JP2005269023A - Ladder resistor type d/a conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ladder resistor type D/A conversion circuit whereby the cost can be reduced by decreasing the number of buffers in use while decreasing the number of resistors in use and a D/A conversion output with high accuracy can be obtained. <P>SOLUTION: A control circuit 23 applies switch control to analog switches 16, 18, 19, 21, 22 to form series connection of first and second ladder resistors 2, 3 thereby causing a state that a voltage V2 is applied between both end terminals of the ladder resistors 2, 3 in the series connection, and provides an output of a D/A conversion signal from an output terminal OUT 2 through a first buffer 14 or a second buffer 15 on the basis of a 4-bit digital signal. Further, the control circuit 23 applies switching control to the analog switches 16, 18, 19 so as to separate the first and second ladder resistors 2, 3 from each other and provides an output of 3-bit D/A conversion signals from output terminals OUT 1, OUT 2 through the first and second buffers 14, 15. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ladder resistor type D / A conversion circuit that outputs a divided voltage of a ladder resistor in which a plurality of resistors are combined as a D / A conversion signal.

This type of ladder resistor type D / A converter circuit is capable of high-speed operation, and is widely used because variations in ladder resistors constituting the voltage divider circuit have little influence on the conversion accuracy. In order to perform an n-bit (n is a positive integer) D / A conversion process, in principle, n 2 resistors are required, but in recent years improvements have been made and various ladder resistance type D / A A conversion circuits have been proposed. As an example of this ladder resistance type D / A conversion circuit, Patent Document 1 discloses a DA converter. FIG. 3 schematically shows the configuration disclosed in Patent Document 1. In this circuit configuration, two different voltages are acquired from the first ladder resistor 2 based on the control of the control circuit 1, and these two voltages are used as the reference voltages VrefL and VrefH of the second ladder resistor 3, and the second ladder is used. By outputting the divided voltage of the resistor 3 by D / A conversion, a highly accurate D / A conversion output can be obtained and the number of resistors can be reduced.
JP-A-1-93932

  In the circuit configuration shown in FIG. 3, it is necessary to generate the reference voltages VrefL and VrefH of the second ladder resistor 3 by buffering the two voltages acquired by the first ladder resistor 2 with the buffers 4 and 5, respectively. , VrefH, at least two buffers 4 and 5 must be provided, and further, a buffer 6 must be provided to output the divided voltage of the second ladder resistor 3 at the subsequent stage. It is necessary to provide a buffer, resulting in high cost. In particular, when it is formed in a semiconductor integrated circuit device, there is a problem that the circuit area formed in the semiconductor chip is increased.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the number of used buffers while suppressing the number of resistors to be used, and to suppress the cost, and to achieve a highly accurate D / A. An object of the present invention is to provide a ladder resistance type D / A conversion circuit capable of obtaining a conversion output.

  According to the first aspect of the present invention, the switching circuit connects the first and second ladder resistors in series based on the switching signal output from the control circuit, and the first and second ladder resistors are connected in series. When switching to the first state in which the first or second predetermined voltage is applied, the control circuit changes the divided voltage of the first or second predetermined voltage by the resistors connected in series of the first and second ladder resistors. Based on the n-bit digital signal, it is output as 2 n D / A converted signals.

  At this time, the divided voltage of the predetermined voltage applied to the ladder resistor is output as 2 n D / A conversion signals based on an n-bit digital signal larger than k bits. A highly accurate D / A conversion output can be obtained as required. That is, since the k-bit and n-bit D / A conversion circuits can be configured only by the first and second ladder resistors, the comparison is made with a configuration in which k-bit and n-bit D / A conversion circuits are separately created. Thus, the number of resistors used can be reduced.

  In addition, a D / A conversion output can be obtained via the first or second buffer in the first state, and a D / A conversion output can be obtained via the first buffer in the second state. Therefore, it is not necessary to configure a buffer other than the first and second buffers for the D / A conversion circuit. Thereby, it is possible to obtain a highly accurate D / A conversion output with high resolution in the second state while suppressing the cost.

  Further, when the switching circuit switches to the second state in which the first and second ladder resistors are disconnected and at least the first predetermined voltage is applied to the first ladder resistor based on the switching signal output from the control circuit, the control is performed. The circuit outputs the divided voltage of the first predetermined voltage given to the first ladder resistor as 2 k power D / A conversion signals based on the k-bit digital signal. In addition, when high-precision D / A conversion output is not required, k-bit D / A conversion output can be obtained by switching as necessary.

