JPS6068728A - Digital-analog converter - Google Patents

Abstract

PURPOSE:To obtain a D/A converter with high accuracy by using a resistor and the 2nd transistor (TR) having an emitter area being n-times the emitter area of the 1st TR proportional to a weighting current. CONSTITUTION:Each element constituting a TR group for generating constant current consists of the 1st TR8 being a reference, the 2nd TR9 having the emitter area being n-times proportional to the weighting current, of the emitter area of the 1st TR8, and the resistor R10, and each element is connected to a prescribed resistor of an R-2R ladder resistance network 5. The temperature coefficient of the current flowing to the 1st TR of each element is negative and the temperature coefficient of the current flowing to the 2nd TR is positive, then the (n) and the resistance value R are set so as to zero the temperature coefficient as a whole thereby compensating the temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current adding type I)/A converter, and particularly to a current adding type I)/A converter.

Conventionally, as shown in FIG. 1, a current adding type D/I1. The converter consists of ■-2 cedar resistors 2 and a group of transistors for current generation 1. Each weighted current output 3 and a base drive circuit 7/T are included. The current with respect to temperature is affected by the temperature characteristics of the transistors in the constant current generation transistor group 1 and the temperature characteristics of the resistances in the ladder resistance network 2 of 2. If these temperature characteristics are not guaranteed at all Temperature changes in the current amount to several thousand ppml0, and are significantly affected by temperature changes inside and around the chip.

This current also changes due to piezoelectric effects due to substrate warpage. In this way, the output current is a little KH bad,
The drawback was that it was easily subject to change due to outside influences.

The object of the present invention is to solve these problems and provide a highly accurate 1)/A converter.

The uninvented 1)/Afm device has a first transistor that serves as a reference in a one-leg current generating circuit, and an emitter area that is n times larger than the emitter area of the first transistor whose weighting is proportional to the current. The collector and base of the first transistor are common, and the emitter is connected to the first emitter through a resistor 1%2, and the second transistor is connected to -a, and the transistor w2 is The output current is compensated by the LR which resists the emitter and rear area.

FIG. 2 shows the q! The r element is composed of a first transistor 8 serving as a reference, a second transistor 9 having an emitter area that is weighted n times larger than the emitter area of the first transistor and is proportional to the current, a resistor RIO, and a resistor RIO. There is. No. of each element.

The emitter of the transistor 8 of No. 1 is connected to the resistor of the R-2R ladder resistor network 5, and a constant current is applied to each resistor. The bases of the valley transistors are commonly supplied with a foot voltage for driving the bases from the base drive circuit 7. 6 The collector of the first transistor is supplied to the output terminal through a switch in accordance with the human input digital signal in the output circuit 6, and is synthesized into an analog signal at the output terminal and output.

FIG. 3 shows each element of the constant current generating transistor group 4. The current ``cref'' flowing through the first transistor 8 serving as a reference is related to the base-emitter voltage VBB and is expressed by the following equation.

It is already well known that 1cref has a negative temperature coefficient because it depends on VBBVC with respect to temperature. Equation (b) can be further expressed as follows.

Here, To is a reference temperature, for example, room temperature.

■Go is the voltage across the gap at absolute zero temperature, θ is a parameter depending on the manufacturing process, and ■BBO is the base-emitter Fukuji at the reference temperature TO.

Since the second transistor 9 has an emitter area Fn times larger than the first transistor 8, the base-emitter voltages V and B between these transistors 8 and 9 are different (ΔVBB
) occurs.

= ■, lnn, , , , , , (from Cl equation (C)) The current 1゜□ flowing through the second transistor is expressed by the temperature, and n is a positive temperature from the above equation (e). Equation 0 (b
) or (b)′ and formula (e) ffi can be used to change the temperature coefficient completely.

Common point 1 between the first transistor 8 and the other end of the resistor RIO
The temperature berth of 1 is calculated by the following formula (fl.

That is, if the right-hand side of equation (f) is set to zero, and the value is set to 几 and nvf-, the temperature can be guaranteed.

Furthermore, in consideration of the temperature distribution kJ, in the layout of each transistor, as shown in Fig. 4, it is possible to place the first transistor 8 as a reference in the center, and the second transistors 9 and 9' to be placed on both sides. It has good guarantee against temperature and can also take measures against piezo effect.

As explained in detail so far, the error increases significantly due to temperature changes, but by adding an inventive compensation circuit and arranging each transistor, a highly accurate D/A conversion device can be easily created. There is an effect that

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional D/A converter, FIG. 2 is a circuit diagram showing an i)/A converter according to an embodiment of the invention, and FIG. 3 is a circuit diagram showing an i)/A converter according to an embodiment of the present invention. FIG. 4 is a circuit diagram showing the configuration of a constant current generating transistor. FIG. 4 is a plan view showing the arrangement of transistors embodying an embodiment of the present invention. 1.4... Transistor group for constant current generation, 2゜5... 几-2㇠ ladder resistance wire, 3.6...
...Output section. 7...Base drive circuit, 8...Reference transistor. 9...Transistor with area n times that of the reference transistor, 10...Resistance R% 11...
...Terminal. <Figure 22 3

Claims (2)

[Claims] (1) In the constant current generating circuit of the current force 1'' nose-shaped L)/A converter, the first transistor serves as a reference and the weighting is based on the emitter surface fI* of the first transistor which is proportional to the current.
has a total emitter area 1 times larger than that of the first transistor, the collector and base are common to the collector and the base of the first transistor, and the emitter has a resistor R [through which the first emitter is connected to the second transistor]. 4! 1)/A characterized by
Conversion device/ (2) Same emitters on both sides of the first transistor. The first and second partial transistors each have a total area, and the twelfth and second partial transistors are connected to the second partial transistor.
The l)/A conversion device according to claim 1, wherein the wiring is arranged in such a manner that the transistor becomes a transistor.