JP4819921B2 - DIFFERENTIAL AMPLIFIER, DATA DRIVER OF DISPLAY DEVICE USING SAME, AND METHOD FOR CONTROLLING DIFFERENTIAL AMPLIFIER - Google Patents

Description

  The present invention relates to a differential amplifier, a display device using the same, and a control method for the differential amplifier.

  Recently, liquid crystal display devices (LCD) characterized by thinness, light weight, and low power consumption have been widely used as display devices, and mobile phones such as mobile phones (mobile phones, cellular phones), PDAs (personal digital assistants), and notebook PCs. It has been widely used in the display section of equipment. Recently, however, the technology for increasing the screen size and moving images of liquid crystal display devices has been increasing, and it has become possible to realize not only mobile applications but also stationary large screen display devices and large screen liquid crystal televisions. As these liquid crystal display devices, active matrix liquid crystal display devices capable of high-definition display are used. First, a typical configuration of an active matrix drive type liquid crystal display device will be outlined with reference to FIG. In FIG. 15, the main configuration connected to one pixel in the liquid crystal display unit is schematically shown by an equivalent circuit.

  In general, a display unit 960 of an active matrix liquid crystal display device includes a semiconductor substrate in which transparent pixel electrodes 964 and thin film transistors (TFTs) 963 are arranged in a matrix (for example, in the case of a color SXGA panel, 1280 × 3 pixel columns × 1024). A pixel row), a counter substrate having one transparent electrode 966 formed on the entire surface, and a structure in which liquid crystal is sealed between the two substrates facing each other.

  When the TFT 963 having a switching function is controlled by a scanning signal and the TFT 963 is turned on, a gradation voltage corresponding to the video signal is applied to the pixel electrode 964, and a potential difference between each pixel electrode 964 and the counter substrate electrode 966. As a result, the transmittance of the liquid crystal changes, and the potential difference is held in the liquid crystal capacitor 965 for a certain period to display an image.

  On the semiconductor substrate, data lines 962 for sending a plurality of level voltages (gradation voltages) applied to each pixel electrode 964 and scanning lines 961 for sending scanning signals are wired in a grid pattern (in the case of the color SXGA panel). The data lines are 1280 × 3 and the scanning lines are 1024), and the scanning lines 961 and the data lines 962 have a large capacitance due to the capacitance generated at the intersection or the liquid crystal capacitance sandwiched between the counter substrate electrodes. It is a load.

  Note that the scanning signal is supplied from the gate driver 970 to the scanning line 961, and the gradation voltage is supplied to each pixel electrode 964 from the data driver 980 through the data line 962.

  Rewriting of data for one screen is performed in one frame period (1/60 · sec), and is sequentially selected for each pixel line (each line) in each scanning line. A gradation voltage is supplied.

  Note that the gate driver 970 only needs to supply at least binary scanning signals, whereas the data driver 980 needs to drive the data lines with multilevel gradation voltages corresponding to the number of gradations. Is done. Therefore, a differential amplifier capable of outputting a high-accuracy voltage is used for the buffer unit of the data driver 980.

  Recently, liquid crystal display devices have been improved in image quality (multicolor), and demand for at least 260,000 colors (RGB 6-bit video data) and 26.8 million colors (RGB 8-bit video data) or more. Is growing.

  For this reason, a data driver that outputs a gradation voltage corresponding to multi-bit video data is required not only to output a voltage with extremely high accuracy, but also to increase the number of elements of a circuit unit that processes the video data. As a result, the chip area has increased, leading to high costs. This problem will be described in detail below.

  FIG. 16 is a diagram showing the configuration of the data driver 980 of FIG. 15, and shows the main part of the data driver 980 in blocks. Referring to FIG. 16, the data driver 980 includes a latch address selector 981, a latch 982, a gradation voltage generation circuit 983, a plurality of decoders 984, and a plurality of buffer circuits 985.

  The latch address selector 981 determines the data latch timing based on the clock signal CLK. The latch 982 latches the video digital data based on the timing determined by the latch address selector 981, and outputs the latched data to each decoder 984 all at once according to the STB signal (strobe signal). . The gradation voltage generation circuit 983 generates gradation voltages having the number of gradations corresponding to the video data. The decoder 984 selects and outputs one gradation voltage corresponding to the input data. The buffer circuit 985 receives the gradation voltage output from the decoder 984, amplifies the current, and outputs it as the output voltage Vout.

  For example, when 6-bit video data is input, the number of gradations is 64, and the gradation voltage generating circuit 983 generates 64 levels of gradation voltages. The decoder 984 includes a circuit that selects one gradation voltage from 64 gradation voltages.

  On the other hand, when 8-bit video data is input, the number of gradations is 256, the gradation voltage generating circuit 983 generates 256-level gradation voltages, and the decoder 984 outputs one piece from the 256-level gradation voltages. A circuit for selecting the gray scale voltage is provided.

  When the number of bits is increased in this way, the circuit scale of the gradation voltage generation circuit 983 and the decoder 984 increases. For example, when the number is increased from 6 bits to 8 bits, each circuit scale becomes four times or more. Therefore, the increase in the number of bits increases the chip area of the data driver LSI and increases the cost.

  On the other hand, a configuration that suppresses an increase in the chip area of the data driver LSI even if the number of bits is increased is proposed in Patent Document 1 described later. FIG. 17 is an example of a configuration proposed in Patent Document 1 (corresponding to FIG. 16 of Patent Document 1).

  Referring to FIG. 17, this data driver is different from the data driver shown in FIG. 16 in the configuration of a gradation voltage generation circuit 986, a decoder 987, and a buffer circuit 988. In the data driver of FIG. 17, the gradation voltage generation circuit 986 generates gradation voltages every two gradations, and the number of gradation voltage lines of the decoder 987 is reduced to about ½ of the decoder 984 of FIG. Yes. The decoder 987 selects two gradation voltages according to the video data and outputs them to the buffer circuit 988. The buffer circuit 988 can amplify and output two input grayscale voltages and a grayscale voltage intermediate between the two grayscale voltages.

  The configuration disclosed in Patent Document 1 described later includes a buffer circuit 988 that can input two gradation voltages and selectively output one of the two gradation voltages and an intermediate voltage between the two gradation voltages. By doing so, the number of gradation voltage lines of the decoder 987 is reduced to half, the circuit scale of the decoder 987 is reduced, and an aim is to realize area saving, that is, cost reduction.

  On the other hand, a configuration that greatly reduces the area of a circuit (digital-to-analog converter, abbreviated as “DAC”) that converts a multi-bit digital signal into an analog signal is described later as Patent Document 2 and Patent. It is proposed in Document 3. Patent Document 3 is an improvement of Patent Document 2 and proposes a configuration that improves the performance of output voltage accuracy. Therefore, Patent Document 3 will be described below. FIG. 18 is a diagram illustrating a configuration of a DAC proposed in Patent Document 3 described later. Referring to FIG. 18, the DAC includes a resistor string that outputs n analog voltages from each tap, and a first switch group that includes n switches S1a to Sna that select one voltage V1 from each tap. , A second switch group consisting of n switches S1b to Snb for selecting a voltage V2 at a level adjacent to the voltage V1, and a third switch group consisting of switches SW1, SW2 and SW3 for selecting one of the voltages V1 and V2. And an amplifier 200 having four differential pairs (Q0A, Q0B), (Q1A, Q1B), (Q2A, Q2B), (Q3A, Q3B). These four differential pairs are each driven by a separate current source, and the output pairs of the four differential pairs are commonly connected to the input / output pairs of the current mirror circuit (QL1, QL2). The output signal is differentially input to the differential amplifier 205 and outputs an output voltage Vout to the output terminal. One of the input pairs of the four differential pairs (Q0A, Q0B), (Q1A, Q1B), (Q2A, Q2B), (Q3A, Q3B) has a feedback configuration commonly connected to the output terminal. . The other input pair of the four differential pairs (Q0A, Q0B), (Q1A, Q1B), (Q2A, Q2B), (Q3A, Q3B) is connected to the first switch group, one of which selects the voltage V1. The remaining three are connected to a third switch group (SW1, SW2, SW3) for selecting one of the voltages V1, V2. The operation of the DAC is performed by first and second switch groups (S1a,... Sna), (S1b,... Snb) by the output of an MSB (Most Significant Bit) subword decoder based on the upper bit signal of the input data. ) To turn on the K-th switch (Ska and Skb), select the voltages of adjacent taps as V1 and V2, and further switch the third switch by the output of the LSB (Least Significant Bit) subword decoder based on the lower bit signal of the input data Controls the switch of the group (SW1, SW2, SW3).

