Abstract: Circuitry capable of controlling a bias voltage for an avalanche photodiode (APD) in accordance with the temperature slope of the breakdown voltage of the APD is disclosed. A reference voltage generating circuit sets a voltage implementing an optimal amplification ratio on an output terminal, and generates a reference voltage by taking account of the temperature slope of the breakdown voltage of the APD. The reference voltage is applied to one input of a voltage comparator. A setting circuit feeds to an adding circuit a preselected voltage for controlling the voltage on the output terminal to a value capable of implementing the optimal multiplication ratio. A temperature compensating circuit feeds to the adding circuit a voltage corresponding to the temperature slope of the above breakdown voltage. The temperature slope is representative of the variation of the breakdown voltage with respect to temperature.

Abstract: A detector array for a laser imaging apparatus comprises a plurality of detectors disposed in an arc around an opening in which an object to be scanned is disposed; and a variable gain integrator operably connected to each detector to accommodate the dynamic range of each detector. A method for collecting data for use in image reconstruction of an object being scanned is also disclosed, comprising the steps of providing a plurality of detectors disposed in an arc around the object to be scanned, including a variable gain amplifier connected to each detector; impinging a laser beam at a point on the object; integrating the input to each integrating amplifier at several time intervals; recording each output at each integration interval for use in image reconstruction; orbiting the detectors and the laser beam to a next point on a circle; and repeating steps until a complete circle has been traversed.

Abstract: A light receiving amplifying device includes a light receiving device for outputting a light signal current which varies with a quantity of received light, a load resistor connected with the light receiving device in series, for generating a detected voltage which varies with the light signal current, and a low frequency current bypass circuit for preventing the detected voltage from being saturated when the detected voltage has a frequency in a low frequency band. The low frequency current bypass circuit is connected with the load resistor in parallel and has an input impedance varying with a frequency of the detected voltage. The device further includes a transimpedance amplifying circuit (inverting amplifying circuit) for transforming an impedance of the detected voltage, and a capacitor for coupling the low frequency current bypass circuit and the transimpedance amplifying circuit (inverting amplifying circuit).

Abstract: A method and circuits are shown for managing the power usage of a receiver circuit by controlling bias current in at least some of the subcircuits of the receiver using a bias current control signal which varies responsive to incoming data signal activity. A circuit is shown wherein an automatic gain control signal controls the gain in a current-mode input amplifier by reducing a bias current in the input amplifier when the activity in the incoming data signal is below an automatic gain control threshold and where the gain of the input amplifier increases responsive to a decreasing level of the bias current. A method is shown wherein the power consumption of a receiver circuit is controlled by generating a bias current control signal which corresponds to the level of activity in a received signal and controlling the bias current, in whole or in part, of at least some of the subcircuits of the receiver using the bias current control signal.

Abstract: A bias voltage supply circuit for an optical receiver includes a high-voltage generation circuit, a current detection circuit, a reference voltage generation circuit, and an operational amplifier. The high-voltage generation circuit supplies a variable bias voltage to an APD having an amplification function. The current detection circuit converts an output current, which is based on the bias voltage supplied from the high-voltage generation circuit, into a voltage signal. The reference voltage generation circuit outputs a constant reference voltage. The operational amplifier outputs a voltage control signal, corresponding to a difference between an output voltage from the current detection circuit and the reference voltage from the reference voltage generation circuit, to the high-voltage generation circuit, thereby variably controlling the bias voltage to be supplied to the photoelectric converting element.

Abstract: A photosensitive detector (1) for detecting luminous flashes (2) is provided with a photosensitive diode (3) which is linked to a positive voltage and to ground via a resistor R1 and which is capable of transforming the luminous flashes into electrical signals and a circuit (4) that processes the electrical signals generated by the photosensitive diode (3). The circuit (4) causes electrical signals which correspond to luminous flashes (2) received by the photosensitive diode (3) and which exhibit a fast rise time to be strengthened, and the circuit (4) causes electrical signals which correspond to luminous flashes (2) received by the photosensitive diode (3) and which vary more slowly in intensity to be attenuated. The circuit (4) is linked directly to the photosensitive diode (3) and includes a differentiator circuit.

