Voltage-controlled filter

About: Voltage-controlled filter is a research topic. Over the lifetime, 5514 publications have been published within this topic receiving 70872 citations. The topic is also known as: VCF.

Novel Compact Ultra-Wideband Bandpass Filter by Application of Short-Circuited Stubs and Stepped-Impedance-Resonator

Abstract: To realize the compact ultra-wideband (UWB) bandpass filters, a novel filter prototype with two short-circuited stubs loaded at both sides of a stepped-impedance resonator (SIR) via the parallel coupled lines is proposed based on a distributed filter synthesis theory. The equivalent circuit of this filter is established, while the corresponding 7-pole Chebyshev-type transfer function is derived for filter synthesis. Then, a distributed-circuit-based technique was presented to synthesize the elements' values of this filter. As an example, a FCC UWB filter with the fractional bandwidth (FWB) @ -10 dB up to 110% was designed using the proposed prototype and then re-modeled by commercial microwave circuit simulator to verify the correctness and accuracy of the synthesis theory. Furthermore, in terms of EM simulator, the filter was further-optimized and experimentally-realized by using microstrip line. Good agreements between the measurement results and theoretical ones validate the effectiveness of our technique. In addition, compared with the conventional SIR-type UWB filter without short-circuited stubs, the new one significantly improves the selectivity and out-of-band characteristics (especially in lower one -45 dB@1-2 GHz) to satisfy the FCC's spectrum mask. The designed filter also exhibits very compact size, quite low insertion loss, steep skirts, flat group delay and the easily-fabricatable structure (the coupling gap dimension in this filter is 0.15 mm) as well. Moreover, it should be noted that, in terms of the presented design technique, the proposed filter prototype can be also used to easily realize the UWB filters with other FBW even greater than 110%.

A method and an apparatus for reducing interference frequencies by using a notch filter

Abstract: A two-pole notch filter is provided, which may detect the presence of an interfering frequency on the basis of its own output signal and a deactivation criterion that is based on the convergence behaviour of the complex zeros. The adaptive notch filter comprises a two-pole filter stage (200) connected to receive a digital input signal and to output a filtered digital output signal and a sequence representing a complex zero z 0 , an adaptive unit configured to adjust a complex zero of said two-pole filter stage on the bases of a real frequency component of an interference signal and an interference detection control unit (340) connected to receive a signal corresponding to said sequence of z 0 , said interference detection control unit comprising a deactivation criterion based on a convergence behaviour of said complex zero for bypassing said two-pole filter stage when said deactivation criterion is met. By cascading a plurality of corresponding filter stages multiple interferers may be tracked and detected independently.

Electrical filters for weighing system circuits

Abstract: A weighing system comprising a transducer operatively connected to a load supporting structure for producing a DC analogue signal voltage having an amplitude which represents a weight condition of a load applied to the structure, at least one signal utilization device, and a circuit for transmitting the DC signal voltage to the signal utilization device and including an electrical filter for attenuating undulating voltage superimposed to the DC signal voltage. The filter includes an amplifier and is characterized by a variable impedance connected to the input of the amplifier for selectively varying the time response of the filter without altering the DC gain thereof. The damping coefficient of the filter is a function only of a preselected value of the percentage by which the filter output voltage initially overshoots its steady state value when the transducer voltage is applied as a step input to the filter.

Variable switched-capacitor filter capable of changing the filter characteristic thereof

Abstract: The variable switched-capacitor filter (VSCF) comprises an input terminal (101), an output terminal (104) and first and second variable switched-capacitor filter blocks (102 and 103, resp.) each having a plurality of capacitors. In each of the filter blocks (102, 103) at least one of the filters is selected in response to a control signal for changing the filter characteristic based on the selected capacitor or capacitors. A first switch (SA) delivers during a first state a first output signal from the first variable switched-capacitor filter block (102) to the output terminal (104), and during a second state, prohibits the first output signal from reaching the output terminal (104). The function of the second switch (SB) is essentially opposite to that of the first switch (SA). The selection of at least one capacitor in the first and the second variable switched-capacitor filter block (102 and 103, resp.) is performed during the second and the first state, respectively. The VSCF accomplishes automatic line equalization without being affected by waveform distortions which result from switching the filter characteristic.

Digital subscriber line (DSL) modem compatible with home networks

Abstract: A cost-effective filter consuming low power and occupying minimal space. The filter may be used in a ADSL modem (or CPE) to filter the signal components other than the ADSL signals. A high pass filter first filters the low frequency components to attenuate (or remove) lower frequency components such as that caused by ADSL transmit echo signals and that used for voice transmission. The high pass filter may be modified by adding a few resistors to limit the voltages of the high frequency signals also. The output of the high pass filter is amplified and passed through a low pass filter to filter the high frequency components (HPNA included). Due to earlier filtering operation of the high pass filter, the signal can be amplified substantially before being sent to the low pass filter. The implementation of the low pass filter is simplified due to the prior amplification.