| 1 |
Front Matter |
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Abstract
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| 2 |
,The converter as a black box, |
Rudy Van De Plassche |
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Abstract
A/D and D/A converters are the link between the analog world of transducers and the digital world of signal processing and data handling. In an analog system bandwidth is limited by device and element performance and by the parasitics introduced. Thermal noise generated in active and passive components limits the dynamic range of an analog system. The ratio between the maximum allowable analog signal and the noise determines the dynamic rangedynamic range of the system. The signal-to-noise (S/N) ratio is a measure of the maximum dynamic range.
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| 3 |
,Specifications of converters, |
Rudy Van De Plassche |
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Abstract
To obtain insight into the design criteria for converters it is important to arrive at a unanimous definition of specifications. These specifications must include the application of converters in conversion systems (see references [14,15]). Dynamic specifications of converters are needed to obtain insight in the applicability of a certain converter in a digital signal processing system: for example, digital audio or digital video. In a conversion system the complete conversion from analog into digital or digital into analog information is performed. Such systems include input or output amplification and anti-alias filtering.
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| 4 |
,Testing of D/A and A/D converters, |
Rudy Van De Plassche |
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Abstract
To verify the different specifications of converters and converter systems it is important to set up test facilities and structures and to agree unanimously on the test procedures. In general, static performance tests can be performed by using digital voltmeters which can be a part of an Automatic Test Equipment set (ATE). Dynamic tests, especially in the case of high-dynamic-range tests, require special equipment. Furthermore, these dynamic tests are generally more difficult to standardize and consume more test time (see [36,37,16,17]). Up until now dynamic test results have been listed very briefly in specification sheets. In this chapter we will determine test configurations and test procedures in order to arrive at a unanimous qualification of converters.
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| 5 |
,High-speed A/D converters, |
Rudy Van De Plassche |
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Abstract
The best-known architecture for a high-speed analog-to-digital converter is the flash converter structure. In this structure an array of comparators compares the input voltage with a set of increasing reference voltages. The comparator outputs represent the input signal in a digital thermometer code which can be easily converted into a Gray or binary output code. The flash architecture shows a good speed performance and can easily be implemented in an integrated circuit as a repetition of simple comparator blocks and a ROM decoder structure. However, this architecture requires 2.-1 comparators to achieve an .-bit resolution. The parallel structure makes it difficult to obtain a high-resolution while maintaining at the same time a large bandwidth, a low power consumption, and a small die area. An alternative to the full-flash architecture is the multi-step A/D conversion principle. In highspeed converters the two-step architecture is the most popular because of the ease of implementation. However, a two-step architecture must be preceded by a sample-and-hold amplifier which performs the sampling of the analog input signal. In the two-step architecture a coarse and fine quantization
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| 6 |
,Limitations of comparators, |
Rudy Van De Plassche |
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Abstract
In most A/D converters the input signal is applied to an amplitude-limiting circuit. This amplitude-limiting circuit can be a differential amplifier stage or the input stage of a comparator. The amplitude of the input signal is usually much larger than the linear range of the input amplifier stages. In this way a limitation of signals for the individual amplifier stages occurs. This amplitude limitation results in variations of the delay times of the zero crossings of the differential stages. This can be explained in the following way. When a sine wave is applied at the input of the A/D converter, it looks as if this sine wave is cut into pieces with a variable slope. This slope depends on the level at which the input signal is equal to a reference voltage level. The variable slope introduces a variable delay of the zero crossing of the output signal. These delays are accordingly signal-slope-dependent. As a result, a nonlinear distortion of the input signal occurs while it travels through the A/D converter system. The moments at which ideal amplifiers would show zero crossings are shifted in time. These time shifts result in errors in the output code of the A/D converter. This del
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| 7 |
,High-accuracy D/A converters, |
Rudy Van De Plassche |
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Abstract
High-resolution monolithic D/A converters are subject to growing interest due to the rapidly expanding market for digital signal processing systems. An example of such a market is digital audio. The large dynamic range of a digital audio system requires converters with resolutions of 16 to 20 bits. Monolithic converters with such a high linearity are difficult to design and require special circuit configurations. The most simple types of D/A converters are obtained with pulse-width modulation systems. These systems require fast logic circuits. In a pulse-width D/A converter structure an output low-pass filter reconstructs the analog signal and removes the modulation signal. Maximum speed of these types of converters is limited to the kHz range. The advantage of these systems is the small amount of accurate components that are needed in a practical implementation.
