JPH0711542B2 - Power consumption measuring device - Google Patents

Description

Detailed Description of the Invention

The present invention relates to an apparatus for automatically measuring the power consumption of a liquid crystal member such as a liquid crystal display element. When evaluating a liquid crystal display element, in addition to its optical characteristics such as response characteristics, drive voltage vs. brightness characteristics, contrast characteristics, and angle characteristics, its power consumption characteristics are also characterized by its low power consumption characteristics. It is an important measurement item. As a means for measuring the current consumption for measuring the power consumption of the liquid crystal display element, a complementary MOS integrated circuit (hereinafter referred to as C-MOS) is used.
An exclusive OR circuit (referred to as an IC) (hereinafter referred to as an exclusive OR circuit) is used to connect a liquid crystal display element to its output terminal and measure the current flowing into the measurement circuit with an ammeter, or Connect a resistor in series with
A method of measuring the voltage drop using a voltmeter can be considered. However, as described above, since the liquid crystal display element has low power consumption, the current flowing through the liquid crystal display element is in the order of microamperes, and the liquid crystal display element is driven by an alternating current. It is difficult to measure with due consideration. Therefore, the present invention develops a measurement circuit using an exclusive OR circuit of a C-MOS IC, and uses an arithmetic unit such as a microcomputer for control to automate the measurement and drive a liquid crystal display element which is a measurement condition. The voltage and drive frequency can be set with a single switch change, that is, the characteristics of the liquid crystal display device can be investigated by changing a plurality of parameters. It is an object of the present invention to provide a power consumption measuring device that can perform efficient measurement processing by calculating and outputting each. Next, one embodiment of the power consumption measuring device according to the present invention will be described as C-
It will be described in detail by comparing with a current consumption measuring circuit using an exclusive OR circuit of a MOS IC. FIG. 1 is a diagram showing a conventional current consumption measuring circuit of a liquid crystal display device using an exclusive OR circuit of a C-MOS IC. In the figure, 1 and 2 are exclusive OR circuits of a C-MOS IC, a, b and d, e are input terminals, and c, f are output terminals. A liquid crystal display element 3 is a member to be detected, and is connected between the output terminals c and f of the exclusive OR circuits 1 and 2. Vp is a direct current voltage which is a drive voltage of the liquid crystal display element 3, one input terminal a of the exclusive OR circuit 1 is connected with this direct current Vp, and the other input terminal b is a drive square wave signal of the liquid crystal display element 3. Oscillator that emits fp (not shown)
Are connected. One input terminal d of the exclusive OR circuit 2 is connected to the DC voltage Vp through the resistor 4 and grounded through the switch 5, and the other input terminal e is connected to the output terminal c of the exclusive OR circuit 1. It
Ground terminals g1 and g2 of two exclusive OR circuits 1 and 2
Is grounded by a parallel connection body of a resistor 6 and a capacitor 7, and a DC voltmeter 8 is connected to both ends of the resistor 6. Since the capacitor 7 contains a high frequency component that is switched by the current driving rectangular signal fp flowing in the exclusive OR circuits 1 and 2, it is provided to bypass this high frequency component. The above is the configuration of the current consumption measurement circuit of the liquid crystal display element 3 using the exclusive OR circuits 1 and 2 of the C-MOS IC.
Next, the operation will be described. Now, assuming that switch 5 is closed, exclusive
One input terminal d of the OR circuit 2 becomes low level (hereinafter referred to as "L"), and the exclusive OR circuit 2 simply functions as a buffer amplifier, so that the logics of the input and the output are in phase. On the other hand, since the DC voltage Vp is always applied to the input terminal a of the exclusive OR circuit 1, the input terminal b
When a driving square wave signal fp as shown in Fig. Is applied, the driving square wave signal fp has a high level (hereinafter referred to as "H"), "L".
