Abstract: A buffer circuit and a multiplexer using the buffer are provided. The buffer may selectively operate at a first mode or a second mode. The buffer includes a first signal input terminal, a first signal output terminal, and a path circuit coupled between the first signal input terminal and the first signal output terminal. The path circuit has a voltage source terminal. In response to the buffer operating at the first mode, a first signal transmission path is formed in the path circuit and between the first signal input terminal and the first signal output terminal. The first signal transmission path is disconnected from the voltage source terminal.

Abstract: The present invention provides an oscillator including a tapped inductor and a cross-coupled pair. The tapped inductor includes a first terminal, a second terminal, a first tap and a second tap. The cross-coupled pair receives two input signals from the first terminal and the second terminal to generate two output signals to the first tap and the second tap, respectively.

Abstract: The present invention provides an oscillator including a tapped inductor and a cross-coupled pair. The tapped inductor includes a first terminal, a second terminal, a first tap and a second tap. The cross-coupled pair receives two input signals from the first terminal and the second terminal to generate two output signals to the first tap and the second tap, respectively.

Abstract: A buffer circuit and a multiplexer using the buffer are provided. The buffer may selectively operate at a first mode or a second mode. The buffer includes a first signal input terminal, a first signal output terminal, and a path circuit coupled between the first signal input terminal and the first signal output terminal. The path circuit has a voltage source terminal. In response to the buffer operating at the first mode, a first signal transmission path is formed in the path circuit and between the first signal input terminal and the first signal output terminal. The first signal transmission path is disconnected from the voltage source terminal.

Abstract: A direct-conversion transmitter including an oscillator, a frequency divider, a transmitter, and a filter is provided. The oscillator generates an oscillating signal with an original frequency. The frequency divider performs frequency dividing on the oscillating signal, so as to generate a carrier signal. The transmitter receives the carrier signal from the frequency divider and generates an output signal based on the carrier signal and a data signal. The filter is coupled between the frequency divider and the transmitter. The filter filters out an interference signal fed-back from the transmitter to the oscillator, wherein the interference signal may cause the oscillating signal to float.

Abstract: A direct-conversion transmitter including an oscillator, a frequency divider, a transmitter, and a filter is provided. The oscillator generates an oscillating signal with an original frequency. The frequency divider performs frequency dividing on the oscillating signal, so as to generate a carrier signal. The transmitter receives the carrier signal from the frequency divider and generates an output signal based on the carrier signal and a data signal. The filter is coupled between the frequency divider and the transmitter. The filter filters out an interference signal fed-back from the transmitter to the oscillator, wherein the interference signal may cause the oscillating signal to float.

Abstract: A transconductor circuit used in a mixer for canceling second-order inter-modulation distortion includes a first transistor and a second transistor, of which the base (gate) ends coupled to a first input end and a second input end, for receiving a differential input signal; and a negative feedback circuit, of which the input end coupled to the emitter (source) ends of the first transistor and the second transistor, of which the out end coupled to the base (gate) ends of the first transistor and the second transistor, for adjusting the voltage of the base (gate) of the first transistor and the second transistor according to the difference between a reference voltage and the detected voltage of the emitter (source) of the first transistor and the second transistor.

Abstract: A signal processing circuit includes a differential input circuit, a first DC filter, a second DC filter, a differential transconductance circuit, and a differential converting circuit. The differential input circuit includes first and second input circuits respectively for receiving first and second input signals to generate first and second processed signals. The first DC filter and the second DC filter, respectively coupled to the first and the second input circuits, receive the first and the second processed signals and output first and second voltage signals. The differential transconductance circuit includes first and second transconductance circuits, respectively coupled to the first and the second DC filters, for converting the first and the second voltage signals to first and second current signals.

Abstract: A signal processing apparatus for a multi-mode satellite positioning system includes a band-pass filter, a local oscillator circuit, a first mixing circuit, a second mixing circuit, an analog-to-digital converter and a baseband circuit. By properly allocating a local frequency, radio frequency (RF) signals of a Global Positioning System (GPS), a Galileo positioning system and a Global Navigation System (GLONASS) are processed via a single signal path to save hardware cost.

Abstract: A transconductor circuit used in a mixer for canceling second-order inter-modulation distortion includes a first transistor and a second transistor, of which the base (gate) ends coupled to a first input end and a second input end, for receiving a differential input signal; and a negative feedback circuit, of which the input end coupled to the emitter (source) ends of the first transistor and the second transistor, of which the out end coupled to the base (gate) ends of the first transistor and the second transistor, for adjusting the voltage of the base (gate) of the first transistor and the second transistor according to the difference between a reference voltage and the detected voltage of the emitter (source) of the first transistor and the second transistor.

Abstract: A mixer having high linearity and an associated transconductor combining programmable gain amplifier and mixer functions are provided. The transconductor includes first and second resistors, a differential amplifier, first and second feedback circuits, and first and second transistors. A differential voltage signal is inputted to first and second input ends of the differential amplifier via the first and second resistors. The first and second feedback circuits are provided between a first output end and the first input end, and a second output end and the second input end of the differential amplifier, respectively. The first output end outputs a first output signal for controlling a first current passing through the first transistor. The second output end outputs a second output signal for controlling a second current passing through the second transistor. The first current and the second current determine a differential current.

