ADS-947MM ETC, ADS-947MM Datasheet - Page 4

• Manufacturer Part Number: ADS-947MM
• Description: 14-Bit/ 10MHz Sampling A/D Converters
• Manufacturer: ETC

ADS-947
CALIBRATION PROCEDURE
Any offset and/or gain calibration procedures should not be
implemented until devices are fully warmed up. To avoid
interaction, offset must be adjusted before gain. The ranges of
adjustment for the circuits in Figures 2 and 3 are guaranteed to
compensate for the ADS-947’s initial accuracy errors and may
not be able to compensate for additional system errors.
A/D converters are calibrated by positioning their digital outputs
exactly on the transition point between two adjacent digital
output codes. This can be accomplished by connecting LED’s
to the digital outputs and adjusting until certain LED’s “flicker”
equally between on and off. Other approaches employ digital
comparators or microcontrollers to detect when the outputs
change from one code to the next.
Offset adjusting for the ADS-947 is normally accomplished at
the point where the MSB is a 1 and all other output bits are 0’s
and the LSB just changes from a 0 to a 1. This digital output
transition ideally occurs when the applied analog input is
+½ LSB (+122µV).
Gain adjusting is accomplished when all bits are 1’s and the
LSB just changes from a 1 to a 0. This transition ideally occurs
when the analog input is at +full scale minus 1½ LSB's
(+1.99963V).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input (pin
2. Apply +122µV to the ANALOG INPUT (pin 21).
3. Adjust the offset potentiometer until the output bits are
18) so the converter is continuously converting.
10 0000 0000 0000 and the LSB flickers between 0 and 1.
OFFSET
ADJUST
CONVERT
ZERO/
ANALOG
A single +5V supply should be used for both the +5V analog and +5V digital.
If separate supplies are used, the difference between the two cannot exceed 100mV.
START
INPUT
+5V
–5V
20k
Figure 3. Typical ADS-947 Connection Diagram
23
18
19
21
0.1µF
4.7µF
+
–5.2V
20
ADS-947
4
24
Gain Adjust Procedure
1. Apply +1.99963V to the ANALOG INPUT (pin 21).
2. Adjust the gain potentiometer until all output bits are 1’s and
3. To confirm proper operation of the device, vary the input
0.1µF
4.7µF
+FS –1 LSB
–FS +1 LSB
INPUT VOLTAGE
the LSB flickers between 1 and 0.
signal to obtain the output coding listed in Table 2.
BIPOLAR
22, 13
+
+5V
SCALE
+3/4 FS
+1/2 FS
–1/2 FS
–3/4 FS
–FS
RANGE
4.7µF
0.1µF
+
0
±2V
Table 2. Output Coding for Bipolar Operation
14
Table 1. Gain and Zero Adjust
10
11
12
15
16
17
INPUT VOLTAGE
1
2
3
4
5
6
7
8
9
(±2V RANGE)
BIT 1 (MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14 (LSB)
DATA VALID
+1.99976
+1.50000
+1.00000
–1.99976
–2.00000
–1.00000
–1.50000
0.00000
ZERO ADJUST
+½ LSB
+122µV
®
MSB
11 1111 1111 1111
11 1000 0000 0000
11 0000 0000 0000
10 0000 0000 0000
01 0000 0000 0000
00 1000 0000 0000
00 0000 0000 0001
00 0000 0000 0000
OFFSET BINARY
GAIN ADJUST
+FS –1½ LSB
+1.99963V
LSB
®