A digital frequency upconversion and downconversion scheme for receivers and transmitters enables high resolution downconversion and upconversion, respectively, with low phase noise. A digital signal processor (DSP) (230) receives temperature measurement information from a temperature transducer associated with a reference oscillator (240), and also receives channel tuning and other information. The DSP adjusts the signal samples accordingly, without adjusting the operation of the oscillator. Additionally, the inventive filtering scheme, preferably implemented in an application specific integrated circuit (ASIC), receives digital filtering coefficient information, digital symbol timing phase control signals, and, in some cases, other information from the DSP. As a result, the scheme enables operation at 1 Hz resolution, with phase noise which is at least 33.5 dB down at 10 Hz in the case of downconversion, and at least 42 dB down at 10 Hz in the case of upconversion.

A digital frequency conversion and tuning scheme for microwave radio receivers and transmitters.

A constant-velocity universal joint (1, 31, 61) provided with an outside joint member (2, 32, 62), an inside joint member (3, 33, 63) arranged within the outside joint member (2, 32, 62), and a torque-transmitting member (4, 34, 64); a track groove (7, 9, 37, 39, 66) in which a rolling surface of the torque- transmitting member (4, 34, 64) engages being formed on the outside joint member (2, 32, 62) and/or the inside joint member (3, 33, 63), wherein the constant velocity universal joint is characterized in that at least one of the structural members of the constant velocity universal joint (1, 31, 61) comprises a metallic sintered body, the relative density of the metallic sintered body is equal to or greater than 80% and less than 100%, a layer hardened by heat treatment is formed on the surface of the metallic sintered body, and annular structural members comprising a metallic sintered body are subjected to cold-rolling.

Constant velocity universal joint

A disclosed method tunes a signal from a channelized spectrum having a predetermined channel spacing. A signal of interest having a predetermined maximum bandwidth is mixed with a local oscillator signal, which has a frequency that is an integer multiple of the channel spacing or one-half of a channel spacing displaced from an integer multiple of the channel spacing. The local oscillator signal is selected to frequency translate the signal of interest to within a near-baseband passband whose lower edge is spaced from DC by at least about the maximum bandwidth of the signal of interest. Problems associated with 1/f noise, DC offsets, and self-mixing products are avoided or substantially diminished. Other methods and systems are also disclosed.

Simplified high frequency tuner and tuning method

A digital signal processing (DSP) radio receiver employs a conventional analog RF tuner to produce an analog intermediate frequency. The receiver performs DSP functions of digitally sampling the analog intermediate frequency at a sampling rate fs, concurrently mixing, filtering, and sample-rate reducing the sampled intermediate frequency using a digital filter for inherently generating a near-zero complex intermediate frequency signal, and synchronously detecting the complex IF signal. In a preferred embodiment, the invention is employed to reproduce AM stereo signals.

Digital quadrature radio receiver with two-step processing

An apparatus for performing digital signal frequency translation in a digital receiver is disclosed. The apparatus uses a plurality of mixer-filter-decimator stages for performing the digital signal frequency translation. The translation function converts the digital signal to an intermediate frequency (IF), where such translation is distributed among the plurality of mixer-filter-decimator stages to thereby simplify the mixing requirements.

Multi-stage digital RF translator

A digital demodulator for separating and demodulating quadrature modulated signals to produce the inphase components and quadrature components of a baseband through simple digital processing. This digital demodulator is constructed by an A/D converter for sampling received modulated signal so as to be converted into digital signals, means for distributing every other sample signal of the sample signals from said A/D converter into two trains of the sample signals, means for inverting the polarity of every other signal of the one signal train so as to provide the inphase components of the baseband, and means for delaying the other signal sequence by one sampling period and thereafter inverting the polarity of every other signal of the delayed signals so as to provide the quadrature components of the baseband.

Digitally processed demodulator for quadrature modulated signals

A carrier recovery phase-locked loop for recovering a carrier from a digitized quadrature phase shift keying modulated wave arriving on time division basis comprises a PLL circuit, first unit, responsive to the received signal, for preparing a phase comparator's characteristic adapted for a binary phase shift keying modulated wave, second unit, also responsive to the received signal, for preparing a phase comparator's characteristic adapted for the quadrature phase shift keying modulated wave and switching unit for selectively supplying output signals from the first and second units to the PLL circuit. During reception of a preamble, the carrier is recovered using the binary phase comparator's characteristic through the PLL circuit.

Carrier recovery phase-locked loop

Disclosed is a digital demodulation technique in which a reception modulated-wave signal is converted into a digital signal in synchronism with a sampling frequency, whereafter carrier regeneration/detection is carried out upon the digital signal to thereby output a detection signal. Then, the detection signal is subject to interpolation and resampling on the basis of a clock frequency established asynchronously with and independently of the sampling frequency, so that a timing component is extracted from the detection signal in synchronism with the clock frequency to thereby output a reception data. In the digital demodulation technique, since the sampling frequency and the clock frequency are established asynchronously with and independently of each other, jitter or the like produced in clock regeneration do not affect the carrier regeneration/detection. Consequently, noiseless reception data with little jitters can be regenerated.

Digital signal processing type demodulation method and demodulation circuit

A quadrature phase modulator constructed by use of a simple digital circuit. Digital signals of sample data obtained by sampling outputs from a roll-off filter with a frequency four times a modulated carrier frequency are stored in an ROM, the outputs corresponding to all combinations of a plurality of successive bits of input data; the plurality of bits are set as an address, and a signal of an in-phase channel and a signal of a quadrature phase channel is alternately read from the ROM with a frequency equal to half the sampling frequency, then the obtained serial signals are subjected to a digital-to-analog conversion to obtain a quadrature phase modulated signal.

Digital modulation apparatus

A modulator for generating a burst-like modulated wave used in a multi-carrier transmission type communication system in which a plurality of modulated waves including at least one burst-like modulated wave exist on the same transmission line and the frequency band occupied by energy of each of the plurality of modulated waves is limited. Polarities of the transmission code which appear before and after either of on-timing and off-timing of the carrier on/off switched to obtain the burst-like modulated wave among the plurality of modulated waves are inverted to each other, whereby the envelope of the burst-like modulated wve can be changed gradually at the carrier on/off timing in order to reduce the interference of the modulated wave with the adjacent channels without degrading the transmission efficiency.

Yasufumi Takahashi

Papers

Digitally processed demodulator for quadrature modulated signals

Carrier recovery phase-locked loop

Digital signal processing type demodulation method and demodulation circuit

Digital modulation apparatus

Modulator for generating a burst-like modulated wave