JPS6029044A - Digital/analog converter - Google Patents

Abstract

PURPOSE:To adjust dispersion of potential difference between base resistance of a transister TR and emitter, and even current value of each current source, thereby making it possible to be used for high bit by connecting base resistance between constant voltage generation measures and multiple transisters TRs. CONSTITUTION:For a D/A converter, multiple transisters Tr11-Tr16 and constant voltage generation operation amplifier OP are provided. To the emitter side of these multiple Tr11-Tr16, R-2R ladder resistance RR11 is connected, and output terminals Iout11-Iout12 are connected to the collector side of these transisters through switches S11-S14. Base resistance Rb is connected between the output side of this operation amplifier OP and base of respective Tr11- Tr16. Resitance Rb adjusts dispersion of potential difference between bases of Tr11-Tr16 and emitter, and entire current values in respective current source are evened, thereby making it possible to be used not only for low bit but also for high bit.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a digital-to-analog converter for converting digital signals into analog signals.

(2) Background of the Technology Recently, encoded digital signals have been widely used for processing and transmitting information, for example, because they provide stable results in terms of quality. However, since the results obtained from such digital signals cannot be used as they are, they are converted into analog signals as necessary, and a digital-to-analog converter is used here.

(3) Prior art and problems However, conventionally, in this type of digital-to-analog converter, for example, for 4 bits, the bases of transistors Tr+ to Tra are commonly connected as shown in FIG. 1, and a resistor Re is connected to the emitter side. There is one in which an R-2R ladder resistor RR is connected to the collector side via switches 81 to S4. Here ■yu is the output terminal.

The above output terminal I is turned on and off by turning on and off the switches 81 to S4 using a 4-bit binary code.

An analog output corresponding to Vr is generated.

By the way, the current source constituted by transistors TrI-Tr4 has a base voltage VIIE common to each transistor.
F, base-emitter voltage Vbe;

When the power supply voltage is V, the current l is determined by VRFF -Vbe -V ■ -□-e. However, although the potential difference between the base and emitter of transistors Tr+ to Tri is actually 0.7 to 0.8 V, it varies within a certain range, so the current values I in each current source are not equal.

Therefore, by trimming the value of the resistor Re on the emitter side, the currents {circle around (1)} in each current source are made equal.

By the way, as shown above, R~ is connected to the collector side of the transistor.
In the case of a converter having a 2R ladder resistor RR, the output impedance is determined by the R2R ladder resistor, so the output impedance cannot be increased and a highly accurate digital-to-analog converter cannot be obtained.

Therefore, as shown in Fig. 2, the conventional output impedance was increased by connecting the bases of transistors Tr1 to Tra in common, and connecting a 2-2R ladder resistor RR to the emitter side, and also connecting transistors Trz to Trb.
Output terminal ■ via switches 31 to S4 on the collector side of
There is one that connects 0IJT I +I OUT 2. Here, OP is a differential amplifier, and transistor T r
+ and resistor RB form a constant voltage circuit, and supply a constant voltage to the bases of the transistors Tr+ to Tr6. Further, the collector side of the transistor Trs is grounded.

According to the above, the output impedance is R
Since it is not influenced by -2R ladder resistance RR, it can be set to a large value.

However, since there is variation in the potential difference between the base and emitter of the transistors Tr+ and Trs, a difference occurs in the current in each current source. Therefore, it is possible to trim the emitter side resistance, that is, the R-2R ladder resistance RR, but if you trim the own emitter side resistance in this way, the relationship between the R-2R ladder resistance will be broken, and the potential drop at this time will be lower in the analog converter. It could only be used for low-level data up to 8 bits at most.

(4) Purpose of the Invention The present invention has been made to eliminate the above-mentioned drawbacks of the conventional technology, and can easily adjust the variation in the potential difference between the base and emitter of the transistor of each current source, and can be used for high-order bits. The purpose is to provide a digital-to-analog converter that makes it possible.

(5) Structure of the Invention The present invention is characterized by a plurality of transistors and an R-2 connected to the emitter and ivy sides of the plurality of transistors.
comprising an R ladder resistor, means for generating a constant voltage, and a base resistor connected between the means for generating the constant voltage and the base of the transistor to adjust variations in potential difference between the base and emitter of the transistor. A digital lure J-log converter featuring the following features:

(6) Examples of the invention An embodiment of the present invention will be described below with reference to FIG.

This embodiment shows an example in which the present invention is applied to a 4-bit digital-to-analog converter.

In FIG. 3, Tr++ to Tre6 are transistors,
An R-2R ladder resistor RR++ is connected to the emitter side of these transistors Tr++ to Tr+s. In addition, an output terminal 1°UTI I+ is connected to the collector side of the transistors Tr+ 2 to Tr Is via switches S++ to Se<.
rotrrl 2 is connected.

On the other hand, OP++ is a differential amplifier whose positive input terminal is grounded, and whose negative input terminal is connected to the collector of the transistor Tr+1, and whose collector is grounded through a resistor R++.

By the way, in the circuit shown in FIG. 3, there may be variations in the potential difference between the bases and emitters of the transistors 'pr++ to Tr+s as in the conventional case, but here, the base resistor R1 is trimmed and each transistor Tr1 is
1 to T r + The potential difference I generated by the current I flowing to the base of a and the base resistance R.

R1) is adjusted so as to cancel out the variation in the potential difference between the base and emitter of each transistor Tr++ to Tr+a, so that the emitter potential Ve of each transistor Tr++ to Tr16 becomes equal. In this case transistor T
Since the variations in potential difference between the bases and emitters of r++ to Tr+ 6 are individually adjusted by the base-side resistor RI+, the influence between the current sources can be eliminated. Therefore, if you do this, the transistor Tr+
Since the current values in the current sources having + to Tr16 can all be made equal, in this state, by turning on and off the switch Sll''S14 with a 4-bit binary code, a corresponding analog output can be obtained with high precision.

(7) Effects of the Invention The digital-to-analog converter according to the present invention can easily adjust the variation in the potential difference between the base and emitter of the transistors Tr++ to Tr+s, so that the current values in each current source can all be made equal. It can be used not only for low-order bits but also for high-order bits.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a conventional digital-to-analog converter, FIG. 2 is a circuit diagram showing another embodiment of the same converter, and FIG. 3 is a circuit diagram showing one embodiment of the present invention. . Tr++~Tr+a...Transistor RRII...
R-2R ladder resistance S++~S+a ・ ・ ・Switch Rh ・・Base resistance 0P11・・Operation amplifier Fig. 1 Fig. 2 ■ Fig. 3 (JV

Claims (1)

[Claims] a plurality of transistors, an R-2R ladder resistor connected to the emitter side of the plurality of transistors, a means for generating a constant voltage, and a resistor connected between the means for generating the constant voltage and the base of the transistor. A digital-to-analog converter comprising a base resistor for adjusting a normalization of a potential difference between the base and emitter of the transistor.