Abstract: An optical signal is converted by a light-receiving element into a photoelectric current. The photoelectric current is converted by a preamplifier into a positive phase voltage and the opposite phase voltage. The peaks of the positive phase output and opposite phase output are sensed and held by a first and second peak sensing circuits. The median between the output of the second peak sensing circuit and the positive phase output of the preamplifier is determined by a first median output circuit. The median between the output of the first peak sensing circuit and the opposite phase output of the preamplifier is determined by a second median output circuit. A level comparison circuit compares the outputs of the first and second median output circuits and produces a signal voltage with a constant amplitude within a specific input voltage range, thereby producing a reception signal.

Abstract: A system and methods for transmitting analog signals, particularly analog signals derived from an optical signal intensity, in a noisy environment over a length of cable. The optical signal is sensed by a photodetector, which is bootstrapped and backbiased to minimize the capacitive effect of the photodetector, and converted to a voltage by a transconductance stage. The voltage signal is then driven over a length of cable by a buffer amplifier having a low impedance output substantially matched to the characteristic impedance of the cable (e.g., twin lead wires having a Z.sub.0 =120), to a second circuit board. The cable length may be, e.g, less than a meter. The second circuit board contains a high gain amplifier stage and circuits for processing the high gain amplifier signal to derive, e.g, a peak pulse amplitude corresponding to the peak intensity of the optical signal sensed at the first circuit board.

Abstract: The present invention provides an amplifier capable of accurately reproducing a signal under various operating environments and an optical receiving circuit using the amplifier. The differential amplifier is constructed such that the amplification factor thereof is set to 0.5, and a variation occurring inside thereof is the same as a variation occurring inside of the differential amplifier. Respective output variations occurring in maximum value holding circuits due to a temperature variation and a power supply voltage variation are canceled by providing differential amplification in the differential amplifier. At this time, an output variation occurring in the differential amplifier is also canceled. Therefore, an output variation occurring in the differential amplifier is made equal in value to the output variation occurring in the differential amplifier, such that the same variation as a signal input is superimposed on the reference input fed to the differential amplifier.

Abstract: A DC coupled burst mode optical receiver circuit having improved sensitivity and improved dynamic range. The output of the receiver's photodiode is single endedly amplified by a main preamplifier and the main preamplifier's output is then converted, using an operational amplifier, e.g., with a gain of 1, to a differential signal which swings symmetrically around a threshold level. More specifically, the output of the main preamplifier is connected to one input of the operational amplifier. The output of a tracking preamplifier, which is identical to the main preamplifier, is coupled to the other input of the operational amplifier. The output of the tracking preamplifier is used to match the DC voltage of the main preamplifier, e.g., by being noise-free and by tracking changes in supply voltage, temperature, and the like. It is used to set the DC reference voltage for the standard operational amplifier functions.

Abstract: An amplifier circuit includes an amplifier which derives an output voltage from an input current, and a bypass circuit which bypasses part of the input current so that the remainder of the input current is applied to the amplifier.

Abstract: A pre-amplifier disclosed in which low noise at the time of small input and linear amplification at the time of large input are compatible. In a pre-amplifier, such compatibility can be realized by constituting a current mirror circuit, with respect to a current of a first stage transistor in a transimpedance portion, by a by-passing transistor which is provided at an input side of the pre-amplifier. In such a configuration, by making a by-pass current flow proportionally to an input instantaneous current at the time of a large input, the transimpedance can be made small equivalently to thereby widen the dynamic range.

Abstract: An opto-coupler comprising an LED and a photo-transistor whose collector resistor is connected in parallel with a diode comprising the emitter-base junction of a second transistor. This diode prevents saturation of the photo-transistor and at the same time, the current through the emitter-base junction diode of the second transistor is amplified by the gain of the second transistor to achieve and optimum signal output level across the collector resistor of the second transistor. The emitter-base junction diode of the second transistor prevents the photo-transistor from saturating and, in so doing, improves the rise and fall times of the collector current of the photo-transistor. The operation of the photo-transistor in a nonsaturation mode and the optimization of its rise and fall times for its collector currents result in an improvement in the data rate of the input signal that can be accommodated by the opto-coupler circuit.

