Abstract: An exemplary ambient noise filtering method includes: sampling ambient noise signals to obtain multiple groups of sampled signals; analyzing each group of the sampled signals in each sampling period to determine ambient noise frequency band(s) in each sampling period, wherein the ambient noise frequency band is a frequency band where the ambient noise distributes; determining main noise frequency band(s) by statistically analyzing all the ambient noise frequency bands, wherein the main noise frequency band is a frequency band where the ambient noise concentrates and mainly distributes; and filtering the ambient noise out of signals generated during a communication by filtering the determined main noise frequency band(s) if the main noise frequency band(s) does not have a same range as that of a speech frequency band. Related exemplary mobile phone performing the method is also provided.

Abstract: A direct conversion radio-frequency (RF) receiver includes a controller and an adaptive continuous-time filter. The adaptive continuous-time filter receives a multiple-bit control signal generated by the controller to adjust a characteristic of the continuous-time filter. The controller generates the multiple-bit control signal in response to process variation in the semiconductor material used to implement the controller and the adaptive continuous-time filter. A method for tuning an adaptive continuous-time filter comprises determining a RC time constant, converting the RC time constant to a digital word, comparing a select bit of the digital word to a respective bit of a predetermined reference word to generate a control bit, applying the control bit to an adjustable element to modify the RC time constant, repeating the determining, converting, comparing and applying steps until the control bits generate an output word and providing the output word to the adaptive continuous-time filter.

Abstract: A method and a device used for displaying wideband information to a user has a return channel made through a cellular mobile terminal providing interactivity. The device includes a receiver for communicating in a first band of radio frequencies and a transmitter for communicating in a second band of radio frequencies. The method includes receiving information in a symbol-wise manner with the receiver in a first band of RF frequencies; generating a notification of an occurrence of a burst transmission from the transmitter; and in response to the notification, terminating the reception of the information for a portion of one symbol time corresponding to a duration of the burst transmission. The method may include an optional step, further in response to the notification, of reducing power consumption by turning off at least a portion of the receiver for a period of time corresponding to the duration of the burst transmission.

Abstract: An electronic device includes a first circuit board having a first audio source and a first reference grounding end, a second circuit board having a second audio source and a second reference grounding end, a flexible board cable, a grounding wiring, a selection unit, and a receiver. The flexible board cable couples the first audio source to the second circuit board. The grounding wiring couples the first grounding end to the second circuit board. The selection unit is used for selecting one from the first and second audio sources to output and selecting one from the first and second reference grounding ends to output. An input end of the receiver is controlled by the selection unit to be connected to the first or second audio sources, and a grounding end of the receiver is controlled by the selection unit to be connected to the first or second reference grounding ends.

Abstract: An apparatus and method for interference cancellation in wireless mobile stations operating concurrently in two or more wireless modes.

Abstract: A method, system, and apparatus for squelching a signal in telecommunications systems. The apparatus includes a filter, two power detectors, a divider, two comparators, a logic gate, and a gain control block. The apparatus receives an input signal, and the power of the signal is detected. The input signal is also filtered to pass only the noise portion of the signal, and the power of the filtered signal is detected. A ratio between the filtered signal power and the input signal power is determined. A first comparator receives the filtered signal power and a second comparator receives the ratio of the filtered signal power and the input signal power. The logic gate receives the outputs from the first and second comparators. The gain control block receives as inputs the logic gate's output and the input signal to the apparatus. The gain control block may attenuate the input signal based on the logic gate's output. The gain control block generates the output signal of the apparatus.

Abstract: Signals propagating on an aggressor communication channel can cause detrimental interference in a victim communication channel. A signal processing circuit can generate an interference cancellation signal that, when applied to the victim communication channel, cancels the detrimental interference. The signal processing circuit can dynamically adjust or update two or more aspects of the interference cancellation signal, such as an amplitude or gain parameter and a phase or delay parameter. Via the dynamic adjustments, the signal processing circuit can adapt to changing conditions, thereby maintaining an acceptable level of interference cancellation in a fluctuating operating environment. A control circuit that implements the parametric adjustments can have at least two modes of operation, one for adjusting the amplitude parameter and one for adjusting the phase parameter. The modes can be selectable or can be intermittently available, for example.

Abstract: A receiver system with dual tuner diversity for background processing and for reducing multipath distortion. The receiver system provides a plurality of antennas with a dual tuner design. One tuner may be used solely for background processing of a received signal while the other tuner may be simultaneously used to reduce multipath distortion.