According to the selection conditions of the third switch group (SW1, SW2, SW3), four level voltages Vo1 to Vo4 obtained by internally dividing the voltages V1 and V2 at different ratios as shown in FIG. 19 are output to the output terminal. In particular,
When all the three switches SW1, SW2, and SW3 in the third switch group select the voltage V1, Vo1 equal to the voltage V1 is output.

  When two of the three switches SW1, SW2, and SW3 select the voltage V1, and one selects the voltage V2, Vo2 is output.

  When one of the three switches selects the voltage V1 and two select the voltage V2, Vo3 is output.

  ・ When all three switches select voltage V2, Vo4 is output.

  In order to linearly output the four level voltages Vo1 to Vo4 with high voltage accuracy, the four differential pairs (Q0A, Q0B), (Q1A, Q1B), (Q2A, Q2B), (Q3A, Q3B) is composed of transistors of the same size, and the current of the current source that drives each differential pair needs to be controlled to be constant. With the configuration and switch control as described above, the DAC of FIG. 18 can output a total of 4n level voltages to the output terminal by the MSB and LSB subwords.

  When the principle of the DAC is applied to the gradation voltage generation circuit 983, the decoder 984, and the buffer circuit 985 in FIG. 16, the number of gradation voltages output from the gradation voltage generation circuit 983 can be further greatly reduced. The number of elements of the decoder 984 for selecting the gradation voltage is also reduced, and the circuit scale can be greatly reduced.

JP 2001-34234 A (FIG. 16) US Pat. No. 5,396,245 (FIG. 5) US Pat. No. 6,246,351 (FIG. 2)

  By the way, the DAC of FIG. 18 can output four levels obtained by dividing the two voltages V1 and V2 by different internal division ratios by the amplifier 200 having four differential pairs. Here, the number of levels excluding the two voltages V1 and V2 is three.

  That is, in the DAC principle of FIG. 18, in order to be able to output a level excluding two voltages V1 and V2, (a + 1) differential pairs and a current source for driving them are required. And Therefore, there is a problem that the number of elements of the amplifier 200 increases and the area increases as the number of levels that internally divide the two voltages V1 and V2 increases.

  Therefore, the problem to be solved by the present invention is to provide an area-saving differential amplifier that can increase the number of levels internally dividing two voltages without increasing the number of differential pairs.

  Another problem to be solved by the present invention is to provide a display device data driver in which the circuit scale of the gradation voltage generation circuit, decoder, and amplifier is greatly reduced by using the differential amplifier. is there.

  Furthermore, another problem to be solved by the present invention is to provide a low-cost display device by using the data driver.

  A differential amplifier according to one aspect of the present invention, which provides means for solving at least one of the above problems, includes two input terminals to which two input signals are supplied, an output terminal, and two of the same polarity. Two differential pairs and two current sources for supplying currents respectively driving the two differential pairs, and one of the input pairs of the two differential pairs is connected to the two input terminals, respectively. The other of the input pairs of the two differential pairs is connected to an output terminal, constitutes a load on the output pair of the two differential pairs, and a signal obtained by combining the output currents of the two differential pairs, A load circuit that outputs from a connection point between the output pair of the two differential pairs and a signal at a connection point between the output pair of the two differential pairs and the load circuit are input and a voltage is output to the output terminal. An amplifier circuit and a power supply for controlling a current ratio flowing through the two current sources; It includes a control circuit.

  In the present invention, the load circuit comprises a current mirror circuit.

  In the present invention, each of the two current sources has a transistor, and the current control circuit variably controls a bias voltage supplied to a control terminal of each of the transistors constituting the two current sources. And it is good also as a structure which controls the electric current sent through each of the said two differential pairs.

  In the present invention, the current control circuit may be configured to control a current ratio of the two current sources so that a total value of currents flowing through the two differential pairs is constant.

  A differential amplifier according to another aspect of the present invention is configured to have two different transistor characteristics between two input terminals to which two input signals are supplied, an output terminal, and a differential pair. Two differential pairs having the same polarity, and two current sources for supplying currents for driving the two differential pairs, respectively, and one of the input pairs of the two differential pairs is the two input terminals. The other input pair of the two differential pairs is connected to an output terminal, and the load of the output pair of the two differential pairs is configured to be obtained by synthesizing the output currents of the two differential pairs. A signal at a connection point between the output pair of the two differential pairs and the load circuit is input to the output terminal. And an amplifier circuit that outputs a voltage.

  The present invention may be configured to include two voltage supply terminals that receive a predetermined voltage signal, and an input control circuit that controls connection / disconnection between the two voltage supply terminals and the two input terminals. .

  A differential amplifier according to another aspect of the present invention drives two input terminals to which two input signals are supplied, an output terminal, two differential pairs of the same polarity, and the two differential pairs, respectively. Two current sources for supplying currents to each other, one of the input pairs of the two differential pairs is connected to the two input terminals, and the other input pair of the two differential pairs is connected to the output terminal. Connected, load the output pair of the two differential pairs, and output a signal obtained by combining the output currents of the two differential pairs from the connection point with the output pair of the two differential pairs. A load circuit, an amplifier circuit that inputs a signal at a connection point between the output pair of the two differential pairs and the load circuit, and outputs a voltage to the output terminal, and a plurality of different voltages are input, The same voltage is included based on the selection control signal. Select two voltages, and a, a selection circuit for supplying to said first and second input terminals. One output voltage is output from the output terminal for one combination of the two voltages selected by the selection circuit.

  In the present invention, when m different voltage levels (where m is a multiple of 8 plus 1) are output from the output terminal, the number of voltages supplied as the input voltage is [{(m−1) / 4} +2], and two voltages including the overlap are selected from the voltages of [{(m−1) / 4} +2], supplied to the two input terminals, and output 1 To the mth voltage level, the voltage supplied as the input voltage is the first, 3 + 4 × k (where k is an integer of 0, 1,..., (M−5) / 4), A configuration including the mth voltage level may be employed.

  A data driver of a display device according to another aspect of the present invention includes the above-described differential amplifier according to the present invention as a buffer unit. Alternatively, the data driver of the display device includes a gradation voltage generation circuit that generates a plurality of voltage levels, a decoder that outputs two voltages selected from the plurality of voltage levels based on input data, and an output from the decoder The above-described differential amplifier according to the present invention is provided as an amplifier circuit that inputs the input voltage and outputs a voltage corresponding to input data from an output terminal.

A method according to another aspect of the present invention includes two differential pairs, each of which receives a signal voltage from each non-inverting input terminal and has two inverting input terminals connected in common to the output terminal. Is supplied to each non-inverting input terminal in an overlapping manner, and a differential amplifier that outputs a voltage obtained by dividing the first and second voltages and the first and second voltages is used. This is a control method that enables the output of 1 (3 is a multiple of 8 plus 1) voltage level, and the first, 3 + 4 × k (where k Is an integer of 0, 1, ..., (m-5) / 4) and at least [{(m-1) / 4} +2] voltage levels consisting of the mth voltage level, and the input voltage Two voltages including duplication from among the voltages [{(m−1) / 4} +2] supplied as And a step of selecting,
Supplying two selected voltages to the non-inverting inputs of the at least two differential pairs.

  According to the present invention, in a differential amplifier having two differential pairs of the same polarity, two input voltages are received, and two input voltages and two or more level voltages dividing between them are output. There is an effect that a differential amplifier that can be realized can be realized.

  Further, according to the present invention, n differential amplifiers (where n is a positive number of 3 or more) can receive two input voltages and output two input voltages and three levels of intermediate voltages. A differential amplifier that can output (2n + 1) or more level voltages at substantially equal intervals by inputting two predetermined combination voltages including the same voltage as two input voltages There is an effect that can be.

  According to the present invention, in a differential amplifier having two differential pairs of the same polarity, two input voltages are received, and two input voltages and two or more level voltages dividing between them are output. By using the differential amplifier that can be used for the output buffer portion of the data driver of the display device, the number of gradation voltages generated by the gradation voltage generation circuit is reduced, and the circuit scale of the decoder and the output buffer portion is reduced. Therefore, the area of the data driver can be saved (cost reduction).

  According to the present invention, n (where n is a positive number of 3 or more) differential amplifiers that can receive two input voltages and output two input voltages and three levels of intermediate voltages. A differential amplifier that can output (2n + 1) or more level voltages at substantially equal intervals by inputting two predetermined combination voltages including the same voltage as two input voltages from among the voltages is provided on the display device. By using it in the output buffer section of the data driver, the number of gradation voltages generated by the gradation voltage generation circuit can be reduced, and the circuit scale of the decoder and the output buffer section can be reduced. It is possible to reduce the cost).

