Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
2001-01-08
2001-10-09
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S143000
Reexamination Certificate
active
06300892
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
Delta-sigma AD converters have been used for digitizing audio signals since approximately the mid-1980s. Numerous investigations and many scientific works over the last three decades have led to a growing field of use for these converters. Such a converter has a control loop whose forward path contains a loop filter and a quantizer and whose feedback path contains a D/A converter. Relatively high-order modulator structures and multibit D/A converters are now also increasingly used to try such converters for the higher-frequency range above the audio range.
Sigma-delta A/D converters sample the analog input signal at a much higher rate than so-called Nyquist converters. In this case, the amplitude resolution is traded for time resolution. A so-called decimation filter can be used, as previously, to generate a data stream with high resolution and at a low rate. The use of multibit D/A converters instead of single-bit D/A converters makes it possible to reduce the oversampling rate substantially on account of the lower quantization noise. In addition, loop filters with a relatively small phase margin and hence a relatively high low-pass filter range gain may be used, which permit an even better signal-to-noise ratio. However, the linearity is in this case essentially dependent only on the accuracy of the D/A converter, because the control loop of the modulator does not suppress the interference from the D/A converter. The oversampling during the delta-sigma modulation means that the interfering influence of the tolerance of the elements in the D/A converter on the useful signal can be significantly reduced using noise shaping. Without noise shaping, a correspondingly large number of D/A elements are selected in the D/A converter on the basis of an input signal, and their output signals are summed to form an output signal for the D/A converter.
In a manner which is known per se, the effects of production-related differences among the elements of the digital/analog converter can be significantly reduced by an appropriate element selection circuit. A corresponding method is described in Electronic Letters, Vol. 31, No. 20, Sep. 28, 1995, for example. To produce noise shaping, the D/A converter used in this context is a circuit including uniform delta-sigma modulators which are coupled through the use of a common vector quantizer. The vector quantizer ensures that the number of elements prescribed by the input signal are selected by the delta-sigma modulators, with specifically those modulators which have the largest output signal being selected. In this case, the vector quantizer also adopts the customary function of a quantizer for the delta-sigma modulation, because the feedback takes place via the output signal from the vector quantizer. To stabilize the entire system, the input signal taken for the delta-sigma modulation is the output component from the vector filter having the smallest value. The architecture presented in the prior art, with the corresponding stabilization through the use of the input signal, necessitates a high level of circuit complexity for the vector quantizer and additionally requires a minimum detection feature. In addition, the chosen structure for the delta-sigma modulators is very sensitive to coefficient errors and therefore requires coefficient multipliers having a large word length for complex filter structures.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a multibit D/A converter which overcomes the above-mentioned disadvantages of the heretofore-known D/A converters of this general type and which has a noise shaping such that the interference from the D/A converter on account of the component tolerances is significantly reduced and the additional circuit complexity mentioned above is avoided. It is a further object of the invention to provide a multibit delta-sigma A/D converter using the multibit D/A converter according to the invention.
With the foregoing and other objects in view there is provided, in accordance with the invention, a multibit digital/analog converter, including:
a multibit digital/analog converter input;
a 1/M divider circuit, M being an integer number;
M summers having summer inputs and summer outputs, respective ones of the summer inputs being connected, via the 1/M divider circuit, to the multibit digital/analog converter input;
a plurality of loop filters;
a plurality of quantizers having respective quantizer inputs and quantizer outputs, each of the summer outputs being connected, via a respective one of the loop filters, to a respective one of the quantizer inputs;
a plurality of DA elements having outputs;
a sorting logic circuit having a control input, sorting logic inputs, and sorting logic outputs;
the sorting logic inputs being connected to respective ones of the quantizer outputs, the sorting logic outputs being connected to respective ones of the DA elements, the control input being connected to the multibit digital/analog converter input;
the sorting logic circuit providing output signals fed back negatively to respective ones of the summer inputs; and
an output summer having output summer inputs respectively connected to the outputs of the DA elements, the output summer providing an analog output signal.
According to another feature of the invention, the quantizers provide, at the quantizer outputs, respective output signals with respective output signal magnitudes. The sorting logic circuit is configured such that the quantizers are sorted based on the output signal magnitudes, and only a given number of the DA elements is connected to given ones of the quantizer outputs, which provide largest ones of the output signal magnitudes. The given number of the DA elements is dependent on a signal at the multibit digital/analog converter input.
According to yet another feature of the invention, the loop filters have respective internal feedback paths.
According to a further feature of the invention, the loop filters include respective integrators and respective internal feedback paths. The integrators have respective limiters in the feedback paths.
With the objects of the invention in view there is also provided, an analog/digital converter configuration, including:
a multibit delta-sigma analog/digital converter having a feedback path;
a multibit digital/analog converter provided in the feedback path, wherein the multibit digital/analog converter includes a multibit digital/analog converter input; a 1/M divider circuit, M being an integer number; M summers having summer inputs and summer outputs, respective ones of the summer inputs being connected, via the 1/M divider circuit, to the multibit digital/analog converter input; a plurality of loop filters; a plurality of quantizers having respective quantizer inputs and quantizer outputs, each of the summer outputs being connected, via a respective one of the loop filters, to a respective one of the quantizer inputs; a plurality of DA elements having outputs; a sorting logic circuit having a control input, sorting logic inputs, and sorting logic outputs; the sorting logic inputs being connected to respective ones of the quantizer outputs, the sorting logic outputs being connected to respective ones of the DA elements, the control input being connected to the multibit digital/analog converter input; the sorting logic circuit providing output signals fed back negatively to respective ones of the summer inputs; and an output summer having output summer inputs respectively connected to the outputs of the DA elements, the output summer providing an analog output signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a linearized multibit digital/analog converter and its use in a multibit delta-sigma analog/digital converter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made t
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
Young Brian
LandOfFree
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