Abstract: The invention relates to a method and arrangement for receiving a frequency modulated signal, and especially for demodulating the signal. The invention is applicable especially in the receiver of a mobile station. One idea of the invention is to convert a radio frequency, frequency modulated signal directly into a low-frequency signal, and to perform the demodulation by forming by means of the falling and rising edges of said low-frequency signal a second signal, the frequency of which is twice the frequency of the low-frequency signal, and by frequency detecting said second signal. By means of the invention, the advantages of the direct conversion technique, such as low power consumption, are achieved in the reception of the frequency modulated signal,. The required components can be advantageously manufactured on an integrated circuit. Besides these advantages, a good quality of the detected signal is achieved.

Abstract: A receiver circuit, which may be used in a leakage detector, includes an RF input, a narrow band filter, and a direct demodulator. The leakage detector in which the receiver circuit may be used is operable to measure leakage in a communication system, the communication system operable to transmit broadband communication signals comprising one or more radio frequency carrier signals modulated by one or more baseband communication signals, wherein each radio frequency carrier signal has a channel frequency. Essentially, the exemplary receiver circuit according to the present invention is operable to generate a baseband leakage signal. To this end, the RF input is coupled to a source of broadband communication signals and receives a broadband communication signal therefrom, the broadband comnunication signal including a first signal associated with a first channel frequency.

Abstract: A radio receiver providing compensation for a direct current offset which includes a first frequency converter for converting a signal received by the receiver to first and second intermediate frequency signals, each signal having an angular frequency &ohgr;r and being in phase quadrature with respect to each other. All analog-to-digital converter for converting the first and second intermediate frequency signals to first and second intermediate frequency digital signals, each having an angular frequency &ohgr;r and being in phase quadrature with respect to each other, a direct current offset being generated within the analog-to-digital converter. A second frequency converter for converting the first and second digital signals and the direct current offset to first and second baseband signals, and low pass filters each having a cutoff frequency &ohgr;T for removing frequency components of the first and second baseband signals which are higher than &ohgr;r.

Abstract: A single chip superhetrodyne AM receiver is disclosed herein. To compensate for process variations in the implementation of the IC, bias currents setting the operating conditions for various amplifiers and other components in the system are adjusted based on frequency control signals in a PLL circuit in the local oscillator. Since the magnitude of the control signal reflects the process variations, the bias currents are adjusted based on the control signal to offset these variations in other portions of the receiver. To further improve the signal to noise ratio of the receiver, the IF filter is tuned within a range so as not to include any integer multiple or integer divisor of the timing reference frequency. Various techniques are described for enabling a complete superhetrodyne AM receiver to be implemented on a single chip which receives an antenna input signal and outputs a digital data signal.

Abstract: Imager rejection circuitry includes a first digital path including a finite impulse response filter 202 having a variable gain stage 204 operable to apply a gain to a first digital signal in response to a coefficient selected from a coefficient table 206 and an adder 205 for summing the first digital signal to the output of the variable gain stage 205 to produce a corrected first digital signal. A second digital path processes a second digital signal and error calculation circuitry 207 determines an error between the first and second signals for selecting a coefficient from the coefficient table 206.

Abstract: A communications device includes a direct-conversion receiver for a radio frequency (RF) signal which is configured to receive the RF signal during defined time slots. A first input receives the RF signal and a first output outputs a baseband signal derived from the RF signal. A mixer module is configured to receive the RF signal and a local signal which is generated by a local oscillator. The mixer module generates an output signal which includes the baseband signal and an offset component. An amplifier module is connected between the first output and the mixer module, and includes a feedback loop which has in a backward path, a track-and-hold circuit. The track-and-hold circuit is configured to track the offset component during a first time slot and to hold a value of the offset component at an end of the first time slot until a subsequent second time slot begins. This held value is applied during the second time slot to the output signal in order to provide for fast compensation of the offset component.

