JPH04213922A - Decode circuit - Google Patents

Abstract

PURPOSE:To prevent spike noise from being caused in an output signal even when an input signal and a strobe signal are changed simultaneously by devising a decode circuit main body to receive an output of a delay adjustment circuit and providing a strobe input signal input terminal controlling an output signal of the circuit main body on the decode circuit. CONSTITUTION:Input signals A, B are inputted to a level detection circuit comprising AND gates 1, 3, 4, 6 and its output is inputted to a delay adjustment circuit 7 comprising a delay gate 14 having a delay gamma and an OR gate 15. Output signals of level detection circuits 1, 3, 4, 6 are respectively inputted to delay adjustment circuits 2, 5 having a different delay and output signals A', B' are inputted to D, E inputs of a decode circuit 9 with a strobe signal. Then an output signal C' of the delay adjustment circuit 7 is inputted to a strobe signal F of the decode circuit main body with a strobe signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decoding circuit, and more particularly to a decoding circuit with a strobe signal for digital signals.

0002

2. Description of the Related Art Generally, the output of a decoding circuit with a strobe signal is often used as a clock signal for a flip-flop or a gate signal for a latch, and a signal free of spike noise is required.

An example of a conventional decoding circuit with a strobe signal is shown in FIG. 3, and a timing diagram illustrating its operation is shown in FIG.

In FIG. 3, NAND gates 32 to 35
and inverters 30 and 31, and a circuit for controlling the output signal of the decoding circuit is comprised of OR gates 36-39.

[0005] Depending on the combination of input signals K and L, one of the output signals N, O, P, and Q is selected. Furthermore, the input signal M is a strobe signal for enabling or disabling the output signal of this decoding circuit.

[0006]

[Problems to be Solved by the Invention] In such a conventional decoding circuit with a strobe signal, as shown in the timing diagram of FIG. 4, the input signal K and the strobe signal M, or the input signal L and the strobe signal M change simultaneously. When this happens, spike noises 40 and 41 are generated in the output, which is not originally expected, due to the deviation in the transition time, which causes a problem in that the circuit at the stage subsequent to the decoding circuit malfunctions.

SUMMARY OF THE INVENTION An object of the present invention is to provide a decoding circuit which prevents spike noise from occurring in an output signal even if an input signal and a strobe signal change simultaneously.

[0008]

[Means for Solving the Problems] A decoding circuit according to the present invention has a configuration including a level detection circuit that detects the levels of a plurality of input signals, and a delay adjustment circuit that adjusts the delay time depending on the output value of the level detection circuit. A decoding circuit main body receives the output signal of the delay adjustment circuit as an input, and a strobe signal input terminal controlling the output signal of the decoding circuit main body.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a decoding circuit with a strobe signal according to an embodiment of the present invention, and FIG. 2 is a timing chart showing the operation of FIG.

In FIG. 1, input signals A and B are input to a level detection circuit consisting of AND gates 1, 3, 4, and 6, and a delay adjustment circuit consisting of a delay gate 14 having a delay amount γ and an OR gate 15. It is input to circuit 7. The output signals of the level detection circuits 1, 3, 4, and 6 are input to delay adjustment circuits 2 and 5, and the output signals A' and B' of the delay adjustment circuits 2 and 5 are inputted to D of the decoding circuit 9 with strobe signal. ,E
The output signal C' of the delay adjustment circuit 7 is input to the strobe signal F of the strobe signal-attached decoding circuit main body 9.

The delay adjustment circuit 2 has a delay gate 11 having a delay amount β, a delay gate 10 having a delay amount γ, and an OR gate 17.

The delay adjustment circuit 5 has a delay gate 13 having a delay amount β, a delay gate 12 having a delay amount γ, and an OR gate 16.

Further, the delay gates 10, 11, 12, 13, and 14 constituting the delay adjustment circuits 2, 5, and 7 each have a delay amount of α, β, α, β, and γ, and α+β<
γ.

This decoding circuit with a strobe signal will be explained below using the timing chart shown in FIG.

In FIG. 2, input signals A, B, C of FIG.
, output signals A', B' of delay gates 2, 5, 7,
C', and the waveforms of output signals G, H, I, and J of the decoding circuit 9 are shown.

In FIG. 2, when input signal A changes from "0" to "1" and input signal C changes from "0" to "1", input signal A changes from AND gate 1 to circuit 2. The signal is input to the main body 9 of the decoding circuit with strobe signal through the strobe signal. At this time, the output signal C' changes from "0" to "
Since the output signal changes from "0" to "1" before changing to "1", the output signals G, H, I, and J all become "1", and no spike noise occurs.

Furthermore, when input signal C changes from "1" to "0" and input signal B also changes from "1" to "0",
The input signal B passes through the AND gate 6→circuit 5 and is input to the main body 9 of the decoding circuit with strobe signal. At this time, since the output signal C' still maintains the "1" state, no spike noise is generated.

[0018]

As described above, the present invention has the effect of not generating spike noise in the output signal even if the input signal and the strobe signal change simultaneously.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a decoding circuit according to an embodiment of the present invention.

FIG. 2 is a timing diagram showing the operating state of each part of the decoding circuit of FIG. 1;

FIG. 3 is a block diagram showing a conventional decoding circuit with a strobe signal.

FIG. 4 is a timing diagram of input and output in FIG. 3;

[Explanation of symbols]

1, 3, 4, 6 Level detection circuit 2, 5, 7
Delay adjustment circuit 8 Inverter

Claims (1)

[Claims] 1. A level detection circuit that detects the level of a plurality of input signals, a delay adjustment circuit that adjusts delay time according to the output value of the level detection circuit, and an output signal of the delay adjustment circuit as input. A decoding circuit comprising: a decoding circuit body; and a strobe signal input terminal for controlling an output signal of the decoding circuit body.