MAX3676E Просмотр технического описания (PDF) - Maxim Integrated

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MAX3676E

622Mbps, 3.3V Clock-Recovery and Data-Retiming IC with Limiting Amplifier

Maxim Integrated 

622Mbps, 3.3V Clock-Recovery and

Data-Retiming IC with Limiting Amplifier

LOL

VCC

6k

PHADJ+ PHADJ- FIL+ FIL-

DQ

SDO+

SDO-

PECL

DDI+

DDI-

PECL

INSEL

PHASE/FREQ

DETECTOR

ADI-

LIMITER

ADI+

42dB

1.23V

BIAS

OFFSET

CORRECTION

POWER

DETECT

Σ

FILTER

I

VCO

Q

622.08MHz

VCC

6k

SCLKO+

SCLKO-

PECL

MAX3676

OLC+ OLC-

CFILT RSSI INV

VTH

LOP

Figure 1. Functional Diagram

_______________Detailed Description

The block diagram in Figure 1 shows the MAX3676’s

architecture. It consists of a limiting-amplifier input

stage followed by a fully integrated clock/data-recovery

(CDR) block implemented with a PLL. The input stage

is selectable between a limiting amplifier or a simple

PECL input buffer. The limiting amplifier provides an

LOP monitor and an RSSI output. The PLL consists of a

phase/frequency detector (PFD), a loop filter amplifier,

and a voltage-controlled oscillator (VCO).

Limiting Amplifier

The MAX3676’s on-chip limiting amplifier accepts an

input signal level from 3.0mVp-p to 1.2Vp-p. The ampli-

fier consists of a cascade of gain stages that include

full-wave logarithmic detectors. The combined small-

signal gain is approximately 42dB, and the -3dB band-

width is 650MHz. Input-referred noise is typically

80µVRMS, providing excellent sensitivity for small-ampli-

tude data streams.

In addition to driving the CDR, the limiting amplifier pro-

vides both an RSSI output and an LOP monitor that

allow the user to program the threshold voltage. The

RSSI circuitry provides an output voltage that is linearly

proportional to the input power (in decibels) detected

between the ADI+ and ADI- input pins and is sensitive

enough to reliably detect signals as small as 2mVp-p

(see Typical Operating Characteristics).

Input DC offset reduces the accuracy of the power

detector; therefore, an integrated feedback loop is

included that automatically nulls the input offset of the

gain stage. The addition of this offset-correction loop

requires that the input signal be AC-coupled when

using the ADI+ and ADI- inputs.

Finally, for applications that do not require the limiting

amplifier, selecting the digital inputs conserves power

by turning off the postamplifier block.

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