  According to the second aspect of the present invention, the second ladder resistor is configured to be capable of outputting different m 2 (m is a positive integer) divided voltage when a second predetermined voltage is applied. In the second state, the switching circuit disconnects the first and second ladder resistors to provide the first predetermined voltage as the reference voltage to the first ladder resistor and supplies the second predetermined voltage to the second state. The control circuit is configured to be switched so as to be applied as a reference voltage to the ladder resistor, and in the second state switched by the switching circuit, the control circuit has a first predetermined first voltage based on a k-bit digital signal. The voltage divided by the ladder resistor is output through the first buffer as 2 k power D / A converted signals, and the second predetermined voltage of the second predetermined voltage is output based on the m-bit digital signal. Since the divided voltage by the ladder resistor is output through the second buffer as a 2 m power D / A conversion signal, when a high-resolution D / A conversion output is not required, a plurality of voltages are output in the second state. The D / A conversion output of the system can be obtained.

According to the invention described in claim 3, since the first and second predetermined voltages are the same voltage, the D / A conversion signal can be output with high accuracy.
Particularly when the D / A conversion circuit is formed in the semiconductor integrated circuit device as in the invention described in claim 4, the chip formation area can be suppressed.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2. In addition, the same code | symbol is attached | subjected and demonstrated to the same part as the structure demonstrated as background art.
FIG. 1 is a schematic block diagram of a ladder resistance type D / A conversion circuit 11 (hereinafter referred to as a D / A conversion circuit). In the present embodiment, an embodiment in which 3-bit and 4-bit D / A conversion circuits are switched and used will be described in order to facilitate understanding of the present invention.

  In FIG. 1, the D / A conversion circuit 11 includes a first ladder resistor 2 (resistors 2 a to 2 h), a second ladder resistor 3 (resistors 3 a to 3 h), and a voltage divided by the first ladder resistor 2. A plurality of analog switches 12 (analog switches 12a to 12h) connected so as to switch and output a voltage, and a plurality of analog switches 13 (analogs) connected so as to switch and output a divided voltage by the second ladder resistor 3 Switches 13a to 13h), a first buffer 14 that buffers the voltage switched and output by the analog switch 12, a second buffer 15 that buffers the voltage switched and output by the analog switch 13, and functions as a switching circuit. The analog switches 16 to 22 and the analog switch groups 12 and 13 and 16 to 22 are switched and controlled based on a switching signal. And a control circuit 23. The first and second buffers 14 and 15 have the same configuration as that of the buffers 4 to 6.

  For example, an analog switch 16, a first ladder resistor 2, and an analog switch 17 are connected in series between a node N1 to which a first predetermined voltage V1 of 3 V is applied as a reference voltage and the ground GND. The first ladder resistor 2 is configured by, for example, eight (plural) voltage dividing resistors 2a to 2h connected in series. These eight (plural) resistors 2a to 2h are composed of resistors having the same resistance value.

  For example, an analog switch 20, a second ladder resistor 3, and an analog switch 19 are connected in series between a node N2 to which a second predetermined voltage V2 of 3 V is applied as a reference voltage and the ground GND. Yes. Similarly, the second ladder resistor 3 is configured by, for example, eight (plural) voltage dividing resistors 3a to 3h connected in series. These eight resistors 3a to 3h are respectively It is comprised by the resistance of the same resistance value.

An analog switch 18 is connected between a common connection point of the analog switch 16 and the first ladder resistor 2 and a common connection point of the second ladder resistor 3 and the analog switch 19.
Analog switches 12a to 12g are connected between a common connection point between the resistors 2a to 2h connected in series and an input terminal of the first buffer 14 (non-inverting input terminal of the operational amplifier), respectively. An analog switch 12 h is connected between the common connection point of the first ladder resistor 2 and the analog switch 17 and the input terminal of the first buffer 14. The output terminal of the first buffer 14 is connected to the output terminal OUT1 and is connected to the output terminal OUT2 via the analog switch 21. An analog switch 22 is connected between the output terminal of the second buffer 15 and the output terminal OUT2.

  Analog switches 13a to 13g are connected between the common connection point between the resistors 3a to 3h connected in series and the input terminal of the second buffer 15 (non-inverting input terminal of the operational amplifier), respectively. An analog switch 13 h is connected between the common connection point of the second ladder resistor 3 h and the analog switch 19 and the input terminal of the second buffer 15. Each of the first and second buffers 14 and 15 is composed of one operational amplifier, and its input terminal is configured as a non-inverting input terminal of the operational amplifier, and the output terminal and the inverting input terminal of the operational amplifier are connected. It is formed by a voltage follower.

