JPH01114216A - Digital/analog converter - Google Patents

Abstract

PURPOSE:To always keep the inter-terminal resistance value of a load circuit constant, and to obtain a stable output by providing the individual resistor of a weighted resistor array with the respective contact points of a first contact point group and a second contact point group in parallel. CONSTITUTION:The title device is provided with a first weighted resistor array 5 provided with plural resistors weighted correspondingly to an input digital code in series, and a second weighted resistor array 6 cascade-connected to the above-mentioned first array, and the load circuit 4 provided with both the first contact point group which acts always to 'open' the individual resistor 5 of the first weighted resistor array, and the second contact point group 8 which acts always to 'close' the individual resistor of the second weighted resistor array 6 and is linked with the first contact point group respectively. Thus, analog quantity is obtained as the output of the load circuit according to an input digital signal, and the total sum of the resistance value of the resistor array of the load circuit comes constant always, and a stable voltage output is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a digital/analog device that outputs an analog quantity from an electrical quantity proportional to the weight of each bit corresponding to an input digital signal represented by a weight code, for example. converter,
In particular, it concerns the conversion into an electrical quantity proportional to the weight code.

[Prior Art] Fig. 5 shows a block diagram of a conventional digital-to-analog converter, in which 1 is a digital signal generator that outputs a digital signal of predetermined bits, and 4 is a digital signal generator that outputs an electric quantity proportional to the weight represented by each bit. 11 is a W quasi-power supply that generates a constant voltage; 16 is a voltage-current converter; and 17 is a summing amplifier.

A conventional digital-to-analog converter is configured as described above, and the input digital signal is a binary or decimal digital word consisting of a predetermined number of bits, and each bit is converted into a digital word. The electric quantity of voltage or current corresponding to the weight of each bit is converted, and by tightening this, an analog signal is output.

The above example is a current addition type digital-to-analog converter.

FIG. 6 shows a circuit diagram of another conventional digital-to-analog converter, in which 18 is a constant current source that opens and closes a group of switches in response to a binary signal from the digital signal generator 1. An analog signal of a predetermined level is obtained by adding currents from a plurality of constant current sources 18, which are proportional to the weight of the input signal having a value corresponding to each bit in the circuit 4, in the summing amplifier 17.

FIG. 7 shows a circuit diagram of another conventional digital-to-analog converter, and is an example using a ladder-shaped resistance circuit. Resistance R
A constant current source 18 is connected to each node of the circuit consisting of
When closed, a voltage proportional to the weight of the input digital signal is added to the output.

[Problems to be solved by the invention] In the conventional digital/analog exchanger as described above,
In the current addition type, Is/20, Ts/21...Is/2 for each bit in proportion to the weight of the panono signal
A plurality of n-1 constant current sources 18 are set.

If n=10, the current ratio is Is /2" - Is 1512, and the ratio of the current with the largest weight to the current with the smallest weight is 1:512
Therefore, it is difficult to realize the constant current source 18 with a predetermined accuracy.

Alternatively, in a ladder resistor circuit the same constant current source 18 can be used, but each pip! For each ~, multiple stages (pu na ε must be pulled).

Another problem is that one end of the output circuit of the digital-to-analog converter is grounded, and its output signal is limited to the summed current or summed voltage obtained by adding up the currents for each pin.

This invention was made in order to solve these problems.The resistance value between the terminals of the load circuit can always be kept constant, power can be supplied more stably than a single power supply, and the output circuit can receive resistance signals other than voltage. The object of the present invention is to obtain a digital-to-analog converter that can provide a balanced output.

[Means for Solving the Invention] A digital-to-analog converter according to the present invention includes two weighting resistors in which a plurality of weighting resistors of predetermined bits corresponding to the weighting of an input digital signal are provided in series and cascaded with each other.
a first contact group consisting of contacts that are individually connected in parallel to each resistor of the first weighted resistor string and are always open and respond individually according to each bit; 2
A load circuit consisting of a second contact group is provided, which is individually connected in parallel to each resistor of the weighted resistance series, and has a contact that is always "closed" and is interlocked for each bit corresponding to the bit of the first contact group. It is something.

[Function] In the present invention, a first weighted resistance string in which a plurality of resistors weighted in accordance with an input digital code are connected in series, and a second weighted resistance string cascade-connected thereto. and the individual resistors in the first small resistor string are always "open".
The first contact group consisting of the individual resistors of the second weighted resistance series is always "closed" and the second contact point consisting of the contacts that are interlocked for each bit corresponding to the pins 1 to 1 of the first contact group is connected respectively. Since the load circuits are installed in parallel, an analog amount can be obtained for the output of the load circuits according to the input digital signal.Predetermined contact points of the first contact group and the second contact group corresponding to each bit are set. Since the ``-1'' and ``close J'' operations are performed at the same time, the sum of the resistance values of the resistance strings of the weighted circuit is always constant, and the resistance value corresponding to the input digital code is set between the terminals of the second weighted resistance string. A stable voltage output can be obtained by attaching a constant current power supply to a resistor string whose resistance value is always constant.

In addition, the load circuit J can have a common intermediate terminal and have a balanced output of resistance or voltage.

[Example] An example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1.4.11 is the same as the conventional digital-to-analog converter, and 2 converts a binary input digital signal into a predetermined a decoder for converting to a hexadecimal digital output, 3
5 is a selection circuit that operates a contact provided in the load circuit 4, 5 is a first weighted resistor string in which a plurality of weighted resistors corresponding to n-ary digital are provided in series, and 6 is a first weighted resistor. A second weighted resistor array 7 having the same configuration as the array 5 and connected in cascade is provided in parallel with each of the individual resistors constituting the first weighted resistor array 5 and is always kept open. A first contact group 8 is provided in parallel with each individual resistor constituting the second weighted resistor 6 and corresponds to the bit of the first contact 7 which is always "closed". a second connection group consisting of contacts interlocking for each bit;
9 indicates a terminal, and 10 indicates an intermediate terminal.

