Floating-point analog-to-digital converter

Details Floating-point analog-to-digital converter Floating-point analog-to-digital converter

1999-08-18

2001-11-13

JeanPierre, Peguy (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Analog to digital conversion

C341S124000

Reexamination Certificate

active

06317070

ABSTRACT:

This invention relates to the kind of analog-to-digital (A/D) converters. The invention relates particularly to A/D converters with a wide dynamic range,
BACKGROUND
The input range of an A/D converter must be designed in such a way that the peak input signal is reliably covered. It means that when (1) the signal amplitude fluctuates in a very large dynamic range, (2) the quantization accuracy must be kept for the smallest signal and (3) the signal needs to be kept linear, a very high resolution A/D converter has to be used. In maw cases, high resolution is merely designed for covering the signal dynamic range rather than the quantization accuracy. For example, in order to obtain a 60 dB signal dynamic range and a minimum 6-bit quantization accuracy, the resolution must be at least 16-bit, a very high demand at high speed. Actually, in such a converter, the resolution for large signals are unnecessarily high. It would be more rational, if the converter offers the same resolution for large end small signals within this range.
Moreover, the trend of low power and low voltage reduces the actual input range, which makes the design of a wide dynamic range A/D converter more difficult since non-ideal factors like component mismatch and amplifier offset are not reduced with the reduction of supply voltage. In such a case, it is very difficult to satisfy large dynamic range with high resolution.
Traditionally, a logarithmic amplifier is used for compressing the signal amplitude in order to expand dynamic range. The accuracy, however, will be seriously degraded for a large compression ratio due to difficulties in designing the logarithmic amplifier. In order to produce linear digital output code a look-up table is usually used, which has to be matched with the amplifier precisely.
The demand on very high resolution A/D converter can be eliminated by the invented floating-point A/D converter, when the resolution is merely needed for covering signal dynamic range. Unlike the known logarithmic amplifier solution, the floating-point A/D converter gives a linear digital output directly. For large and small signals, the effective resolutions are kept constant (or quasi-constant to be accurate), similar to a floating-point number representation. Its resolution and dynamic range can be designed independently, which makes this invention very useful and flexible.
SUMMARY
The object of the invention is to provide a new approach to a wide dynamic range A/D converter in which dynamic rang and resolution are handled separately so high resolution imposed by wide dynamic range can be avoided.
The object is achieved by the invented floating-point A/D converter. Instead of using a single input amplifier, more than one amplifiers are used to produce multiple analog signals covering a wide dynamic range. Their amplifications are weighted in such a way that there is always one amplifier giving a linearly amplified analog signal with a suitable amplitude which will be selected and converted to digital output. The unused signals are either too small or too large (non-linear or saturated). If the amplification ratios are known, e. g. binary, it will be possible to combine the results to form a final digital output. A normal A/D converter is used for converting only the selected signals, which gives a constant resolution to different input signals. Since only the largest linearly amplified signals are sampled and converted, the reachable accuracy is higher than that of a normal A/D converter.


REFERENCES:
patent: 4449120 (1984-05-01), Rialan et al.
patent: 4774474 (1988-09-01), Beauducel et al.
patent: 4990913 (1991-02-01), Beauducel

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