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Appendix A
Digital-to-Analog Converter
Samsung ASIC
A-2
STD150
8. Signal-to-Noise Ratio (SNR)
- This signal to noise ratio depends on the
resolution of the converter and automatically includes specifications of linearity,
distortion, sampling time uncertainty, glitches, noise, and settling time. Over half
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
prescribed 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-
output 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 1/2LSBfor 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,
Final Setting
V
0
+
V
0
1
Slewing
Setting Time to
V
0
V
0
Slew Rate