Abstract: A photon coupled circuit comprises a high quantum efficiency semiconductor light emitter (TDA) coupled with low photon losses to a high quantum efficiency semiconductor light detector (OLD). Bias current is provided to both the light detector (OLD) and light emitter (TDA). The light output of the light emitter (TDA) is modulated by the signal current flowing therein and the current flowing (i.sub.o) in the detector (OLD) is modulated by the light received from the light emitter (TDA). The quantum transfer efficiency or open loop current gain is greater than 0.5 and a portion of the AC current flowing in the light detector (OLD) is applied as feedback to reinforce or oppose the current flowing in the light emitter (TDA).

Abstract: The present invention relates to the use of a pixel design which incorporates an in-pixel amplifier to enhance the signal-to-noise ratio of an image sensor array while maintaining a high sensor fill factor. In addition, this pixel design allows for the addition of an amplifier without having to modify the fabrication process of current sensor arrays.

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 burst optical signal receiver receives optical signals produced in a burst form from a predetermined subscribers. This burst optical signal receiver comprises an identifying circuit for comparing the input level of an input optical signal with a predetermined threshold value to identify the input level; a peak detector for detecting and holding the peak value of the input optical signal; a DC feedback circuit for acquiring the DC level of an output of the identifying circuit; and a circuit for producing the predetermined threshold value from the DC level from the DC feedback circuit and the peak value held in the peak detector and supplying the predetermined threshold value to the identifying circuit. The peak detector has a plurality of peak detection sections having different gains and operational dynamic ranges and causes those peak detection sections to operate in accordance with the input level of the input optical signal.

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 optoelectronic cell structure includes a plurality of pnpn-devices and circuitry for driving these pnpn-devices. The anodes or the cathodes of said pnpn-devices tied together form a competition node allowing differential charge amplification to take place. The unconnected electrode of each of the pnpn-devices is driven by a pair of complementary transistors. Light input on the pnpn-devices is converted into charge carriers. A forward bias amplifies the difference in charge content in the pnpn-devices by differential competition. A reverse bias turns off each pnpn-device at its own pace, the turn-off times rendering an estimate of the charge content in each pnpn-device present before turn-off. The total system forms a sensitive optical receiver for use in optical interconnects between two or more locations.

Abstract: A method and apparatus for receiving infrared signals are provided. The circuit includes preamplifier that includes an integrator that charges based on light detected by a photodiode. The circuit includes a warning circuit that generates a warning flag when the charge on the integrator exceeds a predetermined level. To prevent the integrator from saturation, digital logic resets the preamplifier by dumping the charge on the integrator in response to the warning signal. The digital logic is also configured to reset the integrator at predetermined intervals. When the incoming signal is encoded using pulse position modulation, the interval at which the integrator is reset is the length of a single time slot in the pulse position modulation frame. A sample and hold circuit is provided to hold a previous output of the preamplifier. The difference between the previous output of the preamplifier and the current output of the preamplifier is compared with a threshold voltage to detect pulses on the incoming signal.

Abstract: A highly sensitive optical receiver where one terminal of the photodiode of the receiver is connected to a negatively biased amplifier while the other terminal of photodetector is connected to a positively biased amplifier, where such connections automatically bias the photodiode and use the current from both terminals (anode and cathode) of the photodiode. This invention also provides an optical receiver which has a DC cancellation circuit to eliminate the biasing voltages in the final output signal.

Abstract: A device and method for quantitative determination of an analyte in a biological sample utilizes a non-transparent support medium for retaining a chromatogenic reaction product with the medium being exposed to a source of light for transmitting therethrough a scattered, uniform response light signal which is collected at a photosensitive device whereby the amount of the analyte is correlated to the intensity of the response light signal. The response light signal may be converted to a time-duration signal proportional to light intensity to facilitate the quantitative determination.

Abstract: Circuitry and circuitry layout are provided to achieve a high percentage of photoreceiver area to total area and to stabilize the voltage at the base node of a phototransistor. Voltage stabilization is achieved by a servo circuit in which a negative feedback loop from the base node to an emitter node maintains a bias point, so that photocurrent is efficiently delivered to charge transfer circuitry. In the preferred embodiment, the base node is connected to a gate of a first transistor having a drain that is connected to a source of constant current and to a gate of a second transistor that functions as a source follower. The source of the second transistor is connected to the emitter node of a phototransistor. As photocurrent is generated by the reception of light, an integration capacitor is charged.

