JPS6046717B2 - Driving method of liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system for reducing driving power consumption in matrix driving of a display device.

FIG. 1 shows a matrix drive signal for a conventionally commonly used liquid crystal display device, and FIG. 2 shows an example of the matrix drive signal as an embodiment of the present invention. The example in FIG. 2 is shown in correspondence with the example in FIG. In Figure 1, two digit drive electrodes are used, and each digit drive electrode has D, ', and D.

'Apply the signal. This digit drive signal has a potential level of 0)V)2V. Display of display elements (hereinafter referred to as segments) at the intersection of the matrix for this digit drive signal,
5,′,52′,53′,s,corresponding to the hidden state.
' signal is applied to each segment drive electrode. Here, each segment signal has a potential level of 0 and 2V. Second
The digit electrode drive signals D,,D shown in the figure.

In addition to time T when the potentials are different, there are four times per driving cycle when the potentials are at the same potential at the same time. That is, the duty of the digit drive signal is modulated. Each segment drive signal 5,,S. , Ba, and S also have a time period in which they reach the same potential twice in each driving cycle depending on the state.
Therefore, segment drive signals 5, 50, 50, 50 are also 0.
)V) has a potential level of 2V. FIG. 3 shows a voltage waveform diagram between liquid crystal electrodes. Figures 3a and 3b are examples of display and non-display segments when the conventional drive signal of Figure 1 is applied, and Figures 3c and d are display and non-display segments when the drive signal of Figure 2 is applied.
FIG. 7 is an interelectrode voltage waveform diagram of a non-display segment.

In FIG. 3c, there are two times in each drive period when the interelectrode voltage becomes o, but the waveform is different from that in FIG. 3a. 28! below, compared to the conventional drive signal shown in FIG. The reason why the drive power consumption is reduced when the drive signal is i will be explained.

Although this example uses two-division matrix drive and two-power supply drive, the same applies to general multi-division matrix drive and multi-power supply drive. FIG. 4 shows matrix drive signals D1'', S1'' and D1, S1 shown in FIGS. 1 and 2.
The signal is shown, and the time divisions of the potential state within each cycle of driving are assumed to be 1'' to 4'' and 1 to 5.

FIG. 5a schematically shows the connection of the power supply applied to the liquid crystal display device 10, in which blocks 11 are digit electrodes, blocks 12 are
The blocks indicate the state of the voltage applied to the segment electrodes.

FIG. 5b is a diagram showing combinations of voltage states of the electrodes of the liquid crystal display device when the voltages applied to the digit electrodes are 01V, 2V and the voltages applied to the segment electrodes are 01V, 2V. .

For example, in the block number 13, the digit electrode D is connected to the B terminal, the voltage V segment electrode S is connected to the E terminal, and the voltage is 2V, and similarly in the block 14, the digit electrode is 2V, and the segment electrode is in the O voltage state. It shows that it is connected.

Nine such combinations are shown. Figure 5 C is the fourth
Voltage transition diagram for each time segment of the D1″ and S1″ signals in the figure,
Figures 5C and b show voltage transition diagrams for each time segment of the Dl and Sl signals in Figure 4.The waveform portions in Figure 4 are marked with the same numbers.If the liquid crystal is regarded as one capacitor, If the capacitance is C, then if a capacitor with a capacitance C maintains a voltage V, the charge stored therein is Q=CV.

To add charge DQ to it, work of VdQ must be done, and the work DU at that time is integrated from Q=0 to Q, and this is the energy transfer that occurs in the process of charging the capacitor.

Looking at the energy transfer by the conventional drive system shown in FIG. 5C, in the steps 2''-3'' and 4''-1'' each performs 6 QV of work on the power source.

Also, 1″→2″ and 3″→4″ each receive QV work from the power supply, and 4″→2″→3″-4″→
In a cycle of 1", 10 QV of work is done on the power supply. Looking at the energy transfer of the drive method according to the present invention shown in Figure 5 d, in the process of 3→4 and 6→1, work is done on the power supply of 10 QV. They each do 4 QV's work.

