VITESSE

SEMICONDUCTOR CORPORATION

Advance Product Information

VSC7969

3.125Gb/s Integrated Transimpedance

and Limiting Amplifier with Signal Detect

G52355-0, Rev 2.0

Page 9

02/09/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

Internet: www.vitesse.com

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

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

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

used, the IMON pin can be left unconnected.

Electrical

Min

Typ

Max

Units

Assert

3

5

9

µA

Deassert

1

2.2

3

µA

Hysteresis

1

2

4

dB

Electrical

Min

Typ

Max

Units

Assert

6

10

18

µA

Deassert

2

4.4

6

µA

Hysteresis

1

2

4

dB