Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – With auxiliary means to condition stimulus/response signals
Reexamination Certificate
1998-07-31
2001-09-04
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
With auxiliary means to condition stimulus/response signals
C324S076540
Reexamination Certificate
active
06285197
ABSTRACT:
FIELD OF THE INVENTION
In common information-handling systems a signal is sent from a transmitter to a receiver. For example, a video signal, either digital or analog, is generated by a camera and transmitted to a video tape recorder. The signal is transmitted from the recorder using the tape to a video tape player. Then the video may be transmitted from the player through a cable television system to a television monitor. In another example, a disk drive may generate a digital signal that is transmitted to a port of a computer system and the computer system transmits the digital signal to another computer system through a computer network.
In many such information transmission systems, transmission errors may occur in reception due to a phenomenon referred to by those skilled in the art, as jitter. Jitter describes a particular type of dynamic timing error which occurs in the signal generation, in the transmitter, or in the transmission media. In jitter, the error is dynamic in that the level or amount of timing error varies with time. In jitter, the level of the timing error may vary randomly or periodically and the error usually varies around an ideal or correct timing. The speed or frequency with which the error varies may also change over time. In the arts of phonograph recording and playback and tape recording and playback, this jitter is sometimes referred to as wow or flutter.
Because jitter is generally undesirable in information transmission and often disabling, sophisticated information handling equipment such as transmitters and receivers often include apparatus to ameliorate or compensate for the effects of jitter so that the equipment operates correctly even when input signals include jitter. For example, a transmitter may include a system to reduce or eliminate jitter so that the transmitted signal jitters less than the input signal. A receiver may include circuitry to recognize jitter in the received signal and to modify the signal to eliminate or at least reduce the jitter or recognize signals despite jitter.
BACKGROUND
FIG. 1
shows a typical example of an existing jitter generation system
10
. A jitter controller
11
is coupled to a frequency control input of a controllable oscillator
12
which provides a clock output depending on the input control signal. For example, the clock may be a voltage-controlled oscillator (VCO) which provides a clock signal at a frequency depending on an input voltage that depends on the jitter control. The result is that the clock output is phase or frequency modulated by the jitter control signal provided by the jitter control. The clock output is connected to the clock input of a test signal generator
13
. Then the jitter generation system produces a test signal such as a sine wave or square wave with a frequency that deviates slightly with time depending on the voltage signal from the jitter generator.
Those skilled in the art are referred to U.S. Pat. Nos. 3,558,933 to Meyer, 4,797,586 to Traa, 5,175,454 to Murakami, 5,534,808 to Takaki, 5,572,159 to McFarland, and 5,777,501 to AbouSeido. These patents are related to digital delay lines.
The above citations are hereby incorporated herein in whole by reference.
SUMMARY OF THE INVENTION
Some test signal generation equipment does not have an input for a clock signal or does not provide stable operation when the clock signal is jittered. Most signal generators are designed and optimized to provide a stable signal, and destabilizing the clock signal to provide jittering often will not provide satisfactory jittering. The test output may become unjittered, irregular, or chaotically unstable.
When developing equipment or during production of equipment, especially digital or analog video and audio transmitters and receivers, it would be useful to test the equipment, or at least parts of the equipment, using actual signals such as sample audio or video signals that jitter. Then apparatus for reducing the effects of jitter could be developed that compensated for jitter that listeners or viewers found disturbing, rather than compensating for some theoretical wave pattern that may not even have the same effect on the equipment as an actual sample signal that is jittering. Equipment could more easily and reliably be designed and produced that operated correctly with jittering input. In the invention described herein, a test signal is produced for testing equipment. The test signal is modified by routing it through a variable delay circuit. A control signal is generated to control the variable delay circuit so that a delayed test signal jitters. The jittering test signal is used to test equipment to determine the effect of the jittering signal on the equipment.
The invention avoids the need for destabilizing the operation of the test signal generator. Existing signal generators do not have to be modified to utilize the invention since only the signal is modified after it is generated. This is possible because the invention allows separation between the initial signal generation and the jittering of the test signal. The invention also allows sample signals, such as video patterns, to easily be used as signal sources by subsequently jittering these signals for use as jittering test signal. For example a tape player can provide a stable test signal and a jitter unit can jitter the signal, and if desired, the jittering signal can be recorded and later played back to provide a jittering test signal. Depending on the design of the variable delay circuit and the type of testing required, it will be possible in some cases, to use the same delay unit for providing both jittering analog signals and jittering digital signals.
Other alternatives and advantages of applicant's inventions will be disclosed or become obvious to those skilled in the art by studying the following detailed description with reference to the following drawings which illustrate elements of the claimed inventions.
REFERENCES:
patent: 3558933 (1971-01-01), Meyer
patent: 4797586 (1989-01-01), Traa
patent: 5175454 (1992-12-01), Murakami
patent: 5191234 (1993-03-01), Murakami et al.
patent: 5534808 (1996-07-01), Takaki et al.
patent: 5572159 (1996-11-01), McFarland
patent: 5777501 (1998-07-01), Abouseido
Kerveros J
Metjahic Safet
Philips Electronics North America Corporation
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