JPS6386619A - Digital/analog converter - Google Patents

Abstract

PURPOSE:To contrive to expand the dynamic by range adding the currents selectively outputted from a current unit group that outputs values of a progression of a constant ratio by using digital signals, and using the resulted current as an output current. CONSTITUTION:The respective resistors of a resistor group having resistance values in a prescribed geometrical progression are connected between the emitters or first and second transistors Q11, Q12 and the ground, all the collectors of the first transistor Q11 are connected to a power source Vcc, and the bases are connected to a reference potential power source. And all the collectors of the second transistor Q12 are connected to an output current terminal IOUT, and the based are connected to the respective input terminals for the digital signals. Since the transistor connected in series connection with the load is reduced to one piece, the invalid potential difference due to the forward potential difference of the transistor becomes smaller in value, and the potential difference supplied to the load can accordingly be made larger. As a result, the dynamic range for the load can be made wide.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a digital/analog converter that adds currents selectively output by digital signals from a group of current units that output a series of values at a fixed ratio to obtain an output current. Therefore, the output voltage range (Guinamino range) of the Chinese power supply type converter can be widened.

[Industrial application field]

The present invention relates to a digital/analog converter that adds currents selectively output by digital signals from a group of current units that output values in a sequence of constant ratios to obtain an output current.

In an image display device, for example, when displaying a colored image, a digital signal representing color density is converted into an analog signal, such as an amount of current, that controls the electron beam intensity of a display tube.

A digital/analog converter is used to convert this digital signal into an analog signal.

On the other hand, many recent device power supplies are single-voltage power supplies, and the low power supply voltage is often common to analog signal circuits and digital signal circuits.

Therefore, in order to increase the output voltage change range (resistance value x current change range), that is, the dynamic range of the output, when using circuits with the same current change range, it is necessary to change the load terminal voltage to the device power supply voltage. It is necessary to place them as close as possible to increase the voltage utilization rate.

[Conventional technology]

FIG. 2 shows a circuit diagram of a conventional digital/analog converter.

In FIG. 2, constant current control circuit S, transistor QO
(for temperature characteristic compensation), resistor R0 is connected to the reference voltage V0 at point A.
Set.

Transistors Q, A, Q, are current switching circuits, and the current flowing through transistor Q5 and resistor R3 is as follows:
The base potential of transistor Q1A and transistor Q1.
Compared to the base potential of , a transistor with a higher potential becomes conductive, and a transistor with a lower potential becomes non-conductive.

Transistors Q+a, Q+a, Q+, and resistor R1 form an output current unit UI, and the output current 11 of this unit is the current flowing through resistor R5, and Ir = (
V(l V11io1) /R+.

Here, Vo. , is the base-emitter forward voltage of transistor Q.

The signal "1" of the digital signal is the reference voltage ■.

When the voltage signal is higher and is not input to the input terminal D1 (when the signal is "0"), the current flowing through the resistor R1 is
When a digital signal flowing from the power supply VCC to the resistor R1 via the transistor QIAIQ is input to the input terminal (signal "
1), the output current terminal ■ is outputted from the voltage Vcc via a load (not shown). Output current ■1 flows to the UT through transistors Q, , Q, and resistor R2.

Similarly, when a digital signal is input to the input terminal D2 of the output current unit U2, a current 2 flows through the output current terminal iOUT.

Iz=('/.-Vitoz)/Rz When digital signals are input to input terminals DI and D2, output current terminal I. I for ay.

A current of +l flows.

On the other hand, if the resistance values of the resistors R,, R, are a series of resistance values that are multiples of 2, then 1t = Ir /2. I3=Ir/4.・
...Ia=II/2'-1.

When these currents are selectively generated by digital signals, the output current terminal I. The LIT is outputted by adding a desired multiple of the current (2) to the minimum unit.

For example, as shown in FIG. 3, the digital data signal input to this digital/analog converter is a 4-digit binary number rlollJ.

The focus positions &0, 1, 2°3 of the digital data signal are connected to the terminals D+, Dz, Ds, Da, respectively, and the digital signal of each bit becomes a signal input of the corresponding terminal.

In this case, the output current terminal ■. UT has (IXI/2+
OX1/4+IX1/8+IX]/16)1. = (1
1/16)I.

A current will flow.

That is, an output current of an analog signal in units of 1t, which is represented by digital data whose unit current is (1/16)Ir, flows.

Applying this to the image density example described above, the four 16 gradations represented by the 4-digit digital data signal are converted into corresponding 16-step current values and output.

[Problem that the invention seeks to solve]

However, in this conventional method, two transistors are connected in series in the output current path.

