JPS60167528A - Digital-to-analog converting circuit - Google Patents

Abstract

PURPOSE:To simplify the conversion into a semiconductor and to improve easily the converting accuracy of a D/A converting circuit, by providing a constant current source and (n) stages of control circuits for differential current switching circuits of said current source to specify each constant current value together with addition circuits of each constant current and addition current loads. CONSTITUTION:A constant current source contains TRs Q13-Q16 and resistances R5-R8, and the current values I1-I4 are set at In=AX2<n-1> (A: constant) by those resistances R5-R8. Then TRs Q1-Q4 control the differential current switching circuit of the constant current circuit, and a current mirror circuit A adds the constant currents. Thus inputs D1-D4, output currents and voltages are shown in a table. Here I2=2I1, I3=4I1 and I4=8I1 are satisfied together with TRQ17=Q15, R9=R10 and R12=1/2R9 respectively. Then TRs Q1-Q4 are turned on and off when inputs D1-D4 are set at 0 and 1. Therefore a load current I5 produces a current output of an integer multiple and the output voltage V3 is equal to the output voltage of an integer multiple as shown in the table. As a result, the potentials of 16 stages are produced with 4 bits. The converting accuracy is decided by the accuracy of the resistances which decide each constant current value.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a D
/A conversion circuit.

Conventional configurations and their problems In recent years, advances in semiconductor technology have led to the integration of analog and digital technologies in electronic devices configured with electronic circuits.
/A conversion and A/D conversion are becoming increasingly necessary and important. Furthermore, there is a strong desire to use semiconductors as much as possible in terms of the reliability, shape, and weight of electronic devices themselves. However, in conventional D/A conversion, as shown in Figures 1 and 2 (&) (b) (Q), there is a ladder resistance type that obtains the desired potential by controlling resistance division, and a ladder resistance type that obtains the desired potential by controlling the resistance division. There is a pulse duty type that generates a desired potential by changing the duty ratio and integrating it, but in the former ladder resistance type, D/A conversion accuracy is determined by the accuracy of the resistance value, so accuracy correction is made for each resistance element. It has the disadvantage of requiring a large number of parts, and also has major disadvantages in terms of cost, such as the large chip area and the large number of laser trimming parts when converting the entire device into a semiconductor. In addition, the latter pulse duty type has the advantage of having a small chip area when converted into a semiconductor, but has the disadvantages of noise radiation due to pulse waves and the need for an accurate lock generation circuit, etc., and the range of use is limited. There were disadvantages such as limited availability and high cost.

Purpose of the Invention The present invention provides a D/A that greatly improves the conventional drawbacks as described above and that can be easily installed inside a bipolar IC.
The purpose is to provide a changing circuit.

Structure of the Invention In order to achieve this object, the present invention comprises a constant current circuit using bipolar transistors and a constant current circuit so as to have a constant value, and a current mirror circuit that adds the constant currents of each constant current circuit. Provides a D/A conversion circuit that includes an additional current load, can be easily realized as a semiconductor, eliminates the need for a large number of correction points for accuracy improvement, and can be mounted together with other circuits in the same chip of a bipolar IC. do.

Description of examples Hereinafter, one embodiment of the present invention will be described based on FIG. 3.

FIG. 3 shows a 4-bit D/A conversion circuit. The constant current circuit includes transistor Q13 and resistor R5, transistor Q14 and resistor R6, transistor Q+s and resistor R7.
, a transistor Q1g, and a resistor R8, and their respective constant current values are 11, 2, 3, and 4. In these constant current circuits, transistors Q4s, Q14, Q, ts, Q,
Since a potential of ■1 is applied to the base of Il+, each constant current value can be set arbitrarily by the values of resistors R5, R6, R7, and Ra, and each constant current value in this circuit is In=AX2(A is a constant). Therefore, each constant current value is 2 = 2 = 11 = 11 = 4-8.

Transistors Q, s and Q6, Q7 and Q8, Q9 and Q, 1
0. Q, 11 and Q12 are differential current switching circuits that switch constant current circuits, transistors Ql, Q2, Qs,
Q4 is a control circuit that controls this switching circuit, and each stage becomes a constant current source controlled by the control circuit. Resistor R9, Rl
x, RIO and transistors Q17, Qll+ are current mirror circuits, and are connected to the collectors of transistors Q6, Q8, Qlo, Q, and tz in order to add each constant current. The resistor Fttt is a current mirror load and generates a potential proportional to the collector current of the transistor Qrs. That is, when this potential is Vs and the collector current is S, the output potential is VswRu×knee. The pace potential on one side of the differential current changeover switch is given by (2), and the potential is given on the other side through the resistors R1, IhR8, 14f, so that the transistors Q1, Q2, and
Each constant current is switched by turning Q3 and Q4 on and off. Dl, D2, D3, D4 are control transistors Qt,
This is a control input that turns on and off J, Qs, and Qa.

Now, the transistor Q1 is connected to the inputs D1, D2, and Da%D4.
Qs.

When potential data for turning on and off Q3 and Q4 is input, current output and output voltage as shown in the following table are obtained.

Here, the constant current values It, 2-2, 3, and 4 are as described above, 2-2 1, 3-4 1, 4-8 1, transistor Q17 Breath 8, Resistance R x R1ζResistance R1z - Fire R9 conditions are dropped, input D
It is assumed that transistors Q1 to Q4 are turned off when I to D4 are 0, and turned on when they are 1.

As is clear from the table, the circuit 5 generates a current output that is an integral multiple, and therefore the output voltage v3 becomes an output voltage that is an integral multiple.

Therefore, if each input data is input in binary code, 16 stages of potentials will be generated in the case of 4 bits.

In this way, the D/A conversion circuit can use n stages of constant current sources, and the accuracy of D/A conversion can be determined by focusing on the accuracy of each constant current value. This makes it easier to manage the resistance of each circuit that determines the current value. In addition, from the standpoint of the semiconductor structure, the resistance elements of each stage can be placed close to each other within the chip to minimize mutual distortion, making management and design easy. As is clear from the above explanation, the conversion circuit can be easily installed inside the bibolar E-C, the D/A conversion accuracy can be easily managed, and the circuit itself has a small number of elements, is simple, and can easily convert bits. In addition, the elements that cause defects in the circuit configuration are very different from bipolar semiconductor circuits, so installing this circuit will not increase the defective rate, etc., in terms of productivity, implementation, cost, etc. It is extremely effective.

[Brief explanation of drawings]

Fig. 1 and Fig. 2 show conventional examples, Fig. 1 is a basic configuration diagram of a ladder type, and Fig. 2 (a) (1)) (0) shows various pulse waveforms and their output voltages in a pulse duty type, respectively. FIG. 3 is a circuit diagram of an embodiment of the present invention. (Q13 and R11Q+4 and R6, Q+s and R7, Qts
and Rs)...constant current circuit, (Qll and Q6, Q7 and Q
8, Q9 and Q+o, Ql and Q, u)...differential current switching circuit, (Ql, Q, z, Q3, Q4)...control circuit,
(R9, R12, RIO, Ql7, Qlg)...Current mirror circuit, (Rn)...Load. Fig. 7 No. 2 1 (J Omitted- Riko 9 ≧＼ 0--□--1-

Claims (1)

[Claims] A constant current source composed of a constant current circuit using a bipolar transistor and a differential current switching circuit that switches the constant current circuit, and a control circuit that controls the differential current switching circuit are provided in n stages, and each of the constant current circuits is Constant current value is n-AX2
(A is a constant), and includes a current mirror circuit that adds the constant currents of each constant current circuit and an addition current load.