VITESSE
SEMICONDUCTOR CORPORATION
Advance Product Information
VSC7969
3.125Gb/s Integrated Transimpedance
and Limiting Amplifier with Signal Detect
Signal Detect
The signal detect feature of the VSC7969 provides a CMOS level output corresponding to the input current
level to the transimpedance amplifier. The assert and deassert levels of the signal detect pin can be adjusted by
placing an optional resistor from SD_ADJ to ground. The following tables show the two extremes at which the
signal detect pin will operate; open circuit and short-ciruit to ground.
Table 5: Signal Detect Function, SD_ADJ Open
Electrical
Min
Assert
Deassert
Hysteresis
3
1
1
Typ
5
2.2
2
Max
9
3
4
Units
µA
µA
dB
With SD_ADJ (pin 16) shorted to ground, thresholds are 3dB higher, as shown in Table 6.
Table 6: Signal Detect Function, SD_ADJ Shorted to Ground
Electrical
Min
Assert
Deassert
Hysteresis
6
2
1
Typ
10
4.4
2
Max
18
6
4
Units
µA
µA
dB
Photodetector Current Monitor
The IMON pin provides a linear measurement of the average input current from the photodetector to the
transimpedance amplifier. For example, if 20µA is the average input current to the transimpedance amplifier,
the current through the IMON pin will be 20µA (see the typical operating curve “IMON
Characteristic, 0µA to
200µA).
To use this feature, connect the IMON pin to V
CC
using a resistor less than 2k
Ω
. If this feature is not
used, the IMON pin can be left unconnected.
G52355-0, Rev 2.0
02/09/01
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VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
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