JPS5912679A - Portable liquid crystal television - Google Patents

Abstract

PURPOSE:To attain a portable liquid crystal television with low cost and low power consumption, by constituting plural different CMOS inverters in parallel as a voltage comparator of an A/D converter converting a video signal from an analog into a digital signal. CONSTITUTION:The voltage comparator 16 of the A/D converter of the portable liquid crystal television consists of MOS inverters having different inverting voltage and different ratio of width-length of a gate channel of a P channel MOS transistor (TR) to that of an N channel MOS TR, i.e., (W/L)P/(W/L)N, and the I1- the I15 are connected in parallel. The portable liquid crystal television with low cost and low power consumption is obtained by providing the A/D converter, a dot matrix liquid crystal panel and a battery in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a portable liquid crystal television that is inexpensive and has low power consumption.

Conventionally, conventional systems for liquid crystal televisions using liquid crystal panels are known. One method is a method in which a switching transistor is provided for each picture element of the dot matrix of a liquid crystal panel, and a second method is a method in which a switching transistor is not provided. The method of providing switching transistors is that they are fabricated on a silicon substrate in the same way as a normal MO8 integrated circuit.There is no crosstalk in the liquid crystal panel, the duty is practically 100 inches, and the p1 contrast is good, but the panel itself is Since it is the same as a huge IC, it is extremely costly (and therefore, it is difficult to provide LCD TVs at a reasonable price.Therefore, we developed another method that does not include a switching transistor, a glass plate with 92 electrodes). A liquid crystal panel with a liquid crystal placed between the panels is advantageous in terms of cost, but in that case, an A/D is required to convert the analog signal of the video signal into a digital signal in order to add gradation to the image.
A converter is required. However, the characteristics required of this 4/D converter include high-speed conversion since it handles video signals, and the cost of high-speed A/D converters has been extremely high. Furthermore, since portable liquid crystal televisions need to be operated on batteries, their power consumption is required to be extremely low. Therefore, even if a low-cost liquid crystal panel that does not use switching transistors is used, it has disadvantages such as high cost and high power consumption when configured as a portable liquid crystal television.
It has been difficult to provide a portable LCD television that is inexpensive and has low power consumption.

It is an object of the present invention to eliminate the above-mentioned drawbacks and provide a portable liquid crystal television that is inexpensive and has low power consumption.

The present invention will be described in detail below with reference to drawings of embodiments. Figure 1 is a block diagram of an embodiment of the portable liquid crystal television of the present invention. A television signal received through an antenna 1 is restored to a video signal through a tuner 2, a video intermediate frequency amplification circuit 3, a video detection circuit 4, and a video amplification circuit 5. Reference numeral 6 denotes an audio circuit, which detects and amplifies the audio signal included in the video signal from the video amplification circuit 5, and outputs audio from the speaker 7. Reference numeral 8 denotes a control signal generation circuit, which separates a vertical synchronization signal and a horizontal synchronization signal from the video signal of the video amplification circuit 5, and is equipped with an oscillation circuit to generate the clock, vertical synchronization signal, and horizontal synchronization signal. Control signals such as signals for the vertical retrace period and horizontal retrace period are generated and sent to the line memory IJIO, which will be described later, the pulse width generation circuit 11, and the scanning circuit 13.The clock of the oscillation circuit of the control signal generation circuit 8 is a liquid crystal display. The frequency is determined according to the number of picture elements in the horizontal direction of the panel 15, and the clock is also sent to the A/D converter 9 as a sampling dark wave number.The A/D converter 9 converts the video signal of the video amplifier circuit 5 into digital. However, since it determines the gradation, 4-bit resolution is sufficient based on the resolution of the eye, but several MH2
A high conversion speed is required, and as mentioned above, this part has conventionally had drawbacks.

10 is a line memory), which is composed of a register and a latch circuit, and the liquid crystal panel 15 is, for example, a 4X memory (IJ).
It is composed of 4 horizontal scans and has a memory function for 4 horizontal scans. The line memory 10 stores the contents of the A/D converter 9 as a control signal of the control signal generating circuit 8, and transmits the same to the pulse width generating circuit 11. Pulse width generation circuit 1
1 is for converting the digital value of the video signal in the line memory 10 into a pulse width in order to add gradation to the liquid crystal panel 15 and reduce crosstalk.The output of this pulse width generation circuit 11 is The voltage is transmitted to the X drive circuit 12 and applied to the X electrode of the liquid crystal panel 15.The X electrode of the liquid crystal panel 15 is also connected to a scanning circuit 13 consisting of a shift register controlled by the control signal from the control signal generation circuit 80.
The signal is applied from the X drive circuit 14 according to the output signal of .