Abstract: In order to effectively amplify an electrical signal converted from an optical signal, first and second amplifiers are coupled in series. A controller is arranged such as to receive outputs of the first and second amplifiers and to produce first and second control signals based on the outputs. The first and second amplifiers respectively change gains thereof in response to the first and second control signals. The output of the second amplifier is an output of the arrangement.

Abstract: A laser scan microscope irradiates a sample with a laser beam while simultaneously scanning the laser beam over the sample, and processes an optical signal obtained thereby so as to obtain image data. The laser scan microscope is provided with a photoelectric converting unit, a sensitivity adjuster, and a sampling/converting unit. The photoelectric converting unit converts an optical signal from the sample into an electric signal. The sensitivity adjuster adjusts the sensitivity of the photoelectric converter such that an output value of the photoelectric converting unit becomes closer to a predetermined reference value. The sampling/converting unit samples sensitivity information determined for the photoelectric converter, in accordance with a scanning speed, and converts the sampled sensitivity information into a light measurement value used for obtaining the image data.

Abstract: An optical tracker system comprises an optical sensor 1 and associated signal processing circuitry 12, 24 for conditioning signals output from the sensor and rejecting signal indicative of false sensor information. A signal rejection circuit 24 comprises a guard time monostable 28 arranged to generate a guard time pulse defining a guard time when a pulse is input from the sensor 1, an output monostable 35 arranged to generate an output pulse in response to the guard time pulse, and an output suppress monostable 30 arranged to suppress the output monostable 35 when a false signal condition occurs during the guard time.

Abstract: An active avalanche photo-diode, APD, gain control circuit for use in an optical receiver includes a bias generator for varying the bias on a variable gain APD in response to bias control values generated by a controller. The controller receives the output of the optical receiver and determines the system noise of the receiver for the various bias control values. The system noise is compared to a threshold value for establishing the optimum bias for optimum gain of the APD. The gain control circuit is useable in an optical receiver in an optical time domain reflectometer, OTDR, for increasing the dynamic range of the OTDR.

Abstract: The invention is a circuit for eliminating or reducing unwanted components from an optical output signal. The circuit employs a photodetector for converting a portion of the output signal to an electrical signal, and a feedback loop which passes only the second harmonic band or the frequency difference band for combining with the input biasing signal.

Abstract: A multi-channel electromagnetically transparent voltage probe transmission link system for monitoring a plurality of voltage signals at a plurality of test points of a device under test that is subjected to a radiation field. Each channel includes two voltage probes, an electrical to optical signal transmitter, an optical signal transmission line and a receiver located out of the radiation field. The voltage probes contact and sense the voltage signals at the test point. The electrical to optical transmitters are removably mounted in a common base and are powered by either a common (or shared) power supply and/or by dedicated power supplies, such as rechargeable batteries. The receivers process the optical signals and provide display signals corresponding to the sensed voltage signal at the plurality test points for evaluating the effect of the test radiation field.

Abstract: In an optical receiver including an avalanche photodiode (APD), a monitor circuit monitors the operating point of a preamplifier. A bias control circuit usually transfers a control signal received from an AGC (Automatic Gain Control) control circuit to an APD bias circuit. When the value being monitored by the monitor circuit exceeds a preselected level, the bias control circuit controls the APD bias circuit such that the above value coincides with the preselected level. The various sections of the receiver are free from damage ascribable to an increase in the photocurrent of the APD.

Abstract: In a light transmitter comprises an automatic bias control circuit which automatically controls a bias for an external modulator, a part of a light output/input signal of the external modulator is branched to detect an electrical monitor signal and a gain control signal is generated in inverse proportion to the level of the monitor signal to control the gain of the automatic bias control circuit.

Abstract: Apparatus for monitoring and controlling the operation of one or more high intensity discharge (HID) lamps. An electronic HID lamp power supply is electrically connected to a power source and to the HID lamps. For each lamp, one or more sensors produce one or more output signals respectively representative of one or more parameters (such as light intensity, color temperature, power consumption, temperature, arc voltage, etc.) which respectively define one or more operational characteristics of the lamps.

