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.

FM Feedback demodulator having threshold extension circuit with two-pole crystal filters

Abstract: Demodulation of FM signals employing an FM feedback loop of the present invention includes a first mixer circuit for mixing an IF input signal with a voltage controlled oscillator signal to down-convert the IF input signal to a predescribed center frequency IF signal. This signal is coupled through a tuned amplifier having an automatic gain control loop and is then filtered in a predetection filter and amplified. The predetection filter is composed of a two-pole crystal bandpass filter having a very narrow bandwidth. The filtered signal is then coupled to a frequency discriminator circuit comprised of a frequency detection second mixer and filter circuit, the frequency detection filter circuit being composed of a second two-pole crystal bandpass filter, the bandwidth of which is an order of magnitude larger than that of the predetection filter. The output of the frequency discriminator is coupled through a loop compensation filter to the voltage controlled oscillator so that changes in the output frequency of the voltage controlled oscillator reduce the deviation of the FM signal in the intermediate frequency and frequency discriminator stages. The use of two-pole crystal bandpass filters improves the frequency stability of the system and significantly reduces post detection noise levels, as compared with conventional limiter/discriminator techniques. The two-pole crystal bandpass filters have a Butterworth configuration. In addition to the FM feedback loop, a squelch circuit is also coupled to the output of the frequency discriminator.

Metamaterial Transmission Line Based Bandstop and Bandpass Filter Designs Using Broadband Phase Cancellation

Abstract: This paper presents a methodology of designing a microwave bandstop filter and a bandpass filter by using a Composite Right/Left Handed transmission line (CRLH-TL) as part of a transversal filter. The CRLH-TL can be engineered to have specific phase slope and phase offset. Connecting the CRLH-TL and the conventional microstrip delay line at both input and output can establish a transversal filter where the signal merging at the output has broadband out of phase characteristics. Therefore, the bandstop filter can be created with signal rejection over a wide frequency range. The measured 3dB bandwidth of the bandstop filter is 130% and the minimum insertion loss at the next passband is ?1.7dB. In addition, based on the bandstop filter a bandpass filter with a wide signal rejection range is developed by creating a frequency dependent defect in one branch of the bandstop filter. This is implemented by either attaching a microstrip open stub or capacitively coupling a microstrip resonator to the microstrip delay line. The 3dB passband bandwidth and the minimum insertion loss are 18%, ?1.5dB and 8%, ?2dB corresponding to the open stub and the resonator scheme, respectively.

Receiver if circuit including image rejection mixer and active bandpass filter

Abstract: A receiver IF circuit includes the following: a variable gain amplifier for amplifying an RF input signal; a frequency converter for mixing the amplified RF input signal and a local signal to generate polyphase intermediate-frequency signals that are used for suppressing an image component; a polyphase filter for receiving the polyphase intermediate-frequency signals and outputting an intermediate-frequency signal whose image component is suppressed; a frequency variable band-pass filter for selecting a channel of the intermediate-frequency signal while changing a frequency response in accordance with a supplied control signal; an IF demodulator for demodulating the intermediate-frequency signal; and an automatic gain control for detecting a level of an output signal of the IF demodulator and controlling a gain of the variable gain amplifier in accordance with the detected level. Using the polyphase filter and the frequency variable band-pass filter, the receiver IF circuit can achieve high-performance integration of an image rejection filter and a channel selection filter.

Filter having frequency-dependent transmission properties for electric analog signals

Abstract: In one illustrative embodiment, a basic filter circuit for discrete signals is provided corresponding in filter function to an analog ladder network containing inductive and capacitive components. The reactive components of the analog filter structure are realized in the basic filter circuit as one-port and two-port elements having time delay, while non-reactive components of the analog filter are realized as time-delay-free one-port and plural-port elements. Interface means connect the port elements together in a configuration corresponding to the configuration of the analog filter, with sets of adder and multiplier means of the interface circuitry which couple successive sets of the port elements to each other being correlated with the connective relationship (whether series, series-parallel or parallel) between the corresponding components or branches of the analog filter and with the parameters of the analog components, so that the basic filter circuit essentially simulates the analog filter structure in its filter characteristics.

Voltage-mode multifunction biquadratic filter employing single DVCC

Abstract: A new voltage-mode single-input and four-output multifunction biquadratic filter using single differential voltage current conveyor, three capacitors and two resistors is presented. According to the values of the passive components used, the highpass, bandpass, lowpass and notch filters can be simultaneously obtained from the first circuit configuration. Moreover, the allpass, highpass and bandpass filters can be simultaneously obtained from the second circuit configuration. H-Simulation program with integrated circuit emphasis (HSPICE) simulations using Taiwan Semiconductor Manufacturing Company, Ltd. (TSMC) 0.18 µm level 49 complementary metal oxide semiconductor (CMOS) technology process parameters are given to validate theoretical predictions.