Abstract: In order to simplify the circuitry upon integration of a mobile radio receiver in a terminal for mobile communication, the invention proposes the use of a receiving section in which at least one component is also arranged to receive broadcast signals, steps being taken so as to ensure that the gap arising in the broadcast reception is masked at instants at which control information is received for the mobile communication.

Abstract: To obtain a radio set in a direct conversion system so as not to have any undesired influence of a signal of a transmission system on a reception system. In a transmission system, a frequency Flo of a local signal used in a frequency converting process performed by a frequency converter is expressed as (M/N)·Frx by a frequency conversion circuit. Based on the frequency Flo and the transmission frequency Ftx, a intermediate frequency Ftxif of the transmission system is expressed as Ftxif=Flo−Ftx=(M/N)·Frx−Ftx which is an oscillation frequency of a second local oscillator. Therefore, an equation exists as Ftx+Ftxif={(M/N)·Frx−Ftxif}+Ftxif=(M/N)·Frx, although Ftx+Ftxif leak to the reception system. As a result, since it is different from a reception frequency band, no interference wave is generated for a received signal.

Abstract: To solve the problems associated with conventional signal strength measurements utilizing homodyne receivers, the present invention is able to economically reduce the idle time power usage of a homodyne receiver by “powering down” a part of the homodyne receiver. With certain signal modulations, the power received in each channel of the homodyne receiver is equivalent and, as a result, the estimated received signal strength measurement calculation is simplified, reducing the power usage, which can be very useful, especially in the mobile communications industry.

Abstract: A direct conversion circuit for radio frequency signals is disclosed. The circuit includes a pair of quadrature related mixers, a phase shift unit, and a local oscillator. The pair of quadrature related mixers is coupled to a radio frequency signal input port for mixing down a radio frequency input signal. The phase shift unit is in communication with at least one of the pair of mixers for phase shifting a local oscillator signal. The local oscillator produces the local oscillator signal. The local oscillator includes a non-integer frequency multiplier for multiplying the frequency of a first voltage controlled oscillator signal by a non-integer value to produce the local oscillator signal.

Abstract: A system for a direct digital down conversion of a 10.8 MHz intermediate frequency signal in the personal handy phone system. The present invention includes a system that enables a direct digital down conversion of a 10.8 MHz intermediate frequency signal into a digital baseband signal within cell stations and portable stations of the personal handy phone system. To perform this direct digital down conversion of a 10.8 MHz intermediate frequency signal, one embodiment of the present invention uses a hard limiter circuit, a sampler circuit and a digital down converter circuit. The hard limiter circuit of the present invention receives a 10.8 MHz intermediate frequency signal, utilized within cell stations and portable station of the personal handy phone system, and provides a threshold for it. The sampler circuit uses a 19.2 MHz oscillating clock signal to sample the intermediate frequency signal that is output from the hard limiter circuit. Due to spectral leakage, the 10.

Abstract: In a method for compensating D.C. offset in a direct conversion receiver by a signal (IF.sub.-- I, IF.sub.-- Q) received and demodulated in one of the channels of the reception frequency band of a radio communication system, a correction signal (Q.sub.control) is produced from the signals in the channels of the reception frequency band. The correction signal (Q.sub.control) is combined with the demodulated signal. The apparatus for implementing the method comprises means (12, 17, 18, 19) for producing the correction signal, and means (15, 16) for combining the correction signal with the received and demodulated signal.

Abstract: A radio comprising an FET mixing device for multiplying a first-frequency signal with a second frequency signal to generate a third frequency analog mixer output signal. A local oscillator input port receives a periodic sinusoidal local oscillator signal at a local oscillator frequency from an external local oscillator source. A drive circuit generates a substantially square-wave two-voltage level switching signal for driving said mixing device. An analog-to-digital converter generates a digital representation of said third frequency analog mixer output signal.