Abstract: The present invention has the object of preventing saturation of an optical detector by applying an inverted bias voltage so as to allow accurate measurement of optical spectra. In order to achieve this object, the present invention provides voltage applying means 8 controlled by a control section 6 for applying an inverted bias voltage to the optical detector 3 in order to prevent saturation of the optical detector 3.

Abstract: A negative feedback preamplifier having variable conversion gain control and variable open loop gain control capabilities which can work correctly regardless of semiconductor process variations. The negative feedback preamplifier used to convert an input signal current to a signal in the form of voltage includes: a resistor which determines the current-voltage conversion gain when a small signal current is input to the negative feedback preamplifier; a diode which switches the current-voltage conversion gain when a large signal current is input to the negative feedback preamplifier; a resistor which determines the current-voltage conversion gain when the large signal current is input; a grounded source amplifier including a main FET which is biased such that its transconductance decreases when the large signal current is input; and a bias setting portion (diode) which determines the bias condition associated with the main FET.

Abstract: A hand held label reader is capable of illuminating a label, capturing a digital image of two-dimensional information indicia on the label, and decoding the digital image to provide decoded output data to a terminal. The target label is illuminated by a low variation illuminator that includes a circular LED array mounted behind a plano-concave dispersing lens. The automatic electronic camera, which includes a CCD camera and control circuitry, uses three images to adjust the intensity of the digital image and store a properly exposed image of the label in video RAM. The intensity of the digital image is adjusted by controlling the video system gain via adjusting the CCD array's integration time, the gain of a video amplifier, and the gain provided by an analog-to-digital converter. The gain provided by the analog-digital-converter is adjusted to compensate for the attenuation of light through the camera's lens assembly. For the first image, the digital image is obtained using a default setting for the gain.

Abstract: An amplifier section is supplied with an electric signal outputted from a light-sensitive detector. The amplifier section comprises an amplifying circuit for amplifying the electric signal into an amplified signal having an amplified level. A producing section produces a control signal on the basis of the amplified signal and a reference voltage. A resistor section is connected to the amplifying circuit in parallel. The resistor section has a variable resistance which is varied in accordance with the control signal. A capacitor section has a capacitor and connects the input of the amplifying circuit and the output of the amplifying circuit through the capacitor in response to the control signal.

Abstract: The photocurrent generated by a photodiode receiving light substantially flows through a feedback resistor when the incident light intensity is low. As the incident light intensity increases, the source and drain of a FET connected in parallel to the feedback resistor establish a conducting state therebetween, whereby the photocurrent is divided into a current flowing through the feedback resistor and a current flowing through the FET connected in parallel to the feedback resistor. Accordingly, transimpedance is equivalently lowered, while the feedback resistor is restrained from lowering the output potential. When the incident light intensity is further increased, a gate bias current flows into the gate of an input-stage FET of an amplifier, whereby the photocurrent is divided into the current flowing through the feedback resistor, the current flowing through the FET connected in parallel to the feedback resistor, and the gate bias current.

Abstract: An amplifier circuit (1) is arranged to amplify a signal of variable magnitude from a photodiode (3) having capacitive characteristics. The circuit (1) comprises a first feedback path containing a voltage controlled variable resistor (8) for varying the gain of the amplifier in relation to the magnitude of the signal so as to provide an output signal of substantially uniform magnitude. The first feedback path also contains a capacitor (7) which compensates for adverse effects of reactance in the circuit caused by the capacitance of the photodiode (3) and of the variable resistor (8) in order to optimize the frequency response characteristics of the amplifier. A second feedback path comprising a fixed value resistor (9) becomes operable when the resistance of the first feedback path is large to provide fixed gain amplification of signals received from the photodiode (3).

