resolution of analog to digital converter

The conversion speed of the flash ADC is the sum of the comparator delays and the logic delay (the logic delay is usually negligible). All of the comparator outputs connect to a block of logic that determines the output based on which comparators are low and which are high. A 4-bit ADC will have 16 comparators, an 8-bit ADC will have 256 comparators. A flash ADC uses comparators, one per voltage step, and a string of resistors.

The flash ADC is the fastest type available. The most common types of ADCs are flash, successive approximation, and sigma-delta. So the resolution is 5V/1,024, or 4.88mV a 12-bit ADC has a 1.22mV resolution for this same reference.ĪDCs come in various speeds, use different interfaces, and provide differing degrees of accuracy. A 10-bit ADC has 2 10, or 1,024 possible output codes. The only way to increase resolution without reducing the range is to use an ADC with more bits. However, the maximum voltage that can be measured is now 2.5V instead of 5V. Changing that from 5V to 2.5V gives a resolution of 2.5/256, or 9.7mV. Resolution can be improved by reducing the reference input. Between 39mV and 58.6mV, the output will be 2. Input voltages between 19.5mV and 39mV will result in an output of 1. This means that any input voltage below 19.5mV will result in an output of 0. As mentioned earlier, the resolution is the same as the smallest step size, and can be calculated by dividing the reference voltage by the number of possible conversion values.įor the example we’ve been using so far, the resolution is 19.5mV. The resolution defines the smallest voltage change that can be measured by the ADC. The resolution of an ADC is determined by the reference input and by the word width. Adding the voltages corresponding to each set bit in 0010 1100, we get: Each succeeding bit represents half the range of the previous bit. The most significant bit of this word indicates whether the input voltage is greater than half the reference (2.5V, with a 5V reference). Our 8-bit converter represents the analog input as a digital word. The step size of the converter defines the converter’s resolution. This voltage range is divided into 256 values, or steps. Our example 8-bit ADC can convert values from 0V to the reference voltage. The reference voltage is the maximum value that the ADC can convert. It has one output, an 8-bit digital word that represents the input value. This hypothetical part has two inputs: a reference and the signal to be measured. F igure 1 shows a simple voltage-input ADC.

Resolution of analog to digital converter