Abstract: Devices for measuring one or more properties of a light signal is disclosed. More particularly the invention relates to devices for wavelength and power demodulation based on the use of quantum well electroabsorption photodiodes. In one aspect the invention provides and power and wavelength demodulation system based on a quantum well electroabsorption (QWEA) filtering detector. The input optical signal passes through an optical beam splitter with part of the signal input into a filtering detector which is a multiple quantum well electroabsorption (MQW EA) photodiode having a tunable bandgap and the other part into a reference detector. The input light signal is impinged on the QW diode perpendicular to the plane of the quantum wells. The output of filtering detector is amplified by an amplifier and the output of the reference detector is input into another amplifier. The output from reference detector amplifier serves as a measurement of the power of the input optical signal.

Abstract: An optical receiver communication system converts optical signals modulated by analog or digital waveforms to RF signals. The optical receiver contains an automatic level control circuit to adjust the electronic gain of the system accordingly across a broad bandwidth spectrum. Two impedance matching circuit are designed using broad band matching technique to expand the bandwidth for increasing the maximum receivable frequency to 1 GHz. A RLC impedance matching circuit forms a resonant combination to maintain .+-.1 dB fluctuation between the low-and high-frequency limits of the bandwidth, and a 75 .OMEGA. impedance matching circuit creates a 180.degree. phase shift between the outgoing and the incoming signal for low return loss.

Abstract: Configurable Optical Gates (COGs) are used to transmit and receive optical signals similar to an interconnect device as well as perform a logic function on those signals (they are smart pixels). COGs consist of a laser with an intracavity modulator, an integrated current source and one or more integrated photodetectors to drive the modulators. The devices are monolithically integrated on MultiQuantum Well (MQW) heterostructure. Certain logic functions require that the bottom N- contact which is under individual devices be accessible and electrically isolated from neighboring devices. For this reason, the laser heterostructure is grown on a semi-insulating substrate. Each COG has a built-in light baffle that prevents the laser emission from coupling into the photodetectors. The optical detection of the COG can be disabled during fabrication and the device can be directly modulated by conventional electronics.

Abstract: An improved amplifier architecture for providing an output as a function of light sensed by a photodetector element where the amplifier has an input for receiving the current output from the photodetector element and an output for providing an output that is a clamped function of light sensed by the photodetector element. A feedback circuit is connected between the input and the output of the amplifier. A signal clamp connected to the output of the amplifier that clamps the output of the amplifier to a predetermined value. A summing node having first, second, and third inputs, and an output at which a signal that is a function of sensed light is provided. A first current path connected between the input to the amplifier and to a first input of the summing node for passing excess current from the input of the amplifier to the summing node when the output of the amplifier is at its clamped output.

Abstract: An optical receiving apparatus is provided which is constructed to compensate for a rise in offset level attributable to low-frequency response of a light-receiving device. An offset detecting circuit detects a quantity of electricity indicative of an offset current quantity which corresponds to the zero level of an optical signal within the current quantity output from the light-receiving device, and a current subtracting circuit reproduces the offset current quantity based on the detected quantity of electricity, subtracts the reproduced offset current quantity from the current quantity output from the light-receiving device, and supplies the result to a preamplifier.

Abstract: A preamplifier overload control circuit which enhances the dynamic range of the preamplifier. Separate paths shunt corresponding DC and AC components of the signal from an electro-optical device away from the preamplifier input. The amount of shunting in both paths are controlled by a common control signal, here the average DC value of the signal, such that substantially all of the DC signal is shunted away from the preamplifier input.

Abstract: A transimpedance amplifier (10, 50) is provided for processing a current signal received from a circuit device (12, 52). The circuit device (12, 52) can be a photodiode used to receive infrared transmissions. The transimpedance amplifier (10, 50) includes a first stage (14, 54) coupled to an input node. The first stage (14, 54) has a first amplifier (20, 60) operable to drive the input node and is operable to provide a current signal to a second node (NODE 3, NODE 2) in response to a current signal in the input node. A second stage (16, 56) is connected to the second node (NODE 3, NODE 2). The second stage (16, 56) has a second amplifier (32, 68) and is operable to convert the current signal in the second node (NODE 3, NODE 2) into an output voltage signal (V.sub.OUT) at an output node. A feedback loop (18, 58) can be connected to receive the output voltage signal (V.sub.OUT) and to provide a feedback current signal to cancel ambient noise in the current signal in the input node.

Abstract: A limiting transimpedance amplifier includes an amplifier stage including a feedback resistor, a limiting diode coupled across the feedback resistor, and a stabilization diode coupled to the amplifier stage to compensate for feedback instability introduced by the limiting diode. The amplifier stage includes an input transistor and an output transistor, where the feedback resistor couples an output of the output transistor to an input of an input transistor. A stabilization voltage generator is coupled to the stabilization diode to provide a stabilization voltage that causes the desired compensation.