Abstract: The intensity of each lamp which illuminates an object at an inspection station is controlled by controlling driving voltage applied to a power supply which supplies electrical power to the lamp. A phototransistor is used to sense the intensity of the lamp through an optical fiber. The sensor is followed by a digitally-controlled, variable gain circuit whose output is fed to an A-D converter. A microprocessor analyzes the digital signal from the A-D converter and corrects the driving voltage to the power supply to keep the intensity output of the lamp constant, as seen by a camera of a machine vision system. In this way, feedback corrects for a degraded lamp output due to aging. Preferably, the control of the level of lamp intensity can be changed from a remote system console of the machine vision system to reduce the need for access to internal parts, thereby reducing the probability that human error may cause a malfunction.

Abstract: A high-speed, high-resolution optical scanner system includes a flying spot scanner for scanning a beam across an object bearing information to be read and a high-bandwidth, high-sensitivity optical receiver including an avalanche photodiode for sensing the variation in light intensity of the beam reflected from the object being scanned; a power source for biasing the avalanche diode proximate its reverse breakdown voltage to produce high current gain in response to incident light; and a charge collector circuit responsive to the avalanche photodiode for producing a voltage proportional to the light incident on the avalanche photodiode.

Abstract: An optical power meter which is capable of performing power range switchover operations in short periods of time and are capable of performing optical power measurements over a wide range in short periods of time. The invention comprises a photodiode 101 which outputs an electrical current proportional to the input optical power, an I/V amp 102 which converts this electrical current into voltage, a variable-gain amp 103 for amplifying this voltage, an A/D converter 107 which converts the output voltage from this variable-gain amp into a digital signal, a CPU 110 which processes the digital signal outputted from this A/D converter 107, and saturation detecting comparators 108 and 109 which detect saturation of the I/V amp and the variable-gain amp. The CPU 110 switches the gains of the I/V amp and the variable-gain amp based on the output signals from the saturation detecting comparators.

Abstract: A luminous flux measuring device has a gain slaving circuit (10, 9), that receives an electrical output signal (m) produced by a photoreceiver (1) and includes a gain control circuit (9) and a comparator (10). The gain slaving circuit is connected to an A/D converter and a computer to record and evaluate the signal (m) and has a slave memory containing characteristic values (a,b) of a continuous function (f). The gain slaving circuit produces a slave signal (HT) according to the flux received (.PHI.) by the photoreceiver which signal is sent to the gain control circuit so that G=f(m).

Abstract: A light receipt system has a bias circuit and a light-receipt element. The bias circuit controls light input power to the light-receipt element to the optimum multiplication factor. The bias circuit of the light-receipt element has a first resistor, a second resistor, and a third resistor. The first resistor and the second resistor are connected in parallel, and the light-receipt element is connected between a connection of the first resistor and the second resistor, and the third resistor. A bypass current path is provided, connected to a junction point between the first resistor and the second resistor.

Abstract: The disclosed invention is a photoelectric sensor that is capable of resolving difficult low contrast sensing tasks by adjustment of the sensor's light source intensity, so as to prevent dark state saturation and extend the overall dynamic range of the sensor. The photosensor utilizes an enhanced dynamic (EDR.TM.) control circuit that combines the light source and offset adjustment of the DC amplifier circuit in a closed loop configuration. This connection provides an automatic reduction in the light source intensity as required to avoid saturation. Further, this is accomplished without sacrificing amplifier gain, so that the dynamic operating range of the photosensor is extended to include proper operation at very bright light levels. The EDR control circuit also includes an indicator circuit that is connected to the light intensity control circuit.

Abstract: A sensor system is provided with an amplifier that has as an input signal received from a light sensitive component. The output of the amplifier is determined by its gain factor. The output of the amplifier is continually monitored to determine whether it is in acceptable limits. When a change is required, a variable potentiometer is affected to change its resistance. The variable potentiometer is included as part of a feedback loop of the amplifier and, therefore, a change in its resistance will change the gain factor of the amplifier and achieve the appropriate magnitude of output signal from the amplifier. The system can be operated in either a pushbutton mode or an automatic gain control mode. In the pushbutton mode, the system responds to an operator request for a setup procedure to be accomplished.

Abstract: A large dynamic range infrared receiver with a variable input resistance for use in optical communication systems is described. The variable resistance provides this infrared receiver with three ranges of sensitivity depending on the power of the optical signal incident on the receiver. At low optical power, the variable resistance is high, providing the infrared receiver with high sensitivity. For intermediate optical power the variable resistance is reduced, providing the infrared receiver with medium sensitivity. At high optical power levels, the variable resistance switches to a low value, reducing the infrared receiver's sensitivity and limiting the voltage across the variable resistance.

Abstract: A compact photosensor circuit provides automatic intensity range control for machine vision systems. The circuit may be implemented with standard CMOS integrated circuit technology to provide high sensitivity, fully static operation, and automatic exposure control with no moving parts. For each pixel of an imaging array, a photodetector provides an input photocurrent to a corresponding photosensor circuit. The photodetector is connected to provide an output voltage and an input to the gates of a pair of series-connected FETs that act as an attenuator. The attenuator is connected to a biasing source that provides a floor bias voltage. An output of the attenuator is connected to the gate of a third FET connected to the input photocurrent. The output voltage responds as a function of the light intensity at the photodetector while the bias voltage determines the range of light intensity for normal operation of the photosensor circuit.

Abstract: An electronic gain control is disclosed for the photomultipliers of a gamma camera which assures that all photomultipliers in the camera have uniform gain for any given ganuna event. A specific dynode in the photomultiplier is isolated from the line resistive voltage divider string in the photomultiplier which places each dynode under incremental voltages. A voltage is then applied to the isolated dynode which can vary anywhere from the voltage the isolated dynode would have had if inserted in the voltage divider string to the voltage that the immediately preceding or immediately succeeding dynode in the string has whereby the photomultiplier's gain is controlled. The applied voltage to the isolated dynode is developed electronically by a voltage to frequency converter coupled by an opto-isolator to a gain voltage divider circuit which cycles the applied voltage between two different voltage potentials tapped from the voltage divider string.

Abstract: A system for sensing images using a detector array and correcting errors in the image signals caused by gain and offset variations from detector to detector in the array is disclosed. To correct gain and offset errors, the detector array is dithered by moving the detector line of sight between consecutive frames according to a predetermined pattern. This dithering causes different detectors to image the same location in the scene during different frames, and causes two adjacent detectors to scan between the same two points in the scene during a cycle of the dither pattern. Image data generated from the dithering is used to remove gain and offset errors from the sensed images, and to generate gain and offset correction values to be stored in a table and applied to the sensed images. The system is also adapted to compensate for scene changes when the detector array is installed on a moving platform.

Abstract: There is provided a light-receiving and amplifying device capable of changing its gain at high speed. A cathode of a photodiode PD is connected to a power source V.sub.CC via a current mirror circuit. An anode of the photodiode PD is connected to an input of an amplifier circuit AMP. The amplifier circuit AMP receives a photocurrent from the photodiode PD, converts the photocurrent into a voltage, and amplifies the voltage to form an output signal V.sub.OUT. A control signal of a current having the same magnitude as that of the photocurrent and output from the current mirror circuit is input to a control input terminal of a gain switching circuit. The gain switching circuit is composed of a resistor Rf.sub.1, a resistor Rf.sub.2, and a switch SW. The resistor Rf.sub.1 is connected across the input and the output of the amplifier circuit AMP, and the resistor Rf.sub.2 and the switch SW connected in series are connected across the input and the output of the amplifier circuit AMP.

Abstract: A laser light detector is provided which can be used to detect pulsed laser light that is produced by a rotating laser light source on a construction job site. The laser light detector provides an easily-read display which is indicative of the present level or elevation of the laser light detector with respect to the plane of rotating laser light. The laser light detector has a very large dynamic range, while maintaining a very good signal-to-noise ratio, and can, therefore, be used at both short and long distances from the rotating laser light source. The laser light detector is not dependent upon the energy level received of laser light, or by the spot size of laser light as it reaches the light detectors. Multiple discrete steps of elevation indication are provided, which can easily be increased to a larger number of discrete steps, if so desired. The laser light detector is available with several options, including dead band adjustment, normal or offset on-grade displaying, and averaging.