  Furthermore, according to the present invention, by using the data driver with the reduced area for the display device, it is possible to reduce the cost of the display device and reduce the frame.

It is a figure which shows the structure of the differential amplifier of the 1st Embodiment of this invention. It is a figure which shows the structure of the differential amplifier of the 2nd Embodiment of this invention. It is a figure explaining the 1st effect | action of the 1st Embodiment of this invention. It is a figure explaining the 2nd effect | action of the 1st Embodiment of this invention. It is a figure explaining the 1st effect | action of the 2nd Embodiment of this invention. It is a figure which shows the structure of the digital / analog converter of the 3rd Embodiment of this invention. It is a figure which shows the structure of the digital / analog converter of the 4th Embodiment of this invention. It is a figure which shows the Example of the selection method of the binary input voltage of the 4th Embodiment of this invention. It is a figure which shows the other Example of the selection method of the binary input voltage of the 4th Embodiment of this invention. It is a figure which shows the structure of the differential amplifier of this invention used for simulation. It is a figure which shows the input-output characteristic of the differential amplifier of this invention in a 3rd effect | action. It is a figure which shows the input-output characteristic of the differential amplifier of this invention in a 4th effect | action. It is a figure which shows the other input / output characteristic of the differential amplifier of this invention in a 4th effect | action. It is a figure which shows the input-output characteristic of the differential amplifier of this invention in a 5th effect | action. It is a figure which shows the structure of a display apparatus. It is a figure which shows the structure of the conventional data driver. It is a figure which shows the other example of a structure of the conventional data driver. It is a figure which shows the structure of the conventional digital-analog converter. It is a figure which shows the input / output level correspondence in FIG. It is a figure which shows the structure of the differential amplifier of the 5th Embodiment of this invention.

  To describe the present invention in more detail, it will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the differential amplifier according to the first embodiment of the present invention. Referring to FIG. 1, the differential amplifier according to the first embodiment of the present invention includes a first differential pair (101, 102), a second differential pair (103, 104), a first and a second differential pair. A current mirror circuit (111, 112) connected to each output pair of the differential pair and forming a common active load for the first and second differential pairs, and an output signal of the current mirror circuit (111, 112) And an output circuit 3 for outputting the voltage Vout, and a current control circuit 7 for controlling the currents (I1, I2) flowing through the first and second differential pairs. Hereinafter, the differential pair including the transistors 101 and 102 is also referred to as a differential pair (101, 102).

  The control terminal (gate) of the transistor 101 of the first differential pair is connected to the input terminal T1, and the control terminal (gate) of the transistor 103 of the second differential pair is connected to the input terminal T2. The control terminals of the two differential pairs of transistors 102 and 104 are both connected to the output terminal 3 so that the output voltage Vout is fed back. The terminal voltages of the input terminals T1 and T2 are VT1 and VT2, respectively.

  The current control circuit 7 is connected to the low-potential side power source VSS and drives the current I1 flowing through the first differential pair (101, 102), and the low-potential side power source VSS is connected to the second differential pair. The current control transistor 127 that drives the current I2 flowing through (103, 104), and a switch that can selectively apply a plurality of voltages (VB1 to VB4) to the respective control terminals (gates) of the current control transistors 126 and 127 It is composed of a group (SW1a to SW4a, SW1b to SW4b).

  Further, in FIG. 1, a current mirror circuit (between the output pair of the first differential pair (101, 102) and the second differential pair (103, 104)) and the high potential side power supply VDD ( 111, 112) shows a typical configuration. That is, in the current mirror circuit (111, 112), the source is connected to the power supply VDD, the drain and the gate are diode-connected, and the input of the current mirror circuit is the transistor 112, and the source is connected to the power supply VDD and the gate is the transistor 112. The transistor 111 is connected in common with the gate and the drain forms the output terminal of the current mirror. The input terminal of the current mirror circuit (the drain of the transistor 112) is commonly connected to the drains of the transistors 102 and 104, and the output terminal of the current mirror circuit (the drain of the transistor 111) is commonly connected to the drains of the transistors 101 and 103. The differential stage output terminal 4 is connected to the input terminal of the amplification stage 6.

  The differential amplifier shown in FIG. 1 can output a voltage obtained by internally dividing the voltages VT1 and VT2 of the input terminals T1 and T2 by a predetermined internal division ratio. In accordance with the control of the current ratio between the currents I1 and I2 flowing through the output, a plurality of levels of voltages having different internal ratios can be output.

  FIG. 2 is a diagram showing a configuration of the differential amplifier according to the second exemplary embodiment of the present invention. The differential amplifier according to the first embodiment shown in FIG. 1 has a configuration in which predetermined voltages are applied to the differential input terminals T1 and T2 of the transistors 101 and 103 as VT1 and VT2, respectively. The differential amplifier according to the second embodiment of the present invention includes an input control circuit 8 that selectively inputs the two supply voltages (V1, V2) to the terminals T1, T2. ing. In FIG. 2, the first differential pair (101, 102) and the second differential pair (103, 104) may be composed of transistors having different characteristics.

  On the other hand, fixed voltages VB11 and VB12 are applied to the control terminals of the current control transistors 126 and 127, respectively, and the currents I1 and I2 are controlled to a constant current ratio. Other configurations are the same as those of the differential amplifier of FIG. Therefore, the differential amplifier of FIG. 2 can output a voltage obtained by internally dividing the voltages VT1 and VT2 of the terminals T1 and T2 by an internal ratio according to the current ratio of the currents I1 and I2.

  The input control circuit 8 includes a terminal to which the supply voltage V1 is applied, switches 151 and 152 connected between the terminal T1 and the terminal T2, respectively, a terminal to which the supply voltage V2 is applied, and a terminal T1 and a terminal T2. , And switches 154 and 155 connected to each other. By controlling these switches, two supply voltages (V1, V2) can be selectively applied to the terminals T1, T2, including overlapping.

  In the differential amplifier of the second embodiment shown in FIG. 2, the voltage obtained by internally dividing the voltages VT1 and VT2 of the terminals T1 and T2 by a predetermined internal ratio can be output. By selectively inputting the voltages V1 and V2 to the terminals T1 and T2, it is possible to output a voltage having the same level as the voltages V1 and V2 and two levels of voltages that internally divide the voltages V1 and V2. .

  In the differential amplifiers of the first and second embodiments shown in FIGS. 1 and 2, the first differential pair (101, 102) and the second differential pair (103, 104) are N-channel transistors (same polarity), but may be a differential amplifier including two differential pairs of P-channel transistors, or may be configured with two differential pairs for different polarities. Of course.

  Next, operations of the differential amplifiers of the first and second embodiments shown in FIGS. 1 and 2 will be described below.

  First, in the differential amplifier of the first embodiment shown in FIG. 1, the operation when the voltages VT1 and VT2 at the terminals T1 and T2 are different from each other and satisfy the relationship of VT1 <VT2 is shown in FIG. And with reference to FIG.

  FIG. 3 is a diagram for explaining the operation when the current ratios of the currents I1 and I2 are equal in the differential amplifier of FIG.

  The transistors of the two differential pairs (101, 102) and (103, 104) of the differential amplifier of FIG. 1 have the same characteristics.

  Furthermore, currents (drain-source currents) flowing through the transistors 101, 102, 103, and 104 are denoted by Ia, Ib, Ic, and Id, respectively.

  FIG. 3 is a relationship diagram between the drain-source current Ids (vertical axis) and the voltage V (horizontal axis) with respect to the power supply VSS, and shows two characteristic curves (Ids-Vg characteristics) of the transistors 101 and 102 and the transistors 103 and 104. Is shown.

  In FIG. 3, a characteristic curve 1 corresponds to the transistors 101 and 102, a characteristic curve 2 corresponds to the transistors 103 and 104, and each of the transistors 101, 102, 103, and 104 of the two differential pairs has a characteristic curve. It has operating points a, b, c, and d above.

  Since the transistors 101 to 104 in FIG. 1 have the same characteristics, the two characteristic curves are merely shifted in the horizontal axis direction. Thus, the characteristic curves are shifted between the two differential pairs because the respective tails (source coupling terminals) of the two differential pairs can individually vary in potential.

  Regarding the current relationship between the transistors 101 to 104 under the above conditions, the following equation (1) holds for the differential pair (101, 102).

