JP2000078014A - D/a converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a D/A converter which can freely adjust output amplitude. SOLUTION: One of switches 110-1 to 110-(p+1) is turned on with the control of a high potential side switch control circuit 112. Thus, potential drop quantity by resistance elements 109-1 to 109-p is set and applied potential on the resistance element 102-1 of a resistance string part 101 is adjusted. One of switches 117-1 to 117-(q+1) is turned on with the control of a low potential side switch control circuit 119. Thus, potential drop quantity by resistance elements 116-1 to 116-q is set and applied potential on the resistance element 102-n of the resistance string part 101 is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a D / A converter such as a string type D / A converter.

[0002]

2. Description of the Related Art Conventionally, as a D / A converter, for example,
A type in which voltage division is performed using a resistor string unit is known, and is called a string type D / A converter.
FIG. 4 is a circuit diagram schematically showing a configuration of a conventional string type D / A converter. As shown in FIG.
The resistance string section 401 of the A converter 400 includes n resistance elements 402-1 to 402-n connected in series. One end of the resistor string section 401 is connected to the power supply 405 via the high-potential-side divided resistor section 403, and the other end is connected to the ground 406 via the low-potential-side voltage dividing resistor 404.
It is connected to the.

The switch section 407 includes n + 1 switches 408-1 to 408- (n + 1). One end of each of these switches 408-1 to 408- (n + 1) is connected to the end of each of the resistance elements 402-1 to 402-n, and the other end is connected to the analog output unit 409. I have. Each switch 408-1 to 408- (n + 1)
Of the decoder 410 is controlled by an on / off control signal of the decoder 410. The decoder 410 has an input terminal 41
1 is converted into an on / off control signal, and the switches 408-1 to 408-1 of the switch unit 407 are converted.
408- (n + 1). In such a configuration, the potential difference between both ends of the resistor string 401
The pressure is divided at -1 to 402-n. And the switch unit 4
By turning on one of the switches 408-1 to 408- (n + 1) 07 based on an on / off control signal, an analog output corresponding to a digital signal can be obtained.

[0004]

The conventional AD converter as shown in FIG. 4 cannot obtain a value similar to the design value as the output amplitude of the analog output due to a manufacturing error of the resistor string section 401. It was difficult. Resistance string section 40
1 is caused by the fluctuation of the resistance value at the interconnection point of each of the resistance elements 402-1 to 402-n,
It occurs due to variations in resistance values of −1 to 402-n. Due to these fluctuations and variations, the ratio between the voltage dividing resistance value obtained by each of the resistance elements 402-1 to 402-n and the resistance value of the entire resistance string unit 401 becomes a value different from the design value. For this reason, conventionally, the output amplitude that matches the design value has been ensured by appropriately changing the layout of the integrated circuit.

However, in order to make such a layout change, the mask of the integrated circuit must be corrected. For this reason, the conventional AD converter has a problem that the development period, the development cost, and the like increase when trying to obtain an output amplitude value that accurately matches the design value. Also,
In the D / A converter, the output amplitude of the analog output may need to be changed in accordance with the specifications of the circuit at the subsequent stage. However, this change also involves a change in the layout of the integrated circuit, so that the development period and development cost are increased. And so on.

[0006] As a method of appropriately changing the output amplitude without changing the layout, a resistor string 401 is used.
It is also conceivable to provide a voltage terminal on the high potential side and a voltage terminal on the low potential side in the integrated circuit and directly supply a necessary potential to the resistor string portion 401. However, in this method, a voltage supply system must be provided in addition to the AD converter, which hinders miniaturization and cost reduction of the entire circuit.

A technique of providing a control circuit only on the high potential side of an AD converter is disclosed in Japanese Patent Application Laid-Open No. 61-258533. However, this technique can only adjust the maximum value of the output amplitude. It is not possible to shift the entire amplitude range.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an inexpensive D / A converter capable of freely adjusting the output amplitude without using an external system. With the goal.