Abstract: An electronic gain control is disclosed for the photomultipliers of a gamma camera which assures that all photomultipliers in the camera have uniform gain for any given gamma event. A specific dynode in the photomultiplier is isolated from the line resistive voltage divider string in the photomultiplier which places each dynode under incremental voltages. A voltage is then applied to the isolated dynode which can vary anywhere from the voltage the isolated dynode would have had if inserted in the voltage divider string to the voltage that the immediately preceding or immediately succeeding dynode in the string has whereby the photomultiplier's gain is controlled. The applied voltage to the isolated dynode is developed electronically by a voltage to frequency converter coupled by an opto-isolator to a gain voltage divider circuit which cycles the applied voltage between two different voltage potentials tapped from the voltage divider string.

Abstract: A mirror smudge detecting apparatus for detecting a smudge on a mirror member used in an image forming apparatus such as a copier.

Abstract: The present invention provides a resonance-type optical receiver circuit which keeps predetermined small distortion even when the received light level becomes high. The resonance-type optical receiver circuit varies the resistance value of variable resistance element 80, which is used as a load resistor to optical detector 4, in response to the intensity of output signal 10 of an amplifier. The load resistor varies in response to a variations of the received light level of the optical detector in this manner to keep the input to the amplifier lower than a fixed value.

Abstract: A phase-inverting amplifier includes an input-stage FET, a load thereof and a gain control circuit. The gain control circuit is provided in parallel with the load, and reduces an effective load resistance to lower an open-loop gain of the phase-inverting amplifier when a current flowing through the load exceeds a predetermined value. The gain control circuit is typically a FET whose gate is biased at a constant voltage. A feedback resistor is provided in a negative feedback path of the phase-inverting amplifier. A bypass circuit is provided in parallel with the feedback resistor, and reduces an effective feedback resistance when a feedback quantity exceeds a predetermined value.

Abstract: A laser light detector is provided which can be used to detect pulsed laser light that is produced by a rotating laser light source on a construction job site. The laser light detector provides an easily-read display which is indicative of the present level or elevation of the laser light detector with respect to the plane of rotating laser light. The laser light detector has a very large dynamic range, while maintaining a very good signal-to-noise ratio, and can, therefore, be used at both short and long distances from the rotating laser light source. The laser light detector is not dependent upon the energy level received of laser light, or by the spot size of laser light as it reaches the light detectors. Multiple discrete steps of elevation indication are provided, which can easily be increased to a larger number of discrete steps, if so desired. The laser light detector is available with several options, including dead band adjustment, normal or offset on-grade displaying, and averaging.

Abstract: A method and apparatus are disclosed which allow for the detection of an object (14) by the generation of a radiated beam (18) and a subsequent reflection by the object (14) of a portion (20) thereof. The detection of particulate object material (16) due to a reflection of a portion (22) of the generated beam (18) is minimized.

Abstract: A device for the non-contact control of a sanitary fitting comprises in an emitting/receiving unit, in addition to an emitter and a receiver and their associated detection circuit as is known, a second receiver which can be reached directly by the radiation emitted by the emitter, and with which a second detection circuit is associated. In an initialization mode in front of a stationary reflector, the operating voltage of the emitter or the amplification of the detection circuits is continuously increased by a control unit until the desired sensitivity is reached. The values of representative voltages at which the two detection circuits are triggered are stored in respective stores. The quotient of these two values is put into a third store.

Abstract: A color preserving image intensifier having synchronously reciprocating input and output multi-segmented, multi-color filter slides. To compensate for differences in exposure time of the segments of the filters arising from varying reciprocation velocity due, e.g. to sinusoidal motion, either the intensity of the output image is variably filtered or the intensifier gain is varied. In one embodiment, polarizing filters rotated in synchronicity with the reciprocation of the color preserving filters vary image intensity. In another embodiment, intensifier gain is varied based upon a velocity indicator.

Abstract: There is disclosed a method for driving a photoelectric device comprising a photocathode, and controller for controlling electrons emitted from the photocathode, wherein gate voltages are applied respectively to the photocathode and the controller so that the electrons from the photocathode are not outputted from the controller.

