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Appendix A
Digital-to-Analog Converter
Samsung ASIC
A-2
STDL130
the sampling frequency, this signal to noise ratio must be specified and should
ideally follows the theoretical formula;
S/N
max
= 6.02N + 1.76dB
9. Slew Rate
- Slew rate of a device or circuit is a limitation in the rate of change
of output voltage, usually imposed by some basic circuit consideration such as
limited current to charge of capacitor. Amplifiers with slew rate of a few V/
μ
s are
common and moderate in cost. Slew rates greater than about 75V/
μ
s are usually
seen only in more sophisticated (and expensive) devices. The output slewing
speed of a voltage-output DAC is usually limited by the slew rate of the amplifier
used at its output (if one is used).
10. Settling Time
- The time required, following a prescribed data change from
the 50% point of the login input change, for the output of a DAC to reach and to
remain within a given fraction (usually
±
1/2LSB) of the final value. Typical pre-
scribed changes are full scale, 1MSB and 1LSB at a major carry. Settling time of
current-output DAC is quite fast. The major share of settling time of a voltage-out-
put DAC is usually contributed by the settling time of the output op-amp circuit.
Figure 1-2.
Setting Time
11. Power-Supply Sensitivity
-The sensitivity of a converter to changes in the
power-supply voltages is normally expressed in terms of percent-of-full-scale
change in analog output value (of fractions of 1LSB) for a 1% DC change in the
power supply. Power supply sensitivity may be also expressed in relation to the
specified DC shift of supply voltage. A converter may be considered "good" if the
change in reading at full scale does not exceed 1/2LSB for 3% change in power
supply. Even better specifications are necessary for converters designed for
battery operation.
12. INL (Integral Non Linearity)
- Linearity error of a converter, expressed in %,
ppm of full-scale range or multiples of 1LSB, is a deviation of the analog values
in a plot of the measured conversion relationship from a straight line. The straight
line can be either a "best straight line" determined empirically by manipulation of
the gain and/or offset to equalize maximum positive and negative deviation of the
actual transfer characteristics from this straight line; or it can be a straight line
passing through the endpoints of the transfer characteristic after they have been
calibrated (sometimes referred to as "endpoint" linearity). Endpoint linearity error
issimilartorelativeaccuracyerror.FormultiplyingDAC,theanaloglinearityerror,
at a specified digital code, is defined in the same way as for multipliers, by
deviation from a "best straight line" through the plot of the analog output-input
response.
Final Setting
V
0
+
V
0
1
Slewing
Setting Time to
V
0
V
0
Slew Rate