1. An output switching circuit comprising:
a switching circuit having a first transistor connected to a high-voltage power supply, a second transistor connected to a low-voltage power supply, and an output terminal at a connection node between the first and second transistors;
a comparison unit that compares an input signal with a feedback signal obtained by feedback of an output signal of the output terminal via a low-pass filter to generate a comparison signal; and
a drive pulse generating unit that generates first drive pulses for driving the first transistor and second drive pulses for driving the second transistor in accordance with the comparison signal.
2. The output switching circuit according to claim 1, wherein the comparison unit includes:
a comparator that compares the feedback signal with the input signal;
a sampling circuit that samples an output of the comparator with a reference clock to generate a sampling signal having a first or second level; and
a comparison signal generating circuit that generates, for each first period, the comparison signal having the first or second level and having a pulse width of the first period, in accordance with a pulse width of the first level or second level of the sampling signal.
3. The output switching circuit according to claim 2, wherein
while the comparison signal is at a first level indicating that a voltage of the input signal is higher than a voltage of the feedback signal, the drive pulse generating unit generates the first drive pulse obtained by pulse density modulation of this comparison signal.
4. The output switching circuit according to claim 2, wherein
while the comparison signal is at a second level indicating that a voltage of the input signal is lower than a voltage of the feedback signal, the drive pulse generating unit generates the second drive pulse obtained by pulse density modulation of this comparison signal.
5. The output switching circuit according to claim 2, wherein
while the comparison signal is at a first level indicating that a voltage of the input signal is higher than a voltage of the feedback signal, the drive pulse generating unit generates the first drive pulse having a pulse train with a frequency higher than that of the first period.
6. The output switching circuit according to claim 2, wherein
while the comparison signal is at a second level indicating that a voltage of the input signal is lower than a voltage of the feedback signal, the drive pulse generating unit generates the second drive pulse having a pulse train with a frequency higher than that of the first period.
7. The output switching circuit according to claim 5, wherein
while the comparison signal is at the first level, the drive pulse generating unit gradually increases a time in which the first transistor is conducive in the first drive pulse for each second period that is shorter than the first period.
8. The output switching circuit according to claim 7, wherein
when the comparison signal assumes the first level, the drive pulse generating unit controls the number of conduction pulses of the first transistor in the first drive pulse in an initial second period to a first number, and then gradually increases a conduction pulse width of the first transistor by replacing non-conduction pulses of the first transistor in the first drive pulse with the conduction pulses for each second period.
9. The output switching circuit according to claim 8, wherein
the drive pulse generating unit gradually increases a conduction pulse width of the first transistor in a second half of the second period.
10. The output switching circuit according to claim 7, wherein
when the comparison signal repeats a plurality of times a change in which the comparison signal is switched from the second level to the first level, maintained at the first level within a plurality of the second periods, and then switched from the first level to the second level, the drive pulse generating unit further increases the time in which the first transistor is conductive in the first drive pulse in an initial second period.
11. The output switching circuit according to claim 6, wherein
while the comparison signal is at the second level, the drive pulse generating unit gradually increases a time in which the second transistor is conducive in the second drive pulse for each second period that is shorter than the first period.
12. The output switching circuit according to claim 11, wherein
when the comparison signal assumes the second level, the drive pulse generating unit controls the number of conduction pulses of the second transistor in the second drive pulse in an initial second period to a second number, and then gradually increases a conduction pulse width of the second transistor by replacing non-conduction pulses of the second transistor in the second drive pulse with the conduction pulses for each second period.
13. The output switching circuit according to claim 12, wherein
the drive pulse generating unit gradually increases a conduction pulse width of the second transistor in a second half of the second period.
14. The output switching circuit according to claim 11, wherein
when the comparison signal assumes the second level, the drive pulse generating unit gradually increases the number of conduction pulses of the second transistor in the second drive pulse for each second period.
15. The output switching circuit according to claim 14, wherein
the drive pulse generating unit gradually increases the number of conduction pulses of the second transistor in a second half of the second period.
16. The output switching circuit according to claim 11, wherein
when the comparison signal repeats a plurality of times a change in which the comparison signal is switched from the first level to the second level, maintained at the second level within a plurality of the second periods, and then switched from the second level to the first level, the drive pulse generating unit further increases the time in which the second transistor is conductive in the second drive pulse in an initial second period.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An apparatus for measuring sizes of articles comprising:
a light projecting device for projecting light toward an article from one side of an article;
a photo-sensor device arranged on the other side of the article and including a plurality of photo-detectors arranged in array in a first direction such that light projected from the light projecting device and impinging upon the photo-sensor device without being interrupted by the article is received by one or more photo-detectors;
a driving device for reciprocally moving the light projecting device and photo-sensor device relative to the article in a second direction perpendicular to the first direction;
a shifting device for shifting the photo-sensor device in the first direction into at least first and second positions which are mutually separated by a distance smaller than a pitch at which the photo-detectors are arranged in array;
a control device for controlling the driving device and shifting device such that when the light projecting device and photo-sensor device are moved by the driving device in a forward direction, the photo-sensor device is in the first position and when the light projecting device and photo-sensor device are moved by the driving device in a backward direction, the photo-sensor device is in the second position; and
a signal processing device for processing output signals generated from the photo-detectors under a control of a control signal supplied from the control device to measure size of the article with a resolution higher than the pitch at which the photo-detectors are arranged in array.
2. The apparatus according to claim 1, wherein the photo-detectors in the photo-sensor device are arranged into a single array with the pitch L and the photo-sensor device is shifted in the second direction over a distance of L2.
3. The apparatus according to claim 1, wherein the photo-detectors in the photo-sensor device are arranged into n (n is integer equal to or larger than 2) rows with the pitch L and the n rows of photo-detectors are relatively shifted in the second direction by a distance Ln, and the photo-sensor device is shifted in the second direction over a distance of L2n.
4. The apparatus according to claim 2, wherein the article is placed on a transparent plate and the light projecting device and the photo-sensor device are arranged on respective sides of the transparent plate.
5. The apparatus according to claim 4, wherein the transparent plate is arranged stationary and the light projecting device and photo-sensor device are arranged movably in the first direction.
6. The apparatus according to claim 5, wherein the light projecting device is provided on a lower horizontal portion of a frame and the photo-sensor device is provided on an upper horizontal portion of the frame, and the frame is arranged movably in the first direction.
7. The apparatus according to claim 1, wherein the light projecting device includes plural light emitting elements arranged in the second direction to project a substantially parallel light flux.
8. The apparatus according to claim 7, wherein the number of the light emitting elements is identical with that of the photo-detectors, and the light emitting elements are arranged in array to be corresponding to respective photo-detectors one by one.
9. The apparatus according to claim 8, wherein the array of the light emitting elements is shifted in the second direction together with the photo-sensor device.
10. The apparatus according to claim 3, wherein the article is placed on a transparent plate and the light projecting device and the photo-sensor device are arranged on respective sides of the transparent plate.
11. The apparatus according to claim 10, wherein the transparent plate is arranged stationary and the light projecting device and photo-sensor device are arranged movably in the first direction.
12. The apparatus according to claim 11, wherein the light projecting device is provided on a lower horizontal portion of a frame and the photo-sensor device is provided on an upper horizontal portion of the frame, and the frame is arranged movably in the first direction.