Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-01-13
2002-06-25
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140RC
Reexamination Certificate
active
06410903
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an analog signal processing circuit, a photo detector and an image forming apparatus and, more particularly, it relates to an analog signal processing circuit adapted to produce an output current as a function of the peak value of the input current and also to a photo detector and an image forming apparatus.
2. Related Background Art
Known analog signal processing circuits adapted to produce an output as a function of the peak value of the input current mostly rely on handling the voltage.
FIG. 1
of the accompanying drawings shows a schematic circuit diagram of a peak hold circuit. Referring to
FIG. 1
, there are shown operational amplifiers
201
,
202
, diodes
203
,
204
, a resistor
205
, a switching element for resetting operations
206
, a charge holding capacitor
207
, a voltage input terminal
208
and a voltage output terminal
209
. Thus, peak hold circuits adapted to operate in a voltage mode normally comprise a number of components including operational amplifiers, one or more than one diodes and one or more than one capacitors to make the overall circuit configuration rather bulky. Additionally, the input current is typically applied to a peak hold circuit as shown in
FIG. 1
after modifying it to show a desired voltage value by means of a current-voltage converter circuit to make the overall circuit configuration further bulky.
As pointed out above, known peak hold circuits for producing an output as a function of the peak of the input are accompanied by the problem of a large circuit configuration and hence that of a large area occupied by the circuit and a high power consumption rate.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a peak hold circuit having a relatively small circuit configuration and adapted to operate in a current mode in order to produce an output current as a function of the peak value of the input current.
Another object of the present invention is to provide a photo detector and an image forming apparatus capable of stably outputting signals if the quantity of incident light changes.
Still another object of the present invention is to provide an analog signal processing circuit comprising first and second field effect transistors having the gates commonly connected and the sources to a predetermined first reference potential and a transistor having the first main electrode connected to the gates of the first and second field effect transistors, the second main electrode to the drain of the first field effect transistor and the control electrode to a second reference potential.
Still another object of the present invention is to provide an analog signal processing circuit comprising first and second field effect transistors having the gates commonly connected and the sources to a predetermined first reference potential, a first transistor having the first main electrode connected to the gates of the first and second field effect transistors, the second main electrode to the drain of the first field effect transistor and the control electrode to a second reference potential and a second transistor of a conductivity type different from that of the first transistor having the second main electrode connected to the connection point of the drain of the first field effect transistor and the second main electrode of the first transistor, the control electrode to a third reference potential and the first main electrode to a fourth reference potential, the difference between the second and third reference potentials being so selected as not to turning on both of the first and second transistors simultaneously.
A further object of the present invention is to provide a photo detector comprising a photoelectric converter means, a means for holding a value proportional to the peak output value of the photoelectric converter means and a means for comparing a value proportional to the output value of the photoelectric converter means and a value proportional to the held peak output value. Preferably, in a photo detector having a configuration as described above, a means for holding the peak value of the photoelectric conversion output operates to store the largest value of the incident light and automatically determines the threshold level with a ratio defined by Y/X relative to the amplitude of the output waveform of photoelectric converter means regardless of the value of the incident light, where X represents a proportional constant for the value proportional to the output value of the photoelectric converter means and Y represents a proportional constant for the value proportional to the held peak output value. Then, a horizontal synchronizing signal can be obtained constantly and stably with an enhanced level of precision regardless of fluctuations in the quantity of incident light.
A further object of the invention is to provide an image forming apparatus comprising such a photo detector.
A further object of the invention is to provide a signal processing circuit comprising a current transferring unit for outputting a plurality of electric currents proportional to the input current, a peak holding unit operating in a current mode for receiving the electric current output from the current transferring means and outputting an electric current proportional to the peak value of the input current and a current input/voltage output type current comparing unit for comparing the electric current output from the current transferring unit and the electric current output from the peak holding unit operating in a current mode.
Preferably, the current transferring means comprises a current mirror circuit.
Preferably, the signal processing circuit is adapted to convert a current signal into a voltage pulse.
REFERENCES:
patent: 3973215 (1976-08-01), Ahmed
patent: 4498001 (1985-02-01), Smoot
patent: 4513300 (1985-04-01), Tatsuno et al.
patent: 4544878 (1985-10-01), Beale et al.
patent: 4899348 (1990-02-01), Kiya et al.
patent: 5004901 (1991-04-01), Yoshimoto et al.
patent: 5329115 (1994-07-01), Lim
patent: 5481118 (1996-01-01), Tew
patent: 5521490 (1996-05-01), Manohar
patent: 5616940 (1997-04-01), Kato et al.
patent: 5801581 (1998-09-01), Koizumi
patent: 0507298 (1992-10-01), None
patent: 0535808 (1993-04-01), None
patent: 0788046 (1997-08-01), None
patent: 8907792 (1989-08-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Le Que T.
LandOfFree
Analog signal processing circuit photo detector and image... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Analog signal processing circuit photo detector and image..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Analog signal processing circuit photo detector and image... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2947030