Abstract: A direct conversion receiver (DCR)(10) comprises amplitude modulated interference (AMI) nulling circuitry (32) for achieving enhanced cancellation of AMI. The AMI nulling circuitry (32) includes a first signal processor (42) and a second signal processor (44) for processing first and second differential output signals, respectively, from a mixer (24a). The first signal processor (42) includes an adjustable transfer function that is controlled by a controller (50). The controller (50) adjusts the transfer function of the first signal processor (42) to equalize the magnitudes of AMI components in the first and second differential output signals. The first and second differential output signals are then combined in a manner which cancels the equalized AMI components.

Abstract: A multi-carrier radio system in which pairs of subcarriers are positioned in frequency such that each subcarrier in a pair is the image of the other subcarrier in the pair. By making each subcarrier the image of another subcarrier, the radio system of the present invention permits highly integrated low-IF transceiver implementation. In an exemplary embodiment, a multi-carrier transceiver includes an integrated receiver comprising a first mixer for mixing an input signal with a local oscillator signal to produce an in-phase downconverted signal. Additionally, a first phase shifter phase-shifts the local oscillator signal to produce a quadrature local oscillator signal, and a second mixer mixes the input signal with the quadrature local oscillator signal to produce a quadrature downconverted signal. Thereafter, a second phase shifter phase-shifts, or rotates, the quadrature downconverted signal to produce a rotated quadrature downconverted signal.

Abstract: An I/Q direct conversion receiver has an input (5,6) for receiving an RF signal comprising a wanted signal having in-phase and quadrature phase channels modulated onto in-phase and quadrature carrier signals. A signal splitter (7) divides the receiver RF signal into three in-phase signal components. Three substantially identical mixers (8) are provided and receive respective RF signal components for mixing with local oscillator signals. The first mixer (8a) receives the local oscillator signal shifted by 45.degree., the second mixer (8b) receives the local oscillator signal shifted by -45.degree., whilst the third mixer (8c) receives the local oscillator signal shifted by 180.degree.. A correction signal is generated by summing at a summing amplifier (11) the first and second baseband signals together with the third baseband signal after appropriate scaling.

Abstract: The invention provides a superheterodyne receiver by which undesired radiations are minimized. The superheterodyne receiver includes a voltage-controlled oscillator for forming an oscillation signal of a frequency equal to n times a carrier frequency of an object FM signal, and a frequency divider for dividing the frequency of the oscillation signal to the carrier frequency. The superheterodyne receiver further includes a pair of first mixers for frequency converting the object received signal into a pair of first intermediate-frequency signals using signals from the frequency divider as a first local oscillation signal, and a pair of second mixers for converting the first intermediate-frequency signals into a second intermediate-frequency signal with the second local oscillation signals. The superheterodyne receiver further includes a demodulator for demodulating the second intermediate-frequency signal into an original signal.

Abstract: In a frequency discriminator for a direct conversion receiver having a simple construction, in which operations for FM demodulation by direct conversion are simplified, two-signal components I and Q, which are inphase and quadrature, respectively, in a base band, obtained by direct conversion of an FM signal by means of a local oscillator, a 90.degree. phase shifter, multipliers, LPF and AMP are amplified to a predetermined amplitude and thereafter converted into digital signals by means of A/D converters. These digital signals are given to differentiators to obtain differentials (finite differences) thereof. These values are squared by means of squarers and squares thus obtained are added by means of an adder. An output of the adder is applied to a device for extracting square root to obtain a demodulation output of the FM signal. An ROM may be used in lieu of the squares and the device for extracting square root.

