JPH02311026A - Digital/analog conversion circuit - Google Patents

Abstract

PURPOSE:To attain discrimination of non-detective commodity rate due to a leakage current in the standby state and to reduce power consumption when no analog output is required by providing a current interrupt circuit between a constant current circuit and a current changeover circuit. CONSTITUTION:A complementary signal generating circuit 8 generates two complementary signals when a current changeover circuit 11 selects whether a prescribed current generates from a constant current c 10 outputs to an analog output terminal 4 or an analog complementary signal output terminal 56. When a power consumption reduction control terminal 13 is at a high level, current interrupt circuits 14 each comprising a P-channel insulation gate FET are all made into disconnection state and the current from the circuit 10 does not flow to both the terminals 4, 6. That is, it is possible to stop the current from the constant current circuit by the control of power consumption reduction and when an analog output is not required, the power consumption reduction is attained and the decision of non-defective commodity rate is executed simply and accurately.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to receiving a signal value expressed as a digital value,
The present invention relates to a circuit system of a so-called digital-to-analog converter that converts and outputs a signal value expressed as an analog value.

[Prior Art] 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 format in which currents from a desired number of constant current circuits are added and output, so if you want to obtain a voltage output, you only need to connect a resistor as a load.In a video signal circuit, Since a low value resistor such as 75 ohm or 50 ohm is used as the load resistor, an analog video signal can be obtained with a minimum number of parts by using a segment current type digital-to-analog conversion circuit.

FIG. 2 shows an embodiment of a segment current type digital-to-analog conversion circuit according to the prior art. The characteristics required of the constant current circuit 1O are that each current cell stably supplies a current of a predetermined value, and that the current value generated by fluctuations in the output voltage is not interfered with. In addition, the characteristics required of the current switching circuit 11 are that when it is off, it can reliably cut off the output current, when it is on, it can prevent fluctuations in the output voltage from reaching the constant current circuit, and when it is on, it must ensure that one of the two switching circuits is on. , the other is off and there is no time when both are on or off at the same time.

As described above, since the conventional digital-to-analog conversion circuit has the above-mentioned configuration, it inevitably has the drawback that current from the constant current circuit continues to flow at all times.

In other words, in a system including a conventional digital-to-analog converter, the constant current circuit continues to operate even when analog output is not required, making it impossible to reduce power consumption. Video digital for driving 0.7v P-P ohm load resistance
In the case of a color graphics system with analog conversion circuits for three channels (red, blue, and green), digital
Power consumption in the analog conversion circuit is calculated as follows.

(0,7v/75)*3ch*5v==140mw again. Generally speaking, the method of determining good/defective semiconductor circuits is based on leakage current in the standby state.
A circuit in which current continues to flow, such as a conventional digital-to-analog conversion circuit, cannot detect defective products due to leakage current.

[Problems to be solved by the invention] The present invention solves the drawbacks of the prior art as described above,
At the same time, we have added a power consumption reduction function without sacrificing the advantages of the segment current type digital-to-analog converter circuit, which is high speed and high drive capacity.This reduces power consumption when analog output is not required, and also enables standby state. The purpose of this technology is to enable discrimination between non-defective products and defective products based on leakage current.

[Means to solve the problem]

In a digital-to-analog conversion circuit in which a plurality of unit current cells including a constant current circuit and a current switching circuit controlled by a pair of mutually complementary digital data are connected in parallel, each unit cell has a , a current cutoff circuit is provided, and the current cutoff circuit is arranged to cut off current from the constant current circuit to the pre-distribution current switching circuit in the power consumption reduction state.

[Function] According to the present invention, the current cutoff circuit provided between the constant current circuit and the current switching circuit in each unit current cell cuts off the current when reducing power consumption, so analog output is not required. digital when determining whether the product is good or defective.
The analog conversion circuit can be designed to consume no current.

[Examples] Hereinafter, the present invention will be explained in detail according to Examples. FIG. 1 shows an embodiment of a digital-to-analog conversion circuit according to the present invention. The unit current cell includes a constant current circuit 10, a current cutoff circuit 14, and a current switching circuit 11.

A desired number of digital-to-analog conversion circuits can be obtained by connecting a desired number of the unit current cells in parallel. Current switching circuit 1
1 selects whether to output a constant value of current generated by the constant current circuit 10 to the analog signal output terminal 4 or to the analog complementary signal output terminal 6, depending on the state of the digital signal input terminal 9. . Therefore, the complementary signal generation circuit 8 generates two signals that are complementary to each other and supplies them to the current switching circuit 11. Constant current circuit 10
constitutes a so-called current mirror circuit, and from the viewpoint of accuracy, it is desirable that all constant current circuits 10 be formed on one semiconductor integrated circuit.If the power consumption reduction control terminal 13 is at a high level, , P-channel insulated gate FETs are all turned off, so that current from the constant current circuit 10 no longer flows to the analog signal output terminal 4 or the analog complementary signal output terminal 6. Depending on the application, the analog complementary signal output may not be necessary, and in that case, the analog complementary signal output terminal 6 and the ground terminal 2 may be short-circuited.

[Effects of the Invention] According to the present invention, it is possible to prevent the current from flowing in the constant current circuit by controlling power consumption reduction, so that the current consumption can be reduced when analog output is not required. becomes possible. Furthermore, since leakage current can be measured in a standby state, it is possible to accurately and easily determine whether a product is good or defective.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a digital-to-analog conversion circuit according to the present invention. Figure 2 shows a segmented current digital system using conventional technology.
FIG. 3 is a diagram showing an example of an analog conversion circuit. 1...Positive power supply terminal 2...Grounding terminal 3...Reference voltage terminal 4...Analog signal output terminal 5...Output load resistance 6...Analog complementary signal output terminal 7... Complementary output load resistor 8... Complementary signal generation circuit 9... Digital signal input terminal 10... Constant current circuit 11... Current switching λ circuit 12... Unit current cell 13... Power consumption reduction Switching terminal 14...Order circuit or higher

Claims (1)

[Claims] In a digital-to-analog conversion circuit in which a plurality of unit current cells including a constant current circuit and a current switching circuit controlled by a pair of mutually complementary digital data are connected in parallel, each unit cell has a , comprising a current cutoff circuit, the current cutoff circuit being arranged to cut off current from the constant current circuit to the current switching circuit in a power consumption reduction state. conversion circuit.