In the digital-to-analog converter configured as described above, the binary or binary signal from the digital signal generator 1 is
The 0-ary digital signal is converted into a predetermined n-ary digital signal by the decoder 2, and excites, for example, a relay provided in the selection circuit 3 corresponding to the output of the decoder 2.

The load circuit 4 includes a first weighted resistance string 5 composed of a plurality of weighted resistors connected in series, a second weighted resistance string 6 connected in series thereto, and a first weighted resistance string 6 that is individually connected to each resistor in parallel. The selection circuit 3 consists of a first contact group 7 and a second contact group 8
The corresponding bits are linked by the excitation of the relays in the first contact group 7, and the predetermined contacts in the first contact group 7 change from "open" to "1 closed", and the contacts of the same bit in the second contact group 8 change to "1 closed". Since the operation simultaneously changes from "closed" to "open," the first weighted resistor array 5 and the second weighted resistor array 6 connected in cascade for each bit have an interpolation effect such that one of the contacts is always open. will be held.

Therefore, the sum of the resistance strings between the output heirs 8 of the load circuit 4 is 2°R+2' R+---+2nR and is always constant.

If n-77 bits are used, the total resistance value will be 255Ω.

Further, if the intermediate terminal 9 is used as a common terminal and each terminal 8 is used as an output, a balanced output can be obtained. The output resistance at that time is 1/2 of the total resistance value, that is, 127Ω and 128Ω.

FIG. 2 is a circuit diagram showing an example of a load circuit, and shows an example of a binary coded decimal digital signal, in which the input digital signal is binary and the output of the digital-to-analog converter is a decimal analog quantity. At this time, the first weighted resistance array 5 and the second weighted resistance array in the load circuit 4
The same operation as in the above embodiment can be achieved by simply changing the weighted resistor array 6 and decoder 8.

FIG. 3 is a circuit diagram showing an example of a decoder, and is an example of conversion from input digital decimal to output digital binary.

FIG. 4 is a circuit diagram showing another example of the decoder, and is an example of conversion from input digital binary to output digital decimal.

By selecting the resistance values of the first weighted resistance series 5 and the second weighted resistance series 6 so that the output resistance value at equilibrium becomes a predetermined value, the digital/analog i converter shares the intermediate terminal 9 with each other. A balanced output is obtained from terminal 8 of. The output of the digital-to-analog converter can be made into a voltage output by adding a constant current power source to the terminal 8 to the resistance value as an analog electrical quantity.

Of course, it can also be used to convert measurement signals and remotely transmitted signals into binary and n-ary analog quantities.

Since the digital-to-analog converter output circuit according to the present invention can be of one-end grounded or balanced type, it can be used for measurement and control in a wide range of fields.

Since the sum of the resistance strings between the terminals 8 of the load circuit 4 always forms a constant value 6), the load can be kept constant when a constant current power source is added, and the voltage conversion of the digital-to-analog converter is stable and accurate. This allows for highly accurate measurement and control.

[Effects of the Invention] 'This invention has been explained above, and the load circuit has first and second resistance strings in which weighted resistors are provided in series, and a weighted resistor is connected in parallel to each individual resistor in each resistance string. Due to the simple structure in which each contact of the first contact group and the second contact group is provided, the sum of the resistance strings between the output terminals of the load circuit that operates in response to each bit of the input binary or decimal digital is always a constant value. Therefore, the measurement signal @2 as a remotely transmitted signal
Conversion of base or decimal digital into an analog quantity can be used simply by correcting the resistance values of the decoder and the first and second weighted resistor arrays to predetermined values.

Since the resistance value between the terminals of the load circuit can be kept constant at all times, when a constant current power source is added to output voltage, the load resistance is always constant and a stable output can be obtained.

Further, since the output circuit of the digital-to-analog converter can be used as a balanced output of a resistor or f and tl voltages with a common intermediate terminal, there is an effect that it can be easily used in a control circuit of a balanced input type.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of a load circuit, Fig. 3 is a circuit diagram showing an example of a decoder, and Fig. 4 is a circuit diagram showing an example of a decoder. A circuit diagram showing another example, FIG. 5 (J), a block diagram of a conventional digital to analog converter, FIG. 6 is a circuit diagram of another conventional digital to analog converter, and FIG. 7 is a block diagram of another conventional digital to analog converter. 1 is a circuit diagram of a digital-to-analog converter. In the figure, 1 is a digital signal generator, 2 is a decoder, 3 is a selection circuit, 4 is a load circuit, 5 is a first weighted resistor string, and 6 is a second weighted resistor string. In the weighted resistor array, 7 is a first contact group, 8 is a second contact group, 9 is a terminal, and 10 is an intermediate terminal. Note that the same reference numerals in each figure indicate the same or equivalent parts. Patent applicant Co., Ltd. Tokyo Meter ~ 12- Figure 1 Figure 2

Claims (1)

[Claims] A digital-to-analog converter that includes a weight circuit controlled by an input digital signal having a weight code and outputs an analog electrical quantity proportional to the weight of each input bit, comprising: two sets of weighted resistors, first and second, in which resistors are provided in series and cascade-connected to each other; and resistors in the first weighted resistor series are individually arranged in parallel and are kept "open" at all times. None A first contact group consisting of contacts that respond individually according to each bit, and a resistor of the second weighted resistor string, which are individually arranged in parallel and are always "closed" and correspond to the bits of the first contact group. A digital-to-analog converter comprising a load circuit comprising a second contact group having contacts interlocking for each bit.