Abstract: A wireless communication apparatus includes an RF front-end unit constituting reception and transmission systems, a digital baseband signal processor, and a bias current circuit. The digital baseband signal processor performs a process of a digital baseband receive signal received from a reception system and performs a process of a digital baseband transmit signal supplied to a transmission system. The bias current circuit supplies a reference current to at least a part of a circuit constituting the reception system within the RF front-end unit. The bias current circuit switches the reference current supplied to at least the part of the circuit constituting the reception system within the RF front-end unit, in response to a transmission-operation control signal outputted by the digital baseband signal processor to the transmission system within the RF front-end unit.

Abstract: A variable capacitance circuit capable of switching on and off a variable capacitance function, includes variable capacitance means formed such that variable capacitance elements whose capacitance values change according to a voltage value of a supplied capacitance control voltage are connected so as to be paired and a plurality pairs of variable capacitance elements are connected in parallel forming multiple stages; bias voltage generation means for generating bias voltages of different voltage values based on a constant voltage from a constant voltage source; and an on-off switch for the variable capacitance function, in which the variable capacitance function of the variable capacitance means is turned on by supplying the bias voltage to the variable capacitance element of each stage of the variable capacitance means and turned off by grounding the bias voltage of each voltage value.

Abstract: There are provided, as a low noise amplifier (70) a low noise amplifier (71) with a low gain and a low noise amplifier (72) with a high gain, selectively operable under control of a bias current, and an output from the low noise amplifier (72) and a quadrature demodulator (80) are connected with a serial capacitance (73) and also an output from the low noise amplifier (71) and the quadrature demodulator (80) are serially connected. A control section (66) controls a reception circuit so that the low noise amplifier (71) operates when a reception signal level is high and the low noise amplifier (72) operates when the reception signal level is low. When the low noise amplifier (72) operates, a DC bias current thereof is made flow separately from a DC bias current of the quadrature demodulator (80), and, when the low noise amplifier (71) operates, a DC bias current thereof is shared with the quadrature demodulator.

Abstract: A voltage-controlled oscillator comprising a resonant circuit and MOS transistors which constitute a negative resistance circuit of a differential structure. The resonant circuit consists of an inductance element and a MOS variable capacitance element connected in parallel therewith. The MOS variable capacitance element is divided into plural pairs connected in parallel with each other. A voltage division circuit generates staircase different-step DC bias voltages to be applied respectively to the gates of the plural divided MOS transistors. The divided MOS variable capacitance elements have a common terminal to which a common control voltage is applied. The resonant circuit is capable of reducing a load on the control voltage generator and improving the characteristics of the voltage-controlled oscillator.

Abstract: The object of this invention is to demodulate received signals having different received signal frequencies with the simple circuit configuration. With the present invention, the fixed frequency signals are generated at the fixed PLL unit 310, and simultaneously, the standard frequency signals corresponding respectively to GSM/DCS received RF signals are generated at the channel PLL unit 330. And using the image removal mixer 370 jointly to received RF signals, local oscillation signals having local oscillation frequencies equal to the received signal frequencies of the received RF signals respectively are formed from the fixed frequency signals and the standard frequency signals for receiving. And since the quadrature demodulators 254 and 264 demodulate the received RF signals using corresponding local oscillation signals respectively, the circuit configuration can be simplified by sharing the image removal mixer 370.

Abstract: A variable capacitance circuit capable of switching on and off a variable capacitance function, includes variable capacitance means formed such that variable capacitance elements whose capacitance values change according to a voltage value of a supplied capacitance control voltage are connected so as to be paired and a plurality pairs of variable capacitance elements are connected in parallel forming multiple stages; bias voltage generation means for generating bias voltages of different voltage values based on a constant voltage from a constant voltage source; and an on-off switch for the variable capacitance function, in which the variable capacitance function of the variable capacitance means is turned on by supplying the bias voltage to the variable capacitance element of each stage of the variable capacitance means and turned off by grounding the bias voltage of each voltage value.