Abstract: A noise canceler comprising: a first low-pass filter that a demodulated signal is to be input to; an interpolation processing unit that the demodulated signal after passing through the first low-pass filter and a pulse noise detection signal indicating presence of a pulse noise, are to be input to, the interpolation processing unit configured to perform interpolation processing on a demodulated signal present during a period determined by the pulse noise detection signal, out of the input demodulated signal, based on the input demodulated signal; a replacing processing unit that the demodulated signal subjected to the interpolation processing, the pulse noise detection signal, and the demodulated signal before passing through the first low-pass filter, are to be input to, the replacing processing unit configured to output a signal obtained by replacing a demodulated signal present during the period, out of the demodulated signal before passing through the first low-pass filter, with the demodulated signal sub

Abstract: A method of channel allocation in a cellular communication network wherein a radio channel is to be selected for establishment of a connection in an environment with potentially interfering signals, the method comprising: establishing a radio channel candidate; processing the radio channel candidate with potentially interfering signals and calculating a carrier to interference ratio (CIR) for the selected carrier frequency of the radio channel candidate and the potentially interfering signals; calculating a dominant interference ratio (DIR) being the ratio of the strongest potentially interfering signal with respect to the other potentially interfering signals; and using criteria based on at least one of the dominant interference ratio and the carrier to interference ratio in a selection process for selecting a channel for the connection to be established.

Abstract: In a radio communication system, transmitter and receiver stations share information on a maximum number of bits communicated per symbol. The transmitter station encodes a signal with sufficient error correcting capabilities to create a codeword. The transmitter station allocates the bits from the codeword to each symbol, modulates the symbols using a modulation type which processes symbols each having a number of bits equal to or smaller than the maximum number of bits per symbol, and transmits the modulated symbols. The receiver station demodulates the symbols using a modulation type which processes a larger number of bits per symbol as the transmission path quality is higher from among modulation types which process symbols having a number of bits equal to or smaller than the maximum number of bits per symbol.

Abstract: A wireless communication system, apparatus and a method for compensating offset using the same are disclosed, in which offset due to latency in a power save mode is compensated. The wireless communication apparatus includes a frequency matched unit for compensating offset due to latency that may occur during communication between the wireless communication apparatus and external equipment. The frequency matched unit adds a predetermined time to a clock value of a system clock if power save mode is transited to normal mode. Thus, the offset generated can efficiently be compensated if the power save mode is transited to the normal mode.

Abstract: A squelch detector that differentially detects a presence of a communication signal on a communication channel. The squelch detector being coupled to outputs of a differential offset bias amplifier to receive differential offset biased signals and generate a differential direct current signal.

Abstract: A method implementable in an audio receiver having an input for receiving broadcast signals including a set of channels and a squelching controller includes converting the signals associated with each channel into respective digital signals, and tuning the digital signals associated with a first subset of the channels. For each channel of the first channel subset, a respective set of amplitudes associated with respective frequencies of the associated digital signal is determined. A random-noise-level value associated with each channel of the first channel subset is determined from each set of the signal amplitudes. If a signal amplitude associated with a first channel of the first channel subset exceeds the random-noise-level of the first channel, a second subset of the channels of the set is tuned. Otherwise, the random-noise-levels are provided to the squelching controller.

Abstract: An embodiment is a receiver for a communications system that may substantially block unwanted signals in a frequency range to protect the receiver from overload. Simultaneously, the receiver of an embodiment substantially passes a desired signal so that its information may be processed by the, for example, communications system of which the receiver is part.

Abstract: Various aspects of a method and system for adaptive multi rate and measurements adaptation may include a processor that enables computation of at least one signal level measurement for at least one received signal. The processor may enable cancelling of interfering signals received in addition to the received signal based on processing of a received bit sequence using a first burst process operation (BP) in a first decoding algorithm that utilizes SAIC operations. The processor may also enable cancelling of noise signals received in addition to the received signal based on processing the received bit sequence using a second BP operation that utilizes redundancy and imposes a physical constraint during decoding. The processor may also enable adjustment of the computed at least one signal level measurement.

Abstract: Special DC tone treatment in a wireless communications system, e.g., an OFDM system, is discussed. In the downlink, a wireless terminal receiver introduces self-interference at the DC tone from the RF/baseband conversion. A base station every so often does not transmit on the downlink DC tone while continuing to transmit on other downlink tones. Wireless terminals measure received signal on the downlink DC tone during the time of suspended DC tone transmission, estimate self-interference and apply a correction to other received downlink DC tones. In the uplink DC tone interference is a composite of the assigned wireless terminal transmitter's baseband/RF conversion self-interference and air link noise. During one symbol interval of an N symbol interval dwell, the uplink DC tone is reserved for a special modulation symbol, which is a predetermined function of the other N?1 modulation symbols.

