JP2000162281A - Semiconductor integrated circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten inspection time and to reduce the cost of an inspecting device in a semiconductor integrated circuit device, which incorporates a D/A converter to receive a plurality of bits of an input digital signal as its input and to select and output an analogue voltage of a corresponding level according to the input digital signal, and which is constituted in such a way as to output the output analogue voltage of the D/A converter from its output terminal. SOLUTION: A semiconductor integrated circuit device is provided with a register circuit (parallel/serial converter) 8 for storing multi-gradation digital data after being decoded, a test clock terminal 9 for inputting a test clock to output contents stored in the register 8 serially from the outside, a test mode change-over switch 10 for outputting the output analogue voltage of a D/A converter and an output digital signal from the register circuit 8 alternatively from an output terminal 6, and a test terminal 7 for inputting a switching control signal of the change-over switch 10 from the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D / A converter (DAC) which receives an input digital signal of a plurality of bits as its input, and outputs an analog voltage having a corresponding level according to the input digital signal. And the D /
The present invention relates to a semiconductor integrated circuit device (for example, a multi-gradation liquid crystal driver IC or the like) configured to output an analog voltage output from an A-converter from an output terminal thereof, and particularly to an inspection method thereof.

[0002]

2. Description of the Related Art Multi-tone liquid crystal driver I with a built-in DAC
C has a DAC for each liquid crystal drive output terminal, and outputs an analog voltage from each liquid crystal drive output terminal in accordance with a multi-bit digital signal which is input multi-tone data. For this reason, the inspection of the multi-tone liquid crystal driver IC having a built-in DAC is performed by measuring and determining the analog voltages output from all the DACs.

FIG. 2 shows the configuration of the prior art.

[0004] The input gradation data is stored in an internal circuit 1 and then applied to a DAC bus line 3 via a decoder 2. According to each gradation data, one of the gradation voltage selection switches 5 for determining the output voltage from the reference power supply 4 is selected, and each of the output terminals (1-N) 6 is output via the output amplifier 6 '.
Thus, each gradation voltage is output. In the conventional inspection method, the output analog gray scale voltage is measured by an inspection device having a high-precision voltage measuring device to determine the voltage.

However, the inspection method based on analog voltage measurement uses a single voltage measuring device to measure and determine the voltage output from all the liquid crystal drive output terminals. The test time is greatly increased as compared with a test method in which all outputs are digitally determined at the same time using a separately prepared comparator. Therefore, the inspection items are also limited due to the inspection time. In addition, since the potential difference between the gradation voltages output from the liquid crystal drive output terminal is very small, a highly accurate measuring device is required for measuring and determining the difference.
It will be very expensive.

[0006]

As described above, the conventional inspection method has a problem that the inspection time is greatly increased because the analog voltage is measured and determined. Also,
In order to measure each gradation voltage with high accuracy, there is a problem that an extremely expensive inspection device is required.

The present invention has been made in view of the above-mentioned conventional circumstances, and has a built-in inspection facilitating circuit which enables high-precision measurement with an inexpensive inspection apparatus without increasing the inspection time. It is an object of the present invention to provide a semiconductor integrated circuit device.

[0008]

According to a first aspect of the present invention, there is provided a semiconductor integrated circuit device which receives an input digital signal of a plurality of bits as its input, and has an analog level having a corresponding level in accordance with the input digital signal. In a semiconductor integrated circuit device having a built-in D / A converter for outputting a voltage and configured to output an output analog voltage of the D / A converter from an output terminal of the D / A converter, the input digital signal of a plurality of bits is output. A means for performing parallel-serial conversion and outputting the result from the output terminal is provided.

According to a second aspect of the present invention, there is provided the semiconductor integrated circuit device according to the first aspect of the present invention, wherein the register circuit for storing the input digital signal is provided. Select one of a first external terminal for externally inputting a clock signal for serially outputting stored contents, an output analog voltage of the D / A converter, and an output digital signal from the register circuit. Preferably, an output switching circuit for outputting from the output terminal and a second external terminal for inputting a switching control signal of the output switching circuit from the outside are provided.

That is, according to the semiconductor integrated circuit device of the present invention, instead of the analog voltage output from the D / A converter,
A circuit for outputting a digital signal of a plurality of bits, which is an input signal, from an output terminal is incorporated as an inspection facilitation circuit. With this configuration, an operation test of an internal circuit can be performed. It is possible to switch from the conventional analog voltage determination to the digital signal determination, thereby greatly shortening the inspection time and enabling inspection using an inexpensive inspection device.