[0009]

A D / A converter according to the present invention divides a potential difference between a first reference potential and a second reference potential based on a digital signal to convert the digital signal into an analog voltage. Conversion means for converting the signal into a signal; first control means for controlling the value of the first reference potential supplied to the conversion means; and second control for controlling the value of the second reference potential supplied to the conversion means. And a control unit.

According to such a configuration, the first reference potential and the second reference potential supplied to the conversion means can be changed by the first control means and the second control means, respectively. It is possible to arbitrarily adjust the amplitude of the voltage signal.

Further, in the D / A converter of the present invention,
Preferably, a plurality of switch means are provided, wherein the conversion means includes a resistor string portion formed by connecting a plurality of resistance elements in series, and one ends respectively connected to end portions of the plurality of resistance elements constituting the resistance string portion. And a single analog output unit connected to the other ends of the plurality of switch means constituting the conversion switch unit.

With this configuration, a predetermined potential difference is applied to the resistor string portion. Then, this potential difference is divided and output from the analog output unit.

Further, in the D / A converter of the present invention,
Preferably, the first control means includes a first voltage dividing resistor formed by connecting a plurality of resistive elements in series, and an end of each of the plurality of resistive elements constituting the first voltage dividing resistor. A first control switch unit having a plurality of switch means, one end of which is connected to the same power supply, and the other end of which is connected to the same power supply; and a switch provided in the first control switch unit. It is desirable to have a first control circuit for controlling on / off.

With this configuration, one of the switches of the first control switch section is turned on by the first control circuit. This makes it possible to arbitrarily set the combined resistance of the first control switch section. Therefore, the amount of potential drop by the first control switch unit can be arbitrarily set. The output potential of the first voltage-dividing resistor can be adjusted by setting the potential drop amount.

In practicing the present invention, it is preferable that each of the plurality of switch means constituting the first control switch is a p-channel transistor.

In practicing the present invention, it is preferable that each of the plurality of switch means constituting the first control switch is a CMOS transistor.

Further, in the D / A converter of the present invention,
Preferably, the second control means includes a second voltage dividing resistor formed by connecting a plurality of resistance elements in series, and an end of each of the plurality of resistance elements constituting the second voltage dividing resistor. And a second control switch unit comprising a plurality of switch means, one end of which is connected and the other end of which is grounded, and the on / off of a switch provided in the second control switch unit. It is desirable to have a second control circuit for controlling.

According to this structure, any one of the switches of the second control switch section is turned on by the second control circuit. This makes it possible to arbitrarily set the combined resistance of the second control switch section. Therefore, the amount of potential drop by the second control switch can be set arbitrarily. Therefore, it is possible to adjust the output potential of the second voltage dividing resistor.

In practicing the present invention, each of the plurality of switch means constituting the second control switch is preferably an n-channel transistor.

In practicing the present invention, the plurality of switch means constituting the second control switch are preferably CMOS transistors.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] First, a first embodiment of the present invention will be described by taking a string type D / A converter as an example.
This will be described with reference to FIGS. FIG. 1 is a circuit diagram schematically showing the configuration of the D / A converter according to the present embodiment. In the D / A converter 100 shown in FIG. 1, the resistor string unit 101 includes n resistor elements 1 connected in series.
02-1 to 102-n. Switch section 103
Has n switches 104-1 to 104-n. One end of each of the switches 104-1 to 104-n is connected to one end of each of the resistance elements 102-1 to 102-n, and the other end is connected to one analog output unit 105. Each switch 104-1 to 1
04-n is controlled by a conversion switch control signal of the decoder 106. The decoder 106
The digital signal input from the input terminal 107 is converted into a switch control signal for conversion and sent to each of the switches 104-1 to 104-n of the switch unit 103.

