Alps Electric Co., Ltd.

Kazuharu Aoki

Sadao Igarashi

Satoshi Urabe

Shoichi Asano

Masahiko Saito

Mitsunari Okazaki

Jiro Kikuchi

A balanced-unbalanced conversion circuit includes a first coupling line, an unbalanced terminal connected to the first coupling line, a ground terminal connected to the unbalanced terminal through the first coupling line, a second coupling line electromagnetically coupled to the first coupling line, a first balanced terminal connected to the second coupling line, a second balanced terminal connected to the first balanced terminal through the second coupling line, and a band-reject filter serially connected to the first coupling line to remove predetermined-band signals of high frequency signals transmitted through the first coupling line.

Balanced-unbalanced conversion circuit

A gain control circuit capable of keeping a constant gain without being affected by ambient temperature includes a variable resistor element connected to a power supply terminal, a control unit for controlling the resistance value of the variable resistor element on the basis of a gain control voltage, an amplifying transistor that is supplied with a power supply voltage through the variable resistor element, a current detecting resistor that is interposed between the variable resistor element and a collector of the amplifying transistor, and a voltage detecting unit that detects a drop dropped by the current detecting resistor. The dropped voltage detected by the voltage detecting unit is fed back to the control unit to control the resistance value of the variable resistor element such that a current flowing through the current detecting resistor does not vary.

Gain control circuit capable of reducing change in gain due to variation of ambient temperature

A frequency synthesizer includes a first oscillator that outputs a first oscillation signal. A first phase shifter outputs two first signals which are out of phase by 90&#xb0;. A second oscillator outputs a second oscillation signal. A second phase shifter outputs two second signals which are out of phase by 90&#xb0;. To a first mixer, one of the first signals and one of the second signals are input. To a second mixer, the other one of the first signals and the other one of the second signals are input. An adder adds combined outputs from the first and second mixers. A phase switching device changes the phase relationship between the two first signals or the two second signals input to the first mixer and the second signal. An input allowing/prohibiting switching device allows or prohibits the second signals from being input to the first and second mixers. The adder outputs one of a signal at the same frequency as that of the first oscillation signal, a signal at the sum frequency of the frequencies of the first oscillation signal and the second oscillation signal, and a signal at the difference frequency between the frequencies of the first oscillation signal and the second oscillation signal.

Frequency synthesizer capable of obtaining signals in three frequency bands

A transmission signal which is output from a power amplifier is rectified by a first rectifying circuit and is then input to a first transistor of a voltage-to-current converting circuit, while the reference voltage is output from a second rectifying circuit and is then input to a second transistor of the voltage-to-current converting circuit. The output current of the first transistor is subtracted from the output current of the second transistor via a first current-mirror circuit, and a current that is proportional to the output voltage of the power amplifier is caused to flow to a two-terminal p-n junction electronic device. Then, a voltage that is proportional to the logarithm of the current is output from across the p-n junction electronic device.

Compact transmitter detection circuit with a wide dynamic range

A signal level adjusting circuit includes a first amplifying stage in which output electrodes of output stage transistors are connected to ground through current supplies and are connected with respective output terminals, and a DC voltage at the output terminals has a first voltage value; a second amplifying stage in which control electrodes of input stage transistors are connected with respective input terminals, and a DC voltage at the input terminals has a second voltage value; and a coupling stage, connected between the output terminals and the input terminals, which includes at least one series resistor. The first amplifying stage is incorporated in a bipolar IC, and the second amplifying stage is incorporated in a CMOS IC.

Signal level adjusting circuit using coupling stage for preventing variation from resulting in each operating point of first amplifying stage and second amplifying stage

A receive integrated circuit for a mobile telephone comprising a variable gain amplifier for amplifying a received signal with a variable gain, a low-pass filter for attenuating harmonic components of the signal amplifier by the variable gain amplifier, and a QPSK demodulator for demodulating by quadri-phase shift keying the signal having passed through the low-pass filter, wherein signal lines interconnecting the variable gain amplifier, the low-pass filter and the quadri-phase shift keying demodulator are balanced.

Receiver integrated circuit for mobile telephone

A feedback circuit is connected between the input electrode of amplifying element of an amplifying circuit of the initial stage and the output electrode of amplifying element of an amplifying circuit of the final stage. The feedback circuit is structured by a serial circuit of a voltage dropping means resulting in almost constant voltage drop regardless of an increase or decrease of current and a feedback resistor, and a bias voltage is supplied, via the feedback circuit, to an input electrode of the amplifying element in the amplifying circuit of the initial stage from an output electrode of the amplifying element in the amplifying circuit of the final stage. Thereby, current dissipation is reduced and signal loss is lowered.

Active low-pass filter

A double-balanced modulator in which the bias voltages do not become different by a buffer amplifier or the like connected to the front stage and a carrier wave is not leaked is provided. This modulator comprises a pair of input terminals 2, 3, a pair of preamplifiers 4 for amplifying balance signals supplied to the input terminals 2 and 3, and a double-balanced differential amplifier 23 to which balance carrier signals are supplied and which further amplifies the balance signals that have been amplified by the pair of preamplifiers 4, wherein capacitors 12 are connected in series between the base of a first transistor 7 and one of the input terminals 2, 3 and between the base of a second transistor 8 and the other one of the input terminals 2, 3, respectively.

