______and Applications Information

The MAX3803 is an adaptive equalizer designed to

extend the reach of transmission lines in high-frequency

backplane and rack-to-rack interconnect applications.

The MAX3803 automatically adjusts to attenuation

caused by skin-effect and dielectric losses. Although

optimized for coded and scrambled data between

2.488Gbps and 3.125Gbps, the MAX3803 provides

effective compensation for rates between 1Gbps

and 3.2Gbps.

The MAX3803 consists of low common-mode input and

output buffers, an equalizer core, a DC-offset-correction

loop, and a limiting amplifier (Figure 2).

Low Common-Mode Input and Output

The MAX3803 permits DC-coupling to CML transmitters

and receivers that require termination voltages as low

to maintain compatible common-mode levels between

and can be used to bridge two common-mode require-

ments without the use of DC-blocking capacitors. See

Figure 3 and Figure 4 for the equivalent input and out-

put structures.

Media Equalization

Equalization at the input compensates for high-frequency

loss encountered with FR4 stripline (edge-coupled) or

28AWG twin ax. The equalizer core is an amplifier with a

self-adjusting frequency response.

DC Cancellation Loop

The DC cancellation loop removes the pulse-width dis-

tortion caused by internal offsets. The closed-loop

response creates a low-frequency cutoff of approxi-

mately 15kHz, below which the offset control tracks the

AC signal. This also sets the limit on the maximum time

DC-Coupled, UCSP 3.125Gbps Equalizer

6

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MAX3803

CML

INPUT

CML

OUTPUT

IN+

IN-

OUT+

OUT-

EQUALIZER

DC

CANCELLATION

LOOP

LIMITING

AMPLIFER

Figure 2. Functional Diagram

2

2

22

SIGNAL

SOURCE

IN

OUT

AB

C

CONNECTOR

CONNECTOR

≤40in EDGE-COUPLED TRANSMISSION LINE ON FR4 OR ≤10m 28AWG TWIN AX CABLE

MAX3803

Figure 1. Backplane Interconnect

ESD

STRUCTURES

+1.1V

50

Ω

50

Ω

OUT+

OUT-

Figure 4. CML Output Structure

ESD

STRUCTURES

+1.1V

50

Ω

50

Ω

IN+

IN-

Figure 3. CML Input Structure