The high-potential side control switch unit 108 includes p resistance elements 109-1 to 109-p connected in series,
It has p + 1 switches 110-1 to 110- (p + 1). Each of the switches 110-1 to 110- (p + 1) has one end connected to an end of the resistance element 109-1 to 109-p, and the other end connected to the power supply 111. Each switch 1
ON / OFF of 10-1 to 110- (p + 1) is controlled by the high potential switch control signal of the high potential switch control circuit 112.

The high-potential-side switch control circuit 112 generates a high-potential-side switch control signal based on the high-potential-side control signal input from the input terminal 113, and switches the switches 110-1 to 110 of the high-potential-side control switch unit 108. Send to-(p + 1). The high-potential-side voltage dividing resistor unit 114 includes, for example, one resistor element, divides the potential output from the high-potential-side control switch unit 108, and supplies the divided voltage to the resistor string unit 101.

The low-potential-side control switch unit 115 includes q resistance elements 116-1 to 116-q connected in series,
It has q + 1 switches 117-1 to 117- (q + 1). One end of each of the switches 117-1 to 117-(q + 1) is connected to one end of each of the resistance elements 116-1 to 116 -q, and the other end is connected to the ground 118. ON / OFF of each of the switches 117-1 to 117- (q + 1) is controlled by a low-potential-side switch control signal of the low-potential-side switch control circuit 119.

The low-potential-side switch control circuit 119 generates a low-potential-side switch control signal based on the low-potential-side control signal input from the input terminal 120, and switches 117-1 to 117 of the low-potential-side control switch unit 115. Send to − (q + 1). The low-potential-side voltage dividing resistor section 121 includes, for example, one resistor element, divides the potential output from the low-potential-side control switch section 115, and supplies the divided voltage to the resistor string section 101.

In FIG. 2, (a) shows switches 110-1 to 110 provided in the high potential side control switch unit 108.
3B illustrates a configuration example of − (p + 1), and FIG. 4B illustrates switches 117-1 to 117-1 provided in the low potential side control switch unit 115.
17- (q + 1) is shown. As shown in FIG. 2A, the switches 110-1 to 110- (p
+1) is the p-channel transistor 20
1 can be used. The p-channel transistor 201 has a source connected to the power supply 111, a drain connected to one of the resistance elements 109-1 to 109-p, and inputs a high-potential-side switch control signal from a gate. As shown in FIG. 2B, the switch 1 on the low potential side
As each of 17-1 to 117- (q + 1), an n-channel transistor 202 can be used. The n-channel transistor 202 has a source connected to the ground 118 and a drain connected to the resistance elements 116-1 to 116-1.
16-q, and receives a low-potential-side switch control signal from the gate.

Next, the D / A converter 10 according to the present embodiment
The operation principle of 0 will be described. The uppermost resistive element 104-1 of the resistor string section 101 includes the high-potential-side voltage dividing resistor section 1
14, a predetermined high potential (described later) is applied. The lowermost resistance element 1 of the resistance string section 101
A predetermined low potential (to be described later) is applied to 04-n by the low-potential-side voltage dividing resistor unit 121. By the high potential and the low potential, a predetermined potential difference is given to the resistor string portion 101. The decoder 106 generates a conversion switch control signal based on the digital signal input from the input terminal 107. Then, one of the switches 104-1 to 104-n is turned on by the conversion switch control signal. As a result, the potential difference supplied to the resistor string unit 101 is divided, and the analog output unit 105
Output from

Here, the output potential (high potential) of the high potential side voltage dividing resistor 114 is set as follows. First, the high potential side switch control circuit 112
A high-potential-side switch control signal is generated based on the high-potential control signal input from the third switch. Any one of the switches 110-1 to 110- (p + 1) of the high-potential-side control switch unit 108 is turned on by the high-potential-side switch control signal. As a result, the combined resistance of the high-potential-side control switch unit 108 can be set arbitrarily, and therefore, the amount of potential drop by the high-potential-side control switch unit 108 can be set arbitrarily. By setting the amount of the potential drop, the output potential of the high-potential-side voltage dividing resistor 114 can be adjusted.

