Hewlett-packard Company

Intel Corporation

Stanford Telecommunications, Inc.

Allen P Edwards

Bruce Joseph Currivan

David R Gildea

Norman Franklin Krasner

Stuart L Carp

William G Xenakis

Chung Y Lau

A hybrid fiber/coax digital data transmission system in which data from a plurality of subscribers are transmitted upstream to a headend demodulator in a series of data bursts. The headend demodulator acquires and synchronizes a data burst by detecting a BPSK preamble having a repetitive one and zero pattern (10101010101000). The pattern is detected by integrating clock energy in an envelope of a preamble length transmission and using the last three symbols (0,0,0) as a frame marker after differential decoding. Noise in the system is periodically measured by detecting an empty burst placed periodically in the data stream. A first-in, first-out (FIFO) memory allows closer spacing for the data bursts by permitting asynchronous received and output clocks.

Burst demodulator for use in high speed bidirectional digital cable transmission system

A time division multiple access (TDMA) burst receiver and a method for recognizing and providing a time-of-arrival of a TDMA burst transmission having a selected preamble. The TDMA burst receiver includes a blanker for blanking the TDMA burst transmission when the signal level exceeds a pre-selected noise threshold, a signal threshold detector for providing a first tentative time-of-arrival when a correlation of the TDMA burst transmission and the selected preamble exceeds a first threshold and a second tentative time-of-arrival only when the correlation exceeds a second threshold within a selected time period following the first tentative time-of-arrival, and a state machine for providing an operational time-of-arrival corresponding to the first tentative time-of-arrival when the second tentative time-of-arrival is not received and the second tentative time-of-arrival when the second time-of-arrival is received. A demodulator synchronizes to the operational time-of-arrival for demodulating the TDMA burst transmission and providing an output data sequence. A sequence threshold detector issues a semaphore to the state machine to confirm the operation time-of-arrival when a sequence match between the output data sequence and a sequence of said selected preamble exceeds a sequence match threshold.

TDMA burst receiver

In accordance with the teachings of this invention, a multi-path distortion simulator is constructed having two paths, one path including a delay means, and both paths including phase shifters and attenuators. The phase shifters are closely matched, thereby compensating for drift and errors in the phase shifters. Similarly, the attenuators are closely matched, thereby compensating for drift and errors in the attenuators.

Multi-path fading simulator

A phase shifter providing constant group delay and a wide instantaneous bandwidth is taught. In one embodiment, an input port is connected to an output port with a power splitter formed of a transformer connected between the input port and the output port, and having a center tap serving as a sum port. An impedance, such as a resistor, is connected in parallel with the transformer between the input port and the output port. A reactive network is connected between the sum port and ground, including one or more variable reactance device, such as a varactor, which alter the reactance of the reactive network in response to a control signal. Additional reactive elements are included in the reactive network to provide additional poles and zeros which change frequency in response to the variable reactance elements, in order to provide a group delay which is constant for various reactance values provided by the reactive network between the lowest frequency of interest and a higher frequency of interest.

Tunable phase shifter having wide instantaneous bandwidth

A novel vector signal generator is provided which includes a vector modulator controlled by baseband manipulation circuitry. The output signal from the vector modulator is down converted to a desired output frequency. The baseband manipulation circuitry provides, under digital control from, for example, a microprocessor, adjustments to the phase, carrier leakage, and modulation levels of the I and Q signals. In this manner, a highly accurate vector modulated signal is generated within a wide range of carrier frequencies.

Vector modulation signal generator

A low phase noise RF synthesizer comprises three phase-locked loops. In the preferred embodiment, the base RF signal, 980 to 1520 MHz in 20 MHz steps is generated by one loop, while the high resolution IF signal is generated by a fractional-N loop. The RF and IF signals are combined in a third phase-locked loop, the output sum loop, to produce the output signal. A programmable variable divider divides the IF output frequency, achieving coverage over the necessary frequency range by changing the divide number, so the fractional-N circuit only has to fill in the fine steps between the divide numbers. A reference input frequency in the fractional-N loop has each of the factors 2, 3, and 5 in its divisor, so that the output signal of the synthesizer can be multiplied by any of these factors without producing a fractional frequency. It will be appreciated that the advantages achieved by the aspects of the invention incorporated in certain portions of the synthesizer described have independent utility and could be used in a variety of synthesizer designs. This is particularly true for the variable divider, e.g., divider 191, in the IF reference loop output and for the multi-factor divider, e.g., divider 187, in the IF reference loop input.

Low phase noise RF synthesizer

Calibration of a vector modulator is done using a scalar detector to measure the amplitude of the RF output signal, phase shifters to adjust the relative phases of the I and Q components of the RF carrier, and variable attenuators in the I and Q modulation signal input lines to adjust the relative amplitude of the modulation signals. DC signal sources provide reference signals for the I and Q modulation inputs, carrier leak compensation signals, and calibration signals for balancing the amplitude of the I and Q modulation signals. An iterative four step calibration process is followed until no change in the results is observed. The quadrature phase error is minimized by adjusting the phase shifters. The carrier leakage is minimized by adjusting the carrier leak compensation sources to minimize RF output with the modulation inputs grounded. The amplitudes of the I and Q modulation signals are balanced by adjusting the attenuators until the output amplitudes are equal. Finally, the quadrature calibration signal sources are adjusted until the output amplitudes they produce are balanced.

Calibration of vector modulators using a scalar detector

A digital circuit for use in a power meter provides relative power measurements by storing a value representing a first power measurement and using that value as a reference for processing subsequent power measurements.

Apparatus for relative power measurements in a power meter

A power meter having a remote power transducer is provided with a circuit for measuring the value of a resistor in the transducer to indicate and automatically adjust the power measuring circuitry for the sensitivity of the transducer used.

Growing community of inventors

Palo Alto, CA, United States of America

Allen P Edwards