  The operational amplifier is usually configured by combining several tens of MOS transistors, impedance elements such as various resistance elements and capacitor elements, and particularly when formed in a semiconductor integrated circuit device, the operational circuit 23 described later. The semiconductor chip area is required much more than the internal configuration. In the present embodiment, since the first and second buffers 14 and 15 are composed of only two operational amplifiers, even if formed in the semiconductor integrated circuit device, the first and second buffers 14 and 15 are significantly larger than the conventional configuration described in the background art section. In addition, it is possible to reduce the formation area in the semiconductor chip.

  Each of the analog switches 12, 13, 16 to 22 has a control terminal, and conducts when the control signal applied to the control terminal is at the H level “1”, and the control signal applied to the control terminal is When L level is “0”, it becomes non-conductive. With respect to the circuit configuration described above, the control circuit 23 switches from the output terminal OUT1 or OUT2 to D by applying an H level or an L level to the control terminals of the analog switches 12, 13, 16 to 22 as switching signals. / A conversion signal is output.

Hereinafter, the configuration of the control circuit 23 will be described with reference to FIG.
The control circuit 23 includes a selection signal generation circuit 24 that generates a selection signal of H level or L level, first and second decoders with control terminals 25 and 26, and control terminals 25a of the decoders with control terminals 25 and 26. Decoder valid / invalid control circuits 27 and 28 for supplying control signals to A and 26a, signal generating circuits 29 and 30 for generating digital signals, and a selector 31 for selectively switching and outputting the digital signals supplied from the signal generating circuits 29 and 30, respectively. , And NOT gates 32 to 34.

  Among these, the selection signal generation circuit 24 uses “1” (=) as the selection signal when the ladder resistor type D / A conversion circuit 11 functions as a 4-bit D / A conversion circuit (referred to as the first state). “H” level) is output, and when the ladder resistor type D / A conversion circuit 11 is caused to function as a 3-bit D / A conversion circuit 2 circuit (referred to as a second state), “0” (= “L” "Level) is generated and output.

  When the signal generation circuits 29 and 30 are connected to each other and function as a 4-bit D / A conversion circuit, the signal generation circuit 29 outputs a lower-order 3-bit digital signal from the signal lines D12 to D10 and generates a signal. The circuit 30 outputs a high-order 1-bit digital signal from the signal line D20. At this time, the signal generation circuit 30 outputs an L level “0” to the signal lines D22 and D21.

  When the ladder resistor type D / A conversion circuit 11 functions as two 3-bit D / A conversion circuits, the signal generation circuits 29 and 30 respectively output 3-bit digital signals to the signal lines D12 to D10, D22. ~ D20 is output. Here, as shown in FIG. 2, the signal generation circuit 30 outputs a high-order 1-bit digital signal when the D / A conversion circuit 11 functions as a 4-bit D / A conversion circuit. The signal line D20 of the least significant bit (LSB) when functioning as a 3-bit D / A conversion circuit corresponds to the signal line D20 that outputs a bit digital signal (MSB).

  The signal lines D12 to D10 are connected to one input terminal of the first decoder with control terminal 25 and the selector 31, and the signal generating circuit 29 is generated in the first decoder with control terminal 25 and selector 31. A bit digital signal is provided. The signal lines D22 to D20 are connected to the other input terminal of the selector 31, and a digital signal generated by the signal generation circuit 30 is supplied to the selector 31.

  Since the first and second decoders with control terminal 25 and 26 have the same configuration, the configuration of the decoder 25 with control terminal will be described, and the description of the decoder 26 with control terminal will be omitted instead. As shown in FIG. 2, the basic configuration of the control terminal decoder 25 is a 3-bit decoder configured by combining a plurality of NOT gates 35a to 35f (previous stage) and a plurality of AND gates 37a to 37h (rear stage). A control terminal 25a is provided for this decoder. The control terminal-equipped decoder 26 is configured by combining a plurality of NOT gates 36a to 36f and a plurality of AND gates 38a to 38h.

  The control terminal 25a is connected to the input terminals of the AND gates 37a to 37h constituting the subsequent stage. When the control terminal 25a is given an H level “1”, the function of the decoder 25 with control terminal as a 3-bit decoder is effective. It becomes. Conversely, when the L level “0” is given to the control terminal 25a, the function as the 3-bit decoder is invalidated, and all the outputs of the decoder 25 with control terminal become the L level “0”.