The output potential (low potential) of the low-potential-side voltage dividing resistor section 121 can be set as follows. First, the low-potential-side switch control circuit 119 generates a low-potential-side switch control signal based on the low-potential control signal input from the input terminal 120. Any one of the switches 117-1 to 117- (q + 1) of the low-potential-side control switch unit 115 is turned on by the low-potential-side switch control signal. Thereby, the low potential side control switch unit 1
08 can be arbitrarily set, and the amount of potential drop by the low-potential-side control switch unit 108 can be arbitrarily set.
Can be adjusted.

As described above, according to the D / A converter 100 according to the present embodiment, it is possible to adjust the high potential and the low potential supplied to the resistor string unit 101 by simply adding a simple circuit. It is possible. For this reason, even if an error occurs in the amplitude (amplitude value, local maximum value, and local minimum value) of the analog output signal due to a manufacturing error of the integrated circuit, etc., the high potential and the low potential are changed using the high potential control signal and the low potential control signal. By resetting, it is possible to arbitrarily adjust the amplitude (adjust the amplitude and shift the entire amplitude). Therefore, according to the present embodiment, the amplitude of the analog output signal can be accurately matched with the design value without changing the layout.

When it is desired to change the amplitude of the analog output signal to change the specification, it is only necessary to reset the high potential and the low potential using the high potential control signal and the low potential control signal.

Further, if the high-potential control signal and the low-potential control signal are stored in the high-potential side switch control circuit 112 and the low-potential side switch control circuit 119, the high potential control signal and the low potential side control signal can be stored only when the amplitude of the analog output signal is to be changed. Since the potential control signal and the low potential control signal may be input, there is no need to provide an external system at the time of mounting. Therefore, this embodiment is effective in reducing the size and cost of the circuit.

[Second Embodiment] Next, the first embodiment of the present invention will be described.
The embodiment will be described with reference to FIG. 3 taking a case of a string type D / A converter as an example. In the present embodiment, the switch 11 provided in the high-potential-side control switch unit 108 is used.
0-1 to 110- (p + 1) and the switches 117-1 to 117- provided in the low-potential-side control switch unit 115.
The configuration of (q + 1) is different from that of the first embodiment. FIG.
Are the switches 110-1 to 110- (p + 1), 1
It is a circuit diagram which shows the example of a structure of 17-1-117- (q + 1). As shown in FIG. 3, in the present embodiment, these switches are configured by CMOS transistors including a p-channel transistor 301 and an n-channel transistor 302.

When this switch is used as the high-potential side switches 110-1 to 110- (p + 1), the source of the p-channel transistor 301 and the drain of the n-channel transistor 302 are connected to the power supply 111. Then, the drain of p-channel transistor 301 and the source of n-channel transistor 302 are connected to resistance element 10.
What is necessary is just to connect to 9-1 to 109-p. The gates of the transistors 301 and 302 are supplied with a high-potential-side switch control signal.

On the other hand, when this switch is used as the switches 117-1 to 117- (q + 1) on the low potential side,
The drain of p-channel transistor 301 and the source of n-channel transistor 302 are connected to ground 118, and the source of p-channel transistor 301 and n
The drain of the channel transistor 302 is
116-q. In addition, each transistor 3
The low potential side switch control signal is supplied to the gates of 01 and 302.

When the switches 110-1 to 110- (p + 1) on the high potential side are composed of only p-channel transistors as in the first embodiment described above, the set potential on the high potential side becomes very low. In order to reduce the on-resistance sufficiently, the channel width of such a p-channel transistor must be increased. Therefore, the area of the integrated circuit increases.

