GENNUM CORPORATION

521 - 70 - 06

7

Fig. 11

3. CARRIER DETECT THRESHOLD ADJUST

The threshold level at which loss of carrier is detected is

adjustable via external resistors at the CD_ADJ pin. The

control voltage at the CD_ADJ pin is set by a simple resistor

divider circuit. The threshold level is adjustable from 200m

to 350m. By default (no external resistors), the threshold is

typically 320m. Connecting this pin to Ground disables the

SDO/SDO

muting

function

and

allows

for

maximum

possible cable length equalization.

This feature is designed for use in applications such as

routers where signal crosstalk and circuit noise cause the

equalizer to output erroneous data when no input signal is

present. This problem is not solved by using a Carrier

Detect function with a fixed internal reference because the

signal to noise ratio on the circuit board may be significantly

less than the default signal detection level set by the on-

chip reference. To solve this problem, the GS9024 provides

a user adjustable threshold to meet the unique conditions

that exist in each user's application. Override and internal

default settings are provided to give the user total flexibility.

4. OUTPUT EYE MONITOR

The GS9024 provides an 'Output Eye Monitor' (OEM) which

allows the verification of signal integrity after equalization,

prior to reslicing. The OEM pin is an open collector current

output that requires an external 50

Ω pullup resistor. When

the pullup resistor is not used, the OEM block is disabled

and the internal OEM circuit is powered down. The OEM

provides

a

0.25Vp-p

signal

when

driving

a

5

0Ω

oscilloscope input.

5. I/O DESCRIPTION

5.1. High Speed Analog Inputs (SDI/SDI)

SDI/SDI

are

high

impedance

inputs

which

accept

differential or single-ended input drive.

Figure 12 shows the recommended interface when a single-

ended serial digital signal is used.

Fig. 12

5.2. High Speed Outputs (SDO/SDO)

SDO/SDO are current mode outputs that require external

pullups (see Figure 13). The output signal swings are

800mV when 75

Ω resistors are used. A diode can be

levels down by approximately 0.7 volts. When the output

traces are longer than 1 inