JPH06164402A - D/a converter - Google Patents

Abstract

PURPOSE:To realize a D/A converter having a satisfactory precision and stability even in a bipolar integrated circuit. CONSTITUTION:Plural nodes of a resistor network 11 constituted by connecting plural resistors are driven by plural voltage sources 10a to 10c... respectively, and one prescribed end of the resistor network 11 is used as an output terminal, and respective voltage changes of plural voltage sources 10a to 10c... are outputted as the current change to the current output terminal with prescribed rates determined by the constitution of the resistor network 11, and as the whole, the sum of voltage changes of plural voltage sources 10a to 10c... weighted by certain values is outputted as a current. This current output is converted to a voltage by an operational amplifier 12 and a resistor 13 and is outputted from an output 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D / A converter.

[0002]

2. Description of the Related Art As a conventional D / A converter, FIG.
The circuit shown in is known. This D / A converter is
Published by CQ Publisher on February 20, 1980, "AD
/ DA conversion circuit design "on page 25.

In FIG. 4, according to the control signal supplied to the control inputs of B1 to Bn, the corresponding switches S1 to Sn are connected.
To control. The outputs of the switches S1 to Sn are the voltage source 41.
Voltage Vref or the ground potential. This switch S1
The outputs of .about.Sn drive the resistor network 42 composed of the resistors R and 2R which are resistor ladders. The output current from the resistor network 42 is converted into a voltage by the operational amplifier 43 and is output to the output terminal 44.

In this type of D / A converter, as long as the switches S1 to Sn can be regarded as ideal switches having an ON resistance of 0 and an OFF resistance of ∞, their contribution to the control signal supplied to the control inputs B1 to Bn is resistance. It can be accurately determined by setting the resistances 2R and R of the net 42.

However, in practice, it was difficult to specifically realize the switches S1 to Sn which can be regarded as ideal switches. In particular, if the switch has an ON resistance, the ON resistance of the switch is added to the resistance connected to the switch output. It is not practical because the contribution to the output for each control input deviates from the value determined by the resistance network configuration. For this reason, when implementing a D / A converter in a bipolar integrated circuit in which MOS transistors that are easy to make switches cannot be used,
In many cases, a weighted current type D / A converter was used.

FIG. 5 shows a conventional weighted current type D / A converter. In this circuit, control input B1
The contribution to the output of the control signals supplied to Bn to the resistors R to ^2n- 1R and the switching transistors Q1 to Qn.
It is determined by the emitter area ratio of n.

However, the contribution of the control signals supplied to the control inputs B1 to Bn to the output depends on the resistances R to 2 ^n-1 R.
Not only the relative accuracy of the switch transistors Q1 to Q
It is also affected by the relative accuracy of the emitter area ratio of n and the current amplification factor. In particular, the emitter area ratio is likely to have an error due to manufacturing variations, and if the error is forcibly reduced, it is necessary to use a large-sized transistor, resulting in an increase in manufacturing cost. In addition, since the current amplification factor of the transistor has a property of largely changing due to temperature change, it is difficult to accurately and stably set the contribution to each control input to the output.

As described above, the accuracy of the D / A converter used in the conventional bipolar integrated circuit is not only the resistance ratio whose relative accuracy is relatively easy to be taken, but also the accuracy of the emitter area ratio of the switch transistor and the current amplification factor. However, there is a drawback in that it is difficult to realize a D / A converter having good accuracy and stability, because it is also affected by those whose relative accuracy is difficult to obtain.

[0009]

DISCLOSURE OF THE INVENTION The conventional D / A described above
The converter depends on the emitter area ratio of the transistor, which makes it difficult to obtain relative accuracy, and the current amplification factor of the transistor, which has poor stability.
There is a drawback that it is difficult to realize an A converter. The object of the present invention is to provide D with good accuracy and stability.
The purpose is to realize the / A converter even in a bipolar integrated circuit.

[0010]

According to the D / A converter of the present invention, a plurality of nodes of a resistor network formed by connecting a plurality of resistors are driven by a plurality of voltage sources respectively, and a predetermined value of the resistor network is obtained. One end is used as an output end, and each voltage change of the plurality of voltage sources is output as a current change to the current output end at a predetermined ratio determined by the configuration of the resistor network, and the voltage of the plurality of voltage sources is overall. The current is output as the sum of the weights, each of which has a certain change.

[0011]

With the above-mentioned means, the conversion accuracy depends only on the resistance ratio which allows the relative accuracy to be easily obtained, so that the D / A converter can be realized in a bipolar integrated circuit while having good accuracy and stability. .

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 and 2 are reference power supplies, 3 is control input, 4 is an inverter, 5 and 6 are current sources, and Q1 and Q2.
And Q3 and Q4 are paired transistors, 7
Is a current mirror, 8 is an impedance converter, and 9b is a voltage source output, and constitutes a voltage source 10b. The voltage source output 9b of the voltage source 10b is passed through the resistor 2R of the resistor network 11 and the non-inverting input + is grounded, so that the operational amplifier 12 that realizes a D / A converter with good precision and stability even in a bipolar integrated circuit is provided. Connect to the inverting input of.

The voltage sources 10a, 10c, ... Have the same configuration as the voltage source 10b, and the voltage source output 9a of the voltage source 10a is an inverting input-via the resistor 2R of the resistor network 11.
Connect to. Further, the voltage source output 9c of the voltage source 10c
Is connected to the connection point of the resistors 2R and R connected in series with the output of the voltage source output 9b via the resistors 2R and R. Less than,
The same applies to the voltage sources 10d ... Not shown. The operational amplifier 12 converts the current output from the resistor network 11 together with the feedback resistor 13 into a voltage, and extracts the voltage output from the output 14.

In the voltage source 10b, the transistor pair Q
The current source 5 connected to the common emitters of 1 and Q2 turns on and off the current according to the control signal supplied to the control input 3, and the current source 6 connected to the common emitters of the transistors Q3 and Q4 is connected to the inverter 4. The current is turned on and off in a phase opposite to that of the current source 5.

Thus, when the current source 5 is on, the transistor pair Q1 and Q2, the current mirror 7 and the impedance converter 8 constitute a voltage follower, and the voltage source output 9b is the voltage VH of the reference power source 1. Outputs the same voltage as. When the current source 6 is on, the transistor pair Q3, Q4, the current mirror 7 and the impedance converter 8 form a voltage follower, and the voltage source output 9b has the same voltage VL as the reference power source 2. Is output. Drive the resistor network 11 with this voltage,
The output current of the resistor network 11 is converted into a voltage by the operational amplifier 12 and the resistor 13, and output from the output 14.

According to this embodiment, since the resistor network 11 is driven by the voltage follower output, the voltage source 10
The output impedance of b can be made sufficiently smaller than the value of the resistance network 11. The accuracy of the resistors is relatively high, regardless of the emitter area ratio of the transistor and the current amplification factor of which the temperature stability is poor, unlike the conventional D / A converter. It is almost determined only by the relative accuracy of the group, and a D / A converter having good accuracy and stability can be realized.

FIG. 2 is a more specific circuit diagram of FIG. Transistors Q5 and Q6 and resistors R1 and R2 constitute current sources 5 and 6, and control inputs 21 and 22 having opposite phases to each other.
As a result, only one of the currents flows. The transistors Q7 and Q8 are connected to the current mirror 7
The transistor Q9 and the constant current source 23 form an impedance converter 8.

Transistors Q5 and Q forming the current source 5
For 6, the gate transistor of the I ² L circuit used to create a logic circuit in a bipolar IC can be used as is, so an extra circuit is not required to transfer signals to and from the digital section, and the circuit scale is reduced accordingly. Can contribute to.

FIG. 3 shows another embodiment of the present invention. This embodiment corresponds to the case where the control input signal has three values in the circuit shown in FIG. By controlling so that only one of the current sources 5, 6, 34 is made to flow current by the control input terminals 31, 32, 33,
One of the transistor pairs Q1, Q2 and Q3, Q4 and Q10, Q11 is driven to output the voltage of the reference power source 1, 2, 35 to the voltage source output terminal 36b in accordance with each of the three values.

The operation of the circuit is similar to that of the embodiment of the present invention shown in FIG. Further, in this embodiment, the case where the control input has three values is shown, but it is needless to say that the same idea can be applied to the case where the control input has four or more values.

[0021]

As described above, the D / A of the present invention
According to the converter, since the conversion accuracy depends on only the resistance ratio which allows the relative accuracy to be easily obtained, the converter has good accuracy and stability, and realizes a D / A converter particularly useful in a bipolar integrated circuit. be able to.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a D / A converter of the present invention.

FIG. 2 is a circuit configuration diagram showing the configuration of FIG. 1 more specifically.

FIG. 3 is a circuit configuration diagram showing another embodiment of the present invention.

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

FIG. 5 is a circuit configuration diagram showing another conventional D / A converter.

[Description of Reference Signs] 10a to 10c ... Voltage source, 11 ... Resistor network, 12 ... Operational amplifier.

Claims (2)

[Claims] 1. A plurality of nodes of a resistance network formed by connecting a plurality of resistors are respectively driven by a plurality of voltage sources, and a predetermined one end of the resistance network serves as an output terminal, and each of the plurality of voltage sources is driven. The voltage changes of the above are output as current changes to the current output terminals at respective predetermined ratios determined by the configuration of the resistance network, and as a whole, the current output is the sum of the voltage changes of the plurality of voltage sources with certain weighting. A D / A converter characterized by: 2. A pair of first and second transistors whose emitters are commonly connected, and a first and a second current source which are respectively connected to commonly connected emitter ends of the pair of first and second transistors. A control means for controlling a current to flow through either one of the first or second current sources, and a base of each one of the first and second transistor pairs connected to different reference potentials; Means for connecting the bases of the other transistors of the first and second transistor pairs to the voltage output terminal in a state of being commonly connected, and means for connecting the bases of the first and second transistor pairs to the reference potential. The collectors of the transistors are commonly connected and connected to their inputs,
And a current mirror connected to its output in a state where the collectors of the transistors to which the bases of the pair of transistors are commonly connected are connected, and an impedance conversion means for converting the impedance of the output current of the current mirror and extracting the voltage output from the output. A D / A converter comprising: