GS7025 PRO-LINX™ Serial Digital Receiver

Data Sheet

13813 - 7

October 2009

12 of 23

Figure 3-1: SSI/CD Voltage vs. Cable Length

When the signal strength decreases to the level set at the “Carrier Detect Threshold

Adjust” pin, the SSI/CD voltage goes to a logic “0” state (0.8 V) and can be used to drive

other TTL/CMOS compatible logic inputs. When loss of carrier is detected, the SDO/SDO

outputs are muted (set to a known static state). Additional SSI/CD output source current

can be obtained in applications with a pull-up resistor. An external 5kΩ pull-up resistor

with less than 50pf capacitor loading is recommended.

3.1.2 Carrier Detect Threshold Adjust

Carrier Detect Threshold Adjust is designed applications such as routers where signal

crosstalk and circuit noise cause the equalizer to output erroneous data when no input

signal is present. The GS7025 solves this problem with a user adjustable threshold which

meets the unique conditions that exist in each application. Override and internal default

settings are provided to give the user total flexibility.

The threshold level at which loss of carrier is detected is adjustable via external resistors

at the CD_ADJ pin (see Figure 2-4). The control voltage at the CD_ADJ pin is set by a

simple resistor divider circuit (see Figure 4-1: GS7025 Typical Application Circuit). The

threshold level is adjustable from 200m to 350m. By default (no external resistors), the

threshold is typically 320m. In noisy environments, it is not recommended to leave this

pin floating. Connecting this pin to VEE disables the SDO/SDO muting function and

allows for maximum possible cable length equalization.

3.1.3 Output Eye Monitor Test

The GS7025 also provides an 'Output Eye Monitor Test' (OEM_TEST) which allows the

verification of signal integrity after equalization, prior to re-slicing. The OEM_TEST pin

is an open collector current output that requires an external 50Ω pullup resistor. When

the pullup resistor is not used, the OEM_TEST block is disabled and the internal

OEM_TEST circuit is powered down. The OEM_TEST provides a 100mVp-p signal when

driving a 50Ω oscilloscope input. Due to additional power consumed by this diagnostic

circuit, it is not recommended for continuous operation.

0

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CABLE LENGTH (m)

0

CD_ADJ

CONTROL RANGE