Abstract: In a laser scanning system, an automatic gain control (AGC) circuit for dynamically adjusting the gain of a receiver that is used to receive light reflected from a bar code. The AGC provides a fast adjustment to receiver gain so that the receiver can provide a decodable signal quickly. To accomplish the fast adjustment, the AGC circuit, in addition to sensing the final output of the receiver, includes an additional feedback path from an amplifier in the receiver that is located before the final amplification stage. The additional feedback has a negligible attack time, and adjusts receiver gain quickly, thereby minimizing the time required to reach steady state.

Abstract: A broadband optical receiver which exhibits low noise and distortion characteristics. An active bias feedback circuit stabilizes the quiescent operating currents of a low noise amplifier coupled to the receiver photodetector. A transformer matches the impedance of the amplifier to an attenuator.

Abstract: A sensor board for use with an endpoint controller which monitors light intensity is provided. The sensor board can provide a dynamic range of up to five million because a constant current driver and phase sensitive detector help eliminate noise from the detected signal. The sensor board can also subtract a DC voltage offset from the detected signal and amplify the difference to provide increased resolution of small changes in the detected signal.

Abstract: A film densitometer for generating digital density values as a function of analog transmittance signals received at an input. A comparator coupled to the input compares the transmittance signals to one or more range references characterizing a plurality of ranges of transmittance signal magnitudes, and provides digital transmittance range signals as a function of the comparison. An amplifier amplifies the transmittance signals to provide amplified transmittance base signals. A gain control circuit coupled to the amplifier and the comparator controls the gain factor of the amplifier as a function of the magnitudes of the transmittance signals. The amplified transmittance base signals are converted to digital transmittance base values by an analog-to-digital converter. A lookup table of data characterizing the logarithmic relationship between transmittance base values and density base values is stored in base memory.

Abstract: Disclosed is an equalizing and amplifying circuit in an optical signal receiving apparatus comprising a preamplifier circuit having an input terminal connected to the output of a light receiving element. The preamplifier circuit amplifies the electrical signal from the light receiving element and outputs an amplified signal. An automatic gain control circuit is connected to the output of the preamplifier circuit. The preamplifier circuit comprises a transistor having a common-base, a current source connected to the emitter of the transistor for supplying a bias current to the transistor, and a load resistor connected to the collector of the transistor. The emitter of the transistor is connected to the input terminal, and the collector of the transistor is connected to the output terminal. A negative influence caused by mounting the circuit on a package is avoided and the circuit operates stably in a high frequency range.

Abstract: A distance measuring apparatus comprises a light emitting device for emitting infrared light blinking at a constant frequency toward an object, and a light receiving device for receiving infrared light reflected from the object. The light receiving device can generate two output signals which correspond respectively to positive and negative amounts of deviation of a position of light received therein with respect to a center thereof. The output signals are amplified by amplifiers, respectively. A signal component having a frequency corresponding to the blink frequency of the infrared light is picked up by a picking-up circuit from each of the output signals of the amplifiers. A distance determining device is provided to determine a distance to the object on the basis of the signal components. A gain control circuit for controlling gains of the amplifiers includes a pair of resistor circuits each having a changeable resistance for determining the gain of the corresponding amplifier.

Abstract: An optical data medium driving apparatus which constitutes amplifiers for an output current signal of a photosensor including a plurality of current mirror circuits having different amplification factors in order to switch, in a wide range, the output current signal of the photosensor. The photosensor detects a quantity of the reflected light corresponding to a variation of the quantity of reflected light from an optical data medium having various characteristics. The output is obtained with high accuracy and in a wide band. A servo-circuit is used for an AGC circuit and normalizes a difference signal from each light receiving surface at a photosensor having a plurality of light receiving surfaces. An A/D converter is given the difference signal as an analog input signal and the sum signal as the reference input signal. The A/D converter outputs an offset binary type digital signal, thereby being inexpensive to produce, easy to be integrated having high function, and high in reliability.