JPH0535199A - Liquid crystal driving device - Google Patents

Abstract

PURPOSE:To eliminate the need for an expensive analog amplifier and to reduce the cost of a system by installing capacitance type amplifiers which amplify the output signal voltages of sample holding circuits at a fixed amplification factor. CONSTITUTION:The analog output signal 2 which is outputted by a color palette 1 is sampled and held by (n) sample holding circuits 6-8 in a liquid crystal driving device 5 successively according to a sample holding clock 18 while still narrow in voltage amplitude. Sampled signals 9-10 are voltage-amplified by capacitance type amplifiers 19-21 respectively and outputted to a liquid crystal display unit. Thus, the voltages are amplified after being sampled and held to shorten the cycle of the voltage amplification to only the cycle of a display of one horizontal line, and the operation speed is made slow correspondingly to facilitate the design of the amplifiers. Consequently, the need for the high-speed, expensive analog amplifier is eliminated to obtain the driving device which is decreased in the constituent elements and low in system cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving device used in a liquid crystal display device.

[0002]

2. Description of the Related Art A conventional liquid crystal driving device will be described below. FIG. 3 is a diagram showing a configuration of a conventional liquid crystal display device.

In FIG. 3, 1 is a color palette for converting digital data for liquid crystal display into analog data, and 2 is an analog output signal of the color palette 1.
An analog amplifier 3 receives the analog output signal 2 and amplifies its voltage level. Reference numeral 4 is an analog data signal amplified by the analog amplifier 3.

Reference numeral 5 denotes a liquid crystal driving device, which inputs an analog data signal 4 as data. 6 to 8 are the first to temporarily store the voltage level of the input analog data signal 4.
It is an nth sample and hold circuit. 9-11 is the first
~ 1st to nth sampling voltage signals sampled by the nth sample and hold circuits 6 to 8. 12 to 1
Reference numeral 4 denotes first to nth null amplifiers that current-amplify and output the first to nth sampling voltage signals 9 to 11 with the same voltage value. 15 to 17 are the first to nth null amplifiers 12
To output signal lines 15 to 17
The signal output to is supplied to a liquid crystal display (not shown). Reference numeral 18 denotes the first to nth sample and hold circuits 6 to
8 is a sample and hold clock for storing the analog data signal 4 in 8;

The operation of the conventional liquid crystal driving device configured as described above will be described below.

First, the analog output signal 2 output from the color palette 1 has a low voltage amplitude level, so that the analog amplifier 3 voltage-amplifies it. The analog data signal 4 voltage-amplified by the analog amplifier 3 to a sufficient level is sequentially sampled and held by the n sample and hold circuits 6 to 8 in the liquid crystal drive device 5 in accordance with the sample and hold clock 18. Sample-held first to n-th sampling voltage signals 9 to 11
Are respectively current-amplified by the first to n-th null amplifiers 12-14, and the current-amplified signals are output lines 15-17.
Will be output. By supplying the signals of these output lines 15 to 17 to the liquid crystal display, liquid crystal display corresponding to the digital data input to the color palette 1 is performed.

[0007]

However, in the above-mentioned conventional configuration, since the voltage amplitude level of the analog output signal 2 output from the color palette 1 is low, it is necessary to perform voltage amplification by the analog amplifier 3. Therefore, in the liquid crystal display device as a whole, n null amplifiers 12 to 14 are provided.
Besides, the analog amplifier 3 must be provided, which complicates the circuit configuration and increases the number of elements.

Moreover, since the analog data signal 4 needs to be sequentially stored in each of the sample hold circuits 6 to 8, the analog amplifier 3 must be operated at high speed. Therefore, an expensive analog amplifier capable of high-speed operation must be used, and there is a problem that the system cost becomes high.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a liquid crystal driving device which does not require an expensive analog amplifier, reduces the number of constituent elements, and can configure a liquid crystal display device at a low system cost. And

[0010]

In order to achieve this object, a liquid crystal driving device of the present invention comprises a sample and hold circuit for sampling and holding an analog signal for liquid crystal display, and a sample and hold circuit for sampling and holding the sample and hold circuit. A capacitive amplifier that amplifies the voltage at a fixed magnification is provided, and the signal amplified by the capacitive amplifier is supplied to the liquid crystal display.

[0011]

With this configuration, an expensive analog amplifier is not required, the number of constituent elements can be reduced, and a liquid crystal driving device with low system cost can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a liquid crystal display device including this embodiment. In FIG. 1, 1, 2, 5
Reference numeral 18 is an element having the same function as the element in the conventional example. 1
Reference numerals 9 to 21 are first to n-th capacitive amplifiers, and the first to n-th sample and hold circuits 6 to 8 output the first to first
The nth sampling voltage signals 9 to 11 are input, amplified by a fixed magnification, and then output from the output lines 15 to 17, respectively.

The operation of the liquid crystal drive device of the present embodiment having the above-described structure will be described below.

First, a digital signal for liquid crystal display is input to the color palette 1 and is digital-analog converted. The analog output signal 2 output from the color palette 1 is sequentially sample-held by the n sample-hold circuits 6 to 8 in the liquid crystal driving device 5 according to the sample-hold clock 18 while the voltage amplitude level is low. Sampled and held sampling voltage signal 9
11 to 11 are voltage-amplified by the first to n-th capacitive amplifiers 19 to 21, and output from the output lines 15 to 17 to a liquid crystal display (not shown).