Also, work is zero for 2→3 and 5→6. In the end 1 →
In the cycle 2 → 3 → 4 → 5 → 6 → 1, 6
He will be working as a QV. The above example is a case of a displayed segment, but the energy loss per each period of driving is 6110 compared to the conventional one, and 40% of energy is saved.

For the hidden segments, the energy consumption is the same for the drive waveforms in Figures 1 and 2, 2QV each.
becomes. The driving method shown in FIG. 2 is for the l'2 bias method, but in the case of the driving method using the 113/'<ias method, the driving method according to the present invention saves 50% of energy for non-display segments.

As explained above, the drive method according to the present invention adds a path for discharging the charges stored in both electrodes of the liquid crystal without passing through the power supply in at least part of the process, thereby reducing the power consumption of the liquid crystal drive. It is possible to save. The driving method shown in Figure 2 is an example in which the voltage applied to the display and non-display states of the intersection of the matrix is the same on average, and the effective voltage is equal in each state, but when a certain segment is displayed, If the ratio of the voltage applied to the segment is higher than the average, the voltage applied to that segment should be weighted in a certain way to minimize energy consumption by matching the voltage applied to the digit electrode and the voltage applied to the segment electrode. You may do so.

Also, in correspondence with Fig. 2, the potential V of the digit drive signal at time t is set to O or 2V other than ■, and the segment drive signal is set to have a potential of O or 2V correspondingly. In general, the potential may be determined depending on the state of electrode division. Next, the effective driving voltage of the liquid crystal display device in the case of the driving method shown in FIG. 2 is shown.

The effective voltage VOn of the display segment is the effective voltage Voff of the non-display segment.The operating margin K in this case is K=J100 when t=o, which corresponds to the driving method shown in FIG.

If the duty of the digit drive signal of the drive method shown in FIG. 2 is T/2 (T+t), the duty changes depending on t. According to the example of FIG. 2, the operating margin changes depending on the value of t/T, but when t/T=1/100, K≠2.
When 23t/T=1/10, K≠2.15.

When the value of t/T is small, there is virtually no effect on the contrast of the liquid crystal display device. FIG. 6 shows the experimental results of measuring the current consumption of the display segments when the drive waveform of FIG. 2 was applied to the liquid crystal.

The capacity of the liquid crystal used was 1000PF. The driving voltage is ■
= 2 volts, 2V = 4 volts and T = 7.87TL. Se
The current consumption was measured using the t time as a variable. As mentioned above, the current consumption is reduced by about 40% at t/T''.1/100, and if t/T increases thereafter, it will reach saturation.
Although the time is very short, the effect is great.

FIG. 7 shows a circuit diagram for creating the drive signal shown in FIG. 2, and the circuit will be explained with reference to the timing chart in FIG. 8.

An example of a clock circuit is shown. 20 is an oscillator, 21 is a frequency dividing circuit,
22 is a clock circuit.

The output signals of the frequency divider 21 are φCl, φ1, and φ2.

φc1 is a signal for providing the above-mentioned time t, φ1 is a signal for providing a driving frame period, and φ2 is a signal having a period twice that of φ1. 23, 27, 33 are latch circuits,
26, 30, 36 are inverters, 24, 25, 28, 2
9, 34, and 35 are AND gates, 31, 37 are OR gates, and 32 is an exclusive OR gate.

The latch circuit operates using an inverted signal of φc1. The output of the AND gate 24 is the e signal, the output of the AND gate 25 is the f signal, the output of the OR gate 31 is the b1 signal, and the OR gate 37
Let the output be ■signal. Above E. f,. bl, ■, g
, φ2 signals to create a matrix drive signal. 9th
The figure and FIG. 10 show time charts when creating the digit drive signals Dl, D2 and the segment drive signals Sl, S2, S3, S4.

The output signal Xl of the AND gate block in FIG. 738,
X2, X3, and X4 are converted into X1'', X2'', X3'', and X4'' signals by the level shifter 39 block, respectively.

