Coded data generation or conversion – Analog to or from digital conversion – Increasing converter resolution
Reexamination Certificate
2000-03-14
2001-07-31
Phan, Trong (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Increasing converter resolution
C341S155000
Reexamination Certificate
active
06268814
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to analog-to-digital converters and, more particularly, relates to a technique for improving the accuracy of an analog-to-digital converter.
2. Description of the Related Art
Digital processing of analog signals becomes an increasingly attractive alternative to analog processing as digital hardware becomes increasingly faster, more sophisticated, and more integrated. Also, digital systems are, in general, inherently more flexible and less sensitive to time and temperature fluctuations than analog systems. As a result, a great effort has gone into the development of analog-to-digital converters (ADCs) for transforming an analog signal to a digital representation of that signal with ever-increasing accuracy, speed, and resolution.
Analog-to-digital conversion involves amplitude quantization, where an analog input signal, which may vary continuously over a finite amplitude range, is sampled at a uniform sampling rate to map the analog input signal to a finite number of discrete amplitudes. The input signal dynamic range of an ADC is divided into a specified number of possible discrete amplitudes (i.e., quantization levels), where the number of discrete amplitude levels specifies the resolution of the ADC. For example, an ADC having 2
m
quantization levels generates an m-bit digital output signal, where the value of m defines the resolution of the ADC.
Another important characteristic of an ADC is its linearity (or accuracy), which is a measure of the variance, from a straight line, of the ADC transfer function, i.e., the characteristic mapping of the input signal to the corresponding output signal. Non-linearity in an ADC transfer function typically results in conversion spurs, which are fictitious signals appearing in the frequency domain (e.g., during fast Fourier transform (FFT) analysis) of signals having discontinuities that are associated with deviations from a purely linear response. Most existing techniques for increasing the accuracy of an ADC rely on analog domain methods to minimize the error due to the presence of internal and external noise sources, and to maximize the accuracy and the time and temperature stability of the analog components in the ADC.
For many applications, such as telecommunications, it is important to have low noise at steady state in the absence of an input signal, and a high signal-to-noise ratio when an input signal containing one or more carriers is present at the ADC. Accordingly, it would be useful to provide an improved ADC that reduces the conversion spurs associated with non-linearity of the ADC transfer function.
SUMMARY OF THE INVENTION
The present invention is directed to a technique for increasing the accuracy of an ADC. According to embodiments of the present invention, an analog dither signal is added to the analog input signal prior to amplitude quantization. The dither signal of the present invention has a variable amplitude that is controlled by a processor that analyzes the quantized digital representations of the dithered input signal to determine the appropriate amplitude for the dither signal to be added to the analog input signal. The amplitude of the dither signal is based on the power levels of one or more carriers present in the analog input signal. The addition of the dither signal reduces unwanted conversion spurs caused by non-linearities in the ADC transfer function.
In one embodiment, the present invention is an analog-to-digital converter (ADC) for converting an analog input signal into a digital output signal, comprising (a) a dither signal generator, configured to generate an analog dither signal; (b) a signal coupler, configured to add the analog dither signal to the analog input signal to generate a dithered analog signal; (c) an amplitude quantizer, configured to digitize the dithered analog signal to generate the digital output signal; and (d) a processor, configured to analyze the digital output signal to generate a control signal for controlling the amplitude of the dither signal generated by the dither signal generator, wherein the processor generates the control signal based on a measure of total instantaneous power level of one or more carriers in the analog input signal.
In another embodiment, the present invention is a method for converting an analog input signal into a digital output signal, comprising the steps of (a) generating an analog dither signal; (b) adding the analog dither signal to the analog input signal to generate a dithered analog signal; (c) digitizing the dithered analog signal to generate the digital output signal; and (d) analyze the digital output signal to generate a control signal for controlling the amplitude of the dither signal, wherein the control signal is based on a measure of total instantaneous power level of one or more carriers in the analog input signal.
REFERENCES:
patent: 5252973 (1993-10-01), Masuda
patent: 5493298 (1996-02-01), Bartz
patent: 5940138 (1999-08-01), Lowe
patent: 5963157 (1999-10-01), Smith
patent: 6016113 (2000-01-01), Binder
patent: 6064328 (2000-05-01), Scheidig et al.
Lucent Technologies - Inc.
Mendelsohn Steve
Phan Trong
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