As described above, if the voltage is amplified after the sample and hold, the voltage amplification cycle may be one horizontal display cycle, and the operation speed can be slowed down accordingly, so that the amplifier design is easy.

FIG. 2 is a circuit diagram showing a specific configuration of a pair of sample and hold circuits and a capacitive amplifier in this embodiment.

In FIG. 2, reference numeral 30 denotes an input terminal for an analog signal (Vin) from the color palette 1, which is connected to one terminal of an analog switch (SW-A) 31. Reference numeral 32 denotes a sampling capacitor, the negative (-) terminal of which is connected to the power supply terminal (GND) 33, and the positive (+) terminal of which is the other end of the analog switch (SW-A) 31 and the analog switch (SW-B). It is connected to one end of 34. Reference numeral 35 is a node where the sampling voltage appears.

Reference numeral 36 is an operational amplifier (OP amplifier),
It has a negative input terminal 37 and a positive input terminal 38. An analog switch (SW-A) 39 is connected between the output terminal of the operational amplifier 36 and the negative input terminal 37. Reference numeral 40 denotes an amplification capacitor, the negative (-) terminal of which is connected to the negative input terminal 37 of the operational amplifier 36, and the positive (+) terminal of which is an output terminal of the operational amplifier 36 via an analog switch (SW-B) 41. And an analog switch (SW-A) 42 to a reference voltage (VREF) terminal 43. Reference numeral 44 denotes an output terminal where an output signal (Vout) appears, which is connected to the output terminal of the operational amplifier 36.

The operation of FIG. 2 will be described below. First, SW
At the timing when all the analog switches 31, 39 and 42 of the group shown by -A are turned on and the other analog switches 34 and 41 of the group shown by SW-B are all turned off,
An input signal (Vin) from the input terminal 30 flows into the sampling capacitor 32 via the analog switch 31,
The sampling capacitor 32 is charged. As a result, node 3
The voltage of 5 rises.

At this time, the plus (+) of the amplifying capacitor 40 is used.
A reference voltage (VREF) is applied to the terminal from the terminal 43 via the analog switch 42. On the other hand, the minus (−) terminal of the amplification capacitor 40 is connected to the negative input terminal 37 of the operational amplifier 36, and the analog switch 3
It is connected via 9 to the output terminal of the operational amplifier 36. Therefore, the minus (−) terminal of the amplification capacitor 40 holds the same potential as the power supply terminal (GND) 33.

Next, when all the analog switches 31, 39, 42 shown by SW-A are turned off, and then the analog switches 34, 41 shown by SW-B are turned on, the charges stored in the sampling capacitor 32 are charged. Moves to the minus (−) terminal of the amplification capacitor 40 via the analog switch 34. At this time, since the negative input terminal 37 of the operational amplifier 36 has the same potential as the power supply terminal (GND) 33 as described above, the potential on the plus (+) terminal side of the amplification capacitor 40 is VREF− (sampling voltage 35). × {(capacitance value of sampling capacitor 32) / (capacitance value of amplifying capacitor 40)}. That is, at the output terminal of the capacitive amplifier, a voltage obtained by amplifying the sampling voltage signal by the fixed magnification shown by the above equation is obtained. This voltage is output from the output terminal 44 as the output voltage of the capacitive amplifier and supplied to the liquid crystal display.

In the embodiment, one sample hold circuit is provided for one set of capacitive amplifiers, but a plurality of sample hold circuits may be provided for one set of capacitive amplifiers.

[0024]

The present invention comprises a sample-hold circuit for sampling and holding an analog signal for liquid crystal display, and a capacitive amplifier for amplifying the output signal voltage of the sample-hold circuit at a fixed magnification. The amplified signal is supplied to the liquid crystal display.

With this arrangement, it is not necessary to use an expensive analog amplifier which operates at high speed, so that the number of constituent elements can be reduced and the system cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal display device including a liquid crystal drive device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of a set of sample and hold circuits and a capacitive amplifier of a liquid crystal driving device according to an embodiment of the present invention.

FIG. 3 is a block diagram of a liquid crystal display device including a conventional liquid crystal driving device.

[Explanation of symbols]

 1 color palette 2 analog output signal 3 analog amplifier 4 analog data signal 5 liquid crystal drive device 6 first sample and hold circuit 7 second sample and hold circuit 8 nth sample and hold circuit 9 first sampling voltage signal 10 second Sampling voltage signal 11 nth sampling voltage signal 12 first null amplifier 13 second null amplifier 14 nth null amplifier 15 first output line 16 second output line 17 nth output line 18 sample and hold clock 19th 1 capacitance type amplifier 20 2nd capacitance type amplifier 21 nth capacitance type amplifier 30 analog signal input terminal 31 analog switch 32 sampling capacitance 33 power supply terminal 34 analog switch 35 node where sampling voltage appears 36 operational amplifier 37 negative input Terminal 38 Positive input terminal 39 Analog switch 40 Amplification capacitance 41 Analog switch 42 Analog switch 43 Reference voltage terminal 44 Output terminal

Claims (1)

Claim: What is claimed is: 1. A capacitance-type amplifier comprising: a sample-hold circuit that samples and holds an analog signal for liquid crystal display; and a capacitive amplifier that amplifies a sampling voltage signal of the sample-hold circuit at a fixed magnification. A liquid crystal drive device, which supplies a signal amplified by an amplifier to a liquid crystal display.