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Comment on the following ADC/DAC specifications I. Resolution II. Linearity Ill. Accuracy IV. Settling Time V. Stability.

Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 5 Marks

Year: May 2015

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1. Resolution

Resolution is defined as the number of different analog output voltage levels that can be provided by a DAC.

Simply, resolution is the value of LSB.

$$\text{Resolutions (Volts)}=\dfrac{V_{OFS}}{2^n-1}=\text{1 LBS increment} \\ \text{Where 'n' is the number of number of input bits} \\ V_{OFS} \text{is the full scale output voltage}$$

1. Linearity

Linearity is the maximum deviation in step size from the ideal step size. Some D/A converters are having a linearity error as low as 0.001% of full scale. The linearity of a D/A converter is defined as the precision or exactness with which the digital input is converted into analog output. An ideal D/A converter produces equal increments or step sizes at output for every change in equal increments of binary input.

2. Accuracy

Accuracy is the maximum deviation between the actual converter output and the ideal converter output. The ideal converter is the one which does not suffer from any problem. Whereas, the actual converter output deviates due to the drift in component values, mismatches, aging, noise and other sources of errors.

The relative accuracy is the maximum deviation after the gain and offset errors have been removed. Accuracy is also given in terms of LSB increments or percentage of full-scale voltage.

Normally, the data sheet of a D/A converter specifies the relative accuracy rather than absolute accuracy.

3. Settling Time

It is one of the important dynamic parameter. It represents the time it takes for the output to settle within a specified band ± (1/2) LSB of its final value following a code change at the input (Usually a full-scale change). It depends on the switching time of the logic circuitry due to internal parasitic capacitances and inductances. A typical settling time ranges from 100 ns to 10 μs depending on the word length and type of circuit used.

4. Stability

The ability of a DAC to produce a stable output all the time is called as Stability. The performance of a converter changes with drift in temperature, aging and power supply variations. So all the parameters such as offset, gain, linearity error & monotonicity may change from the values specified in the datasheet. Temperature sensitivity defines the stability of a D/A converter.

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