JP2002314421A - Electronic circuit, and liquid crystal device provided with the electronic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption. SOLUTION: In the case of the electronic circuit that converts a digital reference voltage from a reference voltage generating circuit 2 into an analog signal by a digital/analog converter 3, the reference voltage generating circuit 2 and the digital/analog converter 3 employ many operational amplifiers. Applying a prescribed signal (power down) to the electronic as above properly stops the operational amplifiers so as to reduce the power consumption of the electronic circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic circuit having an amplifier circuit such as a voltage follower circuit, and a liquid crystal device provided with the electronic circuit.

[0002]

2. Description of the Related Art There are various types of electronic circuits having an amplifier circuit, and an example of the circuit configuration will be described below with reference to FIG.

The illustrated electronic circuit 31 includes a reference voltage generating circuit 32 for generating a plurality of reference voltages, a latch 37 for sequentially storing digital input data (digital data) in synchronization with the output of the SR, Latch 3
D / which converts the digital data from 7 into an analog signal
A converter 33 and the like.

Among them, the reference voltage generating circuit 32 is generally used.
The structure shown in FIG.
In series between the reference voltage lines Vref0 to Vref1
A plurality of arranged resistive elements R₁, R₂, R₃, R₄When,
These resistance elements R₁, R₂, R₃, R₄Connected to
OP amplifier (amplifier circuit) A with gain 1₃₁, A₃₂,
A₃₃, A₃₄, A₃₅And is constituted by. So
Then, each OP amplifier A ₃₁, A₃₂, A₃₃, A₃₄,
A₃₅Through the five reference voltages ref0-4 are sufficiently low
Output to D / A converter 33 with high impedance
It is supposed to be.

The D / A converter 33 generally has the structure shown in FIG. 12, and the upper two bits of the output signal from the latch 37 are used for the above-mentioned five reference voltages ref0. 4 are selected and the resistor elements R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ are arranged in series between the two reference voltages as shown in FIG. One reference voltage is selected. OP in that part as shown
Since the amplifier (amplifier circuit) A ₃₆ is provided, the impedance is converted to a sufficiently low impedance and output. In the case of the D / A converter shown in FIG. 12, it is necessary to decode a digital signal to generate a signal for controlling each switch, but this is not shown.

The above-described electronic circuit 31 is used in various devices, and a liquid crystal display device as an example is shown in FIG. The liquid crystal display device shown in FIG. 1 includes an active matrix type liquid crystal panel P.
Has a scanning line 40 and a vertical signal line 41, and a switching element 42 and a pixel electrode 43 are arranged at a pixel portion where they intersect.

Next, the operation of the above-described liquid crystal display device will be described with reference to the timing chart of FIG.

The digital signal (video signal) is stored in the first-stage latch 37 in synchronization with the outputs SR1, SR2, SR3, and SR4 of the SR. Next, the LATCH signal is input, and the video signal stored in the first-stage latch 37 is simultaneously transferred to the second-stage latch 37. This video signal is D
The signal is converted into an analog signal by the / A converter circuit 33, S1 is selected at the same time, one switch connected to the D / A converter 33 is selected, and the analog video signal is transferred to the vertical signal line 41. At this time, one scanning line 40 is selected, the pixel switching element 42 connected to the scanning line is turned on, and the video signal is transmitted to the pixel electrode 43.
Write to. This is, as shown in FIG.
The writing of the video signal for one row is completed by continuing with 1, S2, and S3, and similarly, writing is sequentially performed for all the rows, and the display for one screen can be performed.

[0009]

In the case of the above-described electronic circuit, a plurality of OP amplifiers (amplifier circuits) must be provided in the reference voltage generating circuit 32 and each D / A converter 33. Since the power consumption of the amplifiers A ₃₁ ,... Is large, there is a problem that the power consumption of the electronic circuit itself also increases. In particular,
In a liquid crystal display device, the number of D / A converters and the like have increased with the increase in definition and the number of gradations, and the problem has been remarkable.

