Coded data generation or conversion – Analog to or from digital conversion – Nonlinear
Reexamination Certificate
2000-03-02
2001-09-18
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Nonlinear
C341S155000
Reexamination Certificate
active
06292120
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the field of electronics and, in particular, to automatic gain control for an input to an analog to digital converter.
BACKGROUND
Analog to digital (A/D) converters are used in a wide variety of electronic circuits. An analog to digital converter is an electronic circuit that receives an analog input signal and produces a digital output signal. The digital output signal is produced based on samples of the analog input signal taken over time.
In some circuits, it is desirable to maintain the peak input voltage of the analog signal at or near the maximum value for the range of input signals accepted by the analog to digital converter. Thus, automatic gain control circuits have been used in conjunction with analog to digital converters. Typically, the automatic gain control circuit monitors the input to the analog to digital converter. The automatic gain control circuit further generates a feedback signal based on the monitored input signal. The feedback signal is provided to an amplifier to control the level of the input signal to the analog to digital converter. This feedback signal attempts to keep the peak voltage level of the input signal at or near the full-scale value of the input for the analog to digital converter.
Conventionally, the feedback signal is generated using analog circuitry. For example, such feedback loops typically include one or more of the following analog control blocks: a log amplifier, a summing amplifier, an integrator, and a differentiator. Unfortunately, these analog feedback control loops typically suffer from the so-called “clip” effect. This means that when the input signal exceeds the full-scale input for the analog to digital converter, the control circuitry is unable to quickly reach steady-state operation. Some control loops attempt to use digital circuitry. However, these digital control loops typically suffer from an additional problem relating to the quantization of the control word used to adjust the gain of the input signal for the A/D converter. In this situation, when the control loop reaches a steady-state, it tends to introduce an oscillation effect on the input signal to the A/D converter.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved automatic gain control circuit for an analog to digital converter input.
SUMMARY
The above mentioned problems with analog to digital converters and other problems are addressed by the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention use automatic gain control in a digital feedback path based on samples of the output of the analog to digital converter to create a feedback control circuit. An output of the feedback control circuit is compensated, when necessary, to account for an analog input that exceeds the full scale range of the analog to digital converter. Further, the output of the feedback control circuit is also compensated, when necessary, to set a feedback signal at a selected value to prevent oscillation due to quantization effects in the feedback path.
More particularly, in one embodiment an automatic gain control circuit for an analog to digital converter is provided. The automatic gain control circuit includes an input, coupled to an output of the analog to digital converter, to receive samples output by the analog to digital converter. The automatic gain control circuit also includes a digital to analog converter that is coupled to selectively adjust a magnitude of an input signal for the analog to digital converter. The automatic gain control circuit also includes a microcontroller. The microcontroller is coupled to the input and to the digital to analog converter. The microcontroller is programmed to generate a feedback signal for the digital to analog converter to control the amplitude of the input t digital converter.
REFERENCES:
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patent: 6204787 (2001-03-01), Baird
ADC Telecommunications, “DV 6000, Intermediate Frequency (IF) Video Encoders and Decoders”, pp. 1-4, Dec. 1998.
L.B. Jackson,Digital Filters and Signal Processing,Kulwer Academic Publishers, Boston, Chapters 6 and 11, 1986.
J.G. Proakis and D.G. Manolakis,Digital Signal Processing,Macmillan Publishing, Chapters 7 and 10, New York, 1992.
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Painchaud Dean
Wachter Lawrence J
ADC Telecommunications Inc.
Fogg Slifer & Polglaze, P.A.
Young Brian
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