A variable-frequency LC filter that has sharp attenuation characteristics and that does not increase the size of a substrate and a high-frequency frontend module using such a variable-frequency LC filter are provided. A first variable capacitor and a second variable capacitor are disposed on a principal surface such that strength of magnetic field coupling caused between a first inductor and a third inductor is greater than strength of magnetic field coupling caused between a second inductor and the first inductor and than strength of magnetic field coupling caused between the second inductor and the third inductor.

A band-pass filter is described comprising a first first-order filter stage comprising a first resistor characterized by a first impedance and connected to a first node, referred to as a filter input node, and, through a second node to a first reactive component connected to a third node, the first impedance being such that a first current therethrough is dependent on the difference between the voltages at the first and second nodes; and a second first-order filter stage comprising a second resistor characterized by a second impedance and connected to the second node, and, through a fourth node, to a second reactive component connected to a fifth node. The second impedance is such that a second current therethrough is dependent on the negative of the sum of the voltages at the second and fourth nodes. The band-pass filter further comprises summing means for summing the voltages at the second and fourth nodes to output a voltage at a sixth node.

Provided is a polyphase filter, which is capable of achieving amplitude matching and phase matching while achieving a low insertion loss with a single-stage configuration. A first variable resistor and a second variable resistor have resistance values that are equal to each other, and the resistance values are set so as to correct an amplitude error between orthogonal signals of outputs of a first output terminal to a fourth output terminal. A first variable capacitor, a second variable capacitor, a third variable capacitor, and a fourth variable capacitor have capacitance values that are equal to one another, and the capacitance values are set so as to correct a phase error between the orthogonal signals of the outputs of the first output terminal to the fourth output terminal.

Provided is a polyphase filter, which is capable of achieving amplitude matching and phase matching while achieving a low insertion loss with a single-stage configuration. A first variable resistor and a second variable resistor have resistance values that are equal to each other, and the resistance values are set so as to correct an amplitude error between orthogonal signals of outputs of a first output terminal to a fourth output terminal. A first variable capacitor, a second variable capacitor, a third variable capacitor, and a fourth variable capacitor have capacitance values that are equal to one another, and the capacitance values are set so as to correct a phase error between the orthogonal signals of the outputs of the first output terminal to the fourth output terminal.

An apparatus and method of removing common mode noise in the case of measuring a biosignal using a capacitive coupling active electrode (CCE) is provided. A frequency band of a common mode signal may interact with a shield voltage and thus, a frequency band of a biosignal may be compensated for.

The object is to simplify the configuration of a filter in a reception apparatus. The reception apparatus includes a filter. The filter provided in the reception apparatus selects a signal transmission characteristic that is one of a band stop characteristic or a low pass characteristic. Further, selection of the signal transmission characteristic in the filter provided in the reception apparatus is performed in response to a desired signal and an interference signal. In the filter provided in the reception apparatus, passage of the desired signal and attenuation of the interference signal based on the selected signal transmission characteristic are executed.

The object is to simplify the configuration of a filter in a reception apparatus. The reception apparatus includes a filter. The filter provided in the reception apparatus selects a signal transmission characteristic that is one of a band stop characteristic or a low pass characteristic. Further, selection of the signal transmission characteristic in the filter provided in the reception apparatus is performed in response to a desired signal and an interference signal. In the filter provided in the reception apparatus, passage of the desired signal and attenuation of the interference signal based on the selected signal transmission characteristic are executed.

A control circuit for suppressing electromagnetic interference signal has an input and an output and a variable gain filter circuit with a first gain factor that is variable. The variable gain filter circuit receives a signal indicative of an electromagnetic interference signal and outputs a signal to a controlled signal source, which a second gain factor. The control circuit also has a controller operably connected to the variable gain filter circuit. The controller receives a signal indicative of an output signal at the output of the control circuit and outputs a control signal to the variable gain filter circuit. The control signal is based on the signal indicative of the output signal at the output of the control circuit, and the control signal controls the first gain factor and reduces the electromagnetic interference signal.

Disclosed is receiver for a noise limited system. A front-end circuit amplifies and band-limits an incoming signal. The amplification increases the signal swing but introduces both thermal and flicker noise. A low-pass band limitation reduces the thermal noise component present at frequencies above what is necessary for correctly receiving the transmitted symbols. This band limited signal is provided to the integrator circuit. The output of the integrator is equalized to reduce the effects of inter-symbol interference and then sampled. The samples are used to apply low frequency equalization (i.e., in response to long and/or unbalanced strings of symbols) to mitigate the effects of DC wander caused by mismatches between the number of symbols of each kind being received.

An active filter and an analog-to-digital converter (ADC) configured to suppress out-of-band peaking. An active filter may include an active device configured to provide a power gain to an input signal, a feedback network configured to connect an output of the active device to an input of the active device, and an input impedance network configured to couple the input signal to the input of the active device. A combination of the feedback network and the input impedance network is configured to provide frequency response properties of the active filter such that a frequency domain signal transfer function of the active filter has a constant in numerator.