According to the level, a square wave voltage having an amplitude of Vp is output to the output terminal c, but this voltage is added to the input terminal e of the exclusive OR circuit 2, so that the output terminal f of the exclusive OR circuit 2 that merely functions as a buffer. Also becomes a square wave voltage having an amplitude of Vp, the voltages at both ends of the liquid crystal display element 3 become completely equal, no current flows through the liquid crystal display element 3, and the liquid crystal display element 3 does not light. Next, open the switch 5 to open the exclusive OR circuit 2.
When one of the input terminals d is set to the “H” level, the exclusive OR circuit 2 functions as an inverter. Therefore, the square-wave voltage with the amplitude Vp appearing at the output terminal c of the exclusive OR circuit 1 is inverted by the exclusive OR circuit 2. ,
It is a square wave voltage with an amplitude of −Vp. That is, the voltages Vp and −Vp are applied to both ends of the liquid crystal display element 3, and the liquid crystal display element 3 is turned on. When a current flows through the liquid crystal display element 3, a current flows through the resistor 6 in proportion thereto. When the switch 5 is opened and closed, that is, the liquid crystal display element 3 is repeatedly turned on and off, and the potential difference across the resistor 6 at that time is read by the DC voltmeter 8, the current flowing through the liquid crystal display element 3 from the current flowing through the measuring circuit You can ask. That is, the switch 5 is closed and the reading of the DC voltmeter 8 after the capacitor 7 is fully discharged is set to Voff, then the switch 5 is opened and the DC voltmeter after the capacitor 7 is fully charged. If the reading of 8 is Von, the current I _LC flowing through the liquid crystal display element 3 is given by the following equation. Here, R is the resistance value of the resistor 6. As described above, in the conventional current consumption measuring circuit shown in FIG. 1, the object to be measured alternately opens and closes the switch 5, each time the value of the DC voltmeter 8 is read to calculate the current flowing through the liquid crystal display element 3. There is a need. Also, when the DC voltage Vp for driving the liquid crystal, which is a measurement condition, is changed, the input threshold voltage level of the exclusive OR circuits 1 and 2 by the C-ROM IC fluctuates. Therefore, according to the change of the DC voltage Vp, Since the amplitude of the driving square wave signal fp also needs to be changed, the time spent for measurement is great. The present invention is conceived in view of the drawbacks of the conventional measurement circuit,
The drive voltage of the drive signal for driving the liquid crystal display element is variably applied and switched at arbitrary intervals, and the frequency of the drive signal is also variably set to obtain the current consumption from the current difference before and after switching. The power consumption is calculated from now on. FIG. 2 is a diagram showing an embodiment of the power consumption measuring device according to the present invention. In the figure, reference numerals 1 to 4, 6, and 7 given the same reference numerals as in FIG. 1 indicate the same parts and elements, and description thereof will be omitted. In the figure, reference numeral 9 denotes a microprocessor, which is an arithmetic means and also a control means for controlling the whole. Reference numeral 10 is a memory, and 11 is a control unit. Reference numeral 12 is a D / A converter having a configuration as a drive voltage varying means, and has an action of converting the set value into an analog voltage when the DC voltage Vp is set in the control unit 11. Reference numeral 13 is a buffer amplifier as a drive voltage applying means, which converts the analog output voltage of the D / A converter 12 into C−R.
This is for supplying to the measuring circuit consisting of exclusive OR circuits 1 and 2 by OM IC. Reference numeral 14 denotes an oscillator as a drive signal generating means for generating a drive signal, which produces a drive square signal fp for determining the liquid crystal drive frequency. 15 is a switching transistor as a switching means,
Upon receiving the driving square signal fp from the oscillator 14, it is turned on and off. A switching transistor 16 as a switching means receives a signal from the control unit 11 and turns on and off. Reference numeral 17 denotes an operational amplifier as an operation means, which amplifies the voltage drop of the resistor 6. This operational amplifier
