Coded data generation or conversion – Analog to or from digital conversion – With particular solid state devices
Reexamination Certificate
2001-08-30
2002-05-14
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
With particular solid state devices
C341S143000, C327S100000, C327S101000
Reexamination Certificate
active
06388597
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a DELTA-SIGMA (hereinafter referred to as &Dgr;-&Sgr;) modulator and a &Dgr;-&Sgr; A/D converter having the &Dgr;-&Sgr; modulator. The present invention is applicable to ultra-high communication apparatuses such as software radio and high-frequency measuring apparatuses.
An A/D (analog-digital) converter is a circuit having a function for converting an analog signal into a digital signal and indispensable as an interface between an actual world indicated by analog information and a digital signal processing circuit.
As the conventional A/D converter, there are mainly two types of A/D converter such as the flash type and the &Dgr;-&Sgr; type. In the flash-type A/D converter, an input voltage is divided by means of many resistances, and divided voltages are applied in parallel to comparators to convert an input analog value to a digital value. Therefore, the flash-type A/D converter is capable of operating at a very high speed but incapable of coping with variations of characteristics of elements and has difficulty in obtaining high precision (number of bits).
On the other hand, in the &Dgr;-&Sgr; A/D converter, an input signal is converted into a digital signal of low bit precision at a very high sampling rate. Then a signal having a required frequency is taken out from the digital signal and then high-precision digital data is obtained by converting precision in time base direction into precision in bit. The circuit is capable of coping with variation in a device parameter and making high-precision conversion. The operation principle of the &Dgr;-&Sgr; A/D converter is described below based on a document (“A Simple Approach to Digital Signal Processing” written by C. Marven and G. Ewers; translated by Hiroshi Yamaguchi, published by Maruzen).
FIG. 1
shows a block diagram of the &Dgr;-&Sgr; A/D converter.
The &Dgr;-&Sgr; A/D converter comprises a &Dgr;-&Sgr; modulator (&Dgr;-&Sgr; quantizer) and a digital filter. The &Dgr;-&Sgr; modulator samples an input signal at a very high frequency and coverts the sampled input signal into a pulse density signal. The digital filter decreases a high-frequency component of the signal and converts precision in time base direction into precision in bit to thereby take out a digital signal having high precision.
FIG. 2
shows the simplest construction of the &Dgr;-&Sgr; modulator which is the main part of the &Dgr;-&Sgr; A/D converter. This circuit comprises an integrator and a comparator. This circuit integrates the deviation between an input signal and an output signal and controls an output in such a way as to minimize the deviation. The output signal becomes a pulse signal. As a result, the pulse density is so controlled as to be coincident with an input value, and a pulse density signal proportional to the input value is obtained. At this time, by setting the frequency of a clock signal for sampling much higher than a Nyquist frequency, the A/D converter is capable of obtaining high precision.
As described above, because this circuit has high precision by increasing the sampling rate, the circuit of the &Dgr;-&Sgr; A/D converter has advantages that it is capable of coping with variations of a circuit parameter than the flash-type A/D converter and does not require a high-precision analog element in obtaining high precision.
In the &Dgr;-&Sgr; A/D converter having the above-described characteristics, a very high sampling frequency is necessary for a frequency of a signal to be obtained. Thus the conventional art constructed of a transistor, an operational amplifier, and the like has a problem that it can be used only for an audio signal having a comparatively low frequency or the like.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel &Dgr;-&Sgr; modulator which has overcome the problem of the conventional art and a &Dgr;-&Sgr; A/D converter using the &Dgr;-&Sgr; modulator.
The &Dgr;-&Sgr; modulator according to the present invention has a comparator having a plurality of negative resistance elements which show an N-type differential negative resistance and are connected to each other in series between two terminals and a comparison input transistor connected in parallel to at least one of the negative resistance elements, a clock pulse voltage being applied between the two terminals; a conversion input transistor for converting an input voltage into electric current; a capacitance element connected to an output current terminal of the conversion input transistor and to an input terminal of the comparison input transistor of the comparator; and a feedback transistor to which an output of the comparator is inputted and through which electric current flows into the capacitance element in a direction opposite to a direction of electric current flowing through the conversion input transistor. The &Dgr;-&Sgr; modulator is capable of achieving a high-speed operation, unlike the conventional one.
The above-described negative resistance element can be a resonant tunnel element such as a resonant tunnel diode or other elements showing a differential negative resistance such as an Esaki diode. The transistor can be a field effect transistor, a bipolar transistor or the like.
Further, the present invention is characterized in that the &Dgr;-&Sgr; A/D converter comprises the above-described &Dgr;-&Sgr; modulator and a digital filter. According to this invention, it is possible to realize a high-precision A/D converter operating at an ultra-high frequency.
REFERENCES:
patent: 3120618 (1964-02-01), Flinckinger et al.
patent: 3234400 (1966-02-01), Hart
patent: 3273141 (1966-09-01), Hackett
patent: 6188346 (2001-02-01), Waho et al.
patent: 6208277 (2001-03-01), Hellums et al.
patent: 6229468 (2001-05-01), Broekaert
patent: 6292118 (2001-09-01), Broekaert
Marven and Ewers,A Simple Approach to Digital Signal Processing,translated in Japanese by Hiroshi Yamaguchi, pp. 54-59 (discussed on page 2 of the spec.).
Waho and Yamamoto, “Application of Resonant-Tunneling Quaternary Quantizer to Ultrahigh-Speed A/D Converter,” 1997 27thInternational Symposium on Multiple-Valued Logic, May 28-30, 1997, pp. 35-40.
Itoh et al., “10-Ghz Operation of Multiple-Valued Quantizers Using Resonant-Tunneling Device,”IEICE Transactions on Info. and Systems,vol. E82-D, No. 5, May 1999, pp. 949-954.
Yokoyama et al. “Delta-Sigma Modulator and Delta-Sigma A/D Converter,” Proceedings of the 2000 Electronic Society Conference of IEICE, C-10-3, Sep. 30-Oct. 3, 2000, p. 50.
Maezawa Koichi
Mizutani Takashi
Law Offices of David G. Posz
Nagoya Industrial Science Research Institute
Nguyen Khai M
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