Abstract: A reflective wetting or spot detecting system incorporates a light emitting diode and a solid state photo sensor arranged on the same side of a medium being analyzed. The sensor is carried at one end of an elongated housing with a linear channel extending through. The channel is oriented on a line that is normal to the medium being analyzed. The channel functions as a lensless, passive focuser of reflected radiant energy. The source of radiant energy is located at an acute angle with respect to the medium. A conditioning circuit is coupled to the output of the sensor. The conditioning circuitry includes a current-to-voltage converter, a signal reducing stage, an amplifying stage and a comparator. The signal reducing stage reduces the voltage signal, produced by the current voltage converter, a predetermined amount, thereby effectively providing the amplifier stage with a greater dynamic range than it would have otherwise had.

Abstract: An image sensor of charge storage type and a driving method of the image sensor. A light signal from a photosensitive element is read by an amplifier and the read signal is held in a sample hold circuit of a signal detector. Next, a voltage is given from a variable power source to the amplifier and a signal output from the amplifier is compared with the previously held signal in a comparator in the signal detector. The voltage of the variable power source at an equal point where the two signals are coincident with each other in the comparison is read as a true value. Hence, irrespective of dispersion of characteristics of amplifiers, the correct value can be always detected. The influences of the dispersion of the amplifiers, a temperature change and a time-drift of TFT characteristics are removed to improve S/N.

Abstract: The invention provides a very high speed optical transmission apparatus which is tough against a variation in mark rate using an equalizing amplification circuit of a narrow-band frequency characteristic. The optical transmission apparatus includes an equalizing amplification circuit including a photoelectric conversion circuit for receiving a non-return-to-zero code as a reception signal, a peak value detection circuit, a dc amplifier, a timing extraction circuit, a dc regeneration circuit and an identification circuit. The equalizing amplification circuit includes a differentiating circuit for producing a differentiation equalization waveform of a reception signal of a non-return-to-zero code.

Abstract: Circuitry and method for transferring signals from a photoreceiver array to computational circuitry includes parallel transfer amplifiers that receive periodic offset correction and includes DC removal amplifiers. In a first embodiment, each transfer amplifier has a differential circuit that can be switched from a reset mode to a readout mode. In the readout mode, the voltage state at the output is responsive to first and second inputs, with the second input being connected to a source of a reference voltage. In the reset mode, the inputs are both connected to the reference voltage and the output is temporarily connected to a source of a fixed reset voltage. An offset adjustment signal is generated in response to detection of a voltage difference between the reset voltage and the actual voltage state at the output after the output has been disconnected from the source of the reset voltage. A single offset circuit is used to periodically and sequentially refresh the various transfer amplifiers.

Abstract: Photocurrents outputted by photo detecting circuits (1.sub.1 to 1.sub.n) disposed in first current paths (2.sub.1 to 2.sub.n) are amplified by current amplifying means (3.sub.1 to 3.sub.n) disposed in the first current paths (2.sub.1 to 2.sub.n), respectively. The output currents from the plurality of current amplifying means (3.sub.1 to 3.sub.n) are converted into voltage all by one current-voltage converting means (5). The current amplifying means (3.sub.1 to 3.sub.n) are turned on or off by control signals (3.sub.1S to 3.sub.nS), and therefore the luminance detecting circuit amplifies the current of the required photo detecting element only, and outputs into the current-voltage converting means (5).

Abstract: A current boosted positive feedback logarithmic transresistance amplifier is provided for currency validators. The amplifier has a photo-diode capable of producing a current in response to light, connected to an operational amplifier having both a positive and a negative feedback branch. A logarithmic density amplifier having a feedback resistor and a log diode connected in shunt with the resistor as a dynamic feedback to the amplifier is connected to the positive feedback branch of the current boosting amplifier by way of the log diode. The summing action at the inputs of the current boosting amplifier result in a current at the log diode that is a direct multiple of the current in the photo-diode.

