Abstract: An optical modulation-type detection device has a noise detection mode having (i) an offset canceling (hereinafter referred to as “OC”) period in which (a) the light-reception signal pathway of a pulse signal converting section is cut off so that an offset of the pulse signal converting section is suppressed and (b) the light-reception signal pathway of the pulse signal converting section is reconnected while a state in which the offset is suppressed is being maintained, at an end of the OC period, and (ii) an asynchronous reception period in which whether or not asynchronous reception occurs is detected after the first period, and an object detection mode having a synchronous reception period in which whether or not synchronous reception occurs is detected after the asynchronous reception is not detected in the noise detection mode.

Abstract: An abnormal pulse detection circuit in a receiver of the present invention includes: an incoming pulse edge detection circuit which detects the moment of rise of an input signal and outputs the result of the detection as an edge detection signal; a muting reference pulse generation circuit which generates a muting reference pulse based on the edge detection signal; a logic circuit which outputs a signal indicating a negative AND of the muting reference pulse and the input signal; a muting signal generation circuit which generates a muting signal from the output signal of the logic circuit; and a switching circuit which outputs the input signal or the muting signal. The receiver of the present invention can therefore reduce discomfort in hearing reproduced sound in case where a noise occurs in an audio signal due to a variation in pulse width.

Abstract: An optical modulation-type detection device has a noise detection mode having (i) an offset canceling (hereinafter referred to as “OC”) period in which (a) the light-reception signal pathway of a pulse signal converting section is cut off so that an offset of the pulse signal converting section is suppressed and (b) the light-reception signal pathway of the pulse signal converting section is reconnected while a state in which the offset is suppressed is being maintained, at an end of the OC period, and (ii) an asynchronous reception period in which whether or not asynchronous reception occurs is detected after the first period, and an object detection mode having a synchronous reception period in which whether or not synchronous reception occurs is detected after the asynchronous reception is not detected in the noise detection mode.

Abstract: An optical space communication reception circuit receives a signal in switched-over communication speed modes and under settings corresponding to the communication speed modes. Receiver sensitivity in the respective communication speed modes is set in advance such that maximum communicable distances in the communication speed modes are substantially equal. By this, it becomes possible, for example, in optical space transmission such as infrared communication and the like to enhance a false operation prevention characteristic against disturbance noise, without decreasing maximum communicable distances.

Abstract: An abnormal pulse detection circuit in a receiver of the present invention includes: an incoming pulse edge detection circuit which detects the moment of rise of an input signal and outputs the result of the detection as an edge detection signal; a muting reference pulse generation circuit which generates a muting reference pulse based on the edge detection signal; a logic circuit which outputs a signal indicating a negative AND of the muting reference pulse and the input signal; a muting signal generation circuit which generates a muting signal from the output signal of the logic circuit; and a switching circuit which outputs the input signal or the muting signal. The receiver of the present invention can therefore reduce discomfort in hearing reproduced sound in case where a noise occurs in an audio signal due to a variation in pulse width.

Abstract: In an optical communication-use receiving circuit of the present invention, the pulse width of the received pulse which is a binary signal corresponding to the signal optical pulse is specified by using an integration circuit and a trigger generating circuit. If the pulse width of the received pulse is not shorter than a predetermined value, a signal having a fixed pulse width is outputted as an output signal from a one-shot pulse generating circuit, so that a pulse having a constant pulse width corresponding to the specified communication speed is outputted. Accordingly, if the pulse width deriving from the signal optical pulse is larger than a certain value, the communication is deemed as a low-speed communication, and a pulse having a constant pulse width corresponding to the communication speed is outputted. As a result, it is possible to realize a small-size receiving circuit and a small-size electronic device which require no external switching-over terminal.

Abstract: A receiving circuit stops a one shot timer from generating an output signal immediately after the output signal is outputted to an external entity until a predetermined stretch time elapses. With this arrangement, the receiving circuit will not generate a new output signal even if (i) noises generated by a voltage fluctuation of the output signal appear on an amplified signal immediately after the output signal is outputted (at the end of the output), and (ii) the value of the amplified signal exceeds a threshold value. Therefore, the receiving circuit can make sure that an unnecessary output signal will not be generated due to the noises.