Abstract: Antenna noise temperature is determined for a handheld wireless communication device which typically includes a radio, e.g. having a wireless transceiver and associated circuitry connected thereto, and an antenna connected to the radio. The method includes measuring an antenna thermal noise component, measuring a radio noise component, measuring an environmental background noise component, and determining the antenna noise temperature based upon the measured antenna thermal noise, radio noise, and environmental background noise components. The method may include measuring antenna efficiency, and determining further includes weighting at least one of the measured antenna thermal noise, radio noise and environmental background noise components based upon the measured antenna efficiency.

Abstract: Disclosed is a method for limiting the voltage applied to a component in a radio frequency path (RF path) of a radio frequency excitation system. According to the method, a radio frequency signal (RF signal) is tapped at a first random point of the RF path, and energy is withdrawn from the RF path when the RF signal tapped at the first point or a value proportional to the tapped RF signal exceeds a reference value, resulting in the component being protected against excess voltages due to disturbances.

Abstract: A squelch circuit and a communication apparatus used with the same that are able to generate a squelch signal even if a squelch period is short and an operation of a squelch detecting circuit is insufficient, the circuit having: a squelch detecting circuit detecting the existence of a signal on a communication line in response to a transmission signal or a received signal and generating a first squelch signal; and a squelch control circuit generating a squelch mask signal in response to the first squelch signal and a transmission control signal and generating a second squelch signal based on the squelch mask signal and the control signal. The first squelch signal is controlled by the transmission signal to generate the second squelch signal in which the lacked portion of the first squelch signal is temporally restructured.

Abstract: A portable interference-generating device for inducing desired frame error characteristics, such as desired frame error patterns and rates, at a mobile unit receiving a carrier signal having at least one data channel having a plurality of data frames. The induced frame errors may be used to test a digital radio receiver's behavior in the presence of frame errors that may occur as a result of various impairments in a CDMA wireless communication channel. The portable interference-generating device includes a noise source that provides a noise signal and a pulse generator that is used to gate the noise signal according to a desired frame error characteristic at the mobile unit. The gated noise signal is provided to the mobile unit via a coupling element, which preferably couples the gated noise signal directly to an antenna radiation element on the mobile unit.

Abstract: Signal processing apparatus produces an audio signal suitable for conveying a psychoacoustic perception of a low frequency audio signal to a listener, the apparatus generates harmonics of the low frequency signal by shaping the waveform of the low frequency signal with respect to time and/or level. This may be achieved using a peak-hold generator and a rectifier, or using a peak-hold-decay generator.

Abstract: Embodiments of the present invention can be used to enhance signals in a peer-to-peer radio system, such as a two-way radio system. In one embodiment, the invention includes receiving a communications signal on a channel from a remote radio at a radio using a plurality of antenna elements, such as an antenna array. The received communications signal includes a squelch code. The radio detects the squelch code, and enhances the received communications signal using the squelch code.

Abstract: An apparatus and method for controlling a volume of comfort noise in a mobile communication terminal. The mobile communication terminal includes a vocoder for detecting a decoding rate of voice data received after establishing a voice call to output a detection signal and an amplifier for amplifying an output signal of the vocoder. The method comprises the steps of determining whether the decoding rate of the voice data from the vocoder is ?, recognizing the voice data as silence period data containing only the comfort noise and providing the vocoder with a control signal to lower a volume of the comfort noise, if the decoding rate of the voice data is ?, and controlling a volume of the voice data such that it becomes a volume preset by a user, if the decoding rate of the voice data is not ?.

Abstract: An AM radio receiver comprises an RF amplifier, a first mixer that converts the RF signal to a first intermediate-frequency signal, a first bandpass filter that band-limits the first intermediate-frequency signal, a second mixer that converts the output from the first bandpass filter to a second intermediate-frequency signal, a second bandpass filter that band-limits the second intermediate-frequency signal, an intermediate-frequency amplifier that amplifies the output from the second bandpass filter, an AM detector that demodulates the output from the intermediate-frequency amplifier and provides output of an audio signal, and a noise detector for detecting and eliminating ambient noise. The noise detector comprises a first noise detector that detects noise from the RF signal and eliminates the noise contained in the first intermediate-frequency signal, and a second noise detector that detects noise from the second intermediate-frequency signal and eliminates that noise.