Abstract: An apparatus and method for optical heterodyne conversion and a radiation source and integrated diagnostics using the apparatus and method are disclosed. The radiation source can operate in a high-power narrow-band mode in which a constant-frequency output is provided or in a low-power broadband mode in which the frequency is tunable to allow the radiation source to act as a sweep oscillator. The apparatus or photomixer includes two sets of interdigitated conductive electrodes formed on top of a crystal lattice formed of column III-V compounds, particularly InAlGaAs compounds. Additional column V atoms are interspersed within the lattice structure to form defect energy states in the bandgap of the host material. The region of the material between the interdigitated electrodes is illuminated by optical radiation containing two different frequencies. Photon absorption in the material causes a current at the difference frequency to be generated and coupled to the interdigitated electrodes.

Abstract: A solid-state radiation detector, including a photodiode array, is suitable for use in computed tomography, with the dark current of the photodiodes being compensated. The compensation is accomplished by an adjustable voltage source connected to the photodiode, the voltage of the adjustable voltage source being set by a regulator so that the dark current becomes zero. The regulator receives a signal corresponding to the dark current from a measured value transducer in the form of a current-driven voltage source. The voltage supplied by the adjustable voltage source to the photodiode is maintained constant while x-rays are incident on the overall detector which cause illumination of the photodiode.

Abstract: It is an object of present invention to provide a low-cost photoelectric conversion module in which a signal for compensating noise caused by changes in temperature and variations in power supply is obtained. In the photoelectric conversion module according to the present invention, a first amplifier having an input terminal connected to the anode of a light-receiving element for converting an optical signal into an electrical signal amplifies the electrical signal to obtain an amplified signal. A second amplifier having an input terminal connected to one electrode of a capacitor outputs an amplified signal for compensating noise of the electrical signal amplified by the first amplifier. The other electrode of the capacitor is connected to the cathode of the light-receiving element. The capacitor has a capacitance value equal to the capacitance of the light-receiving element.

Abstract: Automatic Gain Transimpedance Amplifiers for analog applications having high bandwidth, wide dynamic range, and ultra-high linearity. The transimpedance amplifiers includes an operational amplifier and a variable feedback resistance means connected between the input and the output of the amplifier. The variable feedback resistance means may include a single feedback PIN diode, two serially connected feedback PIN didoes, a PIN diode connected to a feedback resistor in parallel, or two serially connected PIN diodes connected to a feedback resistor in parallel. Ultra-high linearity is achieved because the dynamic resistance of the PIN diode under forward bias is substantially linearly dependent on the inverse of the current that passes the diode.

Abstract: An optical receiver, a method of converting an optical signal into an output electrical signal suitable for use by digital circuitry and an optoelectronic data processing system.

Abstract: A transimpedance amplifier circuit includes an inverting voltage amplifier having an input being supplied with an input current and an output carrying an output voltage. A coupling member is connected between the input and the output of the voltage amplifier. The coupling member has two diodes being connected antiserially to one another between the input and the output of the voltage amplifier with a common node point. A transistor has a load path being connected between the common node point and a ground potential. A differential amplifier has one input connected to the input of the voltage amplifier, another input connected to the output of the voltage amplifier, and an output. A low-pass filter is connected downstream of the differential amplifier for furnishing a trigger signal at the output to the transistor.

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: An optical receiving apparatus of the present invention comprises an opto-electric conversion element for converting an optical signal into an electric signal, a differential type preamplifier for sending a non-inverting phase signal and a inverting phase signal of the electric signal and a first and second peak hold circuits for holding peak values of the respective non-inverting and inverting phase signals. Further, the optical receiving apparatus of the present invention comprises a first adder for adding the inverting phase signal to the non-inverting phase peak signal from the first peak hold circuit and a second adder for adding the non-inverting phase signal to the inverting phase peak signal from the second peak hold circuit.

Abstract: A photodetector module contains a package, a photodiode, a preamplifier, a bypass capacitor, a cap with a lens and a sleeve. A parallel plate capacitor is used as the bypass capacitor. The parallel plate capacitor is mounted at the center of the package. The photodiode is stuck on the parallel plate capacitor. Since the photodiode is piled upon the capacitor, the module curtails the area for mounting a capacitor. The fiber, the lens, the photodiode and the capcitor align along a central line with rotational symmetry. The two-story structure reduces the size of the module and the cost of production by decreasing the number of the parts and the steps of production.

Abstract: A transimpedance amplifier has an amplifier unit, a feedback resistor arranged between the output and input ends of the amplifier unit, a voltage clamp unit connected to the opposite ends of the feedback resistor, to clamp a voltage applied to the ends of the feedback resistor and prevent the amplifier unit from saturating, a current absorption unit arranged on the input side of the amplifier unit, to absorb any large input current supplied to the amplifier unit, and a switching selection unit to activate or deactivate the current absorption unit according to an external control signal. The current absorption unit is activated through the switching selection unit when a large input current is produced to write data to a magneto-optic disk in a magneto-optic disk unit in which the transimpedance amplifier is installed.