Abstract: There are provided, as a low noise amplifier (70) a low noise amplifier (71) with a low gain and a low noise amplifier (72) with a high gain, selectively operable under control of a bias current, and an output from the low noise amplifier (72) and a quadrature demodulator (80) are connected with a serial capacitance (73) and also an output from the low noise amplifier (71) and the quadrature demodulator (80) are serially connected. A control section (66) controls a reception circuit so that the low noise amplifier (71) operates when a reception signal level is high and the low noise amplifier (72) operates when the reception signal level is low. When the low noise amplifier (72) operates, a DC bias current thereof is made flow separately from a DC bias current of the quadrature demodulator (80), and, when the low noise amplifier (71) operates, a DC bias current thereof is shared with the quadrature demodulator.

Abstract: A voltage-controlled oscillator comprising a resonant circuit and MOS transistors which constitute a negative resistance circuit of a differential structure. The resonant circuit consists of an inductance element and a MOS variable capacitance element connected in parallel therewith. The MOS variable capacitance element is divided into plural pairs connected in parallel with each other. A voltage division circuit generates staircase different-step DC bias voltages to be applied respectively to the gates of the plural divided MOS transistors. The divided MOS variable capacitance elements have a common terminal to which a common control voltage is applied. The resonant circuit is capable of reducing a load on the control voltage generator and improving the characteristics of the voltage-controlled oscillator.

Abstract: The object of this invention is to demodulate received signals having different received signal frequencies with the simple circuit configuration. With the present invention, the fixed frequency signals are generated at the fixed PLL unit 310, and simultaneously, the standard frequency signals corresponding respectively to GSM/DCS received RF signals are generated at the channel PLL unit 330. And using the image removal mixer 370 jointly to received RF signals, local oscillation signals having local oscillation frequencies equal to the received signal frequencies of the received RF signals respectively are formed from the fixed frequency signals and the standard frequency signals for receiving. And since the quadrature demodulators 254 and 264 demodulate the received RF signals using corresponding local oscillation signals respectively, the circuit configuration can be simplified by sharing the image removal mixer 370.

Abstract: A digital communication apparatus in which a QPSK signal is received and frequency-converted to an intermediate frequency signal, the intermediate frequency signal is subjected to A/D conversion and separation into an I-component and a Q-component to obtain I-component and Q-component digital data, and the original digital data is obtained from the I-component and Q-component digital data. The digital commumication apparatus has an A/D converter circuit for performing the above-mentioned A/D conversion, a level control circuit for controlling the level of a signal supplied to the A/D converter circuit to a predetermined value, and a disturbance signal level detection circuit for detecting the disturbance signal level contained in the received signal.

Abstract: The output of a transmitting voltage-controlled oscillator generated in an offset PLL is used as a signal source for a variable frequency input side of an image removing mixer for generating a local oscillation signal for GSM/DCS reception. A signal obtained by dividing an IF frequency generated by a transmission intermediate frequency (IF) PLL used for the offset PLL for generating a transmission frequency signal is employed for the other input of the image removing mixer. A desired frequency is thereby generated before the mixers of a demodulator.

Abstract: In a WCDMA mode, a mixer employed in a GSM/DCS orthogonal-modulation unit outputs a frequency of 380-MHz obtained as a result of division of a frequency generated by a fixed PLL loop unit by 2 without frequency transformation. The frequency of 380-MHz is further divided by 2 by a frequency divider to give a reference frequency of 190 MHz which is then supplied to a phase comparator employed in an offset PLL loop unit. In the offset PLL loop unit, on the other hand, an oscillation signal generated by a VCO for WCDMA use is mixed by a mixer with the oscillation signal generated by another VCO to give a frequency equal to a difference obtained as a result of subtraction of the oscillation frequency of the VCO for WCDMA use from the oscillation frequency of the other VCO. The difference-frequency signal output by the mixer is filtered by an LPF before being supplied to the phase comparator to be compared with the signal with the frequency of 190 MHz.

Abstract: A receiving apparatus is disclosed which can cope with the fluctuation of input level of RF signal appropriately and has a first amplifier means wherein the amplifying and the attenuating of input signal are selectively performed and for processing the signal in a communication band handled by this apparatus, and a second amplifier means for gain-variably amplifying a signal, which is a signal converted from the output of the first amplification means 13 into the intermediate frequency signal or base band signal, the gain of the second amplifier means being set based on the detection of output level of the second amplifier means, and the selection of the amplification or attenuation in the first amplifier means, (13) being performed based on the detection level of output from the first amplifier means.