Abstract: Methods, systems, and apparatuses for down-converting an electromagnetic (EM) signal by aliasing the EM signal are described herein. Briefly stated, such methods, systems, and apparatuses operate by receiving an EM signal and an aliasing signal having an aliasing rate. The EM signal is aliased according to the aliasing signal to down-convert the EM signal. The term aliasing, as used herein, refers to both down-converting an EM signal by under-sampling the EM signal at an aliasing rate, and down-converting an EM signal by transferring energy from the EM signal at the aliasing rate. In an embodiment, the EM signal is down-converted to an intermediate frequency (IF) signal. In another embodiment, the EM signal is down-converted to a demodulated baseband information signal. In another embodiment, the EM signal is a frequency modulated (FM) signal, which is down-converted to a non-FM signal, such as a phase modulated (PM) signal or an amplitude modulated (AM) signal.

Abstract: A method and apparatus for passband communication using direct conversion avoids 1/f and DC-offset noises by shaping the spectrum of the signal so that it has little energy near zero frequency. After the receiver frequency down-converts the signal to baseband, it filters frequencies in the neighborhood of zero prior to demodulation. Since the spectrum of the signal was shaped by a coder prior to transmission so that it has little energy content near zero frequency, the filtering at the receiver eliminates 1/f and DC-offset noise without reducing significantly the energy of the desired information signal. After the noise has been filtered, the receiver demodulates and decodes the signal to recover the information signal. The coding can be based upon broadening of the amplitude range or the frequency range to create the required spectrum shaping.

Abstract: A mixer for use in a direct conversion receiver includes a compensating differential amplifier which injects equal amplitude opposite phase currents with respect to even order distortion currents. The compensating differential amplifier utilizes an ideal current source. The mixer is an active mixer which utilizes four switching transistors. The even order distortion is introduced by non-linear components which demonstrate strong off-channel signals.

Abstract: An RF quadrature signal generator (320, 370) is configured to receive a clock signal that is buffered by input buffer (404) and then coupled to a frequency divider (412) to produce a divided signal. The divided signal is coupled to a phase shift network (420) to generate a pulse train-pair wherein the two pulse trains of the pulse train-pair are in phase quadrature with one another. Limiting amplifiers (432 and 436) limit the amplitude of the pulse train-pair before they are coupled to a phase determining circuit (460) to generate a control signal representative of the relative phase difference between the amplitude limited pulse train-pair. The control signal is filtered and coupled to an op-amp integrator (474) to produce a feedback signal that is coupled to the phase shift network (420) in order to maintain the amplitude limited pulse train-pair in phase quadrature.

Abstract: A direct conversion receiver (200) is capable of recovering a filtered baseband signal (295) from a radio signal (201) modulated with a baseband signal (202). The direct conversion receiver (200) comprises a radio frequency mixer (205) for converting the radio signal (201) to the baseband signal (202), a lowpass amplifier (210) DC coupled to the radio frequency mixer (205), that amplifies the baseband signal (202) and substantially attenuates components of the baseband signal above a high corner frequency, and a DC offset compensation section (225) DC coupled to the lowpass amplifier (210), that provides a DC offset compensation and a controlled highpass filtering of the baseband signal. A low corner frequency of the DC offset compensation section is smoothly varied from a predetermined maximum value to a predetermined minimum value during a low frequency, low energy portion of the signaling protocol.

Abstract: A direct conversion tuner for tuning either analog or digital television signals includes a first and second channels, each having first and second mixers and an intervening filter stage, coupled between an RF input and an output combining unit. The first mixers receive respective first local oscillator signals which have the same frequency but a quadrature phase relationship. The frequency of the first local oscillator signals is controlled according to the selected channel so that it is located within the spectrum of the respective RF signal. The second mixers receive respective second local oscillator signals which have the same frequency but a quadrature phase relationship. The frequency of the second local oscillator signal is located above the passband of the filter stages.

Abstract: A system is disclosed which can measure and control the absolute phase angles of individual coherent Frequency-Division-Multiplexed (FDM) carriers which have been combined to form a composite signal. User-specified phase relationships for the carriers are predetermined to produce an optimum peak factor (peak power to average power ratio) of the composite signal for a given application. In the preferred embodiment, phase relationships chosen to minimize peak factor can dramatically reduce the presence of intermodulation distortion products which can be detrimental to present communication architectures, such as Community Antenna Television (CATV).

