By Kalwinder KaurJul 31 2013
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In a robotic system, a microcontroller employs discrete values to perform tasks like computation of values and performing comparisons. For this reason, analogue to digital (A/D) converter is used for converting analogue signal into digital signal.
The converter carries out this task using a mapping function that assigns discrete values to the entire range of voltages. However, 0 to 5 V is a typical range for the A/D converter.
Types of A/D Converter
The following are some of major types of A/D converter used in robotic systems:
- Integrating A/D Converter – This converter operates by integrating the input signal over a fixed period of time to reduce noise and eliminate interfering signals. Hence, it is suitable for digitizing constant signals. It is used for applications involving high accuracy and resolution.
- Parallel A/D Converter – This type of converter is used for applications requiring high bandwidth and moderate resolution. It consists of an array of comparators that are clocked to sample the input simultaneously. As these comparators are clocked at high rates, the sample rate of the converter can be correspondingly high.
- Multistep A/D Converter – This converter converts the input signals in a series of steps. It consists of parallel A/D converter and digital to analogue converters. It is used in moderate sample rates, and offers higher resolution or lower power than parallel converters operating at the same rate.
Working Principle
The analogue to digital converter receives analogue signals that are converted into digital numbers within a certain numerical range.
Firstly, the analog sample is measured after a predefined period of time. The voltage is recorded as a number at each time period. The number can be defined as a signal of 0's and 1's.
The sampling rate is defined as the frequency at which the sampling occurs. For instance, if the sampling rate is said to be 22050 Hz, it means 22050 points will be sampled in one second.
The value of each sampling point will be stored on a fixed length variable that uses either 8 bits or 16 bits. Therefore, the lowest value for an 8-bit A/D converter will be 0 and the highest value will be 255.
Likewise, the lowest value for a 16-bit A/D converter will be 0 and the highest value will be 65535. The higher the variable size, better the quality of signal. However, the determination of number of bits required for the conversion process depends on the noise level.
When the conversion is done, the result is a series of discrete-amplitude and discrete-time digital values converted from a continuous-time and continuous-amplitude analogue signal.
Applications
The following are some of the major applications of A/D converter:
- High accuracy voltmeter applications
- High bandwidth and sample rate applications
- Real-time oscilloscope
- Spectrum analyzer.
Sources and Further Reading
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