On the other hand, in the present embodiment, the CMOS
Since a transistor is used, even when the p-channel transistor 301 cannot be fully turned on, the on-resistance can be compensated for by the n-channel transistor 302 and the set potential on the high potential side can be set low. That is, by making the switches 110-1 to 110- (p + 1) CMOS, it is not necessary to increase the channel width of the transistor, so that the area of the integrated circuit can be reduced.

The switches 117-1 to 117-1 on the low potential side
By constructing 17- (q + 1) with CMOS transistors, the p-channel transistor 301 can compensate even if the n-channel transistor 302 cannot be turned on due to the extremely high set potential on the low potential side. . That is, the switches 117-1 to 117- (q + 1) are set to the CMO
The S area can also reduce the area of the integrated circuit. It is clear that the present embodiment can also obtain the same effects as those of the first embodiment.

[0039]

As described in detail above, according to the present invention, a D / A converter capable of freely adjusting the output amplitude of an analog voltage signal can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of a D / A converter according to a first embodiment.

FIGS. 2A and 2B are circuit diagrams each showing an example of a specific configuration of a switch used in the D / A converter shown in FIG. 1;

FIG. 3 is a circuit diagram showing an example of a specific configuration of a switch used in a D / A converter according to a second embodiment.

FIG. 4 is a circuit diagram showing a configuration example of a conventional D / A converter.

[Explanation of symbols]

Reference Signs List 100 D / A converter 101 Resistance string section 102-1 to 102-n Resistance element 103 Switch section 104-1 to 104-n switch 105 Analog output section 106 Decoder 107 Decoder 108 High-potential side control switch section 109-1 to 109 −p, 116-1 to 116-q Resistance elements 110-1 to 110- (p + 1), 117-1 to 117- (q
+1) switch 111 power supply 112 high-potential-side switch control circuit 113, 120 input terminal 114 high-potential-side voltage dividing resistor 115 low-potential-side control switch 118 ground 119 low-potential-side switch control circuit 121 low-potential-side voltage dividing resistor

Claims (8)

[Claims] A converter for converting the potential difference between the first reference potential and the second reference potential based on a digital signal to convert the digital signal into an analog voltage signal; A first control means for controlling a value of the first reference potential, and a second control means for controlling a value of the second reference potential supplied to the conversion means. D / A converter. 2. The method according to claim 1, wherein the converting means includes: a resistor string portion formed by connecting a plurality of resistance elements in series; and one end connected to an end of each of the plurality of resistance elements constituting the resistance string portion. A conversion switch unit comprising a plurality of switch units, and one analog output unit connected to the other ends of the plurality of switch units constituting the conversion switch unit. 2. The D / A converter according to 1. 3. The first control means includes: a first voltage-dividing resistor section formed by connecting a plurality of resistance elements in series; and a first voltage-dividing resistor section comprising a plurality of resistance elements constituting the first voltage-dividing resistor section. A first control switch unit having a plurality of switch means, one end of which is connected to one end and the other end of which is connected to the same power supply; and a first control switch unit. And a first control circuit for controlling the on / off of the switch.
A converter. 4. The D / A converter according to claim 3, wherein each of said plurality of switch means constituting said first control switch is a p-channel transistor. 5. The D / A converter according to claim 3, wherein each of said plurality of switch means constituting said first control switch is a CMOS transistor. 6. The second control means includes: a second voltage-dividing resistor section in which a plurality of resistance elements are connected in series; and a second voltage-dividing resistor section comprising a plurality of resistance elements constituting the second voltage-dividing resistor section. A second control switch unit including a plurality of switch means, one end of which is connected to one end and the other end of which is grounded; and the switch provided in the second control switch unit The D / A converter according to any one of claims 1 to 5, further comprising: a second control circuit that controls on / off of the D / A converter. 7. The D / A converter according to claim 6, wherein each of said plurality of switch means constituting said second control switch is an n-channel transistor. 8. The D / A converter according to claim 6, wherein each of said plurality of switch means constituting said second control switch is a CMOS transistor.