Abstract: A receiver circuit, particularly an integrated, zero IF receiver circuit in which a direct conversion IF stage is separated from an antenna by a further fequency conversion stage which is AC coupled to the direct conversion IF stage. A single crystal oscillator generates a frequency which is multiplied prior to being applied as a local oscillator signal to the further frequency conversion stage and is used to produce another frequency, which is divided to block harmonics, prior to being applied as quadrature related local oscillator signals to the direct conversion IF stage. The direct coversion IF stage includes several dc nulling for compensating for dc offsets.

Abstract: An apparatus and method performs a carrier signal acquisition operation in a receiver of a wireless portable unit. In order to locate and lock onto a carrier signal, a processor in the receiver is configured to sequentially examine each of a plurality of designated frequency bands within a predetermined frequency range, starting with the frequency band having the highest probability of containing the carrier signal. Through this acquisition operation, the carrier signal is easily located when outside of the normal search range of the processor. Since frequency errors due to, for example, the effects of variation and aging of hardware circuits are easily corrected, an inexpensive temperature compensated crystal oscillator may be employed in the receiver of the portable unit.

Abstract: An RF tuner and tuning method employs analog quadrature mixing with a coarse-stepwise tunable local oscillator to a near-baseband passband region, followed by A/D conversion of the I and Q signals, correction of phase, group delay, and amplitude errors, image rejection, and translation to baseband by (1) fixed frequency translation, (2) stepwise channelized translation, or (3) essentially continuously variable tuning over a given digital tuning range. The near-baseband passband region is sized and located such that alternating image rejection provides non-redundant and complete tuning coverage of a desired high frequency spectrum with a local oscillator step size equal to about twice the digital tuning range or about twice the number of channels digitally stepwise tunable times the channel width, effectively doubling the typical local oscillator step size. The digital tuning is preferably performed by a continuously variable bandpass decimating filter with aliasing to within R.sub.D of baseband, where R.sub.

Abstract: In accordance with the present invention, a receiver of the type receiving both a signal subjected to FM (Frequency Modulation) and a signal subjected to orthogonal modulation is capable dealing with the two different kinds of signal by use of a single demodulator. This successfully scales down the circuitry of the receiver.

Abstract: A method and apparatus for providing a homodyne cellular base station. A cellular antenna is coupled to both a conventional signal channel receiver a homodyne receiver. The conventional single channel receiver is configured to receive the control channel from a cellular band signal. The homodyne receiver utilizes a quadrature downconverter and local oscillator to receive the voice channels. The local oscillator is tuned to the frequency of the control channel to limit all DC offsets to the control channel within the homodyne receiver. All DC offsets and the control channel frequency are filtered from the homodyne receiver signal and, the filtered signal is then digitized and digitally processed to separate the signal into each of the traffic channels.

Abstract: A quadrature downconversion stage in a radio frequency receiver compensates for leakage from the quadrature local oscillator to the input of the stage by deriving first and second feedback signals from the quadrature local oscillator. The first feedback signal is 180.degree. out of phase with the in-phase component of the signal supplied to the input of the stage and the second feedback signal is 180.degree. out of phase with the quadrature component of the signal supplied to the input of the stage. The invention reduces or cancels a d.c. offset that can appear at the output of the stage. Another advantage is the reduction of re-radiated signals resulting from the local oscillator leakage. The invention is particularly applicable to direct converters.

Abstract: The device forms first and second signals by mixing the input radio signal with two respective quadrature waves of frequency f.sub.O. An algebraic sum of these two signals is phase-shifted by .+-.45.degree. or .+-.135.degree. at an intermediate frequency f.sub.I. An output signal is formed by an algebraic sum between the phase-shifted signal and the first or second signal, in such a way that, at the intermediate frequency f.sub.I, the output signal has a phase representative of that possessed by the input radio signal at a communication frequency f.sub.C of the form f.sub.O -f.sub.I or f.sub.O +f.sub.I, with rejection of the phase of the input radio signal at the image frequency 2f.sub.O -f.sub.C.

