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AD7703

LC2MOS 20-Bit A/D Converter

Analog Devices 

AD7703

CS

SDATA

t10

DATA

VALID

HI-Z

Figure 4. SSC Mode Data Hold Time

CS

SDATA

t15

DATA

HI-Z

VALID

Figure 5b. SEC Mode Data Hold Time

DRDY

CS

SCLK

SDATA

t12

t11

HI-Z

t13

DB19

t14

DB18

DB1

t16

HI-Z

DB0

Figure 5a. SEC Mode Timing Diagram

CLKIN

CS

SCLK

SDATA

t7

HI-Z

t8

t4

t8

HI-Z

DB19

t5

DB18

HI-Z

t9

DB1

HI-Z

DB0

Figure 6. SSC Mode Timing Diagram

DEFINITION OF TERMS

Linearity Error

This is the maximum deviation of any code from a straight line

passing through the endpoints of the transfer function. The

endpoints of the transfer function are zero-scale (not to be

confused with bipolar zero), a point 0.5 LSB below the first code

transition (000 . . . 000 to 000 . . . 001) and full-scale, a point

1.5 LSB above the last code transition (111 . . . 110 to 111 . . .

111). The error is expressed as a percentage of full scale.

Differential Linearity Error

This is the difference between any code’s actual width and the

ideal (1 LSB) width. Differential linearity error is expressed in

LSB. A differential linearity specification of ± 1 LSB or less

guarantees monotonicity.

Positive Full-Scale Error

Positive full-scale error is the deviation of the last code transition

(111 . . . 110 to 111 . . . 111) from the ideal (VREF ± 3/2 LSB).

It applies to both positive and negative analog input ranges and

is expressed in microvolts.

Unipolar Offset Error

Unipolar offset error is the deviation of the first code transition

from the ideal (AGND + 0.5 LSB) when operating in the

Unipolar mode.

Bipolar Zero Error

This is the deviation of the midscale transition (0111 . . . 111 to

1000 . . . 000) from the ideal (AGND – 0.5 LSB) when operating

in the Bipolar mode. It is expressed in microvolts.

Bipolar Negative Full-Scale Error

This is the deviation of the first code transition from the ideal

(–VREF + 0.5 LSB) when operating in the Bipolar mode.

Positive Full-Scale Overrange

Positive full-scale overrange is the amount of overhead available

to handle input voltages greater than +VREF (for example, noise

peaks or excess voltages due to system gain errors in system

calibration routines) without introducing errors due to overloading

the analog modulator or overflowing the digital filter.

Negative Full-Scale Overrange

This is the amount of overhead available to handle voltages below

–VREF without overloading the analog modulator or overflowing

the digital filter. Note that the analog input will accept negative

voltage peaks even in the Unipolar mode.

Offset Calibration Range

In the system calibration modes (SC2 low), the AD7703 calibrates

its offset with respect to the AIN pin. The offset calibration range

specification defines the range of voltages, expressed as a

percentage of VREF, that the AD7703 can accept and still accurately

calibrate offset.

Full-Scale Calibration Range

This is the range of voltages that the AD7703 can accept in the

system calibration mode and still correctly calibrate full scale.

Input Span

In system calibration schemes, two voltages applied in sequence

to the AD7703’s analog input define the analog input range. The

input span specification defines the minimum and maximum

input voltages from zero to full scale that the AD7703 can accept

and still accurately calibrate gain. The input span is expressed

as a percentage of VREF.

REV. E

–5–

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