XRD87L99 查看數據表（PDF） - Exar Corporation

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XRD87L99

LOW POWER, 2 MSPS, 10-BIT, A/D CONVERTER WITH 8-CHANNEL MUX

Exar Corporation 

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XRD87L99

LOW POWER, 2 MSPS, 10-BIT, A/D CONVERTER WITH 8-CHANNEL MUX

REV. 1.0.0

FIGURE 5. XRD87L99 COMPARATORS WITH CHANGING REFERENCE VOLTAGE

External

Update

References

Clock

Internal

AIN Sample

Window

Ladder Sample

Window (MSB Bank)

Ladder Compare

(LSB Bank)

External

DATA

Settle by Clock Update Time

Short Cycle Sample will be discarded

tS

Reference Stable Time - For Sample A IN1

Hold Reference Value Past

Clock Change for tAP Time

Reference Stable Time - For Sample A IN2

AINX0

Sample AIN1

ΦB

ΦS

Sample AIN1

Sample Ladder

for AIN1

AINX1

ΦB Not Used ΦS

AINX1

Sample Ladder

for AINX1

Sample AIN2

ΦB

ΦS

Sample AIN2

Sample Ladder

for AIN2

Sample Ladder

for AINX2

Compare Ladder

V/S AINX0

Compare Ladder

V/S AIN1

Compare Ladder

V/S AINX1

Compare Ladder

V/S AIN2

DATA AIN0

DATA AINX0

Not Used

DATA AIN1

DATA AINX1

Not Used

1.1 ACCURACY OF CONVERSION: DNL AND INL

The transfer function for an ideal A/D converter is

shown in Figure 6.

FIGURE 6. IDEAL A/D TRANSFER FUNCTION

DIGITAL

CODES

1 LSB

002

001

000

LSB

VREF(-)

V001

V002

OFW=0

OFW=1

3FF

3FE

3FD

V3FE

V3FF

V

V0FW = VREF(+)

The overflow transition (VOFW) takes place at:

VIN = VOFW = VREF(+)

The first and the last transitions for the data bits take

place at:

VIN = V001 = VREF(-) + 1.0 * LSB

VIN = V3FF = VREF(-) - 1.0 * LSB

VREF = VREF(+) - VREF(-)

LSB = VREF / 1024 = (V3FF - V001) / 1022

NOTE: The overflow transition is a flag and has no impact

on the data bits.

In a "real" converter the code-to-code transitions don't

fall exactly every VREF/1024 volts.

A positive DNL (Differential Non-Linearity) error

means that the real width of a particular code is larger

than 1 LSB. This error is measured in fractions of

LSBs.

A Max DNL specification guarantees that ALL code

widths (DNL errors) are within the stated value. A

specification of Max DNL = + 0.5 LSB means that all

code widths are within 0.5 and 1.5 LSB. If VREF = 2.56

V then 1 LSB = 2.5 mV and every code width is within

1.25 and 3.75 mV.

10

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