Abstract: A transceiver (10) in a first embodiment includes a zero intermediate frequency (ZIF) receiver (11), which achieves high throughput operation by reducing receiver latency time due to receiver response within a receiver pass band to carrier spectral components of a modulated carrier frequency. During a receive mode, a receiver local oscillator (LO) frequency is offset from the carrier frequency within the receiver pass band, preferably as determined by worst case errors in the carrier frequency and the LO frequency. During a transmit mode, the receiver LO frequency is modulated in such a way as to suppress the LO center frequency component in the modulated spectrum.

Abstract: To generate a fixed frequency offset in a direct conversion receiver (200) a phase ramp representing the frequency offset if generated. This phase ramp is combined with the demodulated phase component of a received signal. A phase wrap detection and compensation circuit (224) is capable of detecting and compensating for phase wrap that occur in the phase ramp by differentiating the input and detecting when a phase wrap is about to occur and causes a switch (316) to flip between two conditions. A first condition couples the phase ramp to the output. A second condition compensates when a wrap around has been detected. As such, a VCO (218) produces a local oscillator having a fixed frequency offset that is immune from locking problems that occur when a phase wrap is introduced.

Abstract: An integrated image reject mixer (150) generates precise quadrature components using highly matched local-oscillator (LO) path and intermediate frequency (IF) path resistor-capacitor (RC) phase shifting networks (131, 138). Because the LO signal from a local oscillator (127) has a constant amplitude, a phase detector (136) feedback loop easily maintains an accurate ninety-degree phase difference between the quadrature LO signals (122, 124) from the LO path phase shifting network (131). Because the two phase shifting networks are matched, the feedback control signal (137) from the phase detector (136) can also be used to maintain an accurate ninety-degree phase difference between the quadrature IF signals (123, 128) from the IF path phase shifting network (138) despite the dynamically-varying amplitude of the IF signal. Thus, this image reject mixer uses only components that may be easily integrated into an integrated circuit.

Abstract: An automatic balancing circuit for a radio frequency mixer which reduces LO-IF signal leakage, as well as minimizing second order harmonic distortion products is described. The circuit couples to in-phase and out-of-phase signal lines originating from the mixer, and comprises a differential gain network, a differential phase shift network and a combiner. The networks operate under the control of a microprocessor, which adjusts the networks so that the LO leakage signals, when combined, are almost completely eliminated.

Abstract: The invention pertains to a homodyne receiver and a process for direct conversion of angle-modulated carrier signals, especially those that have a d.c.-voltage component in the converted signal (IF). With many types of-modulation the (short-time) d.c. component of the conversion signal contains information about the modulating signal. Additional d.c. offsets are usually separated out by using a bandpass for the IF signal. In the process, however, the information-containing d.c. components of the converted signal are lost; as a result the demodulated signal is disturbed and in particular the distortion factor is raised. To avoid this the invention provides that the local oscillator for generating inphase and quadrature signals has a frequency offset from the carrier frequency of the receiver signal so that the frequency differential between carrier and frequency and oscillator frequency is in the transmission band of the bandpass used to suppress undesirable mixes, carrier reminders and d.c. offsets.

Abstract: Methods and apparatus for detecting, estimating, and compensating for unwanted d.c. offsets in sampled signals in a direct conversion receiver are described. These methods and devices can be used for varying d.c. offsets, ramps, and steps to realize a direct-conversion receiver for modem cellular communication systems that does not suffer performance degradation due to strong interferers.

