Rainbow-electronics MAX3805 Instrukcja Użytkownika Pobierz pdf (Strona 6)

MAX3805

Input Stage with Equalization

The low-noise input stage of the MAX3805 includes two

amplifiers, one with flat frequency response and the

other with a highpass frequency response compensat-

ing for the loss characteristic of 6-mil FR-4 PC board

transmission line. A current-steering network, imple-

mented with a pair of variable attenuators feeding into a

common summing node, provides the means to contin-

uously vary the amount of equalization. The amount of

equalization is controlled by feedback from two power-

detector blocks that set the variable attenuators to

match the loss of a particular transmission path.

Dual Power-Detector Feedback Loop

The MAX3805 adapts the equalizer to a specific path

loss by sampling the output of the summing node with a

pair of frequency-dependent power detectors. The first

power detector has a lowpass bandwidth of 500MHz; the

second power detector has full bandwidth.

NRZ PRBS data has a sin

(f)/f

spectral characteristic.

When this data is passed through a lossy FR-4 path,

high-frequency components are attenuated, while low-

10.7Gbps Adaptive Receive Equalizer

6 _______________________________________________________________________________________

∑

MAX3805

CML IN

FLAT

AMP

BOOST

AMP

VARIABLE

ATTENUATOR

VARIABLE

ATTENUATOR

LIMITING

AMP

CML OUT

LF POWER

DETECTOR

POWER

DETECTOR

LOOP

FILTER

SIGNAL

DETECT

LFPD HFPD

SDO-

SDO+

SDI+

SDI-

CC1

CC2

Functional Diagram

50Ω50Ω

ESD

STRUCTURES

CC2

OUT+

OUT-

Figure 1. CML Output Structure

1 2 3 4 5 6 7 8 9 10

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