Since the response characteristic of 17 should be sufficiently fast with respect to the ON / OFF cycle of the liquid crystal display element display element 3, when the ON / OFF cycle of the liquid crystal display element 3 is set to about 1 second at the shortest, the operational amplifier 17 The frequency bandwidth may be about DC to several hundreds Hertz, which is advantageous for noise resistance and the like. The operational amplifier 17
Must be well-distributed for drift characteristics because it is necessary to accurately amplify low level signals. Reference numeral 18 denotes an A / D converter, which has a function of converting the signal amplified by the operational amplifier 17 into a digital signal and sending it to the microprocessor 9. Reference numeral 19 is a display unit, and 20 is a printer. The above is the configuration of one embodiment of the power consumption measuring apparatus according to the present invention. Next, the operation will be described. When the DC voltage Vp is set in the control unit 11, the set value is converted into an analog voltage by the D / A converter 12, and the exclusive OR circuits 1 and 2 by C-MOS IC are formed via the buffer amplifier 13. Added to measuring circuit. On the other hand, the control unit 11 issues a signal to the oscillator 14 to drive the square wave signal.
Set the frequency of fp. The switching square wave signal fp emitted from the oscillator 14 turns the switching transistor 15 on and off, and the output signal is input to one input terminal of the exclusive OR circuit 1. Here, the output of the oscillator 14, that is, the driving square signal fp of the liquid crystal display element 3 is set to the first
As shown in the example of the figure, the DC voltage Vp is not directly input to the exclusive OR circuit 1 but is input via the switching circuit configured by connecting the load resistance of the switching transistor 15 to the DC voltage Vp. Even if it changes, the oscillator 14 always keeps a constant level, for example, TTL level (supply voltage 5
V) will work. Next, an ON / OFF signal of the liquid crystal display element 3 is applied to one input terminal of the exclusive OR circuit 2 from the control section 11 via the switching transistor 16 according to a command from the microprocessor 9. The use of the switching circuit here has the same purpose as in the case of the driving square wave signal fp. The on / off of the liquid crystal display element 3 depends on the timing control of the microcomputer, but it is necessary to sufficiently consider the on / off cycle. That is, when the liquid crystal display element 3 is turned on and off, a change in current occurs in the measurement circuit, and this change appears as a voltage drop across the resistor 6, and the voltage across the resistor 6 is converted into a direct current by the operational amplifier 17. Amplify. At this time, the AC component of the driving square wave signal fp is bypassed by the capacitor 7. The signal amplified by the operational amplifier 17 is converted into a digital signal by the A / D converter 18, and the digital signal is processed by the microprocessor 9 which is a calculation means. The calculation results are displayed on the display unit 19 and the printer 20.
Displayed or printed on. FIG. 3 shows a measurement flowchart. The state of measurement execution will be described using this flowchart. First, after the start (step [1]), the DC voltage Vp and the frequency of the driving square wave signal fp of the liquid crystal display element 3 are set (steps [2] and [3]), and the measurement is started when the measurement is ready. (Step [4]). First, the liquid crystal display element 3 is turned off (step [5]), and after the behavior of the liquid crystal is sufficiently subdued, the current Ioff flowing to the measurement circuit at the time of off
Here, the voltage drop Voff of the resistor 6 is taken into the arithmetic processing unit (step [6]). At this time, in order to increase the S / N ratio with respect to noise and ripples, sampling may be performed many times and averaging may be performed. Voltage drop captured by the arithmetic processing unit
The Voff data is temporarily stored in the memory 10, and then the liquid crystal display element 3 is turned on (step [7]). Similarly, after the behavior of the liquid crystal has sufficiently subsided, the current Ion flowing in the measuring circuit when turned on, here Von, is taken into the arithmetic processing unit (step [8]). The Voff data stored in the memory 10 is taken out again, and the arithmetic processing unit (Von-Voff)
Execute / etc. (step