  The eight outputs of the decoder 25 with control terminal are connected to the control terminals of the analog switches 12a to 12h for selectively outputting the divided voltage, respectively. Similarly, the control terminals of the analog switches 13a to 13h are The eight outputs of the decoder 26 with control terminal are connected to each other (none is shown). By selectively switching the analog switches 13a to 13h, a D / A conversion signal is output from the analog output terminal OUT1 or OUT2.

  As shown in FIG. 2, the selector 31 constitutes a general selection circuit in which AND gates 31a to 31f and OR gates 31g to 31i are combined. The selection signal of the selection signal generation circuit 24 is a NOT gate 33. Is supplied to the control terminal 31j of the selector 31, and based on this selection signal, the outputs of the signal generating circuits 29 and 30 are selected and output to the input terminal of the second decoder 26 with control terminal. It is like that.

  Specifically, in the first state, when the selection signal generation circuit 24 outputs H level “1”, the output of the signal lines D12 to D10 of the signal generation circuit 30 is output from the control terminal decoder 26 by the function of the selector 31. It is given to the input terminal. Conversely, in the second state, when the selection signal generation circuit 24 outputs L level “0”, the output of the signal lines D22 to D20 of the signal generation circuit 30 is input to the input terminal of the decoder 26 with control terminal by the function of the selector 31. Is to be given to.

  The signal line D20 is connected to the decoder valid / invalid control circuits 27 and 28. The decoder valid / invalid control circuit 27 includes a NOT gate 27a in the previous stage to which the signal of the signal line D20 is given as an input signal, a NOT gate 27b to which the selection signal of the selection signal generating circuit 24 is given as an input signal, and these NOT gates 27a. And an OR gate 27c at a subsequent stage to which the outputs of 27b are given as input signals. The decoder valid / invalid control circuit 28 includes a NOT gate 28a to which the selection signal of the selection signal generation circuit 24 is given as an input signal, and an OR gate 28b to which the signal of the signal line D20 and the output signal of the NOT gate 28a are given as input signals. It is comprised by.

  That is, the selection signal of the selection signal generation circuit 24 is supplied to the control terminal 25a of the decoder 25 with control terminal via the NOT gate 27b and the OR gate 27c of the decoder valid / invalid control circuit 27, and the selection signal generation The selection signal of the circuit 24 is supplied to the control terminal 26a of the decoder 26 with control terminal via the NOT gate 28a and the OR gate 28b of the decoder valid / invalid control circuit 28.

More specifically, when the selection signal generation circuit 24 outputs the L level “0” as the selection signal in the second state, the control terminals of the decoders with control terminals 25 and 26 are given the H level “1”. Thus, both the decoding functions of the decoders with control terminals 25 and 26 are enabled.
Conversely, in the first state, when the selection signal generating circuit 24 outputs the H level “1” as the selection signal, the OR gates 27 c and 28 b are given the L level “0”, and the control terminal decoder 25. The decode functions 26 and 26 are switched between valid / invalid according to the value of the digital signal applied to the signal line D20.

  More specifically, when the digital signal AD3 is applied to the signal line D20 in the first state, when the digital signal AD3 is at the H level “1”, the function of the first decoder 25 with control terminal is invalidated. The function of the decoder 26 with control terminal 2 is validated. Conversely, when the digital signal AD3 is at L level “0”, the function of the first decoder with control terminal 25 is validated and the function of the second decoder with control terminal 26 is invalidated.

  The output of the second decoder valid / invalid control circuit 28 is connected to the control terminal of the analog switch 22 and is connected to the control terminal of the analog switch 21 via the NOT gate 32. The selection signal of the selection signal generation circuit 24 is supplied to the control terminal of the analog switch 18 and is also supplied to the control terminals of the analog switches 16 and 19 via the NOT gate 34. .

In the second state, since the selection signal generation circuit 24 outputs L level “0” as the selection signal, the analog switches 16 and 19 are in the on state, the analog switches 17, 18, and 20 are in the off state, and the first state The second ladder resistors 2 and 3 are disconnected, and the voltages V1 and V2 are applied to both ends of both ladder resistors 2 and 3, respectively.
Further, in the second state, since the output of the decoder valid / invalid control circuit 28 is at the H level “1”, the analog switch 22 is turned on, the analog switch 21 is turned off, and the first and second buffers 14 are turned on. D / A conversion signals can be obtained from 15 and 15, respectively.

