Nec Corporation

Yuji Kakuta

Yoshiaki Fukasawa

Yuichi Taguchi

Yoshiaki Wakabayashi

Realizing a stabilized gain slope without increasing circuit scale or entailing extra time or care for correcting impedance. A resonant circuit that is made up of a capacitor and an inductor is provided in an output stage outside a feedback loop for realizing peaking at a particular frequency and for realizing a gain slope having a desired slope of, for example, 1 dB or more.

Semiconductor circuit with a stabilized gain slope

A semiconductor circuit includes an amplifying circuit and compensates the distortion characteristic in the event of changes in the ambient temperature. If the amplifying circuit is a field effect transistor (FET) amplifying circuit having a grounded source, a compensating circuit in which a thermistor having a negative temperature characteristic and a thermistor having a positive temperature characteristic are connected in a series is provided between the grounding point and the source of the FET to compensate distortion of signals outputted from the FET that is caused by the ambient temperature. The temperature at which distortion is considered a minimum is taken as the reference temperature, and the drain current that flows at this reference temperature is made a minimum such that the drain current increases as the ambient temperature deviates from the reference temperature, thereby suppressing or preventing increase in distortion in the event of changes in the ambient temperature.

Semiconductor circuit in which distortion caused by change in ambient temperature is compensated

Semiconductor circuit in which distortion caused by changes in ambient temperature is compensated

Compensating for fluctuations in the gain characteristic of the gain slope in the event of changes in ambient temperature without increasing circuit scale or adding to costs. A thermistor, which is a thermally sensitive resistance element in which resistance changes with a negative temperature characteristic according to the ambient temperature, is employed as the gate resistance of an FET, and the circuit functions such that fluctuations in the gain characteristic of the gain slope with respect to ambient temperature are canceled out by fluctuations in the value of Q with respect to the ambient temperature, thereby compensating for fluctuations in the gain slope characteristic in the event of changes in the ambient temperature.

Semiconductor circuit compensating for changes in gain slope of the

An input transformer, used as a transmission-line transformer (11), is provided for connection between an unbalanced transmission line (10) and a balanced broadband amplifier (12), in which the input transformer has a fixed middle potential. The transmission-line transformer (11) converts an input signal into two output signals having opposite phase with respect to each other and which are supplied to the broadband amplifier (12). It is therefore possible to cancel secondary distortion in an amplifying unit. As the transmission-line transformer (11) a forced-balun type transmission-line transformer is used which has two input ports (P1, P2) and three output ports (P3, P4, P5), one (P4) of which is grounded. First and second two-wire parallel lines are arranged between the input ports and the output ports via a single glasses-shaped core. The input port and the two output ports have a respective impedance ratio of 1:(1/2):(1/2).

Amplifying unit comprising an input transformer capable of contributing

A plurality of field effect transistors (FET's) (11, 12) are coupled in cascode connection. A drain of the final-stage FET (12) is coupled to a gate of the first-stage FET (11) through a first negative-feedback circuit (13). A drain of the first-stage FET (11) is coupled to the gate of the first-stage FET (11) through a second negative-feedback circuit (14). The first negative-feedback circuit (13) is connected to a first resistor (Rf1) while the second negative-feedback circuit (14) is connected to a second resistor (Rf2).

Negative-feedback amplifier circuit capable of independently controlling

A push-pull wideband semiconductor amplifier for use in, for example, a CATV (cable television) system. The amplifier suppresses deterioration of composite second-order (CSO) distortion in output signals. The push-pull wideband amplifier includes: a divider which divides a signal inputted by way of an input terminal into two signals of differing phase, first and second amplifying circuits each of which amplifies the signal divided by the divider, and a combiner which combines the two signals amplified by the first and second amplifying circuits into one signal and outputs the result signal. The node between the first amplifying circuit and the second amplifying circuit is an imaginary ground point having a potential of 0 V from the standpoint of an alternating-current signal. A termination circuit is provided between this imaginary ground, point and ground and absorbs fluctuation in potential generated at the imaginary ground point. In the event of fluctuation in potential generated at the imaginary ground point, the fluctuation in potential is absorbed by the termination circuit. The standing wave that accompanies fluctuation in potential is therefore not generated, and even-order distortion is suppressed.

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Tokyo, Japan

Yuji Kakuta