    Ia + Ib = I1 (1)

  The following equation (2) holds for the differential pair (103, 104).

    Ic + Id = I2 (2)

  The following equation (3) is established for the current mirror circuit (111, 112).

    Ia + Ic = Ib + Id (3)

  Furthermore, the following equation (4) is established from the current ratio condition (I1 = I2) and (1) and (2).

    Ia + Ib = Ic + Id (4)

  Note that the output terminal 4 (the drain of the transistor 111) of the current mirror circuit applies only a voltage signal to the amplifier circuit 6, and no steady current flows between the amplifier 6 and the output terminal 4.

  When the relational expressions (3) and (4) are solved, the relations of the following expressions (5) and (6) are obtained.

Ia = Id (5)
Ib = Ic (6)

  That is, under the above conditions, the current flowing through the transistors 101 and 104 is equal (Ia = Id) and the current flowing through the transistors 102 and 103 is equal (Ib = Ic) is the stable state of the differential amplifier of FIG. Become.

  The operating points a, b, c, and d at this time exist on the intersections of the characteristic curves 1 and 2 and the straight lines Ids = Ia = Id and Ids = Ib = Ic. Further, since the operating points b and d of the transistors 102 and 104 are common to V = Vout with respect to the horizontal axis V in FIG. 3, the operating points b and d are determined, and the operating points a and c are also determined. As shown. At this time, the figure connecting the four operating points on the characteristic curves of the transistors 101, 102, 103, and 104 is a parallelogram. Since the parallelogram side ad and side bc are equal to each other, the output voltage Vout is an intermediate voltage between the voltages VT1 and VT2.

  As described above, the transistors 101 to 104 have the same characteristics, and the output voltage Vout when the current ratios of the currents I1 and I2 are equal is a voltage (intermediate voltage) that internally divides the voltages VT1 and VT2 into 1: 1.

  Next, the case where the current ratio is changed will be described with reference to FIG. 4 shows that the transistors of the two differential pairs (101, 102) and (103, 104) of the differential amplifier of FIG. 1 have the same characteristics, and that the currents I1 and I2 are approximately twice that of I2. It is a figure which shows an effect | action at the time of setting to the current value (I1 = I2x2) which becomes.

  The terminal voltages VT1 and VT2 are set to VT1 <VT2 as in FIG.

  FIG. 4 shows the relationship between the drain-source current Ids (vertical axis) and the voltage V (horizontal axis) with respect to the power source VSS, as in FIG. Correspondingly, the characteristic curve 2 corresponds to the transistors 103 and 104, and the transistors 101, 102, 103, and 104 of the two differential pairs have operating points a, b, c, and d on the respective characteristic curves. Also in FIG. 4, the above equations (1) to (3) are established as the current relationship of the transistors 101 to 104.

  From the relationship between the currents I1 and I2 (I1 = I2 × 2), the following equation (7) is established.

    Ia + Ib = 2 × (Ic + Id) (7)

  By solving the relational expressions (3) and (7), the following expressions (8) and (9) are obtained.

Ia = (Ic + 3 × Id) / 2 (8)
Ib = (3 × Ic + Id) / 2 (9)

  When the currents I1 and I2 of the current sources 126 and 127 are different, the simple relational expression as in the case of FIG. 3 is not obtained, and the output stable state of the differential amplifier of FIG. It becomes the state.

  Note that the operating points b and d of the transistors 102 and 104 have the same V = Vout with respect to the horizontal axis V.

  At this time, since the current ratio between the currents I1 and I2 is set to be approximately twice that of I2, the output voltage Vout takes a value close to the voltage VT1. Therefore, by adjusting the current ratio of the currents I1 and I2, it is possible to extract the output voltage Vout that internally divides the voltages VT1 and VT2 into about 1: 2.

  Actually, it depends to some extent on the transistor characteristics of the two differential pairs and the magnitudes of the currents I1 and I2, but if these are set optimally, the current ratio of the currents I1 and I2 depends on the output voltage Vout. It is possible to correspond to some extent to the reciprocal of the internal ratio of the voltages VT1 and VT2. However, even in this case, when the voltage difference between the voltages VT1 and VT2 increases, the relationship between the reciprocal of the internal ratio and the current ratio gradually shifts.

  In FIG. 4, the case where the currents I1 and I2 of the current sources 126 and 127 are I1> I2 has been described. However, if I2 = I1 × 2, the output voltage that internally divides the voltages VT1 and VT2 into 2 to 1. It can be easily understood that Vout can be taken out.

  In general, the differential amplifier of FIG. 1 has a configuration in which the input voltage to the terminals T1 and T2 is fixed. If the current ratio of the currents I1 and I2 is I1> I2, the output voltage Vout is a voltage that internally divides the voltages VT1 and VT2 closer to the voltage VT1. If I1 <I2, the voltage is internally divided closer to the voltage VT2. The larger the difference between the current ratios, the larger the voltage VT1 or VT2. A close voltage can be output. By optimizing the conditions, it is possible to make the current ratio of the currents I1 and I2 correspond to the reciprocal of the internal ratio of the voltages VT1 and VT2. Therefore, the differential amplifier of FIG. 1 can output a plurality of levels of voltages that internally divide the voltages VT1 and VT2 if the current control circuit 7 switches and controls the current ratio of the currents I1 and I2.

  Even when the voltages VT1 and VT2 are set to different voltages, any of the plurality of bias voltages (VB1 to VB4) is set to a voltage for turning off the current control transistor 126 or 127 in the current control circuit 7. If one of the currents I1 and I2 is cut off by selecting the bias voltage, the voltage VT1 or VT2 can be output as the output voltage Vout. This is because the differential pair from which the current is cut off is in an inoperative state, and the voltage input to the other differential pair is output by the voltage follower action.

  Therefore, the differential amplifier of FIG. 1 changes the current ratio of the currents I1 and I2 flowing through the differential pairs (101, 102) and (103, 104) by controlling the switch group of the current control circuit 7. The same voltage as the two input voltages and a plurality of levels of voltages that internally divide the two input voltages can be output.

  Next, the operation of the differential amplifier according to the second embodiment of the present invention described with reference to FIG. 2 will be described. In the differential amplifier according to the second embodiment of the present invention, the input control circuit 8 can selectively supply the two supply voltages V1 and V2 (V1 <V2) to the terminals T1 and T2 including the overlap. it can. In FIG. 2, the current ratio of the currents I1 and I2 flowing through the differential pairs (101, 102) and (103, 104) is set to be constant.

  When the same voltage is supplied to the terminals T1 and T2 by the input control circuit 8, that is, when one of the voltages V1 and V2 is commonly input to the terminals T1 and T2 (VT1 = VT2), FIG. The differential amplifier operates in the same manner as a normal voltage follower circuit, and the output voltage Vout is equal to the voltage input in common to the terminals T1 and T2.

On the other hand, a case where different voltages are supplied to the terminals T1 and T2 by the input control circuit 8, that is, a case where one of the voltages V1 and V2 is input to the terminal T1 and the other is input to the terminal T2 will be described below. Here, when the current ratio of the currents I1 and I2 is I1> I2 or I1 <I2, the differential amplifier of FIG. 2 has the output voltage Vout of the terminals T1, T2 as described in FIG. The voltages VT1 and VT2 are divided into a constant internal ratio X to Y (excluding X = Y).
In the case of a differential amplifier in which the current ratio between the currents I1 and I2 is fixed, if there is no input control circuit 8 and two voltages supplied to the terminals T1 and T2 are fixed, the output voltage Vout is X Only one level voltage is internally divided into the internal ratio of Y.

  However, in the differential amplifier of FIG. 2, the voltage supplied to the terminals T1 and T2 can be switched by the input control circuit 8, so that the output voltage Vout is relative to the two voltages supplied to the terminals T1 and T2. It is possible to take a level voltage internally divided into the X to Y internal ratio or another level voltage internally divided into the Y to X internal ratio.

  In other words, the differential amplifier of FIG. 2 can output voltages of a plurality of levels having different internal division ratios by switching the voltages supplied to the terminals T1 and T2 by the input control circuit 8.

  Next, another example of the differential amplifier of FIG. 2 will be described. In the differential amplifier of FIG. 2, the current ratio of the currents I1 and I2 may be equal to I1 = I2, and the transistors of the differential pairs (101, 102) and (103, 104) may be configured with different characteristics. . The operation at this time will be described with reference to FIG.