In the first state, since the selection signal generation circuit 24 outputs the H level “1” as the selection signal, the analog switches 16 and 19 are turned off, and the analog switches 17 and 20 are turned on. The second ladder resistors 2 and 3 are connected in series, and a voltage V2 is applied to both ends thereof.
Further, in the first state, since the selection signal generation circuit 24 outputs L level “0” as the selection signal, the analog switch 21 corresponds to the value of the digital signal AD3 output from the signal generation circuit 30 to the signal line D20. And 22 are switched. In this case, when the function of the decoder with control terminal 25 is enabled and the function of the decoder with control terminal 26 is disabled, the analog switch 21 is turned on, the analog switch 22 is turned off, and the first buffer 14, the D / A conversion signal is output to the output terminal OUT2. Further, when the function of the decoder with control terminal 25 is invalidated and the function of the decoder with control terminal 26 is validated, the analog switch 21 is turned off and the analog switch 22 is turned on, through the second buffer 15. The D / A conversion signal is output to the output terminal OUT2. In this way, the control circuit 23 is configured.

  In this way, the control circuit 23 includes AND gates 37a to 37h, 38a to 38h, 31a to 31f, NOT gates 35a to 35f, 36a to 36f, 27a to 27b, 28a, 32, 33, 34, OR gates 27c, 28b, Since 31g to 31i are formed in combination, the formation area of the control circuit 23 is significantly smaller than that of the first and second buffers 14 and 15 even if they are formed in the semiconductor integrated circuit device. Therefore, when the circuit described in the present embodiment is formed in the semiconductor integrated circuit device, the area of the element formation region depends on the first and second buffers 14 and 15, and the element is compared with the conventional one. There is an effect that the formation area can be greatly reduced.

The operation of the above configuration will be described.
(1) When the selection signal generated by the selection signal generation circuit 24 is “1” (= “H” level) (corresponding to the first state of the present invention)
When the selection signal is given by “1” from the selection signal generation circuit 24, the selector 31 switches so as to supply the digital signals D12 to D10 to the decoder 26 with control terminal. At this time, the analog switches 16 and 19 are switched so that the ladder resistors 2 and 3 are connected in series, and the D / A conversion circuit is synthesized. Further, the decoder valid / invalid control circuits 27 and 28 control the decoders 25 and 26 with control terminals. At this time, a negative signal of the signal given to the control terminal 26a of the decoder 26 with control terminal is given to the control terminal 25a of the decoder 25 with control terminal.

(1-1) When the Most Significant Bit MSB is “1” When the most significant bit MSB is “1”, the L level “0” is given to the AND gates 37a to 37h, respectively. At the same time, the H level “1” is given to the AND gates 38a to 38h, so that the function of the decoder 26 with control terminal is validated.

At this time, since the analog switch 22 is turned on and the analog switch 21 is turned off, the D / A conversion signal is outputted from the analog output terminal OUT2 through the analog switch 22 from the buffer 15.
(1-2) When the Most Significant Bit MSB is L Level “0” When the Most Significant Bit MSB is “0”, the H level “1” is given to the AND gates 38a to 38h, respectively. While the function is validated and the L level “0” is given to the AND gates 37a to 37h, the function of the decoder 25 with control terminal is invalidated.

At this time, the analog switch 22 is turned off and the analog switch 21 is turned on, so that the D / A conversion signal is output from the buffer 14 through the analog switch 21 from the analog output terminal OUT2.
(2) When the selection signal is “0” (= “L” level) (corresponding to the second state of the present invention)
When the selection signal is output as L level “0” from the selection signal generation circuit 24, the selector 31 switches so as to supply the digital signals D 22 to D 20 to the decoder 26 with control terminal. At this time, the digital signals D12 to D10 are given to the decoder 25 with control terminal.

  At the same time, “1” (= “H” level) is always applied to the final stage AND gates 37a to 37h and 38a to 38h constituting the decoders 25 and 26 with control terminals through the decoder valid / invalid control circuits 27 and 28. . Therefore, the decoder 25 with control terminal always functions as a general 3-bit decoder by being supplied with the digital signals D12 to D10. Similarly, the control terminal-equipped decoder 26 always functions as a general 3-bit decoder by receiving the digital signals D22 to D20.