Abstract: A low cost, high performance near direct conversion FM receiver having a single local oscillator is configured to equalize in-phase and quadrature-phase IF signals. The receiver includes a downconverter and a processor. The downconverter receives an RF signal and downconverts the RF signal to an in-phase IF signal (IF.sub.I) and a quadrature-phase IF signal (IF.sub.Q). The processor digitizes IF.sub.I and IF.sub.Q, corrects these signals so that they are substantially equal in magnitude and substantially 90.degree. out of phase, and then downconverts the IF signals to baseband signals (I, Q).

Abstract: A radio frequency receiver and method for operating one is disclosed. The receiver includes a tuning unit, an inphase-quadrature (I/Q) mixer, and a calibrated image rejection processor. The tuning unit selectably tunes to a tuning frequency close but not equal to an input modulated radio frequency and creates thereby a periodic signal having the tuning frequency. The I/Q mixer convolves the modulated radio frequency signal with inphase and quadrature versions of the periodic signal and low pass filters the resultant signals. The calibrated image rejection processor corrects at least one of the filtered resultant signals and performs image rejection on the corrected signals.

Abstract: In a homodyne receiver for the reception of a carrier frequency signal modulated with a low-frequency signal, the sensitivity of the detection of the low-frequency signal is enhanced by two auxiliary modulations before the conversion into the base band. The auxiliary signal utilized for an auxiliary modulation of the local oscillator signal and the supplemental signal employed for an auxiliary modulation of the carrier frequency signal comprise frequencies that can be technologically governed and with economic outlay and enable the simple decoupling of the low-frequency signal from the supplemental signal and, thus, an enhancement of the sensitivity of the homodyne receiver. The decoupling is particularly achieved by a band-pass filtering after the conversion of the carrier frequency signal into the base band, this band-pass filtering being tuned to a specific frequency relationship of the auxiliary signal and the supplemental signal.

Abstract: The invention relates to a transceiver for generating complex I/Q-signals on a transmission frequency (f.sub.TX) and for receiving them on a reception frequency (f.sub.RX). The device comprises a first frequency synthesizer (41) for forming a first mixer signal (f.sub.LI) for the mixer (42) of the first branch that mixes the I-component of the received signal into a lower-frequency I-signal, and a second frequency synthesizer (411, 49, 46) for forming a second mixer signal (f.sub.LQ) for the mixer (421) of the second branch that mixes the Q-component of the received signal into a lower-frequency Q-signal. The device further comprises control means (45) first for directing the phase of the first (f.sub.LI) and the second (f.sub.LQ) mixer signals into the same phase in the mixing effects thereof and, thereafter, into a 90 degree mutual phase shift in the mixing effects thereof when receiving signals for bringing the lower-frequency I- and Q-signals into a 90 degree mutual phase shift.

Abstract: A DBS receiver front end which converts the received signal directly to the baseband representation and maintains a high performance with a new techniques for tracking and counteracting frequency drift, and correcting I/Q angular error and amplitude imbalance. The DBS receiver front end comprises a tuner and a demodulator/decoder. The tuner receives a high frequency signal and converts it to a baseband signal having a frequency offset error. In one embodiment, the DBS receiver front end includes a demodulator/decoder which digitally performs I/Q angular error correction. The tuner converts the high frequency signal to a baseband signal having an in-phase and a quadrature-phase component. Ideally, the components are separated by ninety degrees, but typically an angular error exists. The demodulator/decoder includes an adaptive equalizer for correcting the angular error. Having the equalizer allows for relaxed tolerances in the tuner.

Abstract: A low power zero-IF selective call receiver has a local oscillator (106) that generates an injection signal for a first mixer (104) and a pair of quadrature phase related injection signals (122, 124) for a pair of second mixers (112, 114). The first mixer converts the received carrier signal (102) to an intermediate signal (108). A digital phase shifter/divider (116) coupled to the local oscillator (106) generates the pair of quadrature phase related injection signals (122, 124) at the frequency of the intermediate signal (108) which also equals the frequency of the local oscillator (106) divided by an integer greater then 1. The pair of second mixers (112, 114) coupled to the digital phase shifter/divider (116) converts the in and quadrature phase components (122, 124) of the intermediate signal (108) to respective in and quadrature phase baseband signals (126, 128).