Here, the X1, X2, X3, and X4 signals are assumed to have a voltage of V, and are converted to signals having a voltage of 2V by a level shifter.

This also applies to blocks 40, 42, and 44. Here, if i=1, 2, 3, 4, a D1 signal is generated from the Xi'' signal, and a D2 signal is generated from the Yi'' signal.

Regarding the Xi'' signal, at the timing of X1'', 2
V. ■ for sX2'', 0 for X3'', . The potential of ■ is given at A signal is created.The above segment signals Sl, S2, S3, and S4 may be selected and applied to the segment electrodes using signals from a decoder corresponding to the electrode division.

As explained above, in the driving method according to the present invention, the power supply circuit that drives the display device when the charges stored on the digit drive electrode side and the segment drive electrode side of the display device moves from the state Q1 to the state Q2, for example. Driving power consumption is reduced by providing time for each drive frame to pass through a so-called short-circuited circuit instead of passing through the circuit.

In the example shown in Figure 5b, the amount of work done by the power supply due to the movement of charges is O, and the amount of work caused by the movement of charges is
The charge can be applied in such a way that the amount of work given by the power source is large and the amount of work given by the power supply is large.

Since the effect of reducing drive current consumption can be achieved even with a very short time t, a matrix drive signal is created that stochastically produces the greatest reduction effect, regardless of the difference in effective drive voltage in the same display state. I can do that. That is, looking at the transition diagram in Figure 5d, in addition to the direct transitions of 3→4 and 6→1, there are also transitions via the state of D=0, S=V, or D=■
If the state of 4 is reached via the state of S=2V, only 3QV of work is required, so the reduction effect will be even greater.

In this way, it is desirable to have a path for a minute period t, with respect to the frame period, so that the changes in the voltages applied to the digit drive electrodes and the voltages applied to the segment drive electrodes are as small as possible.

More specifically, for example, D=0. ．． In the case of the state of S=2V, that is, the transition from 3" to 2" in FIG. 5c, the state of D=0 and S=■ changes to D=V. ．． It is good to apply an intermediate voltage to the digit electrodes and segment electrodes for a certain period of time in each drive cycle so that the potential difference is smaller than the potential difference that transitions to reach D=■ and S=0 via S=■. .

[Brief explanation of drawings]

FIG. 1 is a waveform diagram of an example of a conventional matrix drive.
FIG. 2 is a waveform diagram of one embodiment of the matrix drive of the present invention, FIG. 3 is an inter-electrode voltage waveform diagram of the matrix drive of FIGS. 1 and 2, and FIG. FIG. 5 is a waveform diagram showing time divisions within one cycle of matrix drive; FIG. 5 is a state diagram of voltage applied to the electrodes for detailed explanation of the present invention; FIG. 7 is a circuit diagram for creating the drive signal of the present invention. FIG. 8 is a time chart explaining the circuit of FIG. 7. 9 is a digit drive signal creation time chart, FIG. 10 is a segment drive signal creation time chart, 21... Frequency divider, 23, 2
7, 33...Latch circuit.

Claims (1)

[Claims] 1. In a method for driving a liquid crystal display device having a plurality of digit drive electrodes and a plurality of segment drive electrodes corresponding to the digit drive electrodes, the signals applied to the plurality of digit drive electrodes simultaneously have the same potential within one cycle of driving the liquid crystal display. A plurality of digit same potential periods are provided, and the signals applied to the plurality of segment drive electrodes have a phase difference during at least part of the digit same potential periods in which the signals applied to the digit drive electrodes have the same potential at the same time. A period of the same potential as the same potential period of the digit is provided, and when the difference in potential between the digit electrode drive signal and the segment electrode drive signal changes to the maximum in accordance with the display/non-display state, 1. A method for driving a liquid crystal display device, comprising providing a period in which the potentials of a digit electrode drive signal and a segment electrode drive signal are at the same potential.