  5 shows two differential pairs (101, 102) and (103, 104) in the differential amplifier shown in FIG. 2 with a W / L ratio (channel width with respect to channel length L) of the differential pair (101, 102). It is a figure which shows an effect | action when W ratio is set to 2 times the W / L ratio of a differential pair (103,104).

  FIG. 5 shows an example in which the input control circuit 8 selectively inputs the voltage V1 (VT1 = V1) to the terminal T1 and the voltage V2 (VT2 = V2) to the terminal T2, and the voltages V1 and V2 are , V1 <V2.

  FIG. 5 shows the relationship between the drain-source current Ids (vertical axis) and the voltage V (horizontal axis) with respect to the power source VSS, as in FIG. 3, and the characteristic curve 1 corresponds to the transistors 101 and 102. 2 corresponds to the transistors 103 and 104, and the transistors 101, 102, 103, and 104 of the two differential pairs have operating points a, b, c, and d on their characteristic curves.

  Since the differential pairs (101, 102) and (103, 104) are configured with different W / L ratios, the two characteristic curves are shifted in the horizontal axis direction, and the inclinations of the two characteristic curves are also different. ing.

  The current relationship between the transistors 101 to 104 in the differential amplifier of FIG. 2 is the same as that of FIG. 3 when the current ratio of the currents I1 and I2 is I1 = I2, and the above equations (1) to (6) Holds.

  The operating points a, b, c, and d at this time exist at the intersections of the characteristic curves 1 and 2 and the straight lines Ids = Ia = Id and Ids = Ib = Ic. Further, since the operating points b and d of the transistors 102 and 104 have the same V = Vout with respect to the horizontal axis V in FIG. 5, the operating points are as shown in FIG.

  From FIG. 5, the characteristic curve 1 has a slope twice as large as that of the characteristic curve 2 corresponding to the transistor size ratio, and the output voltage Vout at this time is obtained by comparing the voltages VT1 and VT2 of the terminals T1 and T2 with 1 to 2. The voltage is divided internally. Note that the internal ratio with respect to the voltages VT1 and VT2 depends on the size ratio between the two differential pairs (101, 102) and (103, 104). The voltage divided internally can be output.

  Therefore, as shown in FIG. 5, when the input control circuit 8 selectively inputs the voltage V1 (VT1 = V1) to the terminal T1 and the voltage V2 (VT2 = V2) to the terminal T2, the output voltage Vout is the voltage. This is a voltage that internally divides V1 and V2 into 1: 2. On the other hand, when the input control circuit 8 selects and inputs the voltage V2 (VT1 = V2) to the terminal T1 and the voltage V1 (VT2 = V1) to the terminal T2, the output voltage Vout has two pairs of voltages V1 and V2. The voltage is divided internally into 1. As described above, the differential amplifier of FIG. 2 can output a plurality of levels of voltages having different internal ratios by switching the voltages supplied to the terminals T1 and T2 by the input control circuit 8.

  Next, a third embodiment of the present invention will be described. FIG. 6 is a diagram illustrating a configuration of a digital-to-analog converter (abbreviated as “DAC”) according to the third embodiment of the present invention. Referring to FIG. 6, the DAC according to the third embodiment of the present invention includes an amplifier 200 and a third switch group (SW1, SW2, SW3) of the DAC shown in FIG. The differential amplifier 300 using the differential amplifier according to the first embodiment is replaced.

In the DAC of FIG. 6, the means for selecting two voltages input to the terminals T1 and T2 of the differential amplifier 300 has the same configuration as that of FIG. That is, a resistor string that outputs (n + 1) analog voltages V1, V2,..., Vn + 1 from each tap, and one voltage VK from each tap (where K is any one of integers from 1 to n). a first switch group including a n switches of Sna from S1a selecting a second switch group including a n switches of Snb from S1b selects the voltage VK + 1 level adjacent to the voltage V _K The Kth switches (Ska and Skb) of the first and second switch groups are turned on by the output of the MSB subword decoder based on the upper bit signal of the input data, and the voltage of the adjacent tap is set to VK (= VT1 ), VK + 1 (= VT2).

The DAC of the third embodiment of the present invention is different from the DAC shown in FIG. 18 in the third embodiment of the present invention by the output of the LSB subword decoder based on the lower bit signal of the input data. In other words, each switch of the current control circuit 7 is controlled. In other words, in the third embodiment of the present invention, the current control circuit 7 controls the current ratio of the currents I1 and I2 flowing in the differential pairs (101, 102) and (103, 104), so that the terminals T1, It is possible to output a plurality of levels of voltages that internally divide the voltages V _K and V _{K + 1} input to T2. Then, even if the number of voltage levels that internally divide the voltages V _K and V _{K + 1} is increased, the number of differential pairs does not increase, so that a special area saving can be realized as compared with the configuration shown in FIG. In the third embodiment of the present invention, when the number of voltage levels that internally divide the voltages V _K and V _{K + 1} is increased, the number of bias voltages and bias voltage supplied to the control terminals of the current control transistors 126 and 127 are increased. However, the bias voltage can be shared by a plurality of differential amplifiers 300. In this case, since the switch can be configured with a transistor of the minimum size, the influence on the area increase is sufficiently small. On the other hand, in FIG. 18, when the number of voltage levels that internally divide the voltages V1 and V2 selected by the output of the MSB sub-word decoder is increased, the number of differential pairs and current sources that drive the differential pairs and one end of the differential pair are increased. The number of third switch groups for selectively inputting the voltages V1 and V2 increases. In particular, the transistor that forms the differential pair and the current source directly needs to be set to a certain size because the element variation directly affects the accuracy of the linear output, which greatly affects the area increase.

  When the principle of the DAC of FIG. 6 is applied to the gradation voltage generation circuit 986, the decoder 987, and the buffer circuit 988 of FIG. 17, the number of gradation voltages output from the gradation voltage generation circuit 986 is changed to the gradation voltage of FIG. The number can be further reduced to ½ of the number of voltages, the number of elements of the decoder 984 for selecting the gradation voltage can be reduced, and the circuit scale can be significantly reduced.

FIG. 7 is a diagram showing a configuration of a digital-to-analog converter (DAC) according to the fourth embodiment of the present invention. In the DAC shown in FIGS. 18 and 6, two voltages (V _K , V _{K + 1} ) of adjacent taps among n voltages generated from the resistor string are selected and input to the differential amplifier. However, in the fourth embodiment of the present invention shown in FIG. 7, not only two adjacent tap voltages but also two arbitrary tap voltages such as two adjacent tap voltages or three adjacent tap voltages. The number of tap voltages can be reduced with respect to the number of output voltage levels.

Referring to FIG. 7, in the DAC according to the fourth embodiment of the present invention, the means for selecting two voltages input to the terminals T1 and T2 of the differential amplifier 400 includes n analog voltages V from each tap. ₁ , V ₂ ,..., V _n and a voltage V _S (where S is one of integers from 1 to n) for selecting one voltage V _S from each tap. The first switch group composed of the switches S1b to Snb for selecting one voltage V _J (where J is one of integers from 1 to n). It consists of two switch groups, and the S-th and J-th switches (Ssa and Sjb) of the first and second switch groups are turned on by the output of the decoder based on all bit signals (MSB + LSB) of the input data, and overlapped combinations of any of the tap voltage was also included _(V S, V _J Can be selected as the voltage at the terminal T1, T2 (VT1, VT2). Note that the DAC of FIG. 7 can be considered to be obtained by extending the number of voltage supply terminals of the input control circuit 8 to n in the differential amplifier (FIG. 2) of the second embodiment of the present invention.

  In the DAC of FIG. 7, the differential amplifier 400 is a differential amplifier capable of high-precision output while maintaining a predetermined internal ratio even in a voltage range where the voltage difference between the two voltages input to the terminals T1 and T2 is wide. An amplifier is desirable. For example, a differential amplifier that can output an intermediate voltage with respect to two input voltages as described with reference to FIG. 3 is one of the preferred configurations. That is, the differential amplifier 400 includes two differential pairs (101, 102) and (103, 104) that are composed of transistors having the same characteristics in the differential amplifier of FIG. 102) and (103, 104), a differential amplifier having a configuration in which the current ratio of the currents I1 and I2 flowing through each of them is equal (I1 = I2) can be used.

The operation of the differential amplifier 400 is the same as that described with reference to FIG. That is, the output voltage Vout is a voltage that internally divides the voltages VT1 and VT2 of the terminals T1 and T2 into one to one. This effect is established regardless of the voltage difference between the voltages V _S (= VT1) and V _J (= VT2) input to the terminals T1 and T2 in FIG. 7, and the transistors in the two differential pairs are identical. As long as it is a characteristic, it is established regardless of the shape of the characteristic curve. When the transistors constituting the differential pair have a channel length modulation effect or the like, the output voltage Vout gradually deviates from the intermediate voltage when the voltage difference between the two voltages V _S and V _J becomes very large. However, in general, this is an effect that can be achieved over a relatively wide range.

