between the second node and the third node;

a second switching element provided between the first node and the one terminal of the operator;

a third switching element provided between the first node and the third node.

21. The semiconductor integrated circuit device of claim 20, each buffer of the plurality of buffers further comprising a closed circuit added to the second node, the closed circuit including therein a fourth switching element for compensating an electric change in the second node due to the switching of the first switching element.

22. The semiconductor integrated circuit device of claim 19, wherein each buffer of the plurality of buffers includes two buffering circuits arranged in parallel to each another between an input-side node for receiving an input voltage of the buffer and an output-side node for sending an output voltage of the buffer, each buffering circuit of the two buffering circuits including:

an operator capable of receiving the input voltage of the buffer at one terminal via the input-side node and an output voltage of the operator at the other terminal, so as to operate such that the output voltage of the operator is substantially equal to the input voltage;

a capacitor including a first electrode and a second electrode and capable of storing a charge corresponding to a voltage difference between the input voltage and the output voltage of the operator;

a first node connected to the first electrode of the capacitor;

a second node connected to the second electrode of the capacitor;

a third node for receiving an output voltage from the operator;

a first switching element provided between the second node and the third node;

a second switching element provided between the first node and the input-side node of the operator;

a third switching element provided between the first node and the output-side node; and

a fourth switching element provided between the third node and the output-side node.

23. The semiconductor integrated circuit device of claim 22, each buffering circuit of the two buffering circuits further comprising a closed circuit added to the second node, the closed circuit including therein a fifth switching element for compensating an electric change in the second node due to switching of the first switching element.