Abstract: In order to provide a variable gain amplifier of enhanced linearity and wide variable gain range, an AM-modulated signal reception circuit in which the noise of an input portion is reduced so as to improve the follow-up characteristic of an AGC circuit, and an AM-modulated signal detection circuit which produces an output precisely corresponding to a peak value envelope, the variable gain amplifier comprises a differential input amplifier which includes transistors T1 and T2 (in FIG. 8) constituting a differential pair, and a constant current circuit Is operating as an absorption current circuit of the transistors T1 and T2, and a variable impedance which is connected between the sources of the respective transistors T1 and T2, wherein the gain of the differential input amplifier is made variable by variably controlling the value of the variable impedance.

Abstract: In order to provide a variable gain amplifier of enhanced linearity and wide variable gain range, an AM-modulated signal reception circuit in which the noise of an input portion is reduced so as to improve the follow-up characteristic of an AGC circuit, and an AM-modulated signal detection circuit which produces an output precisely corresponding to a peak value envelope, the variable gain amplifier comprises a differential input amplifier which includes transistors T1 and T2 (in FIG. 8) constituting a differential pair, and a constant current circuit Is operating as an absorption current circuit of the transistors T1 and T2, and a variable impedance which is connected between the sources of the respective transistors T1 and T2, wherein the gain of the differential input amplifier is made variable by variably controlling the value of the variable impedance.

Abstract: A first peak hold circuit holds a peak potential of a positive phase voltage signal output from a differential output amplifier, and a second peak hold circuit holds a peak potential of a negative phase voltage signal output from the differential output amplifier. An adding circuit adds an output signal of the first peak hold circuit and an output signal of the second peak hold circuit. A differential input amplifier amplifies and outputs a voltage difference between a reference voltage and an addition result voltage signal of the adding circuit. A current output circuit outputs a DC current based on an output voltage of the differential input amplifier. A current switch circuit converts a DC current to a pulse current so as to supply the pulse current to a laser diode.

Abstract: An analog circuit includes a pair of peak-hold circuits that generate peak signals indicating the peak values of a differential pair of input signals, a first differencing circuit such as a transconductance amplifier that takes the difference between the input signal values, a second differencing circuit such as a transconductance amplifier that takes the difference between the two peak signal values, and a combining circuit such as a resistor circuit that additively combines the outputs of the differencing circuits in such a way as to compensate for direct-current offset in the input signals. Advantages of this circuit structure include reduced power consumption and simplified implementation in an integrated circuit. Low pass filters, capacitor discharging circuits, and unbalanced circuit elements can be used to obtain further advantages.

Abstract: A demodulating circuit includes a differentiating circuit that outputs a differentiated signal indicating voltage changes at rising and falling edges of a received pulse signal, and a hysteresis comparator that compares the differentiated signal with upper and lower threshold voltages, thereby generating a demodulated logic-level signal. The differentiating circuit can rapidly track variations in the direct-current offset of the received pulse signal. Positive feedback can enable the hysteresis comparator to maintain the correct output logic level during runs of 0's or 1's of arbitrary length in the received pulse signal. The demodulating circuit consumes comparatively little power, and is particularly useful for receiving signals transmitted in bursts.

Abstract: A first peak hold circuit holds a peak potential of a positive phase voltage signal output from a differential output amplifier, and a second peak hold circuit holds a peak potential of a negative phase voltage signal output from the differential output amplifier. An adding circuit adds an output signal of the first peak hold circuit and an output signal of the second peak hold circuit. A differential input amplifier amplifies and outputs a voltage difference between a reference voltage and an addition result voltage signal of the adding circuit. A current output circuit outputs a DC current based on an output voltage of the differential input amplifier. A current switch circuit converts a DC current to a pulse current so as to supply the pulse current to a laser diode.

Abstract: A demodulating circuit includes a differentiating circuit that outputs a differentiated signal indicating voltage changes at rising and falling edges of a received pulse signal, and a hysteresis comparator that compares the differentiated signal with upper and lower threshold voltages, thereby generating a demodulated logic-level signal. The differentiating circuit can rapidly track variations in the direct-current offset of the received pulse signal. Positive feedback can enable the hysteresis comparator to maintain the correct output logic level during runs of 0's or 1's of arbitrary length in the received pulse signal. The demodulating circuit consumes comparatively little power, and is particularly useful for receiving signals transmitted in bursts.

Abstract: In order to provide a variable gain amplifier of enhanced linearity and wide variable gain range, an AM-modulated signal reception circuit in which the noise of an input portion is reduced so as to improve the follow-up characteristic of an AGC circuit, and an AM-modulated signal detection circuit which produces an output precisely corresponding to a peak value envelope, the variable gain amplifier comprises a differential input amplifier which includes transistors T1 and T2 (in FIG. 8) constituting a differential pair, and a constant current circuit Is operating as an absorption current circuit of the transistors T1 and T2, and a variable impedance which is connected between the sources of the respective transistors T1 and T2, wherein the gain of the differential input amplifier is made variable by variably controlling the value of the variable impedance.

Abstract: An analog circuit includes a pair of peak-hold circuits that generate peak signals indicating the peak values of a differential pair of input signals, a first differencing circuit such as a transconductance amplifier that takes the difference between the input signal values, a second differencing circuit such as a transconductance amplifier that takes the difference between the two peak signal values, and a combining circuit such as a resistor circuit that additively combines the outputs of the differencing circuits in such a way as to compensate for direct-current offset in the input signals. Advantages of this circuit structure include reduced power consumption and simplified implementation in an integrated circuit. Low pass filters, capacitor discharging circuits, and unbalanced circuit elements can be used to obtain further advantages.

Abstract: The first operation means of a master communication device computes a parity bit of main data. The parity bit and the main data are transmitted to a slave communication device. The second operation means of the slave communication device performs parity check of the main data using this parity bit. The third operation means computes a parity bit of a data constellation comprising a signal for indicating the result of the parity check and the main data to be transmitted to the master communication device. This parity bit is transmitted to the master communication device along with the main data. The fourth operation means of the master communication device performs parity check of the main data using this parity bit. If the result of parity check by the second operation means indicates generation of an error, the result of parity check by the fourth operation means always indicates generation of an error.

Abstract: An optical communication apparatus having a light receiving element 11 for receiving optical signals including an optical signal calling for communication start and an optical communication circuit 13 which includes an amplifier circuit amplifying the photocurrent generated by the light receiving element 11, performs predetermined processing necessary for the optical communication, and outputs a communication terminating signal upon termination of the optical communication, wherein there is provided a first circuit 15 capable of always supplying a bias voltage to the light receiving element 11, turning off a power source 29 for the optical communication circuit by making use of the communication terminating signal when it is outputted, and turning on the power source by making use of the photocurrent Ip generated by the light receiving element when the light receiving element receives the optical signal calling for communication start, whereby the power saving in the standby state can be made more effective c

Abstract: In a high voltage detection circuit, a high voltage detection portion 10 constituted with, for instance, two constant voltage circuits 10a and 10c and a current mirror portion 10b, a strobe input 20 and an output communication device 30 are provided. This high voltage detection circuit outputs a high voltage detection signal S30 if an input voltage Vin, which is equal to or greater than a voltage value set by the constant voltage circuits 10a and 10c is supplied while a strobe control signal ST is provided. When high voltage detection on telephone lines is performed by such a high voltage detection circuit by inputting the results of the detection of a polarity inversion at telephone lines as a strobe control signal ST, only reception of bell signal can be detected. In addition, by resetting the results of polarity inversion detection using the results of high voltage detection, it is possible to identify a non-ringing reception that is not accompanied by a bell signal.