Coded data generation or conversion – Analog to or from digital conversion – Multiplex
Patent
1994-06-07
1996-07-16
Williams, Howard L.
Coded data generation or conversion
Analog to or from digital conversion
Multiplex
341144, 341155, H03M 100
Patent
active
055371132
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an A/D converter and a D/A converter for converting an analog or digital waveform signal to digital or analog waveform signal and, more particularly, to an A/D converter and a D/A converter which implement high-speed, high-resolution waveform conversion through use of a plurality of A/D or D/A conversion parts.
In general, high resolution and high-speed operations are required to convert an analog or digital waveform to a digital or analog signal with high precision. However, high-speed, high-resolution A/D and D/A converters are very expensive. Hence, it is customary in the prior art to implement a converter whose conversion rate, as a whole, is made N-fold by applying waveform signals to a plurality (N) of low-speed, high-resolution converting parts, converting the signals one after another at a fixed time interval while shifting their phases by a time T/N, and outputting the converted versions one after another from the converting parts in a circulating fashion. A description will be given, with reference to FIGS. 1A and 1B, of the case of implementing an A/D converter, for instance.
FIG. 1A is a block diagram of the A/D converter of the above-mentioned prior art example, in which plural, for example, two A/D converting parts AD.sub.1 and AD.sub.2 are connected in parallel to and are driven alternately with each other to thereby implement an A/D converter of an operating speed twice higher than that of a single A/D converting part. The A/D converting parts AD.sub.1 and AD.sub.2 have their inputs connected in parallel to each other and alternately convert the amplitude of the input analog waveforms S.sub.A thereto to digital values D.sub.1 and D.sub.2 at the timing of their clocks CK.sub.1 and CK.sub.2 as shown in FIG. 1B and each hold the converted value until the occurrence of the next clock.
A multiplexer 2 responds to the clocks CK.sub.1 and CK.sub.2 to output the digital values D.sub.1 and D.sub.2 alternately with each other, providing a digital waveform S.sub.D. As shown in FIG. 1B, the digital waveform S.sub.D is composed of outputs a.sub.n and b.sub.n that are provided alternately from the A/D converting parts AD.sub.1 and AD.sub.2 ; thus, the A/D converter outputs data at an operating speed twice higher than that of the individual A/D converting parts AD.sub.1 and AD.sub.2.
In the above-described A/D converter wherein a plurality of A/D converting parts are connected in parallel and are sequentially activated, for example, in the case of FIG. 1A, a gain error and an offset error that are inevitably exist between the A/D converting parts AD.sub.1 and AD.sub.2 will distort the waveform as depicted in FIGS. 2A and 2B. FIG. 2A is a diagram showing a digital data waveform distorted by the gain error; the gain error between the both A/D converting parts is 10% in this example. FIG. 2B is a diagram showing a digital data waveform distorted by the offset error; the offset error between the both converting parts is 10% in this example. In either of FIGS. 2A and 2B, the error appears intact between adjacent pieces of data in the output of the multiplexer 2. Furthermore, since the output from the multiplexer 2 only switches between the outputs from the A/D converting parts AD.sub.1 and AD.sub.2 alternately, the resolution of the output value is the same as that of the individual A/D converting parts AD.sub.1 and AD.sub.2. That is, the construction of FIG. 1A permits the speeding up of the A/D converting operation but fails to improve the resolution of the converted output S.sub.D. In FIG. 1A, by providing an adder in place of the multiplexer 2 and outputting therefrom the sums of adjacent pieces of data, a.sub.1 +b.sub.1, b.sub.1 +a.sub.2, a.sub.2 +b.sub.3, b.sub.3 +a.sub.4, . . . , the distortion by the error between the A/D converting parts AD.sub.1 and AD.sub.2 is averaged and hence is improved, but the resolution is not improved.
The D/A converter for waveform conversion also encounters similar problems. That is, by distributing an input digital wavefor
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patent: 4591832 (1986-05-01), Fling et al.
patent: 4968988 (1990-11-01), Miki et al.
patent: 5268688 (1993-12-01), Meyers et al.
patent: 5355134 (1994-10-01), Kasuga et al.
Advantest Corp.
Williams Howard L.
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