GN2014A Datasheet, PDF (9/18 Pages) Gennum Corporation – XFP Tx Signal Conditioner with VCSEL Driver

3.2 VCO Supply Recommendations
When the Host Board Power Supply output is used to power the GN2014A device,
additional filtering for the VCOVcc supply input is recommended.
This filtering is required to improve power line noise rejection.
Typically, a 1st order RC filter provides sufficient supply noise attenuation (i.e. R5, C1
and C12 in Figure 3-1).
The capacitor C1 = 100nF
The capacitor C12 = 4.7μF
The maximum value of the resistor R5 can be calculated using the following
information:
• Minimum operational voltage (after regulation and including supply noise) at the
VCOVcc supply input (pin 21): VCOVcc _(min) = 2.74Vdc
• Maximum operational current into the VCOVcc supply input:
I_{VCOVcc (max)} = 14.9mA
Example 3-1: Calculating Resistor Values
Vcc = 2.8Vdc.
R5 _(max) = (Vcc - VCOVcc _(min)) / I_{VCOVcc (max)} = 60mV / 14.9mA = 4Ω
The closest lower standard resistor value, which can be used for R5 is 3.9Ω.
When an external LDO voltage regulator is used to power the GN2014A device, R5 =
3.3 Control Interface
The GN2014A control interface consists of five inputs that determine the mode in which
the device is operating:
• Polarity Inversion (POLInv)
• Loop Back Enable (LBEn)
• Retimer Enable (RTEn)
• Cross Point Adjust Polarity (CPAPol)
Table 3-1 describes the conditions at these inputs to enable or disable a particular mode.
Figure 3-2 shows a simplified equivalent circuit common for all control inputs.
GN2014A XFP Tx Signal Conditioner with VCSEL Driver
Data Sheet
39260 - 8
May 2010
9 of 18
Proprietary & Confidential