Abstract: The present invention relates to a receiving system for a multi-sensor antenna and comprising: at least one set of channel filters (310j, 710k, 1 . . . N) filtering the signals Xi(t,f) received by the different antenna sensors, where these signals may include a desired signal (Si(t,f)); a summer (350, 720) summing the filtered signals [Vi(t,f)], where i=1 . . . N, by means of the channel filters and emitting an antenna output signal Y(t,f), at least one calculating module (320, 720) receiving either the sensor signals and aligning them in phase or the signals filtered by the channel filters, said module estimating the transfer function (W(t,f), W k(t,f)) of an optimum filter in a manner to minimize the square difference between the antenna output signals filtered by said filter and the desired signal characterized in that if furthermore comprises at least one statistical analysis module (330, 730) operating on the frequency values of the transfer function.

Abstract: Noise impulses are suppressed in a signal processing circuit by gating an input signal. The gated signal is then smoothed upstream of demodulating the smoothed signal as viewed in a signal flow direction from a signal input to a processed signal output. The signal processing circuit system includes at least a signal gating section followed by a signal smoothing section followed by a demodulating section in that order and as viewed in the signal flow direction. Thus, smoothing takes place prior to demodulation.

Abstract: Embodiments of a squelch detector are described herein.

Abstract: A method for removing direct current (DC) interference from a signal received by a communication receiver is provided that removes both a DC offset signal induced by the communication receiver and transmitter. The method includes removing the estimated DC offset from the received signal, correcting a frequency shift in the received signal, estimating a second DC offset signal induced by a source of the received signal, such as a transmitter and removing the estimated second DC offset from the received signal. The receiver DC offset signal is estimated and removed prior to performing a timing carrier offset correction using Barker code manipulation to remove receiver-induced DC offset interference and to sum all Barker chips after effectively multiplying Barker codes to correlate to a Barker sequence unaffected by the receiver DC offset signal.

Abstract: A method for automatically switching a profile of a mobile phone includes measuring a current environmental noise value of ambient noise surrounding the mobile phone. The current environmental noise value is then compared to a predetermined noise value, and a noise difference is calculated. Next, the profile of the mobile phone is switched based on the value of the noise difference.

Abstract: A squelch circuit for operating at high speed and at high frequencies includes a squelch input unit, a low swing pre-amplifier and a sampling and decision circuit. The squelch input unit pre-processes the positive and negative signals of an input signal to generate four pre-processed signals that are paired and sent to the low swing pre-amplifier. The outputs of the low-swing pre-amplifier are then over-sampled by the sampling and decision circuit. Multi-phase clocks are used to control the over-sampling in the sampling and decision circuit. A logic circuit then determines if the state of the input signal based on multiple samples.

Abstract: An object is to provide a noise removing circuit that can be integrally formed on a semiconductor substrate and can improve the accuracy of noise component removal. The noise removing circuit comprises a highpass filter detecting a noise component included in an input signal, a pulse generating circuit generating a pulse signal corresponding to the detected noise component, an analog delaying circuit 252 delaying the input signal, and an outputting circuit removing the noise component included in the delayed signal according to the output timing of the pulse signal. The analog delaying circuit 252 delays the output timing of the input signal by making switches 51 to 56 electrically continuous in a sequential order, by holding the voltage of the input signal at each time point in a plurality of capacitors 81 to 86, and by extracting the held voltage before being updated by making switches 61 to 66 electrically continuous.

Abstract: A receiver and a composite component for preventing noise produced by sneaking of a local oscillation signal. An FM receiver comprises a high-frequency amplifier circuit 11, a mixing circuit 12, a local oscillator 13, intermediate-frequency filters 14 and 16, an intermediate-frequency amplifier circuit 15, a limit circuit 17, an FM detection circuit 18, and a stereo demodulation circuit 19. The mixing circuit 12 and the local oscillator 13 constitute a one-chip composite component 30 integrally formed on a semiconductor substrate. The frequency of the local oscillation signal is set so that the difference of frequency between the local oscillation signal and a modulated wave signal may be smaller than the occupied bandwidth of the modulated wave signal.

