ADC
Printanalog-to-digital converter. An electronic device, often an integrated circuit, that converts an analog voltage to a digital value. Also abbreviated as A/D Converter.
Two main parameters of interest in A/D converters are the rate at which the converter can sample analog values, and the resolution at which it can resolve the values.
Sampling rate is given in S/s (samples/s) and the resolution is given as a percentage of the maximum voltage that the converter can resolve, or the number of bits that this corresponds to.
ADCs are a core technology in virtual instrumentation. After the analog values have been digitized accurately, any measurement value can be derived using software algorithms, commonly called digital signal processing (DSP).
There are several types of ADC's: half-flash, flash, and integrating.
Units:
The input signal is typically in Volts and the output is a digital representation of the relative voltage, which has to be scaled or converted using an appropriate calibration factor to the actual voltage.
Approaches:
Approach 1
- Flash ADC. A high-speed digitizer that simultaneously compares the input voltage to all possible combinations of digital values. This gives a very short acquisition time compared to other approaches, such as a successive approximation A/D Converters.
Sensors Used:
Primarily used for frequencies of 20 MHz. Therefore, only high-frequency probes are relevant.
Wiring/Configuration/Hardware Considerations:
To optimize the impedance match and give as low noise as possible, flash ADCs are normally preceded by a 50 to 75 ohm input stage.
Software Considerations:
The speed of data acquisition is so high that the data generally must be buffered before being brought into the computer. Dedicated haare, such as FPGAs, may be used to control or signal process the data before passing it on to the PC. The NI products with sampling frequencies of 20 MS/s and above generally use Flash ADCs.
Additional References
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