JPH02311024A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To attain high accuracy without losing the advantage of a segment current type D/A converter circuit by providing a constant current circuit comprising a bipolar transistor(TR) and a current changeover circuit comprising an insulation gate FET or the like on one and same semiconductor substrate. CONSTITUTION:A required number of constant current circuits 22 each comprising a bipolar TR arranged in a 1-chip semiconductor integrated circuit 1 of one and same semiconductor substrate to form a current mirror circuit. Moreover, a current changeover circuit 31 comprising the insulation gate FET in each unit current cell 12 selects whether a current from the circuit 22 is outputted to an analog signal output terminal 8 or to an analog complementary signal output terminal 10. That is, bipolar TRs able to supply a prescribed current over a wide range of operating region are used for the circuits 22 and the insulation gate FETs with excellent on/off characteristic and not requiring the drive current are used for the circuit 31 and they are provided on one-chip. Thus, high accuracy is attained without losing the advantage of the segment current D/A converter circuit of high speed and high driving capability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor integrated circuit, and more particularly to an integrated circuit including a digital-to-analog conversion circuit on a chip.

[Conventional technology]

A segment current method is known as a method of digital-to-analog conversion for video signals that requires high speed, high precision, and high output drive capability.

The segment current method is a method in which a desired number of unit current cells are connected in parallel, each consisting of a constant current circuit that supplies one unit of constant current and a current switching circuit that switches the path of the current from the constant current circuit. It is. The role of the current switching circuit is to output current when it is on and not to output it when it is off, but in order to ensure high-speed operation and current accuracy, it is necessary to flow that current to another path when it is off. In this way, the segment current method is a type in which currents from a desired number of constant current circuits are added and output, so if a voltage output is desired, a resistor may be connected as a load. In a video signal circuit, a low resistance such as 75Ω or 50Ω is used as a load resistance, so if a segment current type digital-to-analog conversion circuit is used, an analog video signal can be obtained with a minimum number of parts.

The characteristics required of a constant current circuit are that each current cell stably supplies a predetermined value of current, and that the current value generated by fluctuations in output voltage is not interfered with. In addition, the characteristics required of a current switching circuit are that when it is off, the output current is reliably cut off, when it is on, it is possible to prevent fluctuations in the output voltage from reaching the constant current circuit, and when the two switches are turned on, one is always on while the other is on. is off and there is no time when both are on or off at the same time.

FIG. 2 shows a basic configuration diagram of a segment current type digital-to-analog conversion circuit, and FIG. 3 shows an embodiment of a segment current type digital-to-analog conversion circuit according to the prior art.

Conventionally, as shown in FIG. 3, there has been a method of constructing a constant current circuit and a current switching circuit using insulated gate FETs.

Although the insulated gate FET satisfies the characteristics required of the above-mentioned current switching circuit, it cannot satisfy the characteristics required of a constant current circuit. Because the fifth
As shown in the figure, the insulated gate FET has poor drain current saturation characteristics and is inferior in its ability to supply a constant current.

Furthermore, conventionally, as shown in FIG. 4, there has been a method of constructing a constant current circuit and a current switching circuit using bipolar transistors.

As shown in FIG. 6, bipolar transistors have very good collector current saturation characteristics and can supply a constant current over a wide range of operation. However, when a bipolar transistor is used in the current switching circuit, a base current must flow in order to turn on, and this base current flows into the constant current circuit, resulting in an error in the output current value. .

As described above, with the conventional segment current type digital-to-analog converter circuit, it is difficult to achieve highly accurate output current.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks of the prior art and simultaneously achieve high precision without sacrificing the advantages of the segment current type digital-to-analog conversion circuit, which are high speed and high drive capability.

[Means to solve the problem]

The semiconductor integrated circuit of the present invention includes a digital-to-analog conversion circuit comprising a plurality of unit current cells each consisting of a constant current circuit and a current switching circuit controlled by a digital signal, and the unit current cell includes: The constant current circuit in the unit current cell is configured with a bipolar transistor, and the current switching circuit in the unit current cell is an insulated gate type FE.
It is characterized in that the circuit including the digital-to-analog conversion circuit is integrated on the same semiconductor substrate.