The X drive circuit 14 and the X drive circuit 12 are composed of transmission gates, and apply voltages of different levels corresponding to selection and non-selection to the liquid crystal panel 15. If a twisted nematic type liquid crystal is used for the liquid crystal panel, the contrast will be good, and in order to improve the contrast, the duty should be about 1/30th of the total.If the number of dots in the X direction of the liquid crystal panel 15 is, for example, 120, then 4 heavy massage) I
If you use Jx, there will be 30 X electrodes, which is convenient for duty. Although the diagram is omitted, in order to make it portable, these blocks have a configuration in which power is supplied from a battery1.
There is.

Next, A / which is also a feature of the portable LCD TV of the present invention
The D converter section will be explained. The block diagram shown in FIG. 941 can be used to accomplish this by using known techniques except for the A/D converter.

Figure 2 is the inversion voltage characteristic diagram of the 0M0S inverter.
The vertical axis shows the inversion voltage of the 0M0S inverter, and the horizontal axis shows the C
It shows the ratio of the width to length of the gate channel of a P channel full and the width to length of the gate channel of an N channel of a MOS inverter. The inversion voltage indicates the input voltage when the output of the CMOS inverter becomes half of the power supply voltage.

Determining the reversal voltage and through current of a CMOS inverter can be divided into process parameters that govern mobility, etc., and design parameters such as gate channel length. Therefore, one way to change the inversion voltage of a COM O13 inverter using the same process parameters is to change the dimensions of the gate channel.

The width-to-length ratio of the gate channel of a P-channel transistor is (W/L) 2% The width-to-length ratio of the gate channel of an N-channel transistor is (W/L)N, and their ratio is (W/L)p/(w7L)H
The value of is important. The characteristics shown in FIG. 2 are obtained when certain characteristic process parameters are used and the power supply voltage f: 10 .ANG.

When the value of (W/L)7)/(W/L)H is changed from O02 to 5, the inversion voltage changes from 6.8v to 3°2vt, and can be changed by 3.6v in the range. Various voltage comparators can be obtained by constructing CMOS inverters with various ratios. For example, in the case of a CMOS inverter with an inversion voltage of 5V, the gate width and gate length of both the N-channel and P-channel may be set to 10 pm. Also, C! whose inversion voltage is 3.2V! When obtaining an MO8 inverter, P
The gate width W of the channel is 50 μm, and the gate length L
f: 10 pm, and N channel W and L are each 10 μm, or alternatively, P channel gate length and gate width are 10 μm, and N channel gate length is 50 μm 1 gate width f 10 If the value of ri'tD (W/L)p/ (W/L)N is 0.2, the inversion voltage will be 3.2V, so in these designs, the required response speed It may be determined based on the current, through current, or ease of manufacturing.

By connecting CMOS inverters having such inversion voltage characteristics in parallel, it is possible to configure a voltage comparator for various voltages. For example, to configure a complete 4-bit A/D converter, it can be configured by connecting 15 types of 0M0S inverters in parallel, and in the above example, approximately 257
Voltage comparisons can be made at mV intervals.

FIG. 3 is a block diagram showing an embodiment of an A/D converter for a portable liquid crystal television according to the present invention. 16 is a voltage comparator, 17 is a buffer section, and 18 is an encoder. 'qL
As mentioned above, the pressure comparator 16 is connected to the P channel MO8)
The ratio of the width-to-length of the gate channel of the transistor to the width-to-length of the gate channel of the N-channel MO8) transistor, t (W / L) p / (W / L) *, is an inversion with different values. Shown are 0M0B inverters with different voltages, 100 to 11, respectively.