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| 8 |
,High-accuracy A/D converters, |
Rudy Van De Plassche |
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Abstract
High-resolution monolithic A/D converters are subject to growing interest due to the rapidly expanding market for digital signal processing systems. The introduction of digital audio recording equipment such as the Digital Compact Cassette (DCC) players requires resolutions of 16 to 18 bits. Monolithic converters with such a high linearity are difficult to design and require special circuit configurations. When a low conversion speed is needed, integrating types of converters can be used. In integrating types of high-resolution A/D converters basically the analog input signal is converted into a time which is proportional to the input signal. Time is measured using a counter with an accurate clock. These systems are relatively slow because of the counting operation in the time-to-number conversion cycle. A speed improvement is obtained by using a coarse and fine conversion cycle in the time-to-number counting operation. A well-known analog-to-digital converter based on this system is the dual slope converter. This converter is mostly used in digital voltmeters.
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| 9 |
,Sample-and-hold amplifiers, |
Rudy Van De Plassche |
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Abstract
In this Chapter sample-and-hold amplifiers are discussed. In most cases practical implementations of these amplifiers are track-and-hold amplifiers. During the sampling mode the input signal is “tracked” and a sample is taken at the moment the system is switched into the hold mode. The terminology sample-and-hold amplifier will be used in this chapter although most systems are track-and-hold amplifiers.
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| 10 |
,Voltage and current reference sources, |
Rudy Van De Plassche |
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Abstract
In A/D and D/A converters the full-scale value is determined by the reference source. A low noise and low temperature coefficient of the output signal of the reference source is very important for high-resolution, high-accuracy converters. A well-known device for stabilizing a reference voltage is a zener diode. In integrated circuits, however, the zener diode can cause problems with the reliability of the circuit. In modern technologies it is not always possible to reverse-bias the emitter-base junction of a transistor to obtain a zener diode operation. The yield of circuits is reduced by reverse-biasing transistors. Today’s reference sources are built using the band-gap voltage of silicon as a low-temperature dependent reference voltage. In this chapter different circuits will be described that use the band-gap principle to stabilize a voltage or a current. Examples of band-gap reference voltages are given in references [76,77,79].
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| 11 |
,Noise-shaping coding, |
Rudy Van De Plassche |
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Abstract
In this chapter noise-shaping techniques to improve the dynamic range of a system will be described. Noise-shaping can be very useful when speed can be exchanged with accuracy. The quantization errors in a noise-shaping system are removed from the signal band of interest. Mostly the suppressed quantization errors appear enlarged as out-of-band noise in the system. With a simple filter these errors are removed. An increased dynamic range of the coder is obtained. In digital systems word length can intelligently be reduced using a noise-shaping operation without losing dynamic range significantly. An ultimate in bit reduction is obtained when the noise-shaping operation reduces the number of bits to 1. Examples of such an operation is sigma-delta analog-to-digital conversion or noise-shaping digital-to-analog conversion based on single-bit word-lengths. The advantage of a 1-bit converter is the extreme linearity of such a device. A very good differential linearity is obtained with these converters. The most important design criteria for these converters will be given. At the moment the dynamic range of a system must be enlarged, but the maximum clock rate of the system cannot be incr
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| 12 |
,Sigma-delta converters, |
Rudy Van De Plassche |
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Abstract
In this chapter noise-shaping techniques applied to analog-to-digital converter systems will be described. Noise-shaping is very useful when speed can be exchanged with accuracy. In reference [96] an overview of theoretical and practical aspects of oversampling converters is given. The quantization errors in a noise-shaping system are removed from the signal band of interest. Furthermore, in an analog-to-digital converter system the input noise is filtered out by the input noise-shaping function. As a result, a reduced bandwidth can be used compared to, for example, successive approximation conversion methods. Again, the removed quantization errors appear with larger amplitudes as out-of-band noise in the system. With a digital filter these errors are removed. An increased dynamic range of the system is obtained. An example of such an operation is sigma-delta analog-to-digital conversion using single bit word-lengths [93,98,97]. The advantage of a 1-bit converter is the extreme linearity of such a device. A very good differential linearity is obtained with these converters. The most important design criteria will be given. The dynamic range performance is related to the noise-shapi
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| 13 |
Back Matter |
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Abstract
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发表于 2025-3-21 17:08:08