Abstract: An infrared transmitter circuit causes an output current to flow to a light emission diode via a current mirror circuit constituted of three transistors by using a current supplied from a power source circuit, so that the light emission diode emits light. When a voltage V1 varied by charging a capacitor with a current flowing from the power source circuit exceeds a reference voltage (voltage V2), an output of a comparator resets a D flip-flop, so that an output of the D flip-flop varies to “0”. Thus, an output of a NAND gate to which that output and a transmission signal are inputted causes a transistor (N-channel FET) to turn ON so as to stop operation of the current mirror circuit, and causes a transistor (P-channel FET) to turn OFF so as to cut a connection between the power source circuit and a power source line. Thus, it is possible to reduce power consumption in operation of a protection circuit which stops supplying the output current to the light emission diode.

Abstract: An amplifier circuit amplifies the difference between an output voltage from a current voltage conversion circuit and a bias voltage. The current voltage conversion circuit converts a photocurrent of a photodiode which detect incoming light into a voltage. A gm-amp charges or discharges a capacity by a current corresponding to the difference between the output voltage from the amplifier circuit and a reference voltage. A field effect transistor supplies a drain current, which is controlled by voltages at the respective terminals of the capacity, to the photodiode, in order to prevent the output voltage of the amplifier circuit from being varied due to the influence of a DC photocurrent flowing in the photodiode. The gate of a field effect transistor, which is connected in parallel to a current voltage conversion resistor, has an identical voltage with the gate of the field effect transistor.

Abstract: When a current mirror circuit is composed of transistors that inevitably form a parasitic photodiode between an epitaxial layer and a substrate layer because of structure of an integrated circuit, a photocurrent increases in proportional to an area of the epitaxial layer. Thus, the area of the epitaxial layer is adjusted in accordance with a current ratio of the current mirror, so as to allow the photocurrent to affect equally on both input and output sides of the current mirror circuit, i.e., so as to cancel the photocurrent. With this, in a current mirror circuit provided in an integrated circuit, it is possible to eliminate the influence of the photocurrent, without considerably increasing an element area or taking special measures to shield light.

Abstract: A carrier detection circuit of the present invention detects groups of pulses having a carrier frequency by using a detector, and integrates, by an integrator, a time in which the groups are detected, so as to generate a carrier detection level. Therefore, a transistor is only requested to have responsibility with respect to a frequency of a base band component, but not to the carrier frequency. This ensures a margin with respect to a response of the transistor, while allowing a feeble current to be used as charging and discharging currents for the capacitor. In this way, even if a capacitor in use has such a small capacity that the capacitor can be incorporated in an integrated circuit, the detection of the carrier is performed accurately.

Abstract: In an optical communication-use receiving circuit of the present invention, the pulse width of the received pulse which is a binary signal corresponding to the signal optical pulse is specified by using an integration circuit and a trigger generating circuit. If the pulse width of the received pulse is not shorter than a predetermined value, a signal having a fixed pulse width is outputted as an output signal from a one-shot pulse generating circuit, so that a pulse having a constant pulse width corresponding to the specified communication speed is outputted. Accordingly, if the pulse width deriving from the signal optical pulse is larger than a certain value, the communication is deemed as a low-speed communication, and a pulse having a constant pulse width corresponding to the communication speed is outputted. As a result, it is possible to realize a small-size receiving circuit and a small-size electronic device which require no external switching-over terminal.

Abstract: A receiving circuit stops a one shot timer from generating an output signal immediately after the output signal is outputted to an external entity until a predetermined stretch time elapses. With this arrangement, the receiving circuit will not generate a new output signal even if (i) noises generated by a voltage fluctuation of the output signal appear on an amplified signal immediately after the output signal is outputted (at the end of the output), and (ii) the value of the amplified signal exceeds a threshold value. Therefore, the receiving circuit can make sure that an unnecessary output signal will not be generated due to the noises.

Abstract: An infrared transmitter circuit causes an output current to flow to a light emission diode via a current mirror circuit constituted of three transistors by using a current supplied from a power source circuit, so that the light emission diode emits light. When a voltage V1 varied by charging a capacitor with a current flowing from the power source circuit exceeds a reference voltage (voltage V2), an output of a comparator resets a D flip-flop, so that an output of the D flip-flop varies to “0”. Thus, an output of a NAND gate to which that output and a transmission signal are inputted causes a transistor (N-channel FET) to turn ON so as to stop operation of the current mirror circuit, and causes a transistor (P-channel FET) to turn OFF so as to cut a connection between the power source circuit and a power source line. Thus, it is possible to reduce power consumption in operation of a protection circuit which stops supplying the output current to the light emission diode.