At this time, the analog switch 22 is turned on when the H level (= “1”) is applied, and at the same time, the analog switch 21 is turned off when the L level (= “0”) is applied. Two signals are output to the analog output terminals OUT1 and OUT2 through the first and second buffers 14 and 15.
According to such an embodiment, in the first state, the control circuit 23 switches and controls the analog switches 16, 18, and 19 so that the first and second ladder resistors 2 and 3 are connected in series. With the voltage V2 applied across the connected ladder resistors 2 and 3, a 4-bit D / A conversion signal is passed through the first and second buffers 14 and 15 based on the 4-bit digital signal. In the second state, the first and second ladder resistors 2 and 3 are separated in parallel, and the voltages V1 and V2 are applied to both ends of the ladder resistors 2 and 3, respectively. Since a 3-bit D / A conversion signal is output through the first and second buffers 14 and 15 based on the 3-bit digital signal, the D / A conversion signal is output as needed. It is possible to obtain the A converted signal into a high resolution or 2-channel output. In addition, the number of resistors 2a to 2h and 3a to 3h constituting the ladder resistors 2 and 3 can be greatly reduced as compared with a configuration in which 4-bit and 3-bit D / A conversion circuits are individually created. become able to.

(Other embodiments)
The present invention is not limited to the above-described embodiment. For example, the following modifications or expansions are possible.
The present invention can also be applied to a D / A converter of a waveform shaping device described in, for example, Japanese Patent Application Laid-Open No. 8-271284 filed by the applicant of the present application.
In the above-described embodiment, the embodiment in which the D / A conversion circuit of 3 bits and 4 bits can be switched is shown. Absent.

1 is a schematic electrical configuration diagram showing an embodiment of the present invention. The figure which shows the circuit composition of the control circuit FIG. 1 equivalent view schematically showing a conventional example

Explanation of symbols

In the drawing, 11 is a ladder resistance type D / A conversion circuit, 14 is a first buffer, 15 is a second buffer, 12a to 12h are analog switches, 13a to 13h are analog switches, and 16 to 22 are analog switches (switching). Circuit), 25 and 26 are decoders with control terminals, 27 and 28 are decoder valid / invalid control circuits, and 31 is a selector.

Claims (4)

A control circuit;
First and second buffers;
A first ladder resistor configured to be capable of outputting 2 k power (k is a positive integer) different divided voltages by applying the first predetermined voltage as a reference voltage;
A second ladder resistor provided separately from the first ladder resistor and configured to output a divided voltage when a second predetermined voltage is applied;
A first and second ladder resistors are connected in series based on a switching signal output from the control circuit, and the first or second predetermined voltage is applied as a reference voltage to the ladder resistor group. A switching circuit that switches between the first state and the second state in which the first and second ladder resistors are separated and at least the first predetermined voltage is applied to the first ladder resistor as a reference voltage;
In the first state switched by the switching circuit, the control circuit includes the first and second ladders connected in series based on an n-bit (n is an integer larger than k) digital signal. The second state in which the divided voltage of the first or second predetermined voltage by the resistor is output through the first or second buffer as 2 n D / A conversion signals and switched by the switching circuit. , A divided voltage of the first predetermined voltage by the first ladder resistor based on a k-bit digital signal is output through the first buffer as 2 k power D / A conversion signals. A ladder resistance type D / A conversion circuit characterized by being configured. The second ladder resistor is configured to be capable of outputting different m 2 (m is a positive integer) divided voltage when a second predetermined voltage is applied,
In the second state, the switching circuit disconnects the first and second ladder resistors to provide the first predetermined voltage as a reference voltage to the first ladder resistor and supplies the second predetermined voltage to the second ladder resistor. Is configured to be switched so as to be given as a reference voltage to
In the second state switched by the switching circuit, the control circuit converts the divided voltage of the first predetermined voltage by the first ladder resistor based on a k-bit digital signal to 2k powers. A D / A conversion signal is output through the first buffer, and a divided voltage of the second predetermined voltage by the second ladder resistor is set to 2 m based on an m-bit digital signal. 2. The ladder resistor type D / A conversion circuit according to claim 1, wherein the ladder resistance type D / A conversion circuit is configured to output the signal as a squared D / A conversion signal through the second buffer.   3. The ladder resistor type D / A converter circuit according to claim 1, wherein the first and second predetermined voltages are the same voltage. 4. The ladder resistor type D / A converter circuit according to claim 1, wherein the ladder resistor type D / A converter circuit is configured in a semiconductor integrated circuit device.

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