Abstract: A charge transfer device is disclosed. The charge transfer device has: a charge transfer section for outputting a signal charge; a voltage signal output circuit for converting the signal charge into a voltage and outputting a voltage signal; a reference signal output circuit for outputting a reference signal of a predetermined voltage, the reference signal output circuit having a circuit constant substantially equal to a circuit constant of the voltage signal output circuit; and a differential operational amplifying circuit for amplifying a difference between the voltage signal from the voltage signal output circuit and the reference signal from the reference signal output circuit and outputting the amplified difference.

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: An integrated circuit photodetector includes a transimpedance amplifier including a differential amplifier stage with PNP emitter-coupled transistors and a PNP input transistor which are biased only by base currents of the emitter-coupled transistors, to achieve low input bias current. Low noise operation is achieved by bypass capacitors coupled between the bases and emitters of the input transistors, respectively. A constant current source supplies a current which develops a small pedestal voltage across a resistor to bias the non-inverting input of the transimpedance amplifier so as to avoid nonlinear amplification of low level light signals. A positively biased N-type guard tub surrounds the photodetector, which is formed in a junction-isolated N region on a P substrate, to collect electrons generated in the substrate by deep-penetrating IR light to prevent them from causing amplification errors.

Abstract: A low-noise FET amplifier is connected to amplify output charge from a che coupled device (CCD). The FET has its gate connected to the CCD in common source configuration for receiving the output charge signal from the CCD and output an intermediate signal at a drain of the FET. An intermediate amplifier is connected to the drain of the FET for receiving the intermediate signal and outputting a low-noise signal functionally related to the output charge signal from the CCD. The amplifier is preferably connected as a virtual ground to the FET drain. The inherent shunt capacitance of the FET is selected to be at least equal to the sum of the remaining capacitances.

Abstract: A photocurrent detector circuit includes a photodiode coupled to an input terminal of a first operational amplifier. A first resistor has a first end coupled to the photodiode and a second end coupled to an output terminal of the first operational amplifier. A first diode has a first end coupled to the photodiode. A second resistor has a first end coupled to a second end of the first diode. A low gain bias network is coupled between a second end of the second resistor and the output terminal of the first operational amplifier. A second diode has a first end coupled to the photodiode. A clamp bias network is coupled between a second end of the second diode and the output terminal of the first operational amplifier. Preferably, the photodiode and the first and second diodes include silicon carbide. The detector may further include second and third operational amplifiers coupled to the output terminal of the first operational amplifier.

Abstract: A galvanic isolation device having a light-emitting diode and a photo-transistor. A control circuit, which is coupled to the light-emitting diode and which controls the light-emitting diode, is provided. A signal generator circuit, which is coupled to the photo-transistor, is also provided. The signal generator circuit includes a fixed-gain amplifier circuit that is coupled to a current path formed by a collector electrode and an emitter electrode of the photo-transistor. A biasing circuit, which is coupled to a base electrode of the photo-transistor, biases the photo-transistor into a saturated state.

Abstract: There is provided a light amplification device including a bandpass filter whose transmission center wavelength can be stabily tuned to the wavelength of an optical signal despite component temperature variations and deterioration over time. The transmission center wavelength of the bandpass filter (14) is swept and the intensity of the transmitted optical signal is simultaneously converted into an electrical signal by a photodetector (42). The electrical signal is subjected to first-order differentiation and second-order differentiation by a differential circuit (43). The wavelength of the optical signal is determined based upon a negative peak value of the current obtained by second-order differentiation. Thereafter, the transmission center wavelength of the bandpass filter is repeatedly swept within a band of several fractions of a nm using a transmission center wavelength obtained based upon the negative peak value.

Abstract: An apparatus and method is provided that improves the dynamic range of an optical transimpedance receiver. The receiver includes a photodetector, a transimpedance front end amplifier and a non-liner feedback. The non-linear feedback means consists of a Schottky diode and shunting the transimpedance resistor with a parasitic capacitor. A lead compensation network is further included in the feedback circuitry to provide stability to the non-linear circuit by advancing the phase shifting of the transimpedance front end by 45 degrees. By stabilizing the frequency off the circuit, the dynamic range is increased from 26.6 dB to 40 dB.