Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
2000-05-02
2002-11-12
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Parameter related to the reproduction or fidelity of a...
C324S076230, C455S067700, C455S067700
Reexamination Certificate
active
06480006
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of automatic test equipment for testing electronic signals, and more particularly, to automatic test equipment for analyzing the noise component of an electronic signal.
BACKGROUND OF THE INVENTION
Automatic test equipment for testing the performance of communications systems, radar systems, and other signal producing devices are known. In this regard, it is often necessary to evaluate the spectral purity of a signal produced by a unit under test (UUT) in order to determine if the UUT is operating within the manufacturer's or end user's specifications. Specifically, a manufacturer or end user may specify the maximum phase noise which may be present on a signal produced by the UUT. The phase noise of a signal is a measure of the random phase instability of the signal.
The phase noise of a UUT can be measured in a variety of ways. For example, the output signal of the UUT can be applied directly into the input of a spectrum analyzer which will display the power spectral density of the signal and the phase noise will be visible in the display as random noise power in the spectral plot. Alternatively, the phase noise can be measured using a second signal source as a reference. The second signal source outputs a signal which is identical to or better than the expected UUT signal, but in phase quadrature (if phase modulation noise is being tested) to the UUT signal, i.e., the second signal source is at the same frequency as the UUT signal, but is phase shifted by 90 degrees. The UUT and the second signal source are input into a mixer and, since the two signals have the same carrier frequency, the signals cancel each other out, leaving a signal comprising the combined phase noise of the UUT and the second signal source. In addition, the phase noise may be measured using the Down Converter/Multiple Direct Spectrum Measurement Technique, which is described in U.S. Pat. Nos. 5,337,014 and 5,179,344, the specifications of which are hereby incorporated by reference herein.
Conventionally, when a UUT signal is analyzed, the technician uses a variety of discrete components including a programmable down converter for translating the input signal into a lower, and more easily analyzed, frequency; a narrow FM tunable synthesizer for generating a reference signal, and a separate spectrum analyzer. Since each of these components has its own unique programming requirements, significant time and effort is often spent programming and integrating these discrete components into an effective phase noise measurement system.
With respect to prior art, U.S. Pat. No. 5,508,661 (Keane et al.) describes a fast tuning YIG frequency synthesizer using a fixed oscillator driving a comb line generator to generate a spectrum of comb lines, one of which is selected by a switched array of fixed-tuned, YIG passband filters. The selected comb line is combined in a mixer with a signal from a local oscillator, which, preferably, is a direct digital synthesizer. The output of the mixer is fed to another switched array of fixed-tuned YIG passband filters where only the desired sideband is selected and the comb line and the other sideband is filtered out. In various alternative embodiments, tunable YIG filters are substituted for each array. Some embodiments also use a reverse slope equalizer to break up the coherent energy in the comb line spectrum at the output of the comb line generator to allow RF amplification to be applied without saturating the amplifier.
U.S. Pat. No. 5,770,977 (Uurtamo) describes a microwave frequency synthesizer with ultra-fast frequency settling and very high frequency resolution. The synthesizer purportedly provides the ability to achieve ultra-fast frequency settling times with good frequency resolution and high absolute accuracy over significant bandwidth at microwave frequencies ranging over three octaves. The implementation is an open-loop system requiring little or no compensation of temperature. This is accomplished by providing a frequency doubled direct digital synthesizer output to up/down convert a microwave frequency source. A special tracking filter architecture coupled to the microwave source provides the suppression of unwanted products. Fixed frequency set-on and swept bandwidths in excess of 300 MHz have been demonstrated. This is accomplished by using a direct digitally synthesized quadrature phased carrier which can be set to any frequency within a 350 MHz bandwidth to coherently up/down convert a low phase-noise microwave frequency to the sum or the difference frequency product. Individual control of differential phase and amplitude over frequency assures very high suppression of unwanted products without the use of additional filtering.
U.S. Pat. No. 5,053,714 (Durand) describes a measuring circuit for the additive phase noise characteristic of a component in the vicinity of a carrier frequency. The measuring circuit is constructed of a central channel and two side channels. Each of these channels contains a model of the component to be characterized. Two phase detecting circuits are employed in which each processes an input signal from one of the side channels with an input signal from the central channel to generate signals which represent phase deviations between the two input signals. An intercorrelation circuit then utilizes the outputs from these phase detecting circuits to determine the characteristic additive phase noise of the component to be characterized by eliminating any additive phase noise superadded by other measuring circuit elements or induced by outside disturbances.
U.S. Pat. No. 5,412,325 (Meyers) describes a phase noise measurement system and method in which three independent signal sources are used to statistically derive the power spectral density of the phase noise content of signals from each of them. This is accomplished by mixing each of the signals two at a time (i.e., signal one with signal two, signal one with signal three, and signal two with signal three) and capturing the resultant difference signals, such as with a waveform recorder, for example. A servo electronics loop is used to remove the carrier and any long term signal drift from the resultant difference signals. Statistical analysis is then used to compute the composite power spectral densities of the resultant difference signals, and to solve for the individual power spectral densities of the original signals. The system and method uses the mathematical relationships between the three sources that have similar magnitudes of phase noise, to compute the power spectral density of the noise content of signals from each source. The system and method purportedly requires a minimum of interconnect hardware and only three inexpensive waveform recorders. Furthermore, the size, weight, and cost of producing the present phase noise test system is said to be relatively low.
U.S. Pat. No. 5,608,331 (Newberg et al.) describes a noise measurement test system for making phase noise and amplitude noise measurements of microwave signals derived from a continuous wave RF source. The system comprises an RF input for receiving an applied RF noise signal and an RF coupler coupled to the RF input for splitting the applied RF noise signal into first and second paths. A mixer that comprises a synchronous phase detector is coupled to receive signals from the first and second paths and which outputs demodulated phase noise. The first path comprises a variable attenuator and a variable phase shifter coupled between the coupler and the first input of the mixer for providing a reference signal input to the synchronous detector. The second path comprises a delay line and an adjustable RF carrier nulling circuit coupled between the coupler and the mixer. A video amplifier is coupled to an output of the mixer for providing a baseband video output signal from the system that is processed to produce noise data.
U.S. Pat. No. 4,748,399 (Caldwell et al.) describes a multichannel phase noise measurement system which is purportedly capable of m
Advanced Testing Technologies Inc.
Deb Anjan K.
Le N.
Roffe Brian
LandOfFree
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