Abstract: A homodyne radio receiving apparatus is provided for mitigating fixed or variable DC offsets produced by residual second order intermodulation terms due to unwanted signals. The homodyne radio receiving apparatus includes an antenna, an antenna by-pass filter, an RF amplifier and a quadrature downconverter. The quadrature downconverter for the complex base band is centered around a desired reception frequency so that the complex baseband signals lie around zero frequency. A supplementary total power detector is provided to measure the total received power through the antenna by-pass filter so that the unwanted terms caused by second order intermodulation are compensated. The compensation is achieved by feeding instantaneous power measurements to a signal processing unit along with the complex baseband signals. The signal processing unit then determines a complex compensation coefficient by correlating the power signal with the complex baseband signals.

Abstract: A digital mixer-filter-decimator (MFD) is disclosed which is reconfigurable so that it can be used in both modes of operation of a dual mode receiver such as an AM/FM receiver. In either mode of operation the MPD performs filtering and decimation operations on separate data streams containing alternate samples of a digital input data stream. In the FM mode a mixing operation is also enabled to produce a complex output comprising in-phase and quadrature components. The mixing operation is disabled in the AM mode and the filtered and decimated outputs are combined to provide a real output. The same decimator filter can be used in both modes.

Abstract: An FM receiver having an RF section, a first tunable mixer stage for the frequency conversion of a desired RF FM reception signal into a first intermediate frequency signal, an IF device and an FM demodulator. In order to enhance the integration of the apparatus, while maintaining a signal processing ability which is free from distortion, the FM receiver includes circuitry incorporated in the signal path for converting a single-phase signal into a pair of signals in mutual phase quadrature. The pair of phase-quadrature signals is applied to in-phase and quadrature signal paths of the IF device. The IF device having a polyphase IF filter incorporated in the in-phase and quadrature signal paths and has a bandpass characteristic which is symmetrical around its resonance frequency. The polyphase IF filter is coupled to the FM demodulator.

Abstract: In a homodyne receiver for the reception of a carrier frequency signal with time-variant carrier frequency, an auxiliary signal is modulated onto the local oscillator signal selected corresponding to the current carrier frequency. A better separation of the local oscillator signals is thereby achieved by a band-pass filtering after the conversion of the carrier frequency signal into the base band. Compared to a homodyne receiver with time-variant carrier frequency but without auxiliary modulation, the RF switch for the selection of the local oscillator signal corresponding to the current carrier frequency can be realized simple and more economical. This advantage of the homodyne receiver is of particular economic significance for employment in mass-produced articles, such as in mobile and wireless communication systems.

Abstract: A transceiver (10) in a first embodiment includes a zero intermediate frequency (ZIF) receiver (11), which achieves high throughput operation by reducing receiver latency time due to receiver response within a receiver pass band to carrier spectral components of a modulated carrier frequency. During a receive mode, a receiver local oscillator (LO) frequency is offset from the carrier frequency within the receiver pass band, preferably as determined by worst case errors in the carrier frequency and the LO frequency. During a transmit mode, the receiver LO frequency is modulated in such a way as to suppress the LO center frequency component in the modulated spectrum.

Abstract: An automatic gain control strategy for zero IF receivers in which the gain of low pass filters (20,22) is altered whilst keeping their bandwidths substantially constant. The low pass filters (20,22) are implemented as gyrator filters, each of which comprise at least one pair of transconductors, the ratio of the transconductances of which are adjustable in such a manner as to maintain the product of their transconductances constant. An electronic signal for adjusting the ratio of the transconductances is derived from an estimate of the instantaneous signal amplitude of the received signal.