Shulou(Shulou.com)06/01 Report--

What this article shares with you is about the sampling principle and type of ADC analog-to-digital conversion. The editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.

ADC includes three basic functions: sampling, quantization and coding. The sampling process is to discretize the analog signal in time and make it into a sampling signal; quantization is to discretize the amplitude of the sampled signal into a digital signal; and coding is to convert the digital signal into a form acceptable to the digital system. How to realize these three functions determines the form and performance of ADC. At the same time, the higher the resolution of ADC, the longer the conversion time and the lower the conversion speed, so the resolution and conversion rate of ADC always restrict each other. Therefore, high speed should be taken into account while developing high-resolution ADC, and high-resolution should be taken into account while developing high-speed ADC. On this basis, power consumption, volume, convenience, multi-function, compatibility with computers and communication networks, and special requirements in application fields should be considered, which also makes the structure and classification of ADC complicated.

ADC has different conversion rates, uses different interface circuits, and can provide different accuracy. The most commonly used ADC types include flash ADC, successive approximation ADC, and sigma-delta ADC.

one

Flash ADC

Flash ADC is one of the fastest conversion rates. The Flash ADC uses a comparator and a set of resistors in each voltage step. Therefore, 4-bit ADC has 16 comparators and 8-bit ADC has 256 comparators. All comparator outputs are connected to a logic device, which determines the output according to the voltage of the comparator.

The conversion rate of flash ADC is the sum of comparator delay and logic device delay (the delay of logic devices is usually negligible). The conversion rate of flash ADC is very fast, but it needs to take up a lot of space; and because of the large number of comparators required, flash ADC is simply a power "black hole" that consumes a high current intensity. The current required for a 10-bit flash ADC is about 0.5A.

One variant of the flash ADC is the semi-flash ADC, which uses the built-in digital-to-analog converter (DAC) to reduce the number of internal comparators. The conversion rate of semi-flash converter is lower than that of real flash converter, but higher than that of other types of ADC.

two

Successive approximation of ADC

The successive approximation converter uses a comparator and a counting logic device to complete the conversion. The first step in the conversion is to verify that the input is more than half of the reference voltage, and if so, set the most significant bit (MSB) of the output to 1. Then subtract half of the output reference voltage from the input value, and then check whether the result is greater than 1x4 of the reference voltage, and so on until all output bits are set to "1" or cleared. The clock cycle required to approach the ADC step by step is the same as the number of output digits required to perform the conversion.

three

Sigma-delta ADC

Sigma-delta ADC uses 1-bit DAC, filtering and additional sampling to achieve very accurate conversion, depending on the reference input and input clock frequency.

The main advantage of Sigma-delta converter is its high resolution. The flash speed and successive approximation ADC use parallel resistance or series resistance. The problem of these methods is that the accuracy of the resistance will directly affect the accuracy of the conversion results. Although the new ADC uses a very accurate laser trimming resistor network, it is still not very accurate in parallel resistors. There is no parallel resistor in the sigma-delta converter, but the convergence result can be obtained by several sampling.

The main disadvantage of Sigma-delta converter is its conversion rate. Because the converter works by additional sampling of the input, the conversion requires more clock cycles. At a given clock rate, the rate of the Sigma-delta converter is lower than that of other types of converters; or, from another point of view, the Sigma-delta converter requires a higher clock frequency for a given conversion rate.

Another disadvantage of Sigma-delta converter is that the structure of digital filter that converts duty cycle information into digital output word is very complex, but Sigma-delta converter is more and more widely used because of its function of adding digital filter or DSP to IC bare chip.

These are the principles and types of ADC analog-to-digital conversion sampling. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.