D/A converter capable of producing an analog signal having levels of a preselected number different from 2.sup.N and communication network comprising the D/A converter
First Claim
1. A digital-to-analog converter for converting a digital input signal of x number of bits into an analog output signal, where is is an integer which is not smaller than three, and where x bits are consecutively placed at first through x-th bit positions, respectively, said analog output signal taking a plurality of levels, wherein the improvement comprises:
- processing means responsive to said digital input signal for processing at least two of said x bit positions as a common bit position to produce a processed digital signal of x number of bits having said common bit position, whereby after said processing siad original digital input signal of x bits becomes a processed digital signal having the same x-number of bits; and
converting means for converting said processed digital signal into the analog output signal which takes the levels of a number which is different from 2x.
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Abstract
In a digital-to-analog converter, a digital input signal of x bits is subjected to digital-to-analog conversion with at least two of x bit positions recognized as a common bit position and converted into analog levels of a number which is different from 2x where x is an integer. At least one additional common bit position may be selected from the x bit positions except the common bit position. The digital input signal may be pre-processed by the use of a logic circuit prior to the digital-to-analog conversion so as to control the number of analog levels. The digital-to-analog converter is applicable to a modulator which produces a quadrature amplitude modulated signal having a circular arrangement of signal points on a phase plane. A demodulator comprises an analog-to-digital converter for converting the above-mentioned analog signal into a reproduction of the digital input signal.
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Citations
7 Claims
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1. A digital-to-analog converter for converting a digital input signal of x number of bits into an analog output signal, where is is an integer which is not smaller than three, and where x bits are consecutively placed at first through x-th bit positions, respectively, said analog output signal taking a plurality of levels, wherein the improvement comprises:
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processing means responsive to said digital input signal for processing at least two of said x bit positions as a common bit position to produce a processed digital signal of x number of bits having said common bit position, whereby after said processing siad original digital input signal of x bits becomes a processed digital signal having the same x-number of bits; and converting means for converting said processed digital signal into the analog output signal which takes the levels of a number which is different from 2x. - View Dependent Claims (2)
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3. A digital-to-analog converter for use in converting a digital input signal of x bits into an analog output signal, where x is an integer which is not smaller than three, said x bits being consecutively placed at first through x-th bit positins, respectively, said analog output signal taking a plurality of levels, wherein the improvement comprises:
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processing means responsive to said digital input signal for processing at least two of said x bit positions as a common bit position to produce a processed digital signal having said common bit position;
said processing means comprising;means responsive to said digital input signal for recognizing said at least two of said x bit positions as said common bit position to produce a recognized signal of the x bits which include said common bit position and which are numbered from first through x-th bits; means responsive to i-th and (i+1)-th bits of said recognized signal for modifying said (i+1)-th bit by said i-th bit into a modivied (i+1)-th bit with said i-th bit kept unchanged, to produce said i-th bit and said modified (i+1)-th bit, where i is an integer between unity and x, both exclusive; means responsive to said i-th bit, said modified (i+1)-th bit, and the remaining bits of said recognized signal for producing said processed digital signal; and converting means for converting said processed digital signal into the analog signal which takes the levels of a number which is different from 2x.
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4. A modulator for use in modulating a pair of quadrature-phase carrier signals by a first and a second digital input signal into an amplitude modulated analog signal, each of said first and second digital input signals being represented by N bits where N represents an integer which is not smaller than three, said amplitude modulated analog signal having an amplitude and phase specified by M2 signal points on a phase plane where M is equal to 2N, said M2 signal points being divisible into normal and specific signal points in a square distribution and divisible into a first part for said normal signal points and a second part for dislocated signal points given by dislocating said specific signal points in a circular distribution, wherein the improvement comprises:
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determining means responsive to said first and second digital input signals for determining whether said first and second digital input signals are representative of either of said normal and specific signal points to produce a control signal representative of either of said first and second parts; code converting means responsive to said control signal and said first and second digital input signals for converting said first and second digital input signals with reference to said control signal into first and second converted digital signals each of which has a preselected number of bit positions different from said N bits to specify said circular distribution; digital-to-analog converting means for individually converting said first and second converted digital signals into first and second analog signals, respectively, each of which takes amplitudes of a number which is different from 2N, by processing at least two of said preselected number of bit positions as a common bit position; and means for combining said first and second analog signals into said amplitude modulated analog signal. - View Dependent Claims (5, 6, 7)
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Specification