Tektronix, Inc.

Cablebus Systems Corporation

Textronic, Inc.

Linley F Gumm

Xiaofen Chen

Thomas L Kuntz

Dana E Whitlow

Kyle L Bernard

Thomas C Hill

Jeffrey D Earls

Larry R Lockwood

Soraya J Matos

Clifford B Schrock

Walter D Fields

Steven R Morton

Leroy J Willmann

William Benedict

A system for simultaneous ACLR measurements encompassing multiple wireless communications channels provides a dual channel processing. The input signal is down converted to produce a wideband signal that is input simultaneously to both a wideband channel having a high speed, low resolution ADC and a narrow band channel having a low speed, high resolution ADC. The resulting data streams from the ADCs are processed by a DSP to provide the simultaneous ACLR measurements.

Simultaneous ACLR measurement

An improved self-adjusting I-Q modulator system has a quadrature modulated carrier output that is input to a waveform acquisition circuit for obtaining a full waveform from which both amplitude and phase measurements are obtained. Calibration occurs by setting respective I and Q inputs to the multipliers to zero and adjusting corresponding variable offset voltages to null the modulated carrier output. Then a voltage reference is selected by each I and Q input path in turn, and the amplitude and phase of the modulated carrier output for each I and Q channel are measured. Respective phase shifters for a carrier signal are adjusted to move the outputs of the phase shifters toward a quadrature relationship in response to the measured amplitude and phase of the full waveform. These steps are repeated until the phases of the I and Q channels are in quadrature.

Self-adjusting I-Q modulator system

A phase lock for a synthesizer phase reference oscillator that is used in conjunction with a conventional DDS circuit to synthesize an RF output frequency includes a second DDS circuit that is added with a reference increment value as an input to provide a phase offset frequency. A frequency/phase comparator compares a frequency reference oscillator output with the phase offset frequency to generate a control signal for phase locking the phase reference oscillator to the frequency reference oscillator. To determine the correct value for the reference increment value, a switch is provided between the frequency/phase comparator and the phase reference oscillator and the control signal is input to an analog-to-digital converter. During a 'turn on' procedure the resulting digitized control signal is observed by a control system as the reference increment value is adjusted until a slow ramp, positive or negative, in the control signal is observed. Then the switch is closed to allow the control signal to phase lock the phase reference oscillator coherently to the frequency reference oscillator. In this way coherence is achieved from unit to unit with a more precise frequency output.

Phase lock for synthesizer phase reference oscillator

A high speed x/sine(x) correction circuit for a digital to analog converter (DAC) functions by implementing a filter with an impulse response that approximates a sine(x)/x response. Each digital data value of an input signal to be converted by the DAC is considered a separate impulse. Each impulse, or initial pulse, is used to create a first reflection pulse by delaying the initial pulse by one clock cycle, inverting the delayed initial pulse and multiplying the delayed initial pulse by a constant less than one, such as dividing the delayed initial pulse by right-shifting the digital data value of the delayed initial pulse. The first reflection pulse is added to the input signal in the clock cycle it is generated prior to input to the DAC. A second reflection pulse may be generated in like manner from the first reflection pulse with an additional clock cycle delay for optimum results, both reflection pulses being added to the input signal in the clock cycle they are generated prior to input to the DAC.

High speed x/sine(x) correction circuit

An improved calibration method for a vector network analyzer stores sparse calibration data, interpolates system error data from the sparse calibration data for each measurement by the vector network analyzer, and creates calibrated measurement data from the system error data and uncorrected measurement data at each measurement frequency. The sparse calibration data may be generated by measuring every Nth frequency step over a calibration frequency range greater than a specified measurement frequency range, or by measuring every frequency step over the calibration frequency range and compressing the resulting measurement data. The interpolation may be achieved by using a curve-fit algorithm, such as a parametric polynomial curve fitting algorithm.