[9]). Here, R is the resistance value of the resistor 6. The obtained calculation result is output to the display unit 19 or the printer 20, and one current consumption measurement is completed (step [10]). In the above embodiments, the measurement conditions were intended to measure the current consumption of a certain liquid crystal display element 3 with respect to a certain DC voltage Vp and a certain frequency of a driving square wave signal fp. However, by changing these parameters, It is also possible to obtain valid measurement data. For example, the liquid crystal display element 3 has a driving square wave signal fp
When the frequency of is changed, the consumption current changes considerably even if the DC voltage Vp is constant. Therefore, the consumption current measuring device according to the present invention is developed, and instead of the oscillator 14, a programmable oscillator as a drive signal varying means, or
If the consumption current is sequentially measured while varying the frequency of the drive square wave signal fp using a variable means such as a VCO (voltage control oscillator), a drive frequency-current consumption characteristic can be obtained. Further, the D / A converter 12 is controlled by the control unit 1 as the drive signal varying means, and the drive voltage-current consumption characteristic can be obtained. This allows the power consumption to be measured. As described in detail above, the present invention includes a drive voltage applying unit that applies a drive voltage for driving a liquid crystal member,
Driving voltage varying means for varying the driving voltage of the driving voltage applying means, and switching means for performing a switching operation to a non-driving state in which the driving voltage is not applied to the liquid crystal member or a driving state in which the driving voltage is applied to the liquid crystal member at arbitrary intervals. Generating means for generating a drive signal for turning on and off the liquid crystal member when the switching means is driving the liquid crystal member, and changing the frequency of the drive signal of the generating means. Drive variable means, and based on the difference in current flowing through the liquid crystal member in the non-driving state or the driving state before and after the switching at an arbitrary interval of the switching means, various driving voltage values of the driving voltage and frequencies of the driving signal Since it has a calculation means for obtaining power consumption for various values and a control means for controlling each of the above-mentioned means, It has the advantages that it can be automated, the operation is extremely simple, and the measurement can be performed in a short time.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional current consumption measuring circuit of a liquid crystal display device using an exclusive OR circuit of a C-MOS IC, and FIG.
FIG. 3 is a circuit diagram of a power consumption measuring device showing an embodiment of the present invention, and FIG. 3 is a measurement flowchart. In the figure, 1 and 2 are exclusive OR circuits, 3 is a liquid crystal display element, 9 is a microprocessor, 10 is a memory, 11 is a control unit, 12 is a D / A converter, 13 is a buffer amplifier, 14 is an oscillating unit, 15 , 46 is a switching transistor, 17 is an operational amplifier, 18 is an A / D converter, 19 is a display unit, and 20 is a printer.

Continuation of the front page (56) Reference JP-A-52-24079 (JP, A) JP-A-55-59347 (JP, A) JP-A-57-38498 (JP, A) JP-A-55-127280 (JP , A) JP-A-51-25162 (JP, A) JP-A-53-31178 (JP, A)

Claims (1)

[Claims] 1. A drive voltage applying unit for applying a drive voltage for driving a liquid crystal member, a drive voltage changing unit for changing the drive voltage of the drive voltage applying unit, and the liquid crystal member for applying an arbitrary interval to the liquid crystal member. Switching means for performing a switching operation to a non-driving state in which a driving voltage is not applied or a driving state in which the driving voltage is applied; and when the switching means is driving the liquid crystal member, the liquid crystal member is turned on. Drive signal generating means for generating a drive signal for off-driving; drive signal varying means for varying the frequency of the drive signal of the drive signal generating means; and non-driving state before and after the switching at an arbitrary interval of the switching means Alternatively, various drive voltage values of the drive voltage and the frequency of the drive signal based on the difference in current flowing through the liquid crystal member in the drive state. Various calculating means for determining the power consumption for the value, the and a control means for controlling each unit, power measurement apparatus which can measure the power consumption.