Abstract: A receiver capable of reducing a low-frequency noise generated when a component is integrally formed on a semiconductor substrate by using CMOS process or MOS process. A high-frequency amplifier circuit 11, a mixing circuit 12, a local oscillator 13, intermediate-frequency filters 14 and 16, an intermediate-frequency amplifier circuit 15, a limit circuit 17, an FM detection circuit 18, and a stereo demodulation circuit 19 constituting an FM receiver are formed as a one-chip component 10. This one-chip component 10 is formed on a semiconductor substrate by using the CMOS process or the MOS process. The amplification elements contained in the mixing circuit 12, the intermediate-frequency filters 14 and 16, the intermediate-frequency amplifier circuit 15, and the local oscillator 13 are formed by using the p-channel type FET.

Abstract: The high-frequency module of the present invention is formed of two sections: first high-frequency circuit 5 having a first filter circuit; and second high-frequency circuit 6 having a second filter circuit. At least any one of the two high-frequency circuits has a conductive case. The structure is highly effective in attenuating a spurious signal, thereby solving the problem that the output level of the spurious signal fed from the high-frequency module is undesirably increased.

Abstract: A transmitter and a receiver share a maximum number of transmission bits per symbol as a parameter. The transmitter modulates an encoded and interleaved transmission signal in accordance with a modulation scheme which enables the transmission of one bit or more per symbol, while the receiver demodulates a received signal based on a channel quality in accordance with a modulation scheme which has a higher modulation level as the channel quality is higher. When the number of demodulated bits per symbol is smaller than the maximum number of transmission bits per symbol, the receiver deinterleaves and decodes a received signal after the demodulation on the assumption that the received signal has likelihoods of zero as much as the number of missing bits.

Abstract: An external noise intrusion prevention device preventing intrusion of external noise into a central conductor of a trunk cable in an up signal frequency band is provided. A first filter circuit 3 letting a signal in frequencies of 54 MHz or higher pass is provided between an input terminal 1 and an output terminal 2. A front filter circuit 4a and a rear filter circuit 4b, which constitute a second filter circuit 4, are provided on both ends of the external noise intrusion prevention device, respectively. A noise elimination circuit 6 formed by cascading two connection transformers 6a and 6b is also provided. The two connection transformers 6a and 6b are connected to each other while being arranged in a line symmetrical manner.

Abstract: A method for measuring a power level of a radio frequency signal in a radio frequency transmitter includes routing a portion of the radio frequency signal to a detector, detecting a signal envelope of the radio frequency signal with the detector, routing the detected signal to a digital signal processor, and talking at least one sample from the detected signal envelope using the digital signal processor and determining a detected power level of the radio frequency signal from the at least one sample, wherein the at least one sample lies in a portion of the detected signal envelope having a known non-random sequence.

Abstract: A flexible printed circuit board has first and second connection portions 18 and 19 where contacts are exposed and first and second path portions 16 and 17 where conductor patterns 11 are arranged that connect the contacts 11a and 11b of the first and second connection portions 18 and 19 together. The first and second path portions 16 and 17 are formed so as to have substantially symmetrical shapes with each other about a predetermined straight line, and the flexible printed circuit board is folded up along the straight line C1 and C2. Alternatively, a flexible printed circuit board has a conductor pattern 11 formed between first and second insulating sheets 12 and 13, and has a shielding conductor 14 fixed to the second insulating sheet 13. The flexible printed circuit board is folded up with the second insulating sheet 13 outside so that the conductor pattern 11 is enclosed inside the shielding conductor 14.

Abstract: A low power consumption RF receiver system that is adapted for receiving and shaping transmitted digital data signals into a digital data stream for processing by a microprocessor is provided. The receiver system comprises an integrated circuit, which includes a data slicer adapted to accept the received digital data signals, shape the signals into a digital data stream, and pass the digital data stream to the microprocessor. The integrated circuit further includes a peak detector adapted to sense ambient circuit noise when digital data signals are not present, develop a voltage reference signal representative of the peak value of the ambient circuit noise, and pass the voltage reference signal to the data slicer.

Abstract: A receiver receives an electromagnetic signal via an antenna mounted on an antenna mast. A signal evaluator determines or measures a signal quality level associated with the received electromagnetic signal. The signal quality compares the determined signal quality level to a threshold minimum signal quality level. A current elevational position of the antenna mast is detected or tracked. The antenna mast is raised to a greater height than the current elevational position if the compared signal quality level is less than the threshold minimum signal quality level and if the current elevational position is less than a maximum height of the antenna mast.