Calibration for vector network analyzer

A network analyzer using time sequenced measurements has a pair of switches for isolating respective mixers from a local oscillator source to ease problems caused by direct leakage from the signal source. The signal source is set to a desired measurement frequency and a local oscillator is set to a desired frequency so that, when mixed, a desired IF frequency is achieved. The signal source output is applied to a return loss bridge, to which also is coupled a device under test, and to a reference channel mixer. A return loss signal from the return loss bridge is applied to a test channel mixer. The LO output is applied in a time sequence via an LO switch first to the reference channel mixer and then to the test channel mixer. An output switch couples the respective mixers to a processor in the same time sequence to provide sequential measurements of magnitude and phase from which reflection coefficients are derived for the device under test. Likewise gain/loss measurements may be made by coupling the device under test between the impedance test port and a transmission test port, the transmission test port also being coupled to a transmission channel mixer to which also is input the LO output via the LO switch in the time sequence. The output of the transmission channel mixer is coupled via the output switch to the processor to obtain the gain/loss measurements.

Network analyzer using time sequenced measurements

A quality cause measurement display is formed by generating an ideal digitally modulated RF transmitter signal. A test instrument is used to measure an overall quality measurement for the transmitter signal as well as individual contributions by each transmitter parameter. Each measured parameter is used to modify the ideal transmitter signal, and a quality measure is determined using the quality measurement algorithm. The individual parameter quality measures are compared with the overall quality measurement to determine percentage contribution of each parameter to the overall quality measurement. From the percentage contribution an operator may understand what is causing problems in the transmitter signal when the overall quality measurement is out of limits.

Quality cause measurement display

An operational amplifier oscillator uses an operational amplifier as a low impedance driver for a resonator, the output from the operational amplifier being a voltage signal at the desired frequency. The operational amplifier has positive and negative feedback paths, with the negative feedback path having a first resistor for driving the impedance at the negative input to a small value when the voltage signal is near a zero crossing and an anti-parallel diode limiter in parallel with the first resistor with an optional series second resistor for driving the impedance at the negative input even smaller when the voltage signal swings away from zero. The positive feedback loop includes a series diode limiter or optional voltage divider. Phase noise is minimized by coupling a filter between the output and the positive feedback path to block the low frequency noise from the positive input of the amplifier.

Operational amplifier oscillator

Cable loss correction of distance to fault (DTF) and time domain reflectometer (TDR) measurements obtains distances to impulses representing reflections from a cable under test from a time domain representation of the cable. For each impulse a plurality of frequency data are generated and amplitude corrected based upon the cable loss at the given distance to the impulse. The resulting frequency data are then converted back to the time domain to present a time domain representation of a corresponding lossless cable showing the impulses at appropriate amplitudes. The impulses representing the reflections from the cable may be obtained by a vector network analyzer that obtains amplitude and phase data for a plurality of test signal frequencies, which data is then converted to the time domain to show the impulses and the distances of the impulses from the measurement end of the cable.

Cable loss correction of distance to fault and time domain reflectometer measurements

A direction finder using spread spectrum techniques has an array of antennas in a predetermined configuration for receiving a signal from a modulated, or interfering, signal source. The individual outputs from each antenna are input to respective direct sequence spread spectrum modulators where each is multiplied by a unique pseudo-random number (PRN) code, unique either in value or in time relationship. The spread spectrum outputs are summed and the summed output is demodulated and digitized to produce a digitized intermediate frequency (IF) signal. The digitized IF signal is processed by a digital signal processing (DSP) engine to determine relative phase or time of arrival of the signal from the modulated signal source at each antenna relative to one of the antennas used as a reference. The relative phases or times of arrival and the predetermined configuration of the antenna array are then used to estimate the direction to the modulated signal source with a high degree of accuracy.

Direction finder system using spread spectrum techniques

Reference frequency spur cancellation in a synthesized measurement receiver is achieved by determining for any given frequency to which the receiver is tuned a list of integer multipliers of the reference frequency that produce spurious signals in the receiver's passband. For those values the amplitude and phase for each spurious signal is determined in the digital domain and subtracted from the digital signal from the receiver. The reference frequency is then offset slightly and the measurement repeated. The maximum values between each measurement are combined to produce a measurement for the input signal without spurious signals.