Abstract: A receiving apparatus for receiving digital broadcasting of a first frequency band and frequency band has a local oscillation circuit for generating a first local oscillation signal, and a frequency conversion circuit for frequency-converting the first local oscillation signal to generate a second local oscillation signal. The received signal of the first frequency band is up-converted to a first intermediate frequency signal using one of the of first and second local oscillation signals, and the received signal of the frequency band is down-converted to the first intermediate frequency signal using the other of the first and second local oscillation signals.

Abstract: A portable telephone which solves problems conventionally associated with using a portable telephone together with a hands-free accessory is disclosed. When the portable telephone is being used on its own and a microphone arm thereof is in a home position, the portable telephone can be put in a waiting state wherein it can receive incoming calls. When the portable telephone is being used on its own and the microphone arm is in a pulled-out position, telephone conversations can be had using a microphone and a speaker built into the portable telephone. When the portable telephone is connected to a hands-free accessory and the microphone arm is in its home position, conversations can be had in a hands-free mode using a microphone and a speaker connected to the hands-free accessory.

Abstract: A radio telephone apparatus for transmitting and receiving information signals as electrical waves includes a main body section towards one end of which a speaker unit is enclosed. A battery casing accommodating a battery which is adapted for supplying power to the main body section is detachably mounted on the other end of the main body section to reduce the size and the thickness of the apparatus. A ringer device is enclosed within the battery casing so that the acoustic sound emitted by the ringer is prevented from reaching the user's ear which is in the vicinity of the speaker unit. The microphone for the radiotelephone apparatus in also enclosed within the battery casing.

Abstract: A charge pump circuit for charging a capacitor in response to a phase difference between first and second input signals comprises a constant current source for providing a first constant current; a constant current sink for absorbing a second constant current; a circuit for substantially equalizing the magnitudes of the first and second constant currents; and a switching circuit for providing the first constant current and the second constant current flowing in opposed directions to the capacitor through an output terminal of the charge pump circuit in response to the phase difference between the first and second input signals to produce a voltage level across the capacitor corresponding to the phase difference. In a phase locked loop system employing such a charge pump circuit, a phase comparator produces a phase difference signal for controlling the provision of the first and second constant currents by the switching circuit to the capacitor.

Abstract: A charge pump circuit for charging a capacitor in response to a phase difference between first and second input signals comprises a constant current source for providing a first constant current; a constant current sink for absorbing a second constant current; a circuit for substantially equalizing the magnitudes of the first and second constant currents; and a switching circuit for providing the first constant current and the second constant current flowing in opposed directions to the capacitor through an output terminal of the charge pump circuit in response to the phase difference between the first and second input signals to produce a voltage level across the capacitor corresponding to the phase difference. In a phase locked loop system employing such a charge pump circuit, a phase comparator produces a phase difference signal for controlling the provision of the first and second constant currents by the switching circuit to the capacitor.

Abstract: A filter apparatus comprised of a multi-layer printed circuit board has a shielded filter with input and output terminals protruding from the circuit board, when the filter is mounted on the printed circuit board. Two insulating substrates form the printed circuit board, and a connective conductive pattern is formed on an inner surface of one of the substrates that faces the other substrate. Conductive layers are formed on respective outer surfaces of the substrate opposing the connection conductive pattern, wherein at least one of the input and output terminals of the filter is connected to the connective conductive pattern and the conductive layers are grounded, thereby shielding the connective conductive pattern.

Abstract: A television receiver can be used both to generate a picture and sound from a broadcast video signal or to generate just a picture from a locally produced video signal, such as one provided by a video camera. A muting apparatus suppresses the sound generated from the broadcast video signal while the television receiver is used as a monitor for the locally produced video signal. The muting apparatus comprises a level shifter that raises the level of the broadcast video signal. A switching means provides to the picture tube of the television receiver either the broadcast video signal or, if the video camera is plugged into the receiver, the locally produced video signal. The level of the signal supplied to the picture tube is sensed; if it is below the predetermined level a muting means connects the audio component of the broadcast video signal to ground to prevent sound from being generated while the receiver is used as a monitor.