Abstract: Disclosed is a transmission envelope detector referred to a squelch detection circuit for effectively detecting an element of transmission data in a high speed serial data transmission system. The squelch detection circuit of the invention includes a differential input level shifter, a first reference voltage generator, an amplifier, a second reference voltage generator, and a comparator. The squelch detection circuit can detect whether the transmission data is a noise or signal element even at a cross point of the transmission data, resulting in achieving stable data transmission.

Abstract: An apparatus (100) for isolating a noise intolerant device (110) from a source of noise includes a digital bus (104/105). A processor (101) outputs clock signals and first data signals and receives second data signals over the digital bus (104/105). A bi-directional buffer (109) is coupled between the digital bus (104/105) and the noise intolerant device (110) disposed in a tuner module. The apparatus (100) operates such that, in dependence upon a control signal, the bi-directional buffer (109) selectively passes the clock signals and the first data signals from the digital bus (104/105) to the noise intolerant device (110), and the second data signals from the noise intolerant device (110) to the digital bus (104/105).

Abstract: The invention relates to the provision of apparatus and a method for the tuning to one of a range of radio frequency signals to receive data which can subsequently be used to generate a radio or television channel selected by the user of the apparatus. The bit error rate of the output of the received radio frequency signal is monitored and, if the bit error rate exceeds the predefined bit error rate limit the apparatus is retuned to a frequency which is equivalent to the selected radio frequency signal plus or minus an offset frequency value. The bit error rate is thereafter monitored and an increase in the offset can be used if required. The invention allows a reduction in data errors which may be caused by interference from other apparatus.

Abstract: System and method for interference cancellation in a digital wireless communications system. A preferred embodiment comprises sampling a received signal wherein the received signal is real-valued, rotating the sampled received signal by a specified amount, extracting in-phase and quadrature phase streams from the rotated, sampled received signal, applying an interference suppression filter and combining the filtered streams. The output of the combining operation can be de-correlated (by whitening) if there is excessive correlation.

Abstract: A diversity reception handset includes a receiver for receiving pilot and plural increments of traffic sent from a base station within a service area of a wireless communications network. The handset includes at least two antennas, a switch for switching a receiver between the two antennas, a time-of-arrival searcher circuit connected to the receiver and responsive to the pilot for determining time of arrival of the received signals and expected time of arrival of each increment, and a controller for controlling the switch based upon determined expected time of arrival of each increment.

Abstract: An impulse noise reducer detects impulse noise in an audio signal by detecting and smoothing the high-frequency amplitude of the audio signal, attenuating the non-smoothed amplitude according to the smoothed amplitude, and comparing the attenuated amplitude with a threshold. Impulse noise is discriminated from high-frequency audio components because the latter tend to occur in longer-lasting bursts and are therefore attenuated more strongly. The impulse noise reducer is simplified because it does not have to perform intermediate-frequency signal processing, and its sensitivity is not affected by adjacent-channel signals because these signals are substantially absent from the audio signal. The impulse noise reducer can be implemented by digital signal processing, and is suitable for use in a medium-wave AM audio broadcast receiver.

Abstract: Orthogonal frequency division multiplexing (OFDM) has been specified by IEEE 802.11a standard as the transmission technique for high-rate wireless local area networks (WLANs). Performance of an OFDM system, however, is heavily degraded by random Wiener phase noise, which causes both common phase error (CPE) and inter-carrier interference (ICI). A method and algorithm is disclosed for efficiently eliminating the effect of phase noise in OFDM based WLANs.

Abstract: A modulated input signal is filtered to reduce noise. The state of the input signal controls the state of a switch. Depending upon its state, the switch connects one of two circuits to a gate. The gate receives the input signal and it passes or blocks the signal depending upon the state of the signal received from the switched circuits. When it is passing the input signal, the output of the gate is equivalent to the input signal. When it is blocking the input signal, the output of the gate is set to a default state. The default state is independent of the input signal. One of the switched circuits gradually modifies the signal provided by the gate to allow the input signal to pass through. The other switched circuit gradually modifies the signal provided to the gate to block the input signal.

Abstract: A squelch circuit with an adjustable reference level, having an input level comparator with a first, a second, a third and a fourth current input terminal, a first and a second input terminal, and an output terminal. A first current source is coupled between the first current input terminal and an operation voltage. A second current source is coupled between the second current input terminal and the operation voltage. A third current source is coupled between the third current input terminal and a ground terminal. A fourth current source is coupled between the fourth current input terminal and the ground terminal. A bias generator is coupled to the first, second, third and fourth current sources to generate current control signals thereto according to a reference current and control bits, such that the first, second, third and fourth current sources generate the same current, which adjusts the reference level.