In this embodiment, a 4-bit A/Di converter is shown as an example. The gates of these 0M0S inverters are connected to the input terminal 19. Further, the outputs of the CMOS inverters indicated by 1 to 6 are input to a correspondingly provided buffer section 17 consisting of a normal 0M0S inverter, and the output thereof is input to an encoder 18. The encoder 18 may be of a known type, but a priority type encoder is preferable. 20 is an output terminal of the engoder 18, and in this case it is 4 bits, so there are 4 terminals. 21 is a clock input terminal for the sampling frequency of the encoder 18, which is inputted from the control signal generation circuit shown in FIG. The data is supplied as gradation data to the line memory shown in the figure.

In the case of the embodiment shown in Fig. 3, the input signal and the video signal are compared at any time, but a sample hold circuit using the above clock is provided on the input side, and a latch circuit is installed in the buffer section or encoder section. It is convenient to provide this in order to suppress the occurrence of glitches. In addition, if overflow detection is required, it is sufficient to add one more inverter to the 15 inverters.To further reduce current consumption, the inverter in the buffer section may be a clocked inverter, or the retrace period may be changed. It may be configured such that the power is turned off only when A/D conversion is not required.

Next, the accuracy will be explained according to the embodiment shown in FIG. The inversion voltage of a voltage comparator has manufacturing errors, but in general, the variation in inversion voltage on the same chip can be controlled to several tens of volts, and 115LE? A value of about B is obtained, and the linearity is sufficient for use in liquid crystal televisions. Further, the variation in inversion voltage between chips may exceed 100 mV, but since the inversion voltage of each 0M0B inverter of the voltage comparator shifts in the same direction, it can be easily corrected by adjusting the brightness of the video signal. Regarding temperature characteristics, MO1i of P channel and N channel? ) The gingister changes in the direction of canceling it out, and it fluctuates slightly to about 2.5V per ℃, but at each C
MOS inverters fluctuate in almost the same way, so if you compensate for the offset voltage of the video signal with temperature, you don't have to worry about it at all. Therefore, the circuit is simple in terms of conversion speed, which is almost invisible in the image, and the voltage comparator is just one CMOS inverter, so there is little delay and it can be used for video signals.Consumption Regarding power, although a through current flows, it can be much smaller than that using bipolar transistors.Furthermore, by setting the delay time to the very edge of the required conversion speed, not only does power consumption become smaller, but It also has the effect of removing noise contained in the video signal, making the image clearer.

As described above, according to the present invention, it is possible to configure a voltage comparator that performs various voltage comparisons as an A/D converter for video signals simply by designing the gate channel of a CMOS inverter, which has been a problem in the past. It solves the high cost and high power consumption of A/D converters all at once, and since there is no need to change the manufacturing process, it can be mixed with other integrated circuits, resulting in a significant reduction in power consumption, and even with 0 MO8 / Since the delay of the voltage comparator of the D converter is only caused by the inverter, it is faster, consumes less power, and operates on a single power supply, making it easier to interface with other logic. Since the conversion speed can be easily designed, it is possible to provide a portable liquid crystal television that has many advantages such as reducing the influence of noise and providing clear images, and the effects are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a portable LCD television according to the present invention, and FIG. 2 is a diagram of inversion voltage characteristics of a CMOS inverter.
FIG. 3 is a block diagram showing an embodiment of an A/D converter for a portable liquid crystal television according to the present invention. 10. antenna, 20. Tuner, 3. . Video intermediate frequency amplification circuit, 40. Video detection circuit, 5. . Video amplification circuit, 60. Audio circuit, 70. Speaker 8. control signal generation circuit, 9. , A/D converter, 106. Line memory, 11, , Pulse width generation circuit, 12,
, Y drive circuit, 130. Scanning circuit, 14, !
Drive circuit, 150. LCD panel, 161. Voltage ratio M device,
17, , buffer section, 180. encoder, 19
°, input terminal, 20 °. Output terminal, 21, , clock input terminal. Above Figure 1 Figure 2 (w/1-)P ('N/L)A/

Claims (1)

[Claims] In a portable LCD TV that has a dot matrix LCD panel, an A/D converter, and a battery, the gate channel of a P-channel MOS transistor is used as a voltage comparator for the nuclear A/D converter that converts the video signal from analog to digital. A portable liquid crystal television set comprising a plurality of 0M0S inverters connected in parallel, each having a different ratio between the width to length of the 0M0S inverter and the width to length of the gate channel of the N-channel MO8 transistor.