JPS62180612A - Semiconductor integrated circuit device - Google Patents

Abstract

PURPOSE:To improve the reliability by incorporating a code conversion circuit converting a natural binary code into the gray code so as to reduce the effect of power noise attended with the switching onto an output terminal. CONSTITUTION:The code conversion circuit 3 converting the natural binary code into the gray code is incorporated to output an output data from the output terminal in the form of gray code. That is, an output data in the natural binary code is obtained at an output line group 4 of a programmable counter 2. The output data is converted into the gray code by using a natural binary code - gray code conversion circuit 3 and the result is outputted from an external output line group 5.

Description

[Detailed description of the invention] [1a technical field of invention] The present invention relates to a semiconductor integrated circuit device.

[Technical background of the invention and its problems]: In recent years, there has been an increase in the degree of integration of semiconductor integrated circuits.
There are things. As the number of pins increases due to higher integration of integrated circuits, power supply noise generated during switching of the output sofa can no longer be ignored.

,・ Using Figure 2, calculate the power supply noise during the above switching.
clarifying the problems of Figure 2 shows a large-scale MO8 integrated circuit (MOS-L
What is the circuit as seen from an output terminal of SI? In the figure, 11 and 12 are the vDD and vss terminals of No. 4, respectively, and 13 is the output terminal of output 1'.
vDD connected to DD terminal, line i"4, V' terminal-1
2, the V88 wire 15 has a resistance IB1.1B and an inductance 191.19.1B, respectively, as shown. enters.

MOS) Lanzostar J e, J7 is an output stage transistor with an output cutout, and a resistor 183 and an inductance 193 are also inserted between the connection point and the output terminal 13. Between the vDD line 1 line color 488 line 15 there is a canopy distance 20. The capacitance 21 connected to the output terminals 1, 9 is that of an external load circuit.

In such a circuit, when the output terminal 13 falls to the "H#H# level L" level, the load capacitance 21
The charges accumulated in the V8S line 15 are discharged through the MOS (MOS) lannostar 12.

In large-scale integrated circuits, the v8s line is long and thin, so this sudden inflow of current causes the potential of the 88 line 15 to rise. and the vDD line 14
The potential also increases. This is the power supply noise generated during switching of the output buffer. As the number of output buffers switching simultaneously within an integrated circuit increases, this power supply noise becomes very large and affects circuit operation. In addition, the more opportunities for simultaneous switching, the more
The reliability of the circuit will be reduced.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor integrated circuit device that reduces the influence of power supply noise accompanying switching of output terminals and improves reliability.

[Summary of the invention]

The present invention is characterized by incorporating a code conversion circuit for converting natural binary code into Gray code in order to output output data from an output terminal of an integrated circuit in Gray code.

〔Effect of the invention〕

Most of the programmable counters of logic LSIs operate sequentially. The same applies to address counters of coefficient ROMs attached to signal processing processors. When outputting data from a renostar that makes such sequential movements to the outside, if the data is converted into a Gray code and output, simultaneous switching of output terminals can be reduced. Therefore, according to the present invention, a highly reliable integrated circuit device with low power supply noise can be obtained.

[Embodiments of the invention]

The present invention will be explained in detail below.

FIG. 1 shows the main structure of one embodiment. In the figure, 1 is a digit integrated circuit, and 2 is a programmable counter whose operations are mostly sequential. The output line group 4 of the programmable counter 2 provides natural binary code □ output data. This output data is converted into a Gray code using a natural binary code/Gray code conversion circuit 3 and outputted from an external output line group 5.

If such a configuration is adopted, there will be fewer opportunities for simultaneous switching of the output line group 5. This becomes clear, for example, by comparing the 4-bit natural binary code and the Gray code as shown in the table below.

=6= As shown in the table, in the Gray code, when the numbers differ by only 1, the code also differs by only one place. Therefore, when the output changes sequentially, in binary code, 01
11-+1000.0011→0100, 1011→
1100, simultaneous switching occurs, whereas such simultaneous switching does not occur in the Gray code.

Therefore, by incorporating the code conversion circuit 3 so that the output data of the programmable counter 2 is gray-coded and output, a highly reliable integrated circuit device with low power supply noise can be obtained.

In addition to the programmable counter as in the above embodiment, examples of registers whose output data moves sequentially include memory address registers. Therefore, even in the case of an integrated circuit that uses all external memory and has a built-in address register for specifying the address of the external memory, a code conversion circuit that converts the output data of the address register into Gray code and outputs it is built-in. In particular, effects similar to those of the above embodiment can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a main part configuration of an integrated circuit according to an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram for explaining power supply noise of a conventional integrated circuit. DESCRIPTION OF SYMBOLS 1... Integrated circuit technology, 2... Programmable counter, 3... Natural binary code-Gray code conversion circuit, 4... Output line group, 5... External output line group.

Claims (3)

[Claims] (1) A semiconductor integrated circuit device characterized by having a built-in code conversion circuit for converting a natural binary code into a Gray code so as to output output data from an output terminal in a Gray code. (2) The semiconductor integrated circuit device according to claim 1, wherein the code conversion circuit converts the output data of the programmable counter into a Gray code and outputs the gray code. (3) The semiconductor integrated circuit device according to claim 1, wherein the code conversion circuit converts output data of an address register for specifying an address of an external memory into a gray code.