Digital Electronics: Principles, Devices and Applications

484 Digital Electronics{D 2C 2MSDB 2A 2D 1C 1B 1A{1D 0C 0LSDB 0A 0MSBLSBMSBLSBMSBLSBD/AConverterO/PFigure 12.11 BCD-input D/A converter (example 12.2).Example 12.3A certain eight-bit D/A converter has a full-scale output of 5 mA and a full-scale error of ±0.25 % offull scale. Determine the range of expected analogue output for a digital input of 10000010.Solution•Full-scale outputStep size =Number of steps= 5 × 10−32 8 − 1= 19.6 A• For a digital input of 10000010 (= 130 10 the analogue output is given by 130 × 19.6 = 2.548 mA.025 × 5 × 10−3• Error =±100=±12.5 A• The expected analogue output will therefore be in the range 2.5355–2.5605 mA.Example 12.4An experimenter connects a four-bit ripple counter to a four-bit D/A converter to perform a staircasetest using a 1 kHz clock as shown in Fig. 12.12. The output staircase waveform is shown in Fig. 12.13.The cause of the incorrect staircase signal is later determined to be a wrong connection between thecounter output and the D/A converter input. What is it?SolutionThe correct staircase waveform would be generated at the output of the D/A converter if thecounter outputs Q 0 (LSB), Q 1 , Q 2 and Q 3 (MSB) were connected to the corresponding inputs