Accordingly, an object of the present invention is to provide an electronic circuit for preventing an increase in power consumption and a liquid crystal device provided with the electronic circuit.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has a reference voltage generating circuit for generating a plurality of reference voltages, and converting the reference voltage from the reference voltage generating circuit into an analog signal. A plurality of D / A converters for conversion;
Wherein at least one of the reference voltage generation circuit and the D / A converter has an amplifier circuit, and an amplifier control circuit that selectively disables the amplifier circuit. It is characterized by the following.

Further, a liquid crystal device according to the present invention comprises a pair of substrates arranged at a predetermined distance apart from each other, a liquid crystal disposed between the pair of substrates, and a pair of liquid crystal arranged to sandwich the liquid crystal. 3. A liquid crystal device comprising an electrode, and the electronic circuit according to claim 1 or 2 for sending a signal to one of the pair of electrodes.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
An embodiment of the present invention will be described.

The electronic circuit according to the present embodiment includes a reference voltage generating circuit 2 and a plurality of D / A converters 3 as shown in FIG. Among them, the reference voltage generation circuit 2
As shown in detail in FIG. 2, a plurality of reference voltages ref0 to ref
4 and the other D / A converter 3 outputs the reference voltage ref from the reference voltage generation circuit 2.
An analog signal is generated based on 0 to ref4. Then, these reference voltage generating circuits 2 and D
Both or at least one of the / A converters 3 has amplifier circuits A ₁ , A ₂ ,... (See FIGS. 2 and 3). The amplifier circuits A ₁ , A ₂ ,... Are configured to be selectively inactivated by an amplifier control circuit (see FIG. 4).

As the D / A converter 3, as shown in FIG. 3, two consecutive reference voltages out of a plurality of reference voltages ref0 to ref4 from the reference voltage generating circuit 2 are set to an upper bit. (Select according to the upper m-bit data of the n-bit digital data), and select one lower bit between these two reference voltages (select according to the lower nm bit data) (Ie, one that performs conversion in two steps).

The amplifier control means detects the state of the upper m bits of the n-bit digital data during a predetermined period, and controls the amplifier circuit in the unselected reference voltage generating circuit to a non-operating state. It is good to use means. A luminance level of a video to be displayed within a predetermined time is detected, and a circuit unnecessary for displaying the luminance level can be stopped. For example, when the display is to be entirely white in a certain frame period, a circuit for generating a voltage level necessary for displaying, for example, black in the frame period is not required, so that they can be stopped.

Further, the D / A converter has means for lowering the resolution, and the means for lowering the resolution is effective only in the upper m bits of the n-bit digital data and ignores the lower nm bits. Means, lower n
It is preferable that the amplifier circuit in the -m bit conversion circuit is made inoperative by the amplifier control means and controlled to bypass.

Further, the D / A converter has means for lowering the resolution, and the means for lowering the resolution is n.
This is a means for validating only the upper m bits of the bit digital data and ignoring the lower nm bits of data, and for inputting the upper m bits of data to the lower nm bit conversion circuit (desirably. Is n = 2x
m) Further, it is preferable that a part or all of the amplifier circuits for generating the plurality of reference voltages are made inoperative by the amplifier control means and controlled so as to be bypassed.

The invention according to claims 3 and 4 of the present application displays full-tone high-quality images in the normal mode,
In the power saving mode, the number of gray levels to be displayed is reduced to achieve power saving. More specifically, only the upper bits of digital data are valid and the lower bits are ignored to reduce the number of gray levels. I have.

The amplifier circuit according to the present invention has a gain of 1
In addition to the voltage follower circuit described above, a circuit having a gain larger than 1 is also included.

On the other hand, the amplifier control circuit 4 includes: a flag which is set by the data of the upper bits to deactivate the reference voltage generating circuit 2 which is not selected; and a resolution limited by using only the data of the upper bits. D
/ A conversion, and inactivates and bypasses the lower-bit conversion circuit; and inactivates and bypasses some or all of the means for generating the plurality of reference voltages. Input data and limit resolution to D / A
Conversion.

