Coded data generation or conversion – Converter calibration or testing
Reexamination Certificate
1997-11-25
2001-07-03
Wamsley, Patrick (Department: 2819)
Coded data generation or conversion
Converter calibration or testing
C341S118000
Reexamination Certificate
active
06255971
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an analog-to-digital (A/D) conversion arrangement and a method in which digital codes are obtained on the basis of respective comparisons between an input signal and at least one reference level. The invention also relates to a signal processing device incorporating such an A/D conversion arrangement.
U.S. Pat. No. 4,831,379 describes a prior-art A/D converter. The prior-art A/D converter comprises an array of 64 input amplifiers. Assuming that i is an integer ranging from 0 to 63, each amplifier Ai amplifies the difference between an analog input voltage and a corresponding reference voltage VRi to produce an amplified output voltage VAi. The amplified output voltages VA
0
-VA
63
are processed in a folding array and an interpolation circuit to produce complementary signals VD
0
/VDN
0
. . . VD
31
/VDN
31
, from which signals an output circuit derives a digital output code.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a type of A/D conversion which, with respect to the background art, allows a better A/D conversion characteristic.
The invention takes the following aspects into consideration. An A/D conversion characteristic is substantially determined by one or more reference levels with which an input signal is effectively compared. In practice, the reference levels with which the input signal is effectively compared deviate to a greater or lesser extent from nominal reference levels with which an optimal A/D conversion characteristic would be obtained if there were no such deviation. The reason for this deviation is that components which, in combination, carry out the A/D conversion suffer from tolerances, temperature dependency, and the like. This not only applies to reference level components which, in combination, provide the reference levels with which the input signal is compared, but it also applies to conversion components which, in combination, carry out the comparison and additional operations in order to obtain a digital code.
In accordance with the invention, the input signal and the respective reference level are interchanged in respect of at least one comparison. If the conversion components were ideal, digital codes obtained before and after an interchange would only differ in sign but not in magnitude, for a certain input signal level. However, since the conversion components suffer from tolerances, temperature dependency, and the like, the digital codes will differ in magnitude as a result of the interchange. In accordance with the invention, the digital codes are processed to obtain digital output codes whose respective signs and magnitudes are, at least on average, substantially independent of any interchanges. This substantially reduces the adverse effects that tolerances, temperature dependency, and the like may have on the A/D conversion characteristic. As an example, in an A/D conversion based on a plurality of reference levels which are nominally equidistant, the invention allows a substantially better linearity than the background art.
Other advantages of the invention are as follows. A satisfactory A/D conversion characteristic can be obtained with components which, with respect to the background art, need to meet less stringent requirements in terms of tolerances, temperature dependency, and the like. Consequently, the invention also allows more cost-efficient implementations than the background art, for example, implementations with MOS transistors only. Another consequence is that, if the A/D conversion is implemented as an integrated circuit, smaller components can be used than in the background art. Smaller components have smaller parasitic capacitances, which is beneficial to the high-frequency properties of the A/D conversion. Furthermore, smaller components leave more room for other circuitry than A/D conversion circuitry. Thus, the invention is particularly suitable for combining A/D conversion and digital signal processing in a single signal processing device, for example in the form of an integrated circuit.
The invention and additional features, which may optionally be used to implement the invention to advantage, are apparent from and will be elucidated with reference to the drawings described hereinafter.
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PHN 15,450, U.S. Patent Application Serial No. 08/704,198, filed Aug. 28, 1996.
PHN 15,909, U.S. Patent Application Serial No. 08/709,401, filed Sep. 4, 1996.
van de Plassche Rudy J.
Venes Arnoldus G. W.
U.S. Philips Corporation
Wamsley Patrick
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