Next, a specific example in which the number of tap voltages can be reduced with respect to the number of output voltage levels by selecting an arbitrary combination voltage (V _S , V _J ) of the first and second switch groups in FIG. 7 will be described. To do. In the following specific example, an example in which linear output in which the output voltage level is equally spaced will be described.

  FIG. 8 is a diagram illustrating an example of a method of selecting two input voltages input to the terminals T1 and T2 of the differential amplifier 400 of FIG. In FIG. 8, there are nine voltages at equal intervals, four different voltages A, B, C, D output from each tap of the resistor string of FIG. 7, and 2 input to the terminals T1, T2. The correspondence of the two voltage combinations is shown in tabular form. The combination of the two voltages may be input to either terminal T1 or T2.

  In FIG. 8, the two voltages input to the terminals T1 and T2 are provided only in 4 or less of 1/2 of the 9-level output voltage. However, for example, when the voltage A is selectively inputted to one of the two terminals (T1, T2), the other two combinations of the voltages A, B, C, and D are possible. In this way, there are 10 combinations of the two voltages by the four voltages, thereby enabling 9-level linear output.

  The four input voltages A, B, C, and D are set to the first, third, seventh, and ninth voltage levels with respect to the nine-level output voltage, respectively.

  At this time, there are two possible combinations of two voltages inputted to the terminals (T1, T2) that realize the output of the fifth level: a combination of voltages B and C and a combination of voltages A and D.

  In FIG. 8, 1 to 8 levels out of 9 levels of output voltages are (0, 0, 0) to (1, 1, 1) with respect to 3-bit digital data (D2, D1, D0). It is possible to correspond to each data.

  FIG. 9 is another specific example of a method of selecting two voltages input to the terminals T1 and T2 of the differential amplifier 400 of FIG.

  Referring to FIG. 9, FIG. 9 shows a 17-level voltage at equal intervals, six different voltages A, B, C, D, E, and F output from each tap of the resistor string of FIG. It is a correspondence diagram of the combination of two voltages input to T1 and T2. The combination of the two voltages may be input to either of the terminals T1 and T2.

  In FIG. 9, there are only six voltages input to the terminals T1 and T2, which are about 1/3 of the 17-level output voltage. However, there are a total of 21 combinations of two voltages by six voltages, thereby enabling a 17-level linear output. The six voltages A, B, C, D, E, and F are set to the first, third, seventh, eleventh, fifteenth, and seventeenth voltage levels, respectively. There are a plurality of combinations of binary inputs for outputting the seventh, ninth and eleventh levels. In FIG. 9, among the 17 level voltages, 1 to 16 levels are set to (0, 0, 0, 0) to (1, 1, 1, 0) with respect to 4-bit digital data (D3, D2, D1, D0). It can correspond to each data of 1).

  8 and 9, the differential amplifier capable of outputting the intermediate voltage of the two voltages input to the terminals T1 and T2 is used to reduce the number of voltages supplied from each tap of the resistor string of FIG. A typical embodiment has been shown for 9-level and 17-level linear outputs, but it can also be applied to multi-level linear output configurations.

  According to the present invention, when the number of output voltages m (where m is a multiple of 8 plus 1) is a linear output, the number of voltages supplied to each tap of the resistor string in FIG. The number of input voltages) can be reduced to [{(m-1) / 4} +2].

  At this time, the voltage supplied from each tap of the resistor string in FIG. 7 is set to the 1st, (3 + 4k) th, and mth levels with respect to m output levels, and k is an integer greater than or equal to 0. , (3 + 4k) th is set to include (m-2) th.

  FIG. 8 shows a case where m = 9 and k = 0, 1, and FIG. 9 shows a case where m = 17 and k = 0, 1, 2, 3.

  As described above, the DAC of FIG. 7 can generate only a voltage with a fixed internal ratio with respect to the two input voltages to the terminals T1 and T2, but the differential amplifier 400 is generated at each tap of the resistor string. By selecting a combination voltage from the n voltages to be selected by the first and second switch groups according to input data, many level voltages more than twice the n voltages output from each tap of the resistor string A number can be output.

  The DAC according to the embodiment of the present invention is applied to the gradation voltage generation circuit 986, the decoder 987, and the buffer circuit 988 shown in FIG. 17, so that the number of gradation voltages output from the gradation voltage generation circuit 986 can be reduced. The number can be further reduced to ½ of the number of regulated voltages, the number of elements of the decoder 984 for selecting the gradation voltage can be reduced, and the circuit scale can be greatly reduced.

  Although the embodiments of the differential amplifier and the digital / analog converter according to the present invention have been described above, the configurations of FIGS. 1 to 7 are transistors without a back gate formed on an insulating substrate such as glass or plastic. It is also possible to adopt a configuration replaced with, and the same operations and effects as those described with reference to FIGS. 1 to 9 can be realized.

  Further, the data driver having the differential amplifier or the digital-analog converter according to the present invention can reduce the cost by reducing the decoder area, and if used as the data driver of FIG. Can be realized.

  In the liquid crystal display device of FIG. 15, the data driver 980 may be individually formed as a silicon LSI and connected to the display unit 960, or a polysilicon TFT (thin film transistor) is formed on an insulating substrate such as a glass substrate. It is also possible to form the circuit integrally with the display portion 960 by using a circuit or the like. In particular, when the data driver and the display unit are formed integrally, the area of the data driver is reduced, so that the frame can be narrowed (the width between the outer periphery of the display unit 960 and the outer periphery of the substrate can be reduced).

  By applying the differential amplifier according to the present invention to any of the data drivers of such a display device, including other methods, it is possible to promote cost reduction and narrowing of the display device. . For example, similarly to a liquid crystal display device, the differential amplifier according to the present invention is applied to a display device such as an active matrix driving type organic EL display that outputs a multi-level voltage signal to a data line for display. Of course, it can be applied.

  Next, simulation results demonstrating the operation and effect of the differential amplifier according to the embodiment of the present invention will be further described as an example with reference to the accompanying drawings.

  FIG. 10 is a differential amplifier simulation circuit for confirming the effect of the first embodiment of the present invention. FIG. 10 is also a diagram showing a specific example of the first embodiment shown in FIG. 1. The amplification stage 6 includes a P-channel transistor 109 that performs charging of the output terminal 3, and an output terminal. 3 and a power source VSS, and is composed of a current source 110 that performs a discharging action. Other configurations are the same as those shown in FIG.

  The transistor 109 is connected between the high potential side power supply VDD and the output terminal 3, and its gate is connected to the output terminal 4 (drain of the transistor 111) of the current mirror circuit (111, 112). The current source 110 is connected between the low potential side power source VSS and the output terminal 3. Although not shown in FIG. 10, a phase compensation capacitor is provided between the transistor 109 and the output terminal 3 as necessary.

  11 includes two differential pairs (101, 102) and (103, 104) configured by transistors having the same characteristics with respect to the differential amplifier of FIG. 10, and currents I1 flowing through the respective differential pairs are shown in FIG. This is an input / output characteristic (simulation) when the operation of FIG. 3 is performed under the condition that the current ratio of I2 is equal (I1 = I2) and the intermediate voltages of the voltages VT1 and VT2 of the terminals T1 and T2 are output.

  FIG. 11 shows the output voltage Vout when the voltage VT1 is constant among the two voltages VT1 and VT2 at the terminals T1 and T2 of the differential amplifier, and the voltage VT2 is changed within a range of ± 0.5V with respect to VT1. The output characteristics are shown.

  At this time, the output voltage Vout is a voltage obtained by dividing the two voltages (VT1, VT2) into two equal parts, and this output expected value is indicated by a broken line in FIG.

  From FIG. 11, the output voltage Vout is in the range of ± 0.5 V centered on 5 V, which is in good agreement with the expected output value (broken line), and the intermediate voltage between the two input voltages can be accurately obtained over a wide voltage range. It can be confirmed that it can be output.

