Telecommunications – Transmitter and receiver at same station
Reexamination Certificate
1999-02-03
2001-10-23
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at same station
C455S078000, C455S252100, C455S259000
Reexamination Certificate
active
06308047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio-frequency integrated circuit for processing radio-frequency signals, and in particular to a radio-frequency integrated circuit used in a radio-frequency transmitter-receiver such as a portable telephone. More particularly, the invention relates to a radio-frequency integrated circuit having a transmission/reception multiplexing switch and a control circuit for controlling transmission/reception modes of the multiplexing switch, which are arranged in an RF front end portion for transmitting and receiving radio-frequency signals in a portable telephone, or a radio-frequency integrated circuit including a power amplifier amplifying a radio-frequency signal and a circuit producing a bias voltage for controlling a gain of the power amplifier.
2. Description of the Background Art
Recently, the market for mobile communications has been growing owing to the widespread use of extremely compact portable telephones. The mobile communications system may use an analog modulation system in which carrier waves are analog-modulated with audio signals for transmission and reception, or may use a system in which audio signals are converted into digital data, and then digital modulation of carrier waves is performed for transmission. For improving portability of such compact portable telephones, efforts have been made to reduce the size, weight and thickness thereof. For implementation of these factors, it is extremely important to reduce chip sizes of components and to enhance a functional integration.
The compact portable telephone system uses carrier waves in a frequency band of the order of gigahertz (GHz), and in the RF front end portion for transmitting and receiving such radio-frequency signals, a GaAs IC chip including MESEFTs (Metal Semiconductor Field effect Transistors) formed of GaAs (gallium arsenide). Miniaturizing technology for GaAs has been less developed compared with silicon technology for forming MOS transistors. Therefore, integration of the GaAs IC chips have not been developed sufficiently, and of reduction in size through high integration of the components thereof have been strongly desired.
FIG. 1
schematically shows a whole structure of a portable telephone in the prior art. In
FIG. 1
, the portable telephone includes an RF front end portion which transmits and receives radio-frequency signals via an antenna ANT, and an audio processing circuit APC which receives a reception signal RX-OUT from the RF front end portion in a receiving operation, and performs predetermined processing on the reception signal to reproduce and apply audio signals to a speaker SPK. Audio processing circuit APC also operates, in a transmitting operation, to receive audio signals from a microphone MIC, and send the received audio signals to the RF front end portion after effecting processing, which is reverse to the processing in the receiving operation, on the audio signals. The portable telephone further includes a controller CTRL which controls operations of audio processing circuit APC and the RF front end portion.
Audio processing circuit APC includes an ADPCM codec which performs coding and decoding in accordance with, e.g., ADPCM (adaptive differential pulse code modulation) as well as circuitry for time-division multiplexing of transmission signals and reception signals. Controller CTRL controls the switching between the transmission mode and the reception mode in audio processing circuit APC, and also controls the time-division multiplexing of the transmission and reception signals and other processing. Controller CTRL produces control signal CONT, which in turn includes several kinds of signals and performs instruction of the transmission/reception modes as well as control of the levels of the transmission and reception signals and other processing in the RF front end portion.
The RF front end portion further includes an oscillator circuit OSC generating a signal of a constant frequency, e.g., of 1.66 GHz, a control logic CTL which generates a signal controlling the operation of the RF front end portion in accordance with control signal CONT transferred from controller CTRL, a mixer MIXt which mixes a coded audio signal transferred from audio processing circuit APC with an oscillating signal transferred from oscillator circuit OSC, a transmission attenuator TXATT which attenuates the signal transferred from transmission mixer MIXt in accordance with the control signal transferred from control logic CTL, a negative voltage generating circuit NVG which generates a negative voltage VG in accordance with a control voltage VNVG transferred from controller CTRL, a power amplifier PA which has a gain controlled by the negative voltage VG transferred from negative voltage generating circuit NVG used as a bias voltage, and performs power amplification of the signal transferred from transmission attenuator TXATT, and a bandpass filter (BPF) BFt allowing passage of signals in a predetermined band of the output signals of power amplifier PA.
Transmission mixer MIXt adds coded audio signal TX-IN transferred from audio processing circuit APC with the oscillating signal transferred from oscillator circuit OSC, to produce a radio-frequency signal suitable for transmission. Transmission attenuator TXATT reduces an amplitude of the signal transferred from mixer MIXt in accordance with a signal transferred from a radio-frequency signal intensity indicator (not shown) included in controller CTRL, and controls the level of the transmission signal.
Power amplifier PA, which will be described later in more detail, includes MESFETs as its components, and receives negative voltage VG as a bias voltage for controlling the gain for operating MESFETs in a reverse bias state with the gate to source. Owing to power amplifier PA, the transmission signal is transferred via antenna ANT with a large power. The carrier wave of the transmission signal transferred from power amplifier PA is in a frequency band of about 1.9 GHz, and the transmission bandpass filter BFt allows passage of the signal in this band.
The RF front end portion further includes a transmission/reception multiplexing switch SW which multiplexes the transmission mode and the reception mode under the control of control logic CTL. Transmission/reception multiplexing switch SW includes a transmission signal input node Wt receiving the transmission signal from the transmission bandpass filter BFt, a transmission/reception node Wa coupled to antenna ANT, and a reception signal output node Wr. Transmission/reception node Wa is coupled electrically and selectively to one of transmission signal input node Wt and reception signal output node Wr under the control of control logic CTL.
In the portable telephone shown in
FIG. 1
, the transmission signal and the reception signal are in the same frequency band of approximately 1.9 GHz, and transmission and reception are switched with this transmission/reception multiplexing switch SW. As already described, audio processing circuit APC transmits and receives the transmission signal and reception signal in a time division manner and, in accordance with this time division operation, control logic CTL sets transmission/reception multiplexing switch SW to one of the transmission mode, reception mode and standby mode.
The RF front end portion further includes a reception attenuator RXATT which attenuates the reception signal transferred from reception signal output node Wr of transmission/reception multiplexing switch SW under the control of control logic CTL, a reception bandpass filter (BPF) BFr which allows passage of signals in a predetermined frequency band of the output signals of reception attenuator RXATT, a low noise amplifier LNA which amplifies the output signal of reception bandpass filter BFr, and a reception mixer MIXr which mixes the output signal of low noise amplifier LNA with the oscillating signal from oscillator circuit OSC, and converts the radio-frequency signal into a signal in a frequency band suitab
Maemura Kosei
Yamamoto Kazuya
Cong Le Thanh
Leydig,Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Thuan T.
LandOfFree
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