When the power supply voltage is low, the forward potential difference generated in this transistor does not reach the potential difference applied to the load, and the influence becomes large.

For example, normally, the forward potential of this transistor reaches 0.5 volts with respect to a power supply voltage of 5 volts, which limits the potential difference across the load, resulting in a narrow range of power variation, ie, dynamic range, of the load.

The present invention was created in view of these points, and an object of the present invention is to provide a digital/analog converter with a large dynamic range.

[Means for solving problems]

To achieve the above object, each resistor of the group of resistors having a predetermined geometric progression of resistance values is connected between the emitters of the two first and second transistors and ground.

All collectors of the first transistors are connected to a power supply, and all bases of the first transistors are connected to a reference potential power supply.

A circuit is formed in which the collectors of all the second transistors are connected to the output current terminal, and the bases are connected to the respective digital signal input terminals.

[Effect]

In such a circuit configuration, the number of transistors installed in series with the load is reduced to one, so the invalid potential difference due to the forward potential difference of the transistor is reduced, and the potential difference applied to the load can be increased accordingly. , the dynamic range of the load can be increased.

〔Example〕

Embodiments of the digital/analog converter of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a circuit configuration diagram of an embodiment of the present invention.

In the figure, a transistor Q0 and a resistor R0 whose collectors and bases are connected to a constant current circuit S are transistors Q
Reference voltage ■ at base A point of 0. generate.

On the other hand, the transistor QllI Q,, and the resistor R
0 forms the unit UI+ of the output current.

The bases of transistors Q and □ are connected to digital signal terminal D.
11.

The transistors Q, , , Q, form a current switching circuit, and the current flowing through the resistor R+ is the transistor QI+
The base potential of QI2 is compared with the base potential of transistor QI2, and the transistor with a higher potential becomes conductive, and the transistor with a lower potential becomes non-conducting.

When the digital human input signal is input to the digital signal terminal D1 (signal "0"), the current II+ is the voltage RV
c Output current terminal I from c via a load not shown. Flows from LIT to resistor R1 via transistor Q11. When the digital input signal is not input to the signal rlJ), the current I11 is equal to the voltage SV. and flows through transistor QI2 to resistor R3.

The current ■ flowing through the resistor R, is 111=(V.-V11!o11)/R+ (=
11).

Here, VIIEQ11 is the base-emitter forward voltage of transistor Q.

Output current UNIF) Current flows when a signal is input to input terminal D2 of U r□! + 2 is 112
″″(Vo VIEQ2+) / R2(=I
z).

Here, ■. . 21 is the base-emitter forward voltage of the transistor QZI.

When the resistors R,, R2... have a series of resistance values with a fixed ratio, and the resistance ratio is a, I+z=Iz/a, l13=III/a"..., and the bit of the digital data signal specifies This current can be selected using a digital signal to obtain a desired output current.

When the resistance ratio a is 2, the digital/analog converter is equivalent to the conventional example described above, but has a large dynamic range.

Note that in the circuit configuration of the present invention, for example, if the type of transistor is changed to a PNP type, the polarity of the power supply voltage, the direction of input/output current, etc. will change, but as long as it is based on the gist of the present invention, the circuit configuration will be It is not limited to FIG.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a digital/analog converter in which the number of transistors connected in series with the load is reduced to reduce the forward potential difference thereof, and the potential difference applied to the load is increased to increase the dynamic range. This is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of an embodiment of the digital/analog converter of the present invention, FIG. 2 is a circuit configuration diagram of a conventional example, and FIG. 3 is a diagram explaining digital/analog conversion. In the figure, R1 is a resistor, Q11 and Q12 are transistors, Dl is an input terminal, Ull is an output current unit, II+ is an output current, Tolla is an output current terminal, A is a reference voltage, and VCC is a power supply. 4 [Turning of bright and missing color example H4, collection No. 1 Turning of Δ column at the end of Fig. 1 False Fig. 2 Fig. Pi't position No + 2 3 Te 9 cycle 7 Rosary change Map 3 of the 6th ward that reveals Hachinodara

Claims (1)

[Claims] Each resistor (R_1) of the resistor group having a resistance value consisting of a predetermined geometric progression is connected between the emitters of the first and second two transistors (Q_1_1, Q_1_2) and ground. all the collectors of the second transistor (Q_1_2) are connected to the power supply (V_c_c), all the bases of the transistors are connected to the reference voltage (A), and all the collectors of the second transistor (Q_1_1) are connected to the reference voltage (A); It consists of a circuit in which the collector is connected to the output current terminal (I_O_U_T) and the base of the transistor is connected to the respective input terminal (D_1), and each of the Output current (I_1_1)
is added to the output current terminal (I_O_U_T) and output.