MicroprocessorsAnalog-to-digital interfacing is an important part of many microprocessor-...

Microprocessors

Analog-to-digital interfacing is an important part of many microprocessor- controlled engineering systems. Although most physical measurement and control involves analog variables, most data collection, information transmission, and data analyses are performed digitally. A/D and D/A circuits provide the interfaces between analog and digital worlds. A D/A converter produces a single analog output signal, usually a voltage, from a multi- bit digital input. One common conversion algorithm produces an analog output proportional to a fixed reference voltage as determined by the equation

where N is the number of bits in the digital input word, n is the decimal value of the binary number represented by all the input bits that are set to 1 in the digital input word, and VREF is a reference voltage. When n is equal to (2N − 1)vOUT is equal to VREF.

• Suppose that the input to an 8-bit D/A converter is 0010 1111 with VREF = 5 V. Find the resulting value of vOUT.

• A 10-bit D/A converter is fed the input word 00 1001 0001 and is given a reference voltage of 5 V. What is the output of the converter?

• What is the smallest increment of analog output voltage that can be produced by a 12-bit D/A converter with a reference voltage of 10 V if the algorithm previously shown is used?

• What is the largest analog output that can be produced by an 8-bit D/A converter if VREF = 12 V?