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D/A Converter Specification

Resolution The resolution of a D/A converter refers to the smallest change in the analog output voltage. It is equivalent to the value of the Least Significant Bit (LSB). For an n bit D/A converter, maximum number of steps is 2N–1. When the reference voltage is V, the least significant bit value is given below:


For an 8-bit D/A converter with a full-scale output of 10 V, the resolution is

 131086.png = 39.2 mV


Accuracy The output voltage of a D/A converter is different from ideal case. Therefore there is always some error. The accuracy is measured from the difference actual output voltage and voltage for ideal case. When the accuracy of D/A converter is ±0.25 per cent, the error of converter is 0.25 × 12/100 = 30 mV for full-scale voltage V = 12 V.
Offset/Zero Scale Error An input code of zero may be expected to give 0 V output. A small offset may be present and the transfer characteristic does not pass through the origin.
Linearity The input–output characteristics of a D/A converter. Zero offset and gain can develop the characteristic, which passes through the origin and full-scale points. But it is not sure that intermediate points will always lie on a straight line. A very small error in the weighting factor for a fraction LSB will cause nonlinearity. Linearity can be expressed by deviation from the ideal line as a percentage, or afraction of LSB. It is generally specified as LSB or ± 131096.png LSB or |ε| < 131099.pngΔ.
Settling Time This is usually expressed as the time taken to settle within half LSB. Generally settling time will be about 500 ns.
Temperature Sensitivity The D/A converters are temperature sensitive. When the digital inputs are fixed, the analog output may be varied with temperature due to the temperature sensitivities of the reference voltages, the operational amplifier and converter circuit resistances, etc. Generally, temperature sensitivity of DACs is about ±50 ppm/ºC in general-purpose converters.

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