Reference frequency spur cancellation in synthesized measurement receivers

An instrumentation receiver suitable for receiving a digitally modulated radio frequency input signal having a pilot signal at the RF frequency and symbol data generated at a symbol frequency generates a digitally modulated intermediate frequency signal having the pilot signal at the intermediate frequency equal to an integer multiple of the digital data's symbol frequency where the integer multiple is equal to or greater than one. A reference signal having a frequency equal to an integer multiple of the symbol frequency where the integer multiple is equal to or greater than one mixes with the IF signal to generate a control signal for controlling a local oscillator that generates a local oscillator signal for mixing with the digitally modulated RF input signal for locking the pilot signal to the reference signal. The instrumentation receiver is usable in a measurement test set for characterizing and monitoring an 8-VSB digital television transmitter or other digitally moduated RF signal containing a pilot at the carrier frequency.

Instrumentation receiver for digitally modulated radio frequency signals

A system for in-service nonlinearity measurements measures such nonlinearities by way of comparing received linear error-corrected unfiltered signal samples with re-generated reference signal samples to calculate magnitude and phase nonlinear error values. Linear distortion is removed from the received signal samples in order to truly characterize nonlinear behavior of the transmitter. The linear error-corrected received signal samples are generated without applying the receiver shaping filtering. Reference signal samples are re-generated from estimated transmitted symbols from the unfiltered linear error-corrected received signal samples. The transmitted symbols are estimated using a multi-region slicer which dynamically estimates constellation decision levels from the unfiltered signal samples. A weighted, least-square based polynomial regression is performed on magnitude and phase nonlinear error values to estimate magnitude and phase nonlinear error functions while suppressing the impact of other non-systematic distortions.

In-service measurement of transmitter nonlinearities

A system and method for in-service transmitter phase noise measurements determines phase nonlinearity by way of comparing unfiltered signal samples and regenerated reference signal samples to calculate phase nonlinearity error. Linear distortion is removed from the received signal samples in order to truly characterize nonlinear behavior of the transmitter. The unfiltered signal samples are generated without applying the receiver shaping filtering. Reference signal samples are regenerated from estimated transmitted symbols derived from the unfiltered signal samples. The transmitted symbols are estimated using a segmented slicer which dynamically estimates constellation decision levels from the unfiltered signal samples. A weighted, least-square based polynomial regression is performed on phase error samples of the unfiltered signal samples to estimate a phase nonlinear error function while suppressing the impact of other non-systematic distortions. The nonlinear phase error is removed from the phase error to produce phase noise containing carrier phase jitter and additive noise. A threshold is determined for replacing phase error values outside the threshold with random values having a distribution equivalent to the carrier phase jitter. The carrier phase jitter may be displayed as a power spectrum of the phase noise.

Measurement test set and method for in-service measurements of phase noise

A signal source provides an output signal which can sweep over a broad frequency range in a well-controlled manner. The signal source includes a voltage controlled oscillator (VCO) producing the output signal and a waveform synthesizer producing a reference signal. The VCO output signal is phase locked to the reference signal. To make the VCO signal continuously sweep over a broad frequency range, the reference signal sweeps repeatedly over a narrow frequency range. During each sweep of the reference signal, the VCO frequency tracks an integer harmonic of the reference signal frequency. The frequency and phase of the reference signal for each successive sweep are abruptly reset at the beginning of each sweep selected such that the VCO signal frequency locks to another integer harmonic of the reference signal frequency and does not change. Thus the VCO signal frequency sweeps continuously throughout the successive sweeps of the reference signal frequency but is unaffected by abrupt changes in reference signal frequency between successive reference signal frequency sweeps.

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Beaverton, OR, United States of America

Linley F Gumm