Double-balanced modulator and quadri-phase shift keying device

An amplifier circuit comprises current-variable mode variable amplifying circuits and for amplifying an IF signal and a current-constant mode variable amplifying circuit for amplifying an RF signal. I and Q signals are applied to the IF-stage variable amplifying circuits and corresponding to two stages through a QPSK modulating circuit and amplified based on an AGC voltage VAGC applied thereto. The IF signal is converted into the RF signal by a mixer, which in turn is applied to the RF-stage variable amplifying circuit where it is amplified based on the AGC voltage VAGC common to the IF stages. The linearly-varied AGC voltage VAGC is converted into an exponentially-varied control current by transistors. Thus, a gain PG �dB! of each of variable amplifying circuits is controlled linearly with the AGC voltage VAGC.

Amplifier circuit having common AGC to IF and RF amplifiers for use in a

An object of the present invention is to provide an AGC voltage correction circuit unaffected by a change in temperature. Since base-emitter voltages V.sub.BE of transistors Q9 and Q10 constituting a first reference current source 7 have temperature dependency, the variations of the gains of amplification transistors Q17 and Q18 dependent on temperature are diminished. Since transistors Q1 and Q2 constituting a second reference current source 2 have temperature dependency, a gain slope concerning amplification transistors Q17 and Q18 relative to temperature is corrected linearly.

AGC voltage correction circuit

A multistage amplifier circuit comprises a current constant mode variable amplifying circuit for amplifying an input signal and current variable mode variable amplifying circuits and for further amplifying the signal amplified by the first variable amplifying circuit. An AGC voltage VAGC is commonly applied between the bases and emitters of an amplification degree control transistor of the current constant mode variable amplifying circuit and amplification degree control transistors of the current variable mode amplifying circuits. Collector currents of the transistors change exponentially with respect to the linearly-varied AGC voltage VAGC. Further, currents each proportional to the collector current of the transistor flow in the transistors. Thus, the gain PG �dB! of the current constant mode variable amplifying circuit changes linearly with the AGC voltage VAGC.

Multistage variable gain amplifier circuit

A transmitting/receiving unit capable of setting the level of power for transmitting an output frequency signal, which correctly correspond to the level of a received frequency signal, without dependency upon change in the environmental temperature, the transmitting/receiving unit including a signal transmitting portion; and a signal receiving portion so as to be capable of generating an output signal, the level of which depends upon the level of a received signal, wherein the signal transmitting portion includes first variable-gain amplifying means having an amplified gain which is varied by first AGC voltage, the signal receiving portion includes second variable-gain amplifying means having an amplified gain which is varied by second AGC voltage, wave-detection means for generating DC voltage which is in proportion to level of an output signal from the second variable-gain amplifying means, and temperature-dependent-type automatic gain control voltage generating means for converting the DC voltage into AGC voltage which depends upon change in environmental temperature, wherein the AGC voltages are used to compensate temperature change of the gain so that the level of the output signal is made to be constant to correspond to the level of the received signal regardless of change in the environmental temperature.

Transmitting/receiving unit having automatic gain control system with

There is provided a gain control circuit which comprises a circuit unit composed of a transistor Q.sub.11, a first gain control unit 12 including transistors Q.sub.12 and Q.sub.13 having emitters connected to each other and a choke coil L.sub.1 having an end connected to the collector of the transistor Q.sub.12 and the other end connected to the collector of the transistor Q.sub.13 for checking a high frequency signal current, and a second gain control unit 15 including transistors Q.sub.14 and Q.sub.15 having emitters connected to each other. Then, the transistor Q.sub.11 of the circuit unit is connected to the node where the emitters of the first gain control unit 12 are connected to each other and the node where the transistor Q.sub.13 of the first gain control unit 12 is connected to the choke coil L.sub.1 is connected to the node where the emitters of the second gain control unit 15 are connected to each other, and a high frequency is input to the base of the transistor Q.sub.11 of the circuit unit. With this arrangement, a power consumption is reduced and the distortion of an output signal is improved.

Gain control circuit

A combination UHF-VHF tuner has a switching diode placed in series with a VHF high-range peaking coil so that the coil forms a parallel resonance peaking circuit when high-range VHF signals are received and the coil acts as a series impedance matching element when a UHF IF signal is coupled from a UHF mixer stage.

UHF-VHF combination tuner

In a VHF tuner, feedback capacitance between the emitter of a local oscillating transistor and the ground in a local oscillator is changed at the low band receiving state and high band receiving state by controlling a switching diode connected in series to a capacitor for feedback capacitance and, a mixer is installed to mix the output of the local oscillator and high frequency input. For an improved mixer biasing circuit, the switching diode in series connection to the capacitor for feedback capacitance is connected to one terminal of a mixing FET in the mixer, and changing of the feedback capacitance in the local oscillator is accompanied by changing of working current of the mixing FET in the local oscillator.

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Fukushima-ken, Japan

Kazuharu Aoki