  The above results also apply to the DAC according to the fourth embodiment of the present invention shown in FIG. 7. In the differential amplifier 400 of FIG. 7, two differential pairs (101, 102) and (103, 104) are obtained. Are configured with transistors having the same characteristics, and the current ratios of the currents I1 and I2 flowing through the respective differential pairs are equal (I1 = I2), the voltages VT1 and VT2 of the terminals T1 and T2 in a wide voltage range. Can be output with high accuracy. Therefore, the effect described with reference to FIGS. 8 and 9 can be realized, and the number of tap voltages can be greatly reduced with respect to the number of output voltage levels.

  12 includes two differential pairs (101, 102) and (103, 104), which are transistors having the same characteristics, with respect to the differential amplifier of FIG. 10, and currents I1 flowing through the respective differential pairs are shown in FIG. It is an input / output characteristic (simulation) when the current ratio of I2 is changed by the control of the current control circuit 7.

  FIG. 12 shows the input / output characteristics when the current ratio of the currents I1 and I2 is controlled to be switched to 2: 1 and 1: 2. The output voltage Vout becomes Vo2 and Vo3, respectively, when the current ratio of the currents I1 and I2 is controlled to be switched to 2: 1 and 1: 2. Also, output expected values that internally divide the voltages (VT1, VT2) of the terminals T1 and T2 into 1 to 2 and 2 to 1, respectively, are indicated by broken line Vo2 output expected value and Vo3 output expected value, respectively.

From FIG. 12, the output voltage Vout corresponds to the reciprocal of the current ratio of the currents I1 and I2 in the internal ratio of the voltages (VT1 and VT2) at the terminals T1 and T2, and the output expected value (within ± 0.1V) (Vo2 output expected value, Vo3 output expected value) can be confirmed. In the voltage range where the output voltage Vout exceeds ± 0.1 V, the output voltage Vout gradually deviates from the expected output value.

  13 includes two differential pairs (101, 102) and (103, 104) configured by transistors having the same characteristics with respect to the differential amplifier of FIG. 10, and currents I1 flowing through the respective differential pairs are shown in FIG. It is a figure which shows the input-output characteristic (simulation result) when changing the current ratio of I2 into 1: 3, 1: 1, and 3: 1 by control of the current control circuit 7. FIG.

  In FIG. 13, the output voltage Vout becomes Vo2, Vo3, and Vo4 when the current ratio of the currents I1 and I2 is controlled to be switched to 3: 1, 1: 1, and 1: 3, respectively. Further, output expected values for internally dividing the voltages (VT1, VT2) of the terminals T1, T2 into 1: 3, 1: 1, and 3: 1 are respectively shown as Vo2 output expected value, Vo3 output expected value shown by broken lines in FIG. This is indicated by the expected Vo4 output value.

  As shown in FIG. 13, the output voltage Vout has an internal ratio of the voltages (VT1, VT2) at the terminals T1, T2 approximately corresponding to the reciprocal of the current ratio of the currents I1, I2, and an output expected value (in the range of ± 0.1V). It can be confirmed that it almost coincides with the broken line. In the voltage range exceeding 0.1 V, Vo2 and Vo4 gradually deviate from the expected Vo2 output value and the expected Vo4 output value, respectively, but the output voltage Vo3 having a current ratio of currents I1 and I2 of 1: 1 is Similar to FIG. 11, the Vo3 output expected value is in good agreement over a wide voltage range.

  FIGS. 12 and 13 show examples in which the internal ratio of the voltages VT1 and VT2 by the output voltage Vout substantially corresponds to the reciprocal of the current ratio of the currents I1 and I2. However, this relationship is related to the transistor characteristics and the current I1. , Depending on the setting of I2.

  12 and 13, the differential amplifier according to the first embodiment of the present invention can output a plurality of voltage levels that internally divide the two voltages input to the terminals T1 and T2 into different ratios. Indicated. It was also shown that a plurality of voltage levels including the same level as the input voltage can be output linearly. The same effect as that of the DAC of the third embodiment of the present invention using the differential amplifier of the first embodiment of the present invention can be realized.

  FIG. 14 shows input / output characteristics (simulation) when using the same amplification stage 6 as in FIG. 10 in the differential amplifier according to the second embodiment of the present invention shown in FIG. FIG. 14 shows that the transistor size W / L ratio of the differential pair (101, 102) is double the transistor size W / L ratio of the differential pair (103, 104) with respect to the differential amplifier of FIG. The current ratio between the currents I1 and I2 flowing through each differential pair is set equal (I1 = I2), and the input control circuit 8 switches and controls the input of the two supply voltages V1 and V2 to the terminals T1 and T2. This is the input / output characteristics.

  In FIG. 14, the output voltage Vout becomes Vo2 and Vo3, respectively, when the voltages input to the terminals (T1, T2) are controlled to be switched to (V1, V2) and (V2, V1). Also, the expected output values that internally divide the voltages (V1, V2) into 1-to-2 and 2-to-1 are shown as the expected Vo2 output value and the expected Vo3 output value in broken lines in the figure, respectively.

  From FIG. 14, it can be confirmed that the output voltage Vout substantially matches the expected output value (broken line) in the range of ± 0.1V. Note that, in the voltage range exceeding 0.1 V, the output voltage Vout gradually deviates from the expected output value. FIG. 14 shows that in the differential amplifier according to the second embodiment of the present invention, it is possible to output a plurality of voltage levels that internally divide the two voltages input to the terminals T1 and T2 into different ratios. It was also shown that a plurality of voltage levels including the same level as the input voltage can be output linearly.

  As described above, as shown in the four simulation results, the differential amplifier of the present invention can output a voltage obtained by dividing the two voltages input to the terminals T1 and T2 into a plurality of voltages. In a voltage range in which the voltage difference is relatively small (for example, about 0.1 V), a voltage divided into a plurality of voltages can be output with high accuracy.

  FIG. 20 is a diagram showing a configuration of a differential amplifier according to the sixth exemplary embodiment of the present invention. In the example shown in FIGS. 1 and 6, the differential amplifier having two differential pairs (101, 102) and (103, 104) having the same polarity has been described. Of course, it is possible to have a configuration in which each of the two polarities includes two differential pairs. The differential amplifier of FIG. 20 is an example of a configuration in which each of the two polarities includes two differential pairs. By including the differential pairs having different polarities, the dynamic range is increased and the linearity is improved. In this respect, it is superior to the configuration of FIG. Referring to FIG. 20, this differential amplifier is connected to an n-channel differential pair (101, 102) driven by a current source 126 connected to a low potential side power supply VSS, and also to the low potential side power supply VSS. N-channel differential pairs (103, 104) driven by the current source 127, two n-channel differential pairs connected between the output pairs of the n-channel differential pairs and the high-potential side power supply VDD. A current mirror circuit (P-channel transistors 111 and 112) that forms a common active load for each output pair of the differential pair, and an amplifier circuit that inputs an output signal of the current mirror circuit and outputs a voltage to the output terminal 3 6 is provided. In FIG. 20, the switch groups SW1a, SW1b to SW4a, SW4b in FIG. 1 are omitted for the convenience of drawing, but two n-channel differential pairs (101, 102), (103, 104) are omitted. The current control circuit 7 for controlling the current sources 126 and 127 for supplying the currents I1 and I2 to be respectively supplied to (1) is configured as shown in FIG.

  Further, the p-channel differential pair (201, 202) driven by the current source 226 connected to the high potential side power supply VDD and the p channel driven by the current source 227 also connected to the high potential side power supply VDD. Type differential pair (203, 204), connected between the output pair of the two p-channel type differential pairs and the low-potential side power supply VSS, and for each output pair of the two p-channel type differential pairs Current mirror circuit (N-channel transistors 211 and 212) forming a common active load, and an amplifier circuit 16 for inputting an output signal of the current mirror circuit and outputting a voltage to the output terminal 3. The current control circuit 17 for controlling the current sources 226 and 227 for supplying the currents I11 and I12 to be supplied to the two p-channel type differential pairs (201, 202) and (203, 204) is omitted for the convenience of drawing. However, it is the same as the current control circuit 7 shown in FIG. The input terminals (gate terminals) of each differential pair have the gates of the transistors 101 and 201 commonly connected to the input terminal T1, the gates of the transistors 103 and 203 commonly connected to the input terminal T2, and the transistors 102, 104, and 202. , 204 are commonly connected to the output terminal 3. Note that the terminal voltages of the terminals T1 and T2 are VT1 and VT2.

