GN2014A Datasheet, PDF (13/18 Pages) Gennum Corporation – XFP Tx Signal Conditioner with VCSEL Driver

3.5 GN2014A Cross Point Adjust
The GN2014A cross point adjust is used to pre-distort the output signal to optimize
optical performance. This is accomplished using two control pins:
1. CPAPol (Pin 10) — Controls direction of crosspoint change, digital pin
2. CPA (Pin 12) — Controls magnitude of crosspoint change, analog control
With CPA voltage set to nominal 0.8V, the output waveform will have a cross point at the
50% level, as indicated in Figure 3-4.
75%
50%
25%
Crossing Point
is at 50% Level
0ps
60ps
120ps
180ps
Time (s)
Figure 3-4: GN2014A Output Signal with CPA voltage set to 0.8V
To increase the cross point to the 75% level, the CPA polarity (pin 10:CPAPol) must be set
HIGH, and the CPA voltage (pin 12:CPA) increased to 3.1V. This results in the output
waveform illustrated in Figure 3-5.
Crosspoint
75%
50%
25%
0ps
60ps
120ps
180ps
Time(s)
Figure 3-5: GN2014A Output Signal when CPA Polarity control input is set
HIGH, CPA = 3.1V
The cross point can be set to an intermediate level between 50% and 75% by setting the
CPA to a voltage between 0.8V and 3.1V.
GN2014A XFP Tx Signal Conditioner with VCSEL Driver
Data Sheet
39260 - 8
May 2010
13 of 18
Proprietary & Confidential