[0011]

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

FIG. 1 is a configuration diagram of a main part of a multi-gradation liquid crystal driver IC with a built-in inspection facilitation circuit according to an embodiment of the present invention.

The input gradation data is stored in an internal circuit 1 and then supplied to a DAC bus line 3 via a decoder 2. According to each gradation data, one of the reference power supply selection (gradation voltage selection) switches 5 for determining the output voltage from the reference power supply 4 is selected, and each output terminal (1 to N) is output via the output amplifier 6 '. 6 outputs the respective gradation voltages.

The input gradation data is inputted in various combinations in order to inspect the internal circuit. If the analog voltage is measured and determined for all of these data combinations, the inspection time greatly increases. For this reason, each gradation data supplied to the DAC bus line 3 via the decoder 2 is converted into a parallel / serial converter (parallel input / serial output register circuit) 8.
In synchronization with a test clock externally input from a test clock terminal (TCLK) 9, the decoded digital gradation data is serially output from an output terminal 6 via an output amplifier 6 ′, and digitally determined by a comparator. I do. At this time, according to each gradation data,
The reference power supply (gray scale voltage) selection switch 5 for selecting the output voltage from the reference power supply 4 is selected at the same time.
By turning on the test mode changeover switch 10 on the parallel / serial converter 8 side and turning off the switch 10 on the DAC side, the serial output signal from the parallel / serial converter 8 is connected to the output amplifier 6 ′, On the other hand, the output of the selected gradation voltage is cut off.

During normal operation, the test clock terminal 9 is not used (for example, fixed to GND), an H level voltage (power supply voltage) is applied to the test terminal 7, and a switch on the DAC side is applied. 10 is turned on, and the switch 10 on the side of the parallel / serial converter 8 is turned off.

FIG. 3 shows a configuration example of each switch (test mode changeover switch and reference power supply selection switch) shown in FIG.

Incidentally, as the parallel / serial converter 8, a latch circuit normally mounted in the decoder unit may be serially connected in order to latch the output of the decoder 2 so as to be used in common. is there.

In the above embodiment, the present invention is embodied in a multi-gradation liquid crystal driver IC. However, the present invention is not limited to this. It goes without saying that the semiconductor integrated circuit device described above can also be effectively implemented.

[0019]

As described in detail above, the semiconductor integrated circuit device of the present invention receives an input digital signal of a plurality of bits as its input, and receives an analog signal having a corresponding level according to the input digital signal. In a semiconductor integrated circuit device having a built-in D / A converter for selectively outputting a voltage and outputting an output analog voltage of the D / A converter from an output terminal thereof, the input digital signal of a plurality of bits is provided. And a means for performing parallel-to-serial conversion on the output from the output terminal. The semiconductor integrated circuit device according to the present invention is the same as the semiconductor integrated circuit device described above, A register circuit for storing a digital signal; and a first circuit for externally inputting a clock signal for serially outputting the stored contents of the register circuit. An output terminal, an output switching circuit for selectively outputting one of an output analog voltage of the D / A converter and an output digital signal from the register circuit from the output terminal, and the output switching circuit. And a second external terminal for inputting a circuit switching control signal from the outside. According to the semiconductor integrated circuit device of the present invention, a conventional analog voltage determination is changed to a digital output. Since it is possible to switch to the signal determination, it is possible to greatly reduce the inspection time, and it is possible to perform an inspection using an inexpensive inspection device.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a multi-tone liquid crystal driver IC according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional technique.

FIG. 3 is a diagram showing a configuration example of each switch shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal circuit 2 Decoder 3 DAC bus line 4 Reference power supply 5 Reference power supply selection switch 6 Output terminal 6 'Output amplifier 7 Test terminal 8 Serial / parallel converter 9 Test clock terminal 10 Test mode switch

Claims (2)

[Claims] A digital signal receiving an input digital signal of a plurality of bits as an input and selectively outputting an analog voltage having a corresponding level according to the input digital signal.
In a semiconductor integrated circuit device having a built-in A converter and configured to output an output analog voltage of the D / A converter from an output terminal thereof, the input digital signal of plural bits is subjected to parallel-serial conversion. And a means for outputting from the output terminal. 2. The semiconductor integrated circuit device according to claim 1, wherein a register circuit for storing the input digital signal and a clock signal for serially outputting the stored contents of the register circuit are externally input. A first external terminal, an output switching circuit for selectively outputting one of an output analog voltage of the D / A converter and a digital signal output from the register circuit from the output terminal. A second external terminal for externally inputting a switching control signal of the output switching circuit.