Abstract: An amplifier circuit AMP1 amplifies the difference between an output voltage from a current voltage conversion circuit 1 and a bias voltage. The current voltage conversion circuit 1 converts a photocurrent of a photodiode PD which detect incoming light into a voltage. A gm-amp AMP2 charges or discharges a capacity C1 by a current corresponding to the difference between the output voltage from the amplifier circuit AMP1 and a reference voltage V3. A field effect transistor M3 supplies a drain current, which is controlled by voltages at the respective terminals of the capacity C1, to the photodiode PD, in order to prevent the output voltage of the amplifier circuit AMP1 from being varied due to the influence of a DC photocurrent flowing in the photodiode PD. The gate of a field effect transistor M1 which is connected in parallel to a current voltage conversion resistor R1 has an identical voltage with the gate of the field effect transistor M3.

Abstract: When a current mirror circuit is composed of transistors that inevitably form a parasitic photodiode between an epitaxial layer and a substrate layer because of structure of an integrated circuit, a photocurrent increases in proportional to an area of the epitaxial layer. Thus, the area of the epitaxial layer is adjusted in accordance with a current ratio of the current mirror, so as to allow the photocurrent to affect equally on both input and output sides of the current mirror circuit, i.e., so as to cancel the photocurrent. With this, in a current mirror circuit provided in an integrated circuit, it is possible to eliminate the influence of the photocurrent, without considerably increasing an element area or taking special measures to shield light.

Abstract: A direct current input power supply voltage Vcc is outputted to the load side via a PNP type transistor having a small Vce. A base thereof is driven by a base current from which noise is removed in a power source noise removing circuit. An input to the noise removing circuit is produced by shifting a level from the Vcc side by a direct current level shift circuit. Since an output voltage Vs varies with reference to Vcc and a voltage drop is relatively small owing to the transistor, an operation voltage on the load side can be ensured. The noise removing circuit is constituted by a gm amplifier. In order to increase a noise removing rate at low frequencies, by setting gm of a time constant C/gm to a small value, it is possible to set a capacity to a value which allows integration.

Abstract: When a current mirror circuit is composed of transistors that inevitably form a parasitic photodiode between an epitaxial layer and a substrate layer because of structure of an integrated circuit, a photocurrent increases in proportional to an area of the epitaxial layer. Thus, the area of the epitaxial layer is adjusted in accordance with a current ratio of the current mirror, so as to allow the photocurrent to affect equally on both input and output sides of the current mirror circuit, i.e., so as to cancel the photocurrent. With this, in a current mirror circuit provided in an integrated circuit, it is possible to eliminate the influence of the photocurrent, without considerably increasing an element area or taking special measures to shield light.

Abstract: The present invention has an object to control easily the pulse width of an output by operating a limiting circuit appropriately even if the power voltage is low. A limiting circuit is provided on the input side of a hysteresis comparator circuit to prevent saturation. A limit voltage Vlimit is set by a bias circuit so as to change in accordance with the operation of the hysteresis comparator circuit. When an input voltage Vsig exceeds a hysteresis threshold voltage Vth, the limit voltage Vlimit is dropped in response to a drop of the hysteresis threshold voltage Vth. Thus, the width of the pulse width can be controlled while maintaining the condition that the limit voltage Vlimit is higher than the hysteresis threshold voltage Vth.

Abstract: When a current mirror circuit is composed of transistors that inevitably form a parasitic photodiode between an epitaxial layer and a substrate layer because of structure of an integrated circuit, a photocurrent increases in proportional to an area of the epitaxial layer. Thus, the area of the epitaxial layer is adjusted in accordance with a current ratio of the current mirror, so as to allow the photocurrent to affect equally on both input and output sides of the current mirror circuit, i.e., so as to cancel the photocurrent. With this, in a current mirror circuit provided in an integrated circuit, it is possible to eliminate the influence of the photocurrent, without considerably increasing an element area or taking special measures to shield light.