ADN2849

Rev. Pr. G | Page 10 of 17

The capacitors used AC-coupling and the decoupling of the

VBB pin must have an impedance less than 50Ω over the

required operating frequency range. Generally this is achieved

using values from 10nF to 100nF.

The retiming feature of the ADN2849 allows the user to remove

the data dependent jitter present on the DATAP and DATAN

pins by applying the data and clock signals to the ADN2849’s

internal latch. The retiming feature can be enabled or disabled

depending on the logic level applied to the CLK_SELB pin as

described in table 7. Note that any jitter present on the CLKP

and CLKN pins is added to the output.

Table 7.

CLK_SELB logic level

Retiming function

High

Disabled

Low

Enabled

If the retiming feature is disabled the CLKP and CLKN inputs

can be left floating.

The CLK_SELB is a 5V TTL and CMOS compatible digital

input. Its equivalent circuit is shown in figure 20.

CLK_SELB

180K

60K

40K

VEE

VEE

GND

GND

Figure 20. Equivalent circuit of the CLK_SELB pin

CROSS POINT ADJUST

The cross point adjust function allows the user to move the eye

crossing level in the modulation voltage to compensate for

asymmetry in the EA modulator electrical-to- optical transfer

function. Figure 21 shows an example on how the cross point

adjust can compensate the asymmetry of the EA modulator

transfer function. The 50% cross point in the optical eye can be

obtained in this case by moving the cross point of the signal

applied to the EA modulator away from the 50% point.

Optical

Output

Electrical

Input

Figure 21. Cross point adjust compensation

The cross point is controlled by the differential voltage applied

to the CPAP and CPAN pins. The equivalent circuit of the

CPAP and CPAN pins is shown in figure 22.

100

Ω

100

Ω

100

µA

100

µA

CPAP

CPAN

VEE

VEE

VEE

VEE

VEE

VEE

GND

GND

Figure 22. Equivalent circuit of the CPAP and CPAN pins

Preliminary Technical Data