JPS63135024A - D/a converter - Google Patents

Abstract

PURPOSE:To output a stable analog current with simple constitution without the need of any constant voltage power supply by setting the constant current value of a constant current element of an individual conversion circuit receiving a digital signal from a 2nd digit to twice of the constant current value of the constant current element of the individual conversion circuit receiving a digital signal of the preceding digit and connecting series circuit comprising a switch and a constant current element in the individual conversion circuit in parallel so as to impress a voltage. CONSTITUTION:The constant current element 81 of the 1st individual conversion circuit 1 is set to a constant current value having a resolution when a digital signal is converted into an analog signal and the constant current value of the 2nd-n-th constant current elements 82-8n of the 2nd-nth individual conversion circuits is set to twice the constant current value of the 1st-(n-1)th constant current elements 81-8(n-1) of the 1st (n-1)th individual conversion circuits 1-(n-1). Moreover, the series circuits each comprising the photodetector (71-7n) and the constant current element (81-8n) of the 1st-nth individual conversion circuits 1-n are connected in parallel, power is supplied from a power terminal V2 and an analog signal is outputted to an output terminal. Thus, a stable analog current is outputted without constant voltage power supply.

Description

[Detailed description of the invention]

[Field of Application] The present invention relates to a D/A converter which inputs a digital signal of at least 2 bits constituting each digit in a binary setting and changes an output current value in an analog manner in response to the input signal. [Background Art] Generally, when a control device and a load device are connected by an electric wire and the control device controls the load device using an analog signal, if this analog signal is an analog voltage, the input terminal may be damaged due to loss in the electric wire due to the distance. Since there is a voltage difference between the output terminal and the output terminal, the analog signal is sometimes converted into an analog current. Furthermore, if the control device performs digital processing, a D/A converter is required to convert the digital signal into an analog signal. In order to satisfy both of the above requirements, the input signal is 2 as shown in Figure 2.
A digital signal of at least 2 bits constituting each digit is input to a D/A converter (a), the output voltage is changed in analog form in correspondence with the digital signal, and this output voltage is passed through an amplifier (b). There has been a D/A converter that generates an output current of an analog value by inputting it to a transistor (c) and changing the base current of the transistor (c). In the case of the above, since the analog voltage is first converted and then converted to analog current, each circuit must be powered at a constant voltage due to the stability of the analog voltage and the stability of the analog current. It had to be supplied, and equipment for that purpose was needed. [Object of the Invention] An object of the present invention is to provide a D/A converter that can output a stable analog current without a constant voltage power supply. [Disclosure of the Invention] Accordingly, the D/A converter of the present invention receives an input signal of at least 2-bit digital signal constituting each digit in a binary setting, and outputs an output signal in response to this input signal. In a D/A converter that changes a current value in an analog manner, a plurality of individual conversion circuits each having a constant current element connected in series to a switch that opens and closes depending on an input signal is provided, and each individual conversion circuit converts each digit of a digital signal. The constant current value of the constant current element of the individual conversion circuit that inputs the signal and then inputs the digital signal from the second digit is twice the constant current value of the constant current element of the individual conversion circuit that inputs the digital signal of the previous digit. By setting the switch of each individual conversion circuit and the series circuit of the constant current element in parallel and applying voltage, it is possible to output a stable analog current using the constant current element without using a constant voltage power supply. It is something. Embodiment Below, the present invention will be explained based on FIG. 1, which shows an embodiment of the present invention.1 to n (n is a number of 2 or more) are first to n-th individual conversion circuits, and inputs 11 to Transistors 31 to 3 are connected to 1n via base resistors 21 to 2n.
A series circuit of light emitting elements 61 to 6n of resistors 41 to 4n and photocouplers 51 to 5n is connected in series between the collectors and emitters of the transistors 31 to 3n. Constant current elements 81 to 8n are connected in series to elements 7e to 7n. Moreover, power is supplied to the series circuit of transistors 31 to 3n, resistors 41 to 4n, and light receiving elements 71 to 7n from power supply line 1. Further, each of the first to n-th individual conversion circuits 1 to n described above inputs a digital signal of at least n bits constituting each digit in a binary setting, and converts the first digit of the digital signal to the first one. It corresponds to the individual conversion circuit 1, and the n-th digit corresponds to the n-th individual conversion circuit n. Thus, the constant current element 81 of the first individual conversion circuit 1 is set to a constant current value that has the resolution when converting a digital signal to an analog signal, and the constant current element 81 of the second to n-th individual conversion circuits 2 to n The constant current elements 82 to 8n correspond to the first to (n-1)th individual conversion circuits l to (n-1) corresponding to the front digits.
The constant current value is set to twice the constant current value of the constant current elements 81 to 8 (n-1) in 1). Furthermore, the series circuits of the light receiving elements 71 to 7n of the first to n-th individual conversion circuits 1 to n and the constant current elements 81 to 8n are connected in parallel, respectively, and power is supplied from the electric terminal A2 to the output terminal. Outputs an analog signal. 9 is the light receiving element 7 of the first to n-th individual conversion circuits 1 to n;
This constant current element is connected in parallel to the series circuit of constant current elements 1 to 7n and constant current elements 81 to 8n, and is used to set the initial value current in the absence of a digital signal. Constant current value is set. For example, as a specific example, if the input digital signal is a 4-bit input, the output analog signal is 4 to 20 mA, and the resolution is 2 mA, n of the individual conversion circuit is 4, and the constant current value of the constant current element 9 is 4 mA, the constant current value of the constant current element 81 of the first individual conversion circuit 1 is 2 mA, the constant current value of the constant current element 82 of the second individual conversion circuit 2 is 4 mA, and the constant current value of the constant current element 82 of the second individual conversion circuit 3 is 4 mA. The constant current value of current element 83 is 8m
A. The constant current value of the constant current element 84 of the fourth individual conversion circuit 4 is 16 mA, and the digital signal is

At [0000], the analog signal is 4 mA, when the digital signal is [0001], the analog signal is 6 mA, when the digital signal is (0111), the analog signal is 18 mA, and when the digital signal is (1000), the analog signal is 20 mA. In the example, the switches are connected to photocouplers 51 to 5n.
Although the light receiving elements 71 to 7n are used, relays may also be used. Further, although the constant current elements 81 to 8n and 9 are shown as constant current diodes in the drawings, they are not particularly limited. [Effects of the Invention] In the above configuration, a plurality of individual conversion circuits each having a constant current element connected in series to a switch that opens and closes in response to an input signal is provided, and each digit of the digital signal is transmitted to each individual conversion circuit. Set the constant current value of the constant current element of the individual conversion circuit that inputs the digital signal from the second digit to twice the constant current value of the constant current element of the individual conversion circuit that inputs the digital signal of the previous digit. However, since the switches of each individual conversion circuit and the series circuit of constant current elements are connected in parallel and a voltage is applied, it is not necessary to convert analog voltage to analog current as in the past, but directly converts digital signals to analog current. Therefore, there is no need for a constant voltage power supply, and it is possible to provide a D/A converter that can output a stable analog current with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a D/A converter according to the present invention, and FIG. 2 is a circuit block diagram of a conventional D/A converter. 1 to n - individual conversion circuits, 11 to In- inputs, 21
2n to 2n-resistors, 31 to 3n-...transistors, 4
1 to 4n-resistor, 51 to 5rt-photocoupler,
61 to 6n - light emitting element, 71 to 7n - light receiving element, 81 to 8n constant current element, 9 constant current element, vl -
Electric tA line, V2. -Power terminal.

Claims (1)

[Claims] (1) In a D/A converter that inputs at least a 2-bit digital signal constituting each digit in a binary setting, and changes the output current value in analog in response to this input signal, the input signal A plurality of individual conversion circuits each having a constant current element connected in series to a switch that opens and closes is provided, and signals of each digit of the digital signal are input to each of the individual conversion circuits. Set the constant current value of the constant current element of the conversion circuit to twice the constant current value of the constant current element of the individual conversion circuit that inputs the digital signal of the previous digit, and set the constant current value of the constant current element of the constant current element of each individual conversion circuit to D characterized in that series circuits of are connected in parallel and a voltage is applied.
/A conversion device.