Also in the differential amplifier of FIG. 20, the current control circuits 7 and 17 can extract an output voltage that internally divides the two voltages (VT1 and VT2) into an arbitrary ratio. Also, in the example shown in FIGS. 2 and 7, similarly to FIG. 20, the configuration may include two differential pairs for different polarities, and each of the two polarities may have two differential pairs. The structure provided may be sufficient. In this case, the current source 126, 127, 226, 227 is set to a predetermined current value with respect to the differential amplifier of FIG. 20, and the input control circuit 8 of FIG. 2 is added to the terminals T1, T2, or Needless to say, the resistor string of FIG. 7 and the switches S1a to Snb may be added.
In the differential amplifiers of the first and second embodiments shown in FIGS. 1 and 2, the first differential pair (101, 102) and the second differential pair (103, 104) are N-channel transistors (same polarity), but may be a differential amplifier including two differential pairs of P-channel transistors, or may be configured with two differential pairs having different polarities. Of course.

  In the example shown in FIGS. 1, 2, 6, and 7, the connection point between the output pair of the two differential pairs (101, 102) and (103, 104) and the load circuit (111, 112) is amplified. The amplification stage 6 is configured by a differential amplification stage, and the output pair of two differential pairs (101, 102) and (103, 104) and the load circuit (111, 112). The connection point pair may be differentially connected to the input pair of the amplification stage 6. In the example shown in FIGS. 1, 2, 6, and 7, the load circuit (111, 112) is common to the two differential pairs (101, 102), (103, 104). Of course, a load circuit may be provided individually.

  The present invention has been described with reference to the above-described embodiments. However, the present invention is not limited to the above-described embodiments, and those skilled in the art within the scope of the invention of each claim of the present application claims. It goes without saying that various modifications and corrections that can be made are included.

  The differential amplifier described in the above embodiment is configured by a MOS transistor, and the driving circuit of the liquid crystal display device may be configured by a MOS transistor (TFT) made of, for example, polycrystalline silicon. In the above embodiment, the example applied to the integrated circuit is shown, but it is needless to say that the present invention can also be applied to a discrete element configuration.

T1, T2 Input terminal 3 Output terminal 6, 16 Amplification stage 7, 17 Current control circuit 8 Input control circuit 4, 14 Output terminal (differential stage output terminal)
101, 102, 103, 104, 211, 212 N-channel transistor 111, 112, 201, 202, 203, 204, 109 P-channel transistor 126, 127, 226, 227, 110 Current source 151, 152, 154, 155 Switch 200 Amplifier 205 Differential amplifier 300, 400 Differential amplifier 960 Display section 961 Scan line 962 Data line 963 TFT
964 Pixel electrode 965 Liquid crystal capacitance 966 Common electrode (counter substrate electrode)
970 Gate driver 980 Data driver 981 Latch address selector 982 Latch 983, 986 Gradation voltage generation circuit 984, 987 Decoder 985, 988 Buffer circuit

Claims (9)

A resistor string connected between the first voltage supply terminal and the second voltage supply terminal and outputting a plurality of voltages having different voltage levels from the plurality of taps;
The plurality of voltages output from the plurality of taps of the resistor string and a digital signal are input, and from among the plurality of voltages,
A combination of two identical voltages output from the same tap of the resistor string;
A combination of two different voltages with adjacent voltage levels output from two adjacent taps of the resistor string; and
A combination of two different voltages that are not adjacent to each other in voltage levels output from two different non-adjacent taps of the resistor string;
Is selected corresponding to the digital signal,
A selection circuit for outputting the two voltages of the selected combination;
A differential amplifier that inputs the two voltages output from the selection circuit and amplifies and outputs an intermediate voltage of the two voltages;
A digital-to-analog conversion circuit comprising: For the first to fourth voltages (A, B, C, D) having different voltage levels that are input to the selection circuit as the plurality of voltages,
The selection circuit uses the two voltages as
(1) First and first voltages (A, A),
(2) first and second voltages (A, B),
(3) Second and second voltages (B, B),
(4) first and third voltages (A, C),
(5) The second and third voltages (B, C) or the first and fourth voltages (A, D),
(6) Second and fourth voltages (B, D),
(7) Third and third voltages (C, C),
(8) Third and fourth voltages (C, D),
(9) Fourth and fourth voltages (D, D),
It is possible to select and output nine combinations of
The digital-analog converter circuit according to claim 1, wherein the differential amplifier is capable of outputting first to ninth voltage levels different from each other as output voltage levels.   The first to fourth voltages correspond to the first, third, seventh, and ninth output voltage levels with respect to the first to ninth voltage levels of the output voltage level. The digital-to-analog converter circuit according to claim 2. For the first to sixth voltages (A, B, C, D, E, F) having different voltage levels that are input to the selection circuit as the plurality of voltages,
The selection circuit uses the two voltages as
(1) First and first voltages (A, A),
(2) first and second voltages (A, B),
(3) Second and second voltages (B, B),
(4) first and third voltages (A, C),
(5) Second and third voltages (B, C),
(6) First and fourth voltages (A, D),
(7) The third and third voltages (C, C) or the second and fourth voltages (B, D),
(8) First and fifth voltages (A, E),
(9) Third and fourth voltages (C and D), or second and fifth voltages (B and E), first and sixth voltages (A and F),
(10) Second and sixth voltages (B, F),
(11) Fourth and fourth voltages (D, D), or third and fifth voltages (C, E),
(12) Third and sixth voltages (C, F),
(13) Fourth and fifth voltages (D, E),
(14) Fourth and sixth voltages (D, F),
(15) Fifth and fifth voltages (E, E),
(16) Fifth and sixth voltages (E, F),
(17) Sixth and sixth voltages (F, F),
The following 17 combinations can be selected and output.
2. The digital-analog converter circuit according to claim 1, wherein the differential amplifier is capable of outputting first to seventeenth voltage levels different from each other as output voltage levels.   The first to sixth voltages are the first, the third, the seventh, the eleventh, the fifteenth, the seventeenth, and the seventeenth, with respect to the first to seventeenth voltage levels of the output voltage level. 5. The digital-to-analog converter circuit according to claim 4, wherein the digital-to-analog converter circuit corresponds to the output voltage level. For the first to third voltages (A, B, C) having different voltage levels input to the selection circuit as the plurality of voltages,
The selection circuit uses the two voltages as
(1) First and first voltages (A, A),
(2) first and second voltages (A, B),
(3) Second and second voltages (B, B),
(4) first and third voltages (A, C),
(5) Second and third voltages (B, C)
It is possible to select and output five combinations of
The digital-to-analog converter circuit according to claim 1, wherein the differential amplifier is capable of outputting different first to fifth voltage levels as output voltage levels. For [{(m−1) / 4} +2] (where m = 8 × n + 1, n is a positive integer) input to the selection circuit,
The selection circuit selectively outputs the two voltages corresponding to the digital signal from the [{(m−1) / 4} +2] voltages.
The differential amplifier can output first to mth voltage levels as output voltage levels,
The [{(m−1) / 4} +2] voltages are first, (3 + 4 × k) (where k is 0) with respect to the first to mth voltage levels of the output voltage level. 2. The digital-to-analog converter circuit according to claim 1, wherein the digital-to-analog converter circuit corresponds to an m-th output voltage level. The differential amplifier is
First and second input terminals;
An output terminal for outputting an output signal;
A first and second difference each having an input pair with a first and a second input and an output pair with a first and a second output corresponding to the first and second inputs, respectively. Moving pair,
First and second current sources for supplying current to the first and second differential pairs, respectively;
With
The first input of the input pair of the first differential pair is connected to the first input terminal and the second input is connected to the output terminal;
The first input of the input pair of the second differential pair is connected to the second input terminal and the second input is connected to the output terminal;
A first connection point where the first outputs of the output pairs of the first and second differential pairs are connected in common;
A second connection point where the second outputs of the output pairs of the first and second differential pairs are connected in common;
A current mirror circuit having an input and an output connected to the second connection point and the first connection point;
An amplification stage that receives the signal at the first connection point as an input and outputs the inverted amplified signal to the output terminal;
With
8. The method according to claim 1, wherein the two voltages output from the selection circuit are respectively input to the first and second input terminals, and an intermediate voltage between the two voltages is amplified and output. The digital-to-analog converter circuit according to 1. Multiple output terminals,
A plurality of digital-to-analog converter circuits according to claim 1 corresponding to the plurality of output terminals,
The plurality of voltages output from the resistor string are input in common to the selection circuits of the plurality of digital-analog conversion circuits,
Video digital data corresponding to the plurality of output terminals as the digital signal is input to the selection circuits of the plurality of digital-analog conversion circuits, respectively.
A data driver for a display device, wherein output signals from the differential amplifiers of a plurality of digital-analog conversion circuits are output from the plurality of output terminals, respectively, in accordance with the video digital data.

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