ADS-945EX データシートの表示（PDF） - DATEL Data Acquisition products

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ADS-945EX

14-Bit, 10MHz Sampling A/D Converters

DATEL Data Acquisition products  

ADS-945

®

®

CALIBRATION PROCEDURE

(Refer to Figure 2 and Table 1)

Note: Connect pin 18 to ANALOG GROUND (pin 19) for

operation without zero/offset adjustment. Connect pin 9 to

ANALOG GROUND (pin 8) for operation without gain

adjustment.

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 circuit in Figure 2 are guaranteed to

compensate for the ADS-945'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.

For the ADS-945, offset adjusting 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 (+76.3µV).

Gain adjusting is accomplished when all bits are 0's and the

LSB just changes from a 0 to a 1. This transition ideally

occurs when the analog input is at +full scale minus 1 ½ LSB's

(+1.249771V) .

Note: Due to inherent system noise, the averaging of several

conversions may be needed to accurately adjust both offset

and gain to 1LSB of accuracy.

Zero/Offset Adjust Procedure

1. Apply a train of pulses to the START CONVERT input

(pin 32) so the converter is continuously converting.

2. Apply +76.3µV to the ANALOG INPUT (pin 4).

3. Adjust the offset potentiometer until the output bits are

10 0000 0000 0000 and the LSB flickers between 0 and 1.

Gain Adjust Procedure

1. Apply +1.249771V to the ANALOG INPUT (pin 4).

2. Adjust the gain potentiometer until all output bits are 0's and

the LSB flickers between 0 and 1.

3. To confirm proper operation of the device, vary the applied

input voltage to obtain the output coding listed in Table 1.

Note: A single +5V supply can be used for both the +5V

ANALOG and the +5V DIGITAL. If separate supplies are

used, the difference between the two can not exceed

100mV. This also applies to the –5.2V supply requirements.

Datel recommends using ferrite beads to separate the analog

and digital supplies (FAIR-RITE # 2643000301.)

Table 1. Output Coding

OUTPUT CODING INPUT RANGE

MSB

LSB

±1.25V

BIPOLAR

SCALE

00 0000 0000 0000

00 0111 1111 1111

00 1111 1111 1111

01 1111 1111 1111

10 1111 1111 1111

11 0111 1111 1111

11 1111 1111 1110

11 1111 1111 1111

COMP. OFF. BINARY

+1.249847

+0.937500

+0.625000

0.000000

–0.625000

–0.937500

–1.249847

–1.250000

+FS –1 LSB

+3/4 FS

+1/2FS

0

–1/2FS

–3/4FS

–FS +1 LSB

–FS

+5V

10µF

0.1µF

10µF

–5.2V

0.1µF

+5V

10µF

0.1µF

10µF

–5.2V

0.1µF

+15V

10µF

0.1µF

10µF

–15V

+15V

20kΩ

0.1µF

–15V

55

DIGITAL

SUPPLY

54 DIGITAL

58-60 GROUND

57

DIGITAL

SUPPLY

69

ANALOG

SUPPLY

64-68

ANALOG

GROUND

63

ANALOG

SUPPLY

ADS-945

12

13 ANALOG

15-17 GROUND

13

START CONVERT 32

+10 REF. OUT 7

18

OFFSET

ADJUST

GAIN

ADJUST

9

Figure 2. ADS-945 Connection Diagram

53 BIT 1 (MSB)

52 BIT 2

51 BIT 3

50 BIT 4

49 BIT 5

48 BIT 6

47 BIT 7

46 BIT 8

45 BIT 9

44 BIT 10

43 BIT 11

42 BIT 12

41 BIT 13

40 BIT 14 (LSB)

34 OUTPUT ENABLE

33 OVERFLOW

30 T/H STATUS

29 T/H STATUS

4 ANALOG INPUT

+15V

0.1µF

20kΩ

–15V

4

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