MAX3657 데이터 시트보기 (PDF) - Maxim Integrated

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MAX3657

155Mbps Low-Noise Transimpedance Amplifier

Maxim Integrated 

155Mbps Low-Noise Transimpedance

Amplifier

Functional Diagram

IN

MON

VCCZ

FILT

TRANSIMPEDANCE

AMPLIFIER

MAX3657

VOLTAGE

OUTPUT

RF

AMPLIFIER

BUFFER

ROUT

+1.0V

DC-CANCELLATION

CIRCUIT

LOWPASS

FILTER

ROUT

OUT+

OUT-

ROUT

ENABLE

Detailed Description

The MAX3657 transimpedance amplifier is designed for

155Mbps fiber-optic applications. The functional dia-

gram of the MAX3657 comprises a transimpedance

amplifier, a voltage amplifier, a DC-cancellation circuit,

and a CML output buffer.

Transimpedance Amplifier

The signal current at the input flows into the summing

node of a high-gain amplifier. Shunt feedback through

resistor RF converts this current into a voltage. Schottky

diodes clamp the output signal for large input currents

(Figure 1).

Voltage Amplifier

The voltage amplifier provides additional gain and con-

verts the transimpedance amplifier single-ended output

signal into a differential signal.

Output Buffer

The output buffer provides a reverse-terminated volt-

age output and is designed to drive a 200Ω differential

load between OUT+ and OUT-. For optimum supply-

noise rejection, the MAX3657 should be terminated with

a differential load. The MAX3657 single-ended outputs

do not drive a DC-coupled grounded load. The outputs

should be AC-coupled or terminated to VCC. If a single-

ended output is required, both the used and the unused

outputs should be terminated in a similar manner.

DC-Cancellation Circuit

The DC-cancellation circuit uses low-frequency feed-

back to remove the DC component of the input signal

(Figure 2). This feature centers the input signal within

the transimpedance amplifier’s linear range, thereby

reducing pulse-width distortion.

The DC-cancellation circuit is internally compensated

and does not require external capacitors. This circuit

minimizes pulse-width distortion for data sequences

that exhibit a 50% mark density. A mark density signifi-

cantly different from 50% causes the MAX3657 to gen-

erate pulse-width distortion. Grounding the FILT pin

disables the DC-cancellation circuit. For normal opera-

tion, the DC-cancellation circuit must be enabled.

The DC-cancellation current is drawn from the input and

creates noise. For low-level signals with little or no DC

component, the added noise is insignificant. However,

amplifier noise increases for signals with significant DC

component (see the Typical Operating Characteristics).

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