AD9220ARSZ datasheet(24/32 Pages) AD

24 / 32 page

REV. E

–24–

AD9221/AD9223/AD9220

1.25k

0.1 F

10 F

2.5k

+5V

REF43

VREF(+)

VREF(–)

DAC08

IOUT

0.1 F

2.5k

0.1 F

2.5k

0.1 F

2.5k

162

2.5k

100

1.1k

U2A

1.25V

39mV

U2B

CH1

CH2

CH3

CH4

CH5

CH6

CH7

CH8

ADG608

1.25V

OUT

VREF(+)

VREF(–)

DAC08

IOUT

2.5k

100

AD9221/

AD9223/

AD9220

SENSE

VREF

VINA

VINB

BIT 1 – BIT 12

OTR

2.50V

100

2.5k

Figure 35. Typical Multichannel Data Acquisition System

The offset calibration circuitry consists of a DAC, U5 and

the buffer amplifier, U4. The DAC is configured for a bipolar

adjustment span of

±64 LSB with a 1/2 LSB resolution span

with respect to the AD9221/AD9223/AD9220. Note that both

current outputs of U5 were configured to provide a bipolar

adjustment span. Also, RC is used to decouple the output of

both DACs, U3 and U5, from their respective op amps.

The calibration procedure consists of a two step process. First,

the bipolar offset is calibrated by selecting CH2, the 2.5 V sys-

tem reference, of the analog multiplexer and preloading the DAC,

U5, with a midscale code of 1000 0000. If possible, several

readings of the A/D should be taken and averaged to determine

the required digital offset adjustment code, U5. This averaged

offset code requires an extra bit of resolution since 1 LSB of U5

equates to 1/2 LSB of the AD9221/AD9223/AD9220. The

required offset correction code to U5 can then be determined.

Second, the system gain is calibrated by selecting CH2, a 1.25 V

input that corresponds to –FS of the A/D. Before the value is

read, U4 should be preloaded with a code of 00 (Hex). Several

readings can also be taken and averaged to determine the digital

gain adjustment code to U2A. In this case, 1 LSB of the A/D

corresponds to 1 LSB of U4.

Due to the AD9221/AD9223/AD9220’s excellent INL perfor-

mance, a two-point calibration procedure (i.e., –FS to midscale)

instead of an endpoint calibration procedure was chosen. Also,

since the bipolar offset is insensitive to any gain adjustment (due

to the differential SHA of the A/D), an iterative calibration

process is not required. The temperature stability of the circuit

is enhanced by selecting a dual precision op amp for U2 (e.g.,

OP293) and low temperature drift, thin film resistors. Note that

this application circuit was not built at the release of this data

sheet. Please consult Analog Devices for application assistance

or comments.

AD9220ARSZ датащи(PDF) 24 Page - Analog Devices

AD9220ARSZ датащи(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

датащи скачать

ссылки URL