Abstract: A proportional to absolute temperature (PTAT) sensor is capable of reducing a sensing error resulted from a mismatch between circuit components. The PTAT sensor includes a control unit, a sensing unit and a calculation unit. The control unit generates a control signal. The sensing unit, comprising at least a pair of circuit components having a matching relationship, senses an absolute temperature under the first connection configuration and the second connection configuration respectively to generate a first voltage value and a second voltage value, wherein the first connection configuration and the second connection configuration are decided by interchanging the circuit connections of the pair of circuit components according to the control signal. And the calculation unit, coupled to the sensing unit, calculates a PTAT voltage value according to the first voltage value and the second voltage values.

Abstract: A signal processing circuit includes a differential input circuit, a first DC filter, a second DC filter, a differential transconductance circuit, and a differential converting circuit. The differential input circuit includes first and second input circuits respectively for receiving first and second input signals to generate first and second processed signals. The first DC filter and the second DC filter, respectively coupled to the first and the second input circuits, receive the first and the second processed signals and output first and second voltage signals. The differential transconductance circuit includes first and second transconductance circuits, respectively coupled to the first and the second DC filters, for converting the first and the second voltage signals to first and second current signals.

Abstract: A signal processing apparatus for a multi-mode satellite positioning system includes a band-pass filter, a local oscillator circuit, a first mixing circuit, a second mixing circuit, an analog-to-digital converter and a baseband circuit. By properly allocating a local frequency, radio frequency (RF) signals of a Global Positioning System (GPS), a Galileo positioning system and a Global Navigation System (GLONASS) are processed via a single signal path to save hardware cost.

Abstract: A mixer with high linearity and a low operating voltage is provided. The mixer includes a transconductor and a switch circuit. The transconductor receives a differential voltage signal and outputs a differential current signal accordingly. The transconductor includes a first resistor, a second resistor, a differential amplifier, a first current source and a second current source. The switch circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first and second switches are coupled to a first input of the differential amplifier, while the third and fourth switches are coupled to a second input of the differential amplifier. The first and third switches are mutually coupled to provide an output of the mixer, while the second and fourth switched are mutually coupled to provide another output of the mixer. Each of the first, second, third and fourth switches determines whether to allow the differential current signal to pass through according to a differential control signal.

Abstract: A proportional to absolute temperature (PTAT) sensor is capable of reducing a sensing error resulted from a mismatch between circuit components. The PTAT sensor includes a control unit, a sensing unit and a calculation unit. The control unit generates a control signal. The sensing unit, comprising at least a pair of circuit components having a matching relationship, senses an absolute temperature under the first connection configuration and the second connection configuration respectively to generate a first voltage value and a second voltage value, wherein the first connection configuration and the second connection configuration are decided by interchanging the circuit connections of the pair of circuit components according to the control signal. And the calculation unit, coupled to the sensing unit, calculates a PTAT voltage value according to the first voltage value and the second voltage values.

Abstract: A multi-modulus divider and a method for performing frequency dividing by utilizing a multi-modulus divider are disclosed. The multi-modulus divider comprises a multi-modulus dividing circuit, a pulse generating circuit, and a modulus signal generating circuit. The multi-modulus dividing circuit comprises several serially connected divider cells, of which a predetermined one may be bypassed. The multi-modulus dividing circuit generates an output frequency according to an input frequency and a divisor. A range of the divisor comprises a plurality of numerical intervals. The pulse generating circuit generates a pulse signal. The modulus signal generating circuit generates a determination result by determining which numerical interval the divisor belongs to, and inputs, according to the determination result, the pulse signal into the predetermined divider cell to be one of references which the predetermined divider cell refers to when outputting a modulus signal.

Abstract: A band selecting method applied to a voltage controlled oscillator (VCO) of a phase locked loop (PLL) and an associated method is provided. The band selecting method generates an open-loop control voltage according to a temperature signal; inputting the open-loop control voltage into the VCO; switching sequentially between a plurality of frequency bands of the VCO and generating a plurality of voltage controlled signals for the frequency bands; selecting a preferred voltage controlled signal and its corresponding frequency band as an operating band for the PLL.

Abstract: A multi-modulus divider and a method for performing frequency dividing by utilizing a multi-modulus divider are disclosed. The multi-modulus divider comprises a multi-modulus dividing circuit, a pulse generating circuit, and a modulus signal generating circuit. The multi-modulus dividing circuit comprises several serially connected divider cells, of which a predetermined one may be bypassed. The multi-modulus dividing circuit generates an output frequency according to an input frequency and a divisor. A range of the divisor comprises a plurality of numerical intervals. The pulse generating circuit generates a pulse signal. The modulus signal generating circuit generates a determination result by determining which numerical interval the divisor belongs to, and inputs, according to the determination result, the pulse signal into the predetermined divider cell to be one of references which the predetermined divider cell refers to when outputting a modulus signal.

Abstract: A mixer in a smaller signal differential model includes a load circuit, a switch quad, and a transconductor. The switch quad further including a first current path and a second current path is coupled to the load circuit. The connecting node of the switch quad and the load circuit is a differential-output terminal. The transconductor further includes a first resistor, a first operational amplifier, a second operational amplifier, a first current mirror, and a second current mirror. The resistor is coupled between two first input terminals of the first operational amplifier and the second operational amplifier. A current control terminal of the first current mirror is coupled to the first input terminal of the first operational amplifier, and a current mirroring terminal of the first current mirror is coupled to the first current path.