The above-described electronic circuit 1 is preferably used for a liquid crystal device. Specifically, a liquid crystal element is constituted by a pair of substrates arranged at a predetermined distance, a liquid crystal arranged between the pair of substrates, and a pair of electrodes arranged to sandwich the liquid crystal. It is preferable that the above-described electronic circuit is connected to one of the pair of electrodes to transmit a signal. FIG. 5 is a diagram showing an active matrix type liquid crystal element as an example.
A scanning line arranged on one substrate (active matrix substrate) is shown, and reference numeral 41 indicates a vertical signal line arranged on the same substrate. Those scanning lines 40 and vertical signal lines 41
A pixel electrode 43 is connected to each pixel intersecting via a switching element 42, and a video signal is applied to the vertical signal line 41 from the electronic circuit 1.

Next, effects of the present embodiment will be described.

According to the present embodiment, the amplifier circuits A ₁ ,
Since A ₂ ,... Are selectively turned off by the amplifier control circuit 4, the power consumption of the electronic circuit itself can be reduced.

[0025]

The present invention will be described below in more detail with reference to examples.

(Embodiment 1) In this embodiment, as shown in FIG. 1, an electronic circuit 1 was made up of a reference voltage generating circuit 2, a D / A converter 3, a latch 7, and the like.

The reference voltage generating circuit 2 is shown in FIG.
As shown in detail, the two reference voltage lines Vre on the input side
Four resistance elements R between f0 and Vref1₁, R₂, R
₃, R₄And five OP amplifiers
(Amplifier circuit) A₁, A₂, A ₃, A₄, A₅The illustrated
And the two input reference voltages Vr
Five levels of reference voltages re based on ef0 and Vref1
f0 to ref4 are output.

These OP amplifiers A ₁ , A ₂ , A ₃ , A
_4, the _{A 5} represents a control circuit (amplifier control circuit) having the structure shown in FIG. 4 4 connects the signal (power Down0～
4) was input to individually or selectively activate or deactivate as required.

Next, the operation of this embodiment will be described.

Now, in the control circuit 4 shown in FIG.
The two signals (power down 2 to 4) are defined as high signals, and the remaining two signals (power down 0, power down 0,
Assume that 1) is a low signal.

In this case, the OP of the reference voltage generation circuit 2
Amplifier A₁, A₂, A₃, A₄, A ₅Of which, high
Three signals (power down 2-4) input
OP Amplifier A₃~ A₅Is a switch Sw shown in FIG.
1 and Sw2 are conducting and switch Sw3 is non-conducting.
All current paths in the circuit are interrupted and the output
It becomes an impedance state. As a result, these O
P amplifier A₃~ A₅Is in the non-operating state (power saving mode).
You.

On the other hand, the OP amplifiers A ₁ and A ₂ , to which the low signal has been input, switch the switch Sw by the inverted signal of the power down signal, the power down B signal.
When the switch 3 is conducting, the switches Sw1 and Sw2 become non-conducting and become active, so that the output is in a sufficiently low impedance state (that is, a normal mode in which it is operating). As described above, the control circuit 4 is a circuit that can select only a necessary reference voltage level by referring to the upper two bits.

For example, in FIG. 2, when the upper two bits of digital data are only (00) in a certain period,
The actually required reference voltage levels are only ref0,1. As described above in such a case OP amplifier A ₃ ~
Without problems with the A ₅ inoperative, power can be saved by doing so.

That is, the upper two bits of digital data (here, 0 bits) are set within a predetermined period.
0, 01, 10, and 11), there is no data that appears, in other words, when there are few types of data that appear as higher-order data (for example, an image with a small change in luminance is displayed on a liquid crystal display device). In such a case, for example, when there is little change in digital data during a certain period), the power consumption can be significantly reduced by applying this embodiment. Therefore, the power consumption can be reduced by applying this embodiment, which is effective when the battery is used.

(Embodiment 2) In this embodiment, the D / A converter 3 having the structure shown in FIG. 3 was used. Other configurations (for example, the reference voltage generation circuit 2 and the latch 7) are the same as those in the first embodiment.

