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D/A Converter Errors and Parameters
3
Actual
Ideal
Analog Output Voltage
2
1
Actual
Offset
Offset Error
(+ 1 1/4 LSB)
0
Nominal
Offset
000 001 010 011
Digital Output Code
Figure 14–7. D/A Offset Error
14.5.1.2 Gain Error
Related to the offset error is the offset error temperature coefficient, which is the change
in offset over temperature. This is usually specified in ppm/C.
Offset error is critical in dc applications. For this reason, a buffer op amp must be selected
that does not contribute to the problem — its own offset voltages should be much less than
that of the converter. In ac applications, the offset error is not important and can be ignored.
The buffer op amp can be selected for low THD, high slew rate, or whatever other
parameters are important for the application.
The gain of the D/A converter may greater than or less than the gain needed to produce
the desired full-scale analog voltage (Figure 14–8). The gain error is the difference in
slope between the ideal D/A output gain and the actual gain.
Interfacing D/A Converters to Loads
14-11