MAX3935(2002) 查看數據表（PDF） - Maxim Integrated

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MAX3935
(Rev.:2002)

10.7Gbps EAM Driver

Maxim Integrated 

10.7Gbps EAM Driver

VTT

50Ω

CLK+

50Ω

50Ω

CLK-

DATA+

50Ω

50Ω

DATA-

50Ω

VTT

50Ω

Q

D

50Ω

1mA

RTEN

MODEN

75Ω

75Ω

0

PWC

MUX

100Ω

MOD2

MOD1

100Ω

MODN1

MOD

MODN2

BIAS

L

1

IMOD

IBIAS

1mA

RMOD

RBIAS

5kΩ

5kΩ

EAM

50Ω

50Ω

PWC+

RPWC

2kΩ

VEE

PWC-

Figure 3. MAX3935EGJ Functional Diagram

MODSET

BIASSET

BIASMON

VEE MODMON

VEE

IBIAS

=

VBIASREF

7.5Ω

To keep the bias and modulation currents in compli-

ance, the following constraint on the total current must

be made for 50Ω EAM modules:

|VEE| - (IBIAS + IMOD) ✕ 30Ω ≥ 1.55V

External Op Amp Selection

External op amps are required for regulating the bias

and modulation currents. The ability to operate from a

single supply with input common-mode range extend-

ing to the negative supply rail is critical in the op amp

selection. Low bias current and high PSRR also are

important. Bias current to the inverting input passes

through a 5kΩ resistor. This could add an error to the

voltage produced by the modulation and bias current-

sense resistors. The op amp gain bandwidth must be

high enough to regulate at the power-supply ripple fre-

quency on VEE.

Pulse-Width Control Setup

Two methods of control are possible when pulse predis-

tortion is desired to minimize distortion at the receiver.

The pulse width can be set with a 2kΩ potentiometer (or

equivalent fixed resistors); or applying a voltage, with

VEE + 1V common mode, to the PWC pins can set it. See

Table 1 for the desired effect of the pulse-width setting.

Table 1. Pulse-Width Control

PULSE

WIDTH

100%

>100%

<100%

RP, RN for

RP + RN = 2kΩ

1kΩ or Open

RP > RN

RP < RN

VPWC+, VPWC- for

VCM = VEE + 1V

VPWC+ = VPWC- = VEE + 1V

VPWC+ > VPWC-

VPWC+ < VPWC-

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