Tests for non-linear distortion using digital signal processing
First Claim
1. A test system for measuring a non-linear distortion created by a reference test signal transported on a signal path comprising:
- a transmitter for transmitting the reference test signal;
a receiver, for receiving an impaired reference test signal, wherein the impaired reference test signal comprises the reference test signal as impaired while passing between the transmitter and receiver through the signal path;
a digital signal processor connected to an output of the receiver to receive the impaired reference test signal from the receiver, the digital signal processor;
storing a copy of the reference test signal;
computing an impulse response of the signal path using the copy of the reference test signal and the impaired reference test signal;
calculating the energy in the impulse response during time periods of the impulse response that contain primarily non-linear distortion energy.
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Accused Products
Abstract
A system for determining a composite signal level at which a signal path begins to generate non-linear distortion. A reference test signal, which is preferably a short-duration burst of repeatable broadband energy, is passed through the signal path and received on a digital signal acquisition unit. An impaired received reference test signal is comprised of the transmitted reference test signal, linear distortion components, and non-linear distortion components. The impaired received reference test signal is digitally processed to reveal the non-linear distortion components. The impaired received reference test signal may be processed with a stored reference test signal to find a time-domain impulse response from which the uncorrelated distortion energy can be measured. Alternately, a reference test signal, such as an orthogonal frequency division multiplex (OFDM) reference signal with spectral holes, can be processed in the frequency domain to find the non-linear distortion energy that enters the spectral holes. Alternately, a transfer function of a signal path, showing an output voltage as a function of an input voltage, can be generated from a two-burst waveform comprised of a clipping high-level sinewave and non-clipping low-level sinewave. As the reference test signals are elevated in level, the magnitude of the non-linear distortion products can typically be observed to increase.
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Citations
18 Claims
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1. A test system for measuring a non-linear distortion created by a reference test signal transported on a signal path comprising:
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a transmitter for transmitting the reference test signal;
a receiver, for receiving an impaired reference test signal, wherein the impaired reference test signal comprises the reference test signal as impaired while passing between the transmitter and receiver through the signal path;
a digital signal processor connected to an output of the receiver to receive the impaired reference test signal from the receiver, the digital signal processor;
storing a copy of the reference test signal;
computing an impulse response of the signal path using the copy of the reference test signal and the impaired reference test signal;
calculating the energy in the impulse response during time periods of the impulse response that contain primarily non-linear distortion energy. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
calculating one of;
a total energy in the impulse response, or the energy in the impulse response during time periods of the impulse response that contain primarily signal energy correlated to the reference test signal;
calculating a ratio based on the energy during time periods that contain primarily non-linear distortion energy and one of;
the total energy in the impulse response, or the energy during time periods that contain primarily signal energy.
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12. A test system for measuring a non-linear distortion created by a signal path comprising:
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a transmitter for transmitting a reference test signal wherein the reference test signal comprises an OFDM reference test signal having at least one spectral hole;
a signal path;
a receiver for receiving an impaired reference test signal comprising the reference test signal as impaired while passing between the transmitter and receiver through the signal path;
a digital signal processor connected to an output of the receiver for measuring a total amount of energy within the impaired reference test signal and for measuring an amount of energy within the at least one spectral hole;
wherein the non-linear distortion energy is determined from the energy contained within the at least one spectral hole. - View Dependent Claims (13)
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14. A test system for determining a transfer function of a signal path comprising:
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a transmitter for transmitting a two-burst waveform comprised of a low-level sinewave part and a high-level sinewave part;
a signal path;
a receiver for receiving the two-burst waveform as impaired while passing between the transmitter and receiver through the signal path; and
a digital signal processor connected to an output of the receiver for determining a non-linear transfer function of the signal path by plotting the time samples of the low-level sinewave on a first axis and delayed time samples of the high-level sinewave on a second axis. - View Dependent Claims (15, 16, 17, 18)
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Specification