mp8798 Exar Corporation, mp8798 Datasheet - Page 8

• Manufacturer Part Number: mp8798
• Description: Cmos Very Low Power, 1 Msps 10-bit Analog-to-digital Converter With 4-channel Mux
• Manufacturer: Exar Corporation

shows a 3-bit converter transfer curve with greatly exaggerated
DNL errors to show the deviation of the real transfer curve from
the ideal one.
computer draws a line parallel to the ideal transfer line. By defi-
nition the best fit line makes equal the positive and the negative
INL errors. For example, an INL error of –1 to +2 LSB’s relative
to the Ideal Line would be +1.5 LSB’s relative to the best fit line.
Clock and Conversion Timing
MP8798
Figure 7. gives a visual definition of the INL error. The chart
After a tester has measured all the transition voltages, the
Rev. 3.00
7
6
5
4
3
2
1
EZS
Output
Codes
A
Figure 7. INL Error Calculation
IN
INL
V
Real Transfer Line
DD
LSB
15 pF
Control
R Series
40
Analog Input (Volt)
Figure 9. Analog Input Equivalent Circuit
Ideal Transfer Line
1 pF
Best Fit Line
4
EFS
Selection
Channel
4
R MUX
500
10 pF
8
clock pulses intermittently when a conversion is desired. The
timing of Figure 8a shows normal operation, while the timing of
Figure 8b keeps the MP8798 in balance and ready to sample the
analog input.
Analog Input
The user may set V
then vary the input DC and AC levels to match the V
Another method is to first design the analog input circuitry and
then adjust the reference voltages for the analog input range.
One advantage is that this approach may eliminate the need for
external gain and offset adjust circuitry which may be required
by fixed input range A/Ds.
put circuitry that is capable of driving the A
shows the equivalent circuit for A
CLOCK
CLOCK
A system will clock the MP8798 continuously or it will give
DATA
DATA
The MP8798 has very flexible input range characteristics.
The MP8798’s performance is optimized by using analog in-
40
300
Figure 8. Relationship of Data to Clock
N
REF(+)
S
b. Single sampling
a. Continuous sampling
S
N+1
N
and V
4 pF
60 pF
87 pF
B
REF(–)
IN
N
.
to two fixed voltages and
160
+
87 pF
BALANCE
1/2 [ V
+ V
IN
N+1
N
REF(–)
input. Figure 9.
REF(+)
]
REF
range.