[For production]

According to the present invention, a bipolar transistor capable of supplying a constant current over a wide range of operating regions is used in a constant current circuit, and has excellent on/off characteristics.
By using an insulated gate FET that does not require a drive current in the current switching circuit, a unit current cell with ideal characteristics can be realized.

Furthermore, although a plurality of unit current cells are required to configure a digital-to-analog conversion circuit, by providing the necessary number of unit current cells all on one semiconductor integrated circuit, each unit current It becomes possible to minimize variations in characteristics between cells.

〔Example〕

Hereinafter, the present invention will be explained in detail based on examples. FIG. 1 shows a first embodiment of a semiconductor integrated circuit according to the present invention. In FIG. 1, a semiconductor integrated circuit indicated by 1 includes a logic circuit indicated by 2, a connection terminal with other circuits indicated by 3, and a digital-to-analog conversion circuit indicated by 4, The digital-to-analog converter circuit consists of a plurality of unit current cells indicated by 12. A necessary number of constant current circuits made of bipolar transistors shown as 22 of each unit current cell 12 are arranged in one chip of the semiconductor integrated circuit 1 on the same semiconductor substrate to form a current mirror circuit. .

Insulated gate type F indicated by 31 of each unit current cell 12
The current switching circuit by ET outputs the current from the constant current circuit 22 to the analog signal output terminal indicated by 8, or
Alternatively, it is selected whether to output to the analog complementary signal output terminal indicated by 10.

Depending on the application, the analog complementary signal output may not be necessary, and in that case, the analog complementary signal output terminal 10 and the ground terminal 6 may be short-circuited. At this time, since the short-circuit connection can be performed within the semiconductor integrated circuit 1, there is no need to provide the analog complementary signal output terminal 10.

〔Effect of the invention〕

According to the present invention, since a bipolar transistor is used in the constant current circuit, and the constant current circuit is arranged on one chip of semiconductor integrated circuit to form a so-called current mirror circuit, Each unit current cell generates a highly accurate constant current. Furthermore, since the current switching circuit is composed of an insulated gate FET, no error occurs in the current value. In this way, it has become possible to realize a semiconductor integrated circuit including a highly accurate digital-to-analog conversion circuit as a whole.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of a semiconductor integrated circuit according to the present invention. FIG. 2 is a basic configuration diagram of a segment current type digital-to-analog conversion circuit. Figure 3 shows a segmented current digital system using conventional technology.
FIG. 2 is a diagram showing a first example of an analog conversion circuit. Figure 4 shows segment current type digital using conventional technology.
FIG. 3 is a diagram showing a second example of an analog conversion circuit. FIG. 5 is a diagram showing drain voltage versus drain current characteristics of an insulated gate FET. FIG. 6 is a diagram showing collector voltage-collector current characteristics of a bipolar transistor. 1... Semiconductor integrated circuit 2... Logic circuit 3... Connection terminal with other circuits 4... Segment current type digital-to-analog conversion circuit 5... Positive polarity power supply terminal 6... Ground Terminal 7...Reference voltage terminal 8...Analog signal output terminal 9...Output load resistance 10...Analog complementary signal output terminal 11...Complementary output load resistance 12...Unit current cell 20... - Constant current circuit 21... Constant current port 22 by insulated gate type FET...
・Constant current circuit 30 using bipolar transistors...Current switching circuit 31...Current switching circuit 32 using insulated gate FETs...Current switching circuit using bipolar transistors Applicant Suzu Seiko Epson Corporation Agent Patent Attorney Kisanbe (1 other person) 1 yuan”3)
Illustration outside the drawing

Claims (1)

[Scope of Claims] A semiconductor integrated circuit including a digital-to-analog conversion circuit comprising a plurality of unit current cells each comprising a constant current circuit and a current switching circuit controlled by a digital signal, the unit current cell comprising: The constant current circuit in the unit current cell is configured with a bipolar transistor, and the current switching circuit in the unit current cell is an insulated gate type FE.
What is claimed is: 1. A semiconductor integrated circuit comprising: T, wherein a circuit including the digital-to-analog conversion circuit is integrated on the same semiconductor substrate.