Abstract: A bandwidth-adjustable filter includes an operational amplifier, a first resistor, a first capacitor and a first resistor ladder circuit. The operational amplifier has a negative input terminal and a positive input terminal The first resistor is coupled to one of the input terminals of the operational amplifier. The first capacitor is coupled to the first resistor. The first resistor ladder circuit is coupled in parallel to the first resistor for changing the resistance of the first resistor so as to adjust the bandwidth of the filter.

Abstract: A multi-band receiver is disclosed. The multi-band receiver includes a low-noise amplifier (LNA) and a mixer. The LNA includes a switched receiving circuit, a loading circuit, and a switching circuit. The switched receiving circuit has a first receiving circuit for receiving a first signal corresponding to a first frequency, and a second receiving circuit for receiving a second signal corresponding to a second frequency. The loading circuit is utilized for providing a specific load to the switched receiving circuit. The switching circuit is used for controlling whether the first signal or the second signal is transferred to the loading circuit. The mixer is coupled to the low-noise amplifier for receiving an output signal generated from the LNA and for down-converting the output signal.

Abstract: A variable gain amplifying circuit, which applies a resistor ladder to obtain a more precise gain, is disclosed. The amplifying circuit includes an input, an operational amplifier (op-amp), a resistor unit and a feedback resistor. The feedback resistor is coupled between an output and an inverting input of the op-amp. The resistor unit includes at least one resistor ladder. The resistor unit further includes a switching unit for controlling whether the at least one resistor ladder is coupled between the input of the amplifying circuit and the inverting input of the op-amp. A differential amplifying circuit for more precise gain adjustment is also disclosed.

Abstract: A linear-in-decibel variable gain amplifier used for receiving an input voltage and generating an output voltage according to a first controlling voltage and a second controlling voltage. A voltage gain, that is, the ratio between the output voltage and the input voltage, has a denominator that is a pure exponential function, and the value of the pure exponential function is determined by the first controlling voltage and second controlling voltage.

Abstract: A linear decibel-scale variable gain amplifier includes an amplifying stage for generating an output voltage according to a differential input voltage, and a gain-controlling stage for outputting a gain-controlling voltage to the amplifying stage according to a first controlling voltage and a second controlling voltage. A voltage gain of the linear decibel-scale variable gain amplifier is inversely proportional to a simple exponential function, and the value of the simple exponential function is determined by the difference between the first controlling voltage and the second controlling voltage. The value of the voltage gain is unaffected by changes of the thermal voltage.

Abstract: A variable gain amplifier having a linear decibel-scale gain comprises an amplifying stage for generating an output voltage according to a differential input voltage, and a gain-controlling stage for outputting a gain-controlling voltage to the amplifying stage according to a first controlling voltage and a second controlling voltage. A voltage gain of the variable gain amplifier is inversely proportional to a simple exponential function, and the value of the simple exponential function is determined by the difference between the first controlling voltage and the second controlling voltage.

Abstract: A method and device for calibrating in-phase and quadrature-phase (IQ) mismatch. The device is used in a direct down-conversion circuit of a communication system. The device has a first mixer for mixing an RF signal with a first carrier signal, so as to generate an in-phase analog signal; a second mixer for mixing the RF signal with a second carrier signal, so as to generate a quadrature-phase analog signal; an operation unit for executing a Least Mean Square (LMS) algorithm and thereby generating a compensation signal according to the in-phase analog signal and the quadrature-phase analog signal; and a calibration unit for compensating the in-phase analog signal and the quadrature-phase analog signal according to the compensation signal, so as to calibrate the IQ mismatch between the in-phase analog signal and the quadrature-phase analog signal.

Abstract: A method and an apparatus of IQ mismatch calibration in a radio communication system. The method includes receiving a radio frequency signal, mixing the radio frequency signal with a first carrier to generate an In-phase analog signal, mixing the radio frequency signal with a second carrier to generate a Quadrature-phase analog signal, detecting a phase offset between the In-phase analog signal and the Quadrature-phase analog signal, computing at least a tuning parameter according to the phase offset, and calibrating at least one of the In-phase analog signal and the Quadrature-phase analog signal according to at least one of the phase offset and the tuning parameter such that the In-phase analog signal and the Quadrature-phase analog signal are orthogonal after calibration.

Abstract: A linear decibel-scale variable gain amplifier includes an amplifying stage for generating an output voltage according to a differential input voltage, and a gain-controlling stage for outputting a gain-controlling voltage to the amplifying stage according to a first controlling voltage and a second controlling voltage. A voltage gain of the linear decibel-scale variable gain amplifier is inversely proportional to a simple exponential function, and the value of the simple exponential function is determined by the difference between the first controlling voltage and the second controlling voltage. The value of the voltage gain is unaffected by changes of the thermal voltage.

Abstract: A variable gain amplifier having a linear decibel-scale gain comprises an amplifying stage for generating an output voltage according to a differential input voltage, and a gain-controlling stage for outputting a gain-controlling voltage to the amplifying stage according to a first controlling voltage and a second controlling voltage. A voltage gain of the variable gain amplifier is inversely proportional to a simple exponential function, and the value of the simple exponential function is determined by the difference between the first controlling voltage and the second controlling voltage.

Abstract: A linear-in-decibel variable gain amplifier used for receiving an input voltage and generating an output voltage according to a first controlling voltage and a second controlling voltage. A voltage gain, that is, the ratio between the output voltage and the input voltage, has a denominator that is a pure exponential function, and the value of the pure exponential function is determined by the first controlling voltage and second controlling voltage.