EVAL-ADN2811-CML データシートの表示（PDF） - Analog Devices

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EVAL-ADN2811-CML

OC-48/OC-48 FEC Clock and Data Recovery

Analog Devices 

ADN2811

DEFINITION OF TERMS

MAXIMUM, MINIMUM, AND TYPICAL

SPECIFICATIONS

Specifications for every parameter are derived from statistical

analyses of data taken on multiple devices from multiple wafer

lots. Typical specifications are the mean of the distribution of

the data for that parameter. If a parameter has a maximum (or a

minimum), that value is calculated by adding to (or subtracting

from) the mean six times the standard deviation of the distribution.

This procedure is intended to tolerate production variations. If

the mean shifts by 1.5 standard deviations, the remaining 4.5

standard deviations still provide a failure rate of only 3.4 parts per

million. For all tested parameters, the test limits are guardbanded

to account for tester variation and therefore guarantee that no

device is shipped outside of data sheet specifications.

INPUT SENSITIVITY AND INPUT OVERDRIVE

Sensitivity and overdrive specifications for the quantizer involve

offset voltage, gain, and noise. The relationship between the logic

output of the quantizer and the analog voltage input is shown in

Figure 6. For a sufficiently large positive input voltage, the output is

always Logic 1; similarly for negative inputs, the output is always

Logic 0. However, the transitions between output Logic Levels 1

and 0 are not at precisely defined input voltage levels but occur

over a range of input voltages. Within this zone of confusion,

the output may be either 1 or 0, or it may even fail to attain a

valid logic state. The width of this zone is determined by the

input voltage noise of the quantizer. The center of the zone of

confusion is the quantizer input offset voltage. Input overdrive

is the magnitude of signal required to guarantee the correct

logic level with 1 × 10−10 confidence level.

OUTPUT

1

NOISE

0

OFFSET

INPUT (V p-p)

OVERDRIVE

SENSITIVITY

(2× OVERDRIVE)

Figure 6. Input Sensitivity and Input Overdrive

Data Sheet

SINGLE-ENDED VS. DIFFERENTIAL

AC-coupling typically drives the inputs to the quantizer. The

inputs are internally dc biased to a common-mode potential of

~0.6 V. Driving the ADN2811 single-ended and observing the

quantizer input with an oscilloscope probe at the point indicated in

Figure 7 shows a binary signal with an average value equal to the

common-mode potential and instantaneous values both above

and below the average value. It is convenient to measure the peak-

to-peak amplitude of this signal and call the minimum required

value the quantizer sensitivity. Referring to Figure 6, since both

positive and negative offsets need to be accommodated, the

sensitivity is twice the overdrive.

10mV p-p

VREF

SCOPE

PROBE

ADN2811

PIN

+

QUANTIZER

VREF

50Ω 50Ω

Figure 7. Single-Ended Sensitivity Measurement

5mV p-p

VREF

SCOPE

PROBE

ADN2811

PIN

+

QUANTIZER

NIN

VREF

50Ω 50Ω

Figure 8. Differential Sensitivity Measurement

Driving the ADN2811 differentially (see Figure 8), sensitivity

seems to improve by observing the quantizer input with an

oscilloscope probe. This is an illusion caused by the use of a

single-ended probe. A 5 mV p-p signal appears to drive the

ADN2811 quantizer. However, the single-ended probe measures

only half the signal. The true quantizer input signal is twice this

value since the other quantizer input is complementary to the

signal being observed.

Rev. C | Page 8 of 20

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