JPH0152933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for binarizing an analog signal whose DC level varies, and more particularly to a binarizing circuit improved to generate an envelope signal based on a slice level.

In general optical reading devices that read optical barcodes by moving a light spot using laser beam scanning or the like and photoelectrically converting the reflected light, a black level envelope and a white level envelope are formed for the input analog signal. A method is used in which the midpoint level of both envelope signals is used as a slice level for binarization.

In such devices, the distance between the medium on which the optical barcode is recorded and the reading window of the laser beam scanning device varies depending on the operator, so we try to avoid differences in input waveforms due to the difference in distance between the medium and the reading window of the laser beam scanning device. In order to eliminate this, the depth of focus of the light spot of the reading window of the laser beam scanning device is lengthened. Therefore, the optical spot diameter tends to increase. Therefore, when the width of the black part of an optical barcode is extremely wide and narrow, the difference in the amplitude of the input waveform becomes large, and when the width becomes extremely small, the conventional midpoint is used as the slice level for binarization. There were limits to this method. Therefore, even if the input waveform is enveloped, the black part of the optical barcode is wide and
Binarization for minute changes when the amplitude of the input waveform is small or the period is long due to narrow width, the distance between the reading window of the laser beam scanning device and the recording medium due to operator handling, the printing density of an optical bar code, etc. However, there was a problem that binarization could not be performed if the slice level could not be used for discrimination.

The purpose of the present invention is to eliminate the above-mentioned problems by inputting a slice level potential to both envelope circuits as a steady potential in a circuit that binarizes an analog signal whose DC level fluctuates. This is achieved by a binarization circuit that forms an envelope waveform based on the output of the steady potential circuit.

The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the circuit configuration of a conventional binarization method. An analog signal a is input to an amplifier circuit 1, and the amplified analog signal is connected to envelope circuits 2A, 2B and a comparator circuit 4. The envelope circuit 2A generates a positive envelope waveform, and the envelope circuit 2B generates a negative envelope waveform, which are output to the slice level generation circuit 3. The slice level generation circuit 3 detects the midpoint of the positive and negative envelopes and inputs it to the comparator circuit 4 as a slice level. Therefore, the comparator circuit 4 compares the slice level with the amplified waveform of the analog signal a, and calculates the digital signal b.
was outputting. However, if the waveform of the analog signal a has a large amplitude, there is no problem, but if the signal has a small amplitude, the discharge part of the envelope waveform and the sliced signal overlap, and the slice level and the sliced signal overlap, and the comparator circuit 4 There will be cases where it cannot be determined. Therefore, in this case, there was a problem that the reading device would receive an erroneous converted signal or would be in a hang-up state where the reading device could not read the signals.

FIG. 2 is a block diagram showing a circuit configuration according to an embodiment of the present invention. A steady potential circuit 5 is newly added to the circuit configuration explained in FIG. Output. In this case, the steady-state potential circuit 5 is composed of, for example, an amplifier circuit and an integrating circuit, and inputs a slice level to the positive input terminal of the amplifier circuit, shorts the negative input terminal and output terminal, and lowers the output impedance. ,
Furthermore, it is formed to have a buffer function so as to transmit a steady potential by providing an integrating circuit for suppressing level fluctuations before and after the amplifier circuit. The envelope circuits 2A and 2B have a circuit configuration that forms an envelope waveform based on this slice level. Therefore,
Even when the waveform of the analog signal a has a slight change, the discharge part of the envelope waveform no longer overlaps with the signal to be sliced, and the conventional cases of erroneous conversion or inability to discriminate in the comparator circuit 4 are eliminated. Note that when using a method of inverting the signal using the envelope circuits 2A and 2B, the same function can be obtained by providing an inverting circuit (indicated by a dotted line) when inputting to the comparator circuit 4. FIG. 3 is an explanatory diagram of steady-state potential used in the present invention. The waveform A of the analog signal is configured to form a positive envelope waveform D and a negative envelope waveform E, respectively, with slice level C as a reference, and this slice level C is set as a steady potential. A shows the case where the amplitude of the analog signal waveform A is large, and b shows the case where the amplitude of the analog signal waveform A is small. In this way, since the envelope waveforms D and E based on the steady potential C maintain the curvatures of D' and E' shown by the dotted lines, they do not overlap even if they approach the steady potential C.

FIG. 4 is an explanatory diagram of waveforms, where a is an explanatory diagram of a conventional waveform and b is an explanatory diagram of a waveform according to the present invention. As shown in a, conventionally, the waveform A of the analog signal has a large amplitude.
Waveform A' with small amplitude is made into positive envelope waveforms D and D', respectively, and negative envelope waveforms E and E' to determine slice levels C and C', which are midpoints.
However, in the case of the waveform A' having a small amplitude, there is a portion where the sliced signal C' and the discharge portions of the envelope waveforms D' and E' overlap. Therefore, the waveforms converted to digital signals are B' and B', and the ideal waveforms to be binarized are F and F', respectively, so in the case of waveform A with a large amplitude, satisfactory conversion can be performed. , in the case of waveform A' with small amplitude, it becomes waveform B', and the ideal exchange could not be achieved. As shown in Fig. b, in the present invention, whether the analog signal waveform is waveform A with a large amplitude or waveform A' with a small amplitude, the discharge parts D, D', E, and E' of the envelope waveform are connected to the sliced signals C and C'. There will be no overlap. Therefore, the waveforms B and B' converted into digital signals are both the same as the ideal waveform FF' which is desired to be binarized, so that satisfactory binarization conversion of the analog signal can be performed.

As explained above, in the present invention, by enveloping the analog signal a based on the slice level C, reliable binarization can be performed regardless of the amplitude. If this method is applied to a variety of applications, such as the conventional problems caused by the width of the black and white portion of the barcode, the distance between the reading window of the laser beam scanning device and the medium, and the print density of the barcode, etc., will be eliminated. Therefore, there is an advantage that the barcode can be read over a wide range and can be read accurately.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional circuit configuration, FIG. 2 is a block diagram showing a circuit configuration according to the present invention,
3 and 4 are waveform explanatory diagrams according to the present invention. In the figure, 1... amplifier circuit, 2A, 2B... envelope circuit, 3... slice level generation circuit, 4
. . . comparator circuit, 5 . . . steady potential circuit.

Claims (1)

[Claims] 1. A pair of positive side and negative side envelope circuits that convert an input waveform into an envelope waveform, a slice level generation circuit that outputs the midpoint between the outputs of the two envelope circuits as a slice level, and a comparator circuit. A circuit that binarizes an analog signal by comparing the input waveform and the slice level using the comparator circuit, and inputs the potential of the slice level as a steady potential of both envelope circuits. A binarization circuit comprising a steady potential circuit that holds a potential at the slice level.