AD671KD-500 AD [Analog Devices], AD671KD-500 Datasheet - Page 11

• Manufacturer Part Number: AD671KD-500
• Description: Monolithic 12-Bit 2 MHz A/D Converter
• Manufacturer: AD [Analog Devices]

REV. B
OUTPUT DATA FORMAT
The AD671 provides both MSB and MSB outputs, delivering
data in positive true straight binary for unipolar input ranges
and positive true offset binary or twos complement for bipolar
I
Figure 12 shows the typical logic supply current vs. conversion
rate for various capacitive loads on the digital outputs.
LOGIC
vs. CONVERSION RATE
Figure 11. Overrange or Underrange Logic
MSB
MSB
OTR
Input
Range
0 to +5 V
0 to +10 V
–5 V to +5 V
–5 V to +5 V
NOTES
1
2
Voltages listed are with offset and gain errors adjusted to zero.
Typical performance.
Figure 12. I
Capacitive Loads on the Digital Outputs
UNDER = "1"
OVER = "1"
Coding
Straight Binary
Straight Binary
Offset Binary
2s Complement
(Using MSB)
1.0
0.5
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1k
LOGIC
Table III. Output Data Format
10k
vs. Conversion Rate for Various
CONVERSION RATE – Hz
Analog
Input
0 V
+5 V
>+5.00061 V
0 V
+10 V
–5 V
0 V
+4.99756 V
–5 V
0 V
+4.99756 V
–0.00061 V
–0.00122 V
+10.00122 V
–5.00122 V
+4.99878 V
–5.00122 V
+4.99878 V
–11–
100k
1
input ranges. Straight binary coding is used for systems that ac-
cept positive-only signals. If straight binary coding is used with
bipolar input signals a 0 V input would result in a binary output
of 2048. The application software would have to subtract 2048
to determine the true input voltage. Most processors typically
perform math on signed integers and assume data is in that for-
mat. Twos complement format minimizes software overhead
which is especially important in high speed data transfers, such
as a DMA operation. The CPU is not bogged down performing
data conversion steps, hence increasing the total system
throughput.
1M
CL = 30pF
CL = 50pF
CL = 0pF
Digital
Output
0000 0000 0000
0000 0000 0000
1111 1111 1111
1111 1111 1111
0000 0000 0000
0000 0000 0000
1111 1111 1111
1111 1111 1111
0000 0000 0000
0000 0000 0000
1000 0000 0000
1111 1111 1111
1111 1111 1111
1000 0000 0000
1000 0000 0000
0000 0000 0000
0111 1111 1111
0111 1111 1111
10M
OTR
1
0
0
1
1
0
0
1
1
0
0
0
1
1
0
0
0
1
2
AD671