JPH05130391A - Dither generator - Google Patents

Abstract

PURPOSE:To eliminate the need for a ROM used to store a dither pattern and to revise optionally the dither pattern. CONSTITUTION:Unstable multivibrators 1a-1d as plural oscillation means oscillate a pulse signal of a frequency not in the relation of a common multiple to each other. D flip-flops 2a-2d as plural sampling means sample outputs of the astable multivibrators 1a-1d for each prescribed time. Thus, a binary signal with a prescribed bit number changed irregularly for each prescribed time is obtained. A multiplier 3 as a multiplier means applies weighting in response to a level to each output of the D flip-flops 2a-2d and calculates the product. Thus, an irregular output changing for each prescribed time is obtained in which an appearance ratio of a large number and a small number is smaller than an appearance ratio of an intermediate number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dither generator used in, for example, a facsimile machine for performing gradation recording using a dither method.

[0002]

2. Description of the Related Art A conventional dither generator stores a dither pattern in a ROM.

[0003]

However, in the conventional dither generator, the ROM for storing the dither pattern is required, and the manufacturing cost is high. Moreover, the dither pattern could not be changed arbitrarily. The present invention has been made in view of the above-mentioned conventional problems.
It is an object of the present invention to provide a dither generation device which does not require a ROM for storing patterns and which can arbitrarily change a dither pattern.

[0004]

SUMMARY OF THE INVENTION The present invention comprises a plurality of oscillating means for oscillating pulse signals having frequencies that are not in a multiple relationship with each other, and a plurality of sampling means for sampling the outputs of these oscillating means at predetermined time intervals. It is characterized in that each output of these sampling means is provided with a multiplying means for weighting according to its level and calculating a product of them.

[0005]

The plurality of oscillating means oscillate pulse signals having frequencies that are not in a multiple relationship with each other. The plurality of sampling means samples the output of the oscillating means at predetermined time intervals.
As a result, a binary signal having a predetermined number of bits that changes irregularly every predetermined time is obtained. The multiplying unit weights each output of the sampling unit according to its level and calculates the product of them. As a result, an irregular output is obtained in which the appearance rates of the large number and the small number are smaller than the appearance rate of the intermediate number, and which change every predetermined time. Therefore, no ROM is required to store the dither pattern. Further, the dither pattern can be arbitrarily changed by changing the oscillation frequency or duty ratio of the oscillation means. Further, since the appearance rates of the large number and the small number are smaller than the appearance rate of the intermediate number, it is possible to reduce the noise feeling due to the extreme dither.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a circuit diagram of a dither generator according to an embodiment of the present invention, in which the output terminals of the unstable multivibrator 1a to 1d as the oscillating means are connected to the input terminals of the D flip-flops 2a to 2d as the sampling means. There is. The output terminals of the D flip-flops 2a to 2d are connected to the input terminals of a multiplier 3 as a multiplication means, and the sampling clocks of a predetermined frequency are input to the clock input terminals of the D flip-flops 2a to 2d. The multiplier 3 is A
ND circuits 4a to 4k, EX-OR circuits 5a and 5b,
It is composed of NOR circuits 6a and 6b and OR circuits 7a to 7c.

Next, the operation will be described. The unstable multivibrators 1a to 1d output pulse signals a to d as shown in FIG. That is, the non-stable multivibrator 1a-1
d oscillates at oscillation frequencies different from each other and not in a multiple relationship with each other. The D flip-flops 2a to 2d are
At the rising edge of the sampling clock e as shown in FIG. 2, the pulse signals a to d output from the unstable multivibrators 1a to 1d are latched, and the pulse signals f to i as shown in FIG.
Is output. The multiplier 3 includes D flip-flops 2a to 2
Each of the pulse signals f to i, which is the output of d, is weighted as "1" if it is a low level and "2" if it is a high level, and the product of the pulse signals f to i is calculated. Two
An output such as j of is supplied to the output end. That is, the input / output of the multiplier 3 is determined based on the truth table as shown in FIG.

As described above, the dither can be output without using the ROM for storing the dither pattern.
Further, the dither pattern can be arbitrarily changed by changing the oscillation frequency or duty ratio of the unstable multivibrators 1a to 1d. Since the multiplier 3 is provided,
Since the appearance rates of the large number and the small number are smaller than the appearance rate of the intermediate number, it is possible to reduce the noise feeling due to the extreme dither.

In the above embodiment, the outputs of the D flip-flops 2a to 2d are weighted as "1" for low level and "2" for high level, but this is not always the case. It is not necessary to do so, and arbitrary weighting can be performed.

[0010]

As described above, according to the present invention, a plurality of oscillating means for oscillating pulse signals having frequencies that are not in a multiple relationship with each other, and a plurality of sampling means for sampling the outputs of these oscillating means at predetermined time intervals. Means and a multiplying means for calculating the product of the outputs of the sampling means by weighting the outputs according to the level thereof, the dither is output without using the ROM for storing the dither pattern. it can. Moreover, the dither pattern can be arbitrarily changed by changing the oscillation frequency or the duty ratio of the oscillation means. In addition, because the multiplication means is provided,
Since the appearance rates of the large number and the small number are smaller than the appearance rate of the intermediate number, it is possible to reduce the noise feeling due to the extreme dither.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a dither generator according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram of each part of the circuit of FIG.

FIG. 3 is an explanatory diagram of input / output of a multiplier.

[Explanation of symbols]

1a to 1d Astable multivibrator (oscillating means) 2a to 2d D flip-flop (sampling means) 3 Multiplier (multiplying means)

Claims (1)

[Claims] 1. A plurality of oscillating means for oscillating pulse signals having frequencies that are not in a multiple relationship with each other, a plurality of sampling means for sampling the outputs of these oscillating means at predetermined time intervals, and a plurality of outputs for each of these sampling means. A dither generating device, comprising: a multiplying unit that performs weighting according to a level and calculates a product of them.