In this embodiment, when the D / A converter 3 is to be driven (normal mode), power
What is necessary is just to make a down signal into a low signal. This allows
Switch Sw5 is conductive, because the switch Sw4 is that the operating state of the OP amplifier A ₆ becomes nonconductive, become similar to the circuit shown in the circuit is consequently 12 shown in FIG, D / A converter It becomes a driving state as 3.

On the other hand, when the D / A converter 3 is to be set in the non-drive state (power saving mode),
What is necessary is just to make a down signal into a high signal. As a result, the switch Sw4 becomes conductive, and the OP amplifier A ₆
Is turned off and the switch Sw5 is turned off, so that the lower two bits of the digital data are don't care, and as a result, the analog output is higher than the upper two bits.
Determined by bits only. At this time, the analog output is r only by the upper two bits of the digital data.
One of ef1 to ef4 is output. At this time, the analog output can be directly output by the voltage follower circuit (amplifier circuit) that outputs ref1 to ref4 through the series-connected resistor elements in the drawing, and thus can be fixed with a sufficiently low impedance.

[0038] As described above, in this embodiment, by limiting the resolution of the D / A (the lower two bits of the digital data and do not care), the OP amplifier A ₆ included in each D / A circuit non It can be operated to save power. For example, in the case of a device that is frequently used outdoors, such as a digital camera or a camcorder, the display image on the liquid crystal panel may have a low number of gradations as long as the composition and focus of the image can be confirmed. In such a case, the power consumption can be reduced by applying this embodiment, which is particularly effective when the battery is used.

(Embodiment 3) In this embodiment, a reference voltage generating circuit having a structure indicated by reference numeral 12 in FIG. 7 was used. Other configurations were the same as in the first embodiment. Then, the reference voltage generating circuit 12, and to power down signal may only enter into the three OP amplifier _{A 12, A 13, A 14} .

When the user wants to enter the power saving mode,
The power down signal is changed to a high signal. As a result, the OP amplifiers A ₁₂ , A ₁₃ , and A _{14 are in a} non-operating state, ref 1 to 3 are in a high impedance state, and only ref 0 and ref 4 are supplied.

That is, in this embodiment, as in the second embodiment, the power consumption can be reduced by lowering the resolution.

(Embodiment 4) In this embodiment, a reference voltage generating circuit having a structure indicated by reference numeral 22 in FIG. 8 was used. Other configurations were the same as in the first embodiment. In the reference voltage generating circuit 22, when the power saving mode, all of the OP amplifier _{A 21, A 22, A 23} , A 24, A 2 5 is inoperative, the switch Sw6, Sw7 is in a conductive state, Vr
ef0,1 is bypassed to ref0,4.

According to this embodiment, the same effect as that of the third embodiment can be obtained.

(Embodiment 5) In this embodiment, a D / A converter having a structure indicated by reference numeral 13 in FIG. 9 was used. Other configurations were the same as those of the first embodiment.

When a low signal is input as a power down signal, the switches Sw10, Sw13, Sw1
4 are conducting, the switches Sw11, Sw12, Sw1
5 is in a non-conductive state, and as a result, the circuit is driven as a D / A converter as in the circuit shown in FIG. 12 (normal mode).

On the other hand, as a power down signal, h
When the high signal is input, the switches Sw11, Sw1
2 and Sw15 are conducting, the switches Sw10 and Sw1
3, Sw14 becomes non-conductive. As a result, this circuit becomes a circuit for performing D / A conversion between ref0 and ref4 by serial resistance division with the upper two bits, and the lower two bits become don't care. That is, ref1 to ref3 are not used, and it is possible to realize power saving by limiting the resolution.

According to this embodiment, the same effect as that of the third embodiment can be obtained.

In the above description, the digital data is 4 bits, and the D / A conversion is performed in two steps by dividing these into the upper 2 bits and the lower 2 bits.
These can be easily extended to more bits, and the upper and lower bits do not necessarily have to have the same number of bits, but can be arbitrarily selected by the designer to meet the requirements of the system design. Needless to say, there is.

[0049]

As described above, according to the present invention,
Since the amplifier circuit is configured to be selectively inactivated by the amplifier control circuit, the power consumption of the electronic circuit itself can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the structure of an electronic circuit according to the present invention.

FIG. 2 is a diagram illustrating an example of a structure of a reference voltage generation circuit used in an electronic circuit.

FIG. 3 is a diagram illustrating an example of the structure of a D / A converter used in an electronic circuit.

FIG. 4 is a diagram illustrating an example of a structure of a control circuit connected to an electronic circuit.

FIG. 5 illustrates an example of a structure of a liquid crystal device to which an electronic circuit is applied.

FIG. 6 is a diagram showing an example of a detailed structure of an OP amplifier used in an electronic circuit.

FIG. 7 is a diagram showing another example of the structure of the reference voltage generation circuit used in the electronic circuit.

FIG. 8 is a diagram showing another example of the structure of the reference voltage generation circuit used in the electronic circuit.

FIG. 9 is a diagram showing another example of the structure of the D / A converter used in the electronic circuit.

FIG. 10 is a diagram showing an example of the structure of a conventional electronic circuit.

FIG. 11 is a diagram showing an example of the structure of a conventional reference voltage generation circuit.

FIG. 12 is a diagram showing an example of the structure of a conventional D / A converter.

FIG. 13 is a timing chart showing the operation of a conventional liquid crystal device.

[Explanation of symbols]

1 electronic circuit 2 the reference voltage generating circuit 3 D / A converter 4 voltage follower control circuit (amplifier control circuit) 41 vertical signal lines (electrodes) _A 1, _{A 2} ... OP amplifier (amplifier circuit)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/36 G09G 3/36 H03M 1/70 H03M 1/70 F term (Reference) 2H093 NA16 NA51 NC26 ND39 5C006 AF54 AF68 AF69 AF82 BB15 BC11 BC16 BF26 BF43 FA47 5C080 AA10 BB05 DD26 JJ02 JJ03 JJ04 5J022 AB09 BA08 CB00 CD04 CE08 CF02 CF07 CF09

Claims (6)

[Claims] 1. An electronic circuit comprising: a reference voltage generation circuit for generating a plurality of reference voltages; and a plurality of D / A converters for converting a reference voltage from the reference voltage generation circuit into an analog signal. An electronic circuit, characterized in that at least one of a voltage generation circuit and the D / A converter has an amplifier circuit, and an amplifier control circuit for selectively inactivating the amplifier circuit. 2. The D / A converter selects two reference voltages among a plurality of reference voltages from the reference voltage generation circuit in accordance with upper m bits of n-bit digital data, and selects these two references. 2. The electronic circuit according to claim 1, wherein one of the voltages is selected according to data of lower nm bits, between the voltages. 3. 3. The amplifier control means detects a state of m high-order bits of n-bit digital data in a predetermined period, and controls an amplifier circuit in a reference voltage generating circuit which is not selected to a non-operating state. 3. The electronic circuit according to claim 2, wherein the electronic circuit is means. 4. The D / A converter has means for lowering the resolution, and the means for lowering the resolution is effective only in the upper m bits of the n-bit digital data and ignores the lower nm bits. Means, the lower nm
3. The electronic circuit according to claim 2, wherein the electronic circuit is a means for controlling the amplifier circuit in the bit conversion circuit to be inoperative and bypassed by the amplifier control means. 5. The D / A converter has means for lowering the resolution, wherein the means for lowering the resolution is effective only in the upper m bits of the n-bit digital data and the lower nm bits are Means for ignoring, and means for inputting upper m-bit data to a lower nm-bit conversion circuit (preferably n = 2 × m);
3. The electronic device according to claim 2, wherein the amplifier control unit controls a part or all of the plurality of reference voltage generating units to be inoperative and bypassed. circuit. 6. A liquid crystal element comprising: a pair of substrates disposed at a predetermined distance apart from each other; a liquid crystal disposed between the pair of substrates; and a pair of electrodes disposed so as to sandwich the liquid crystal. A liquid crystal device comprising: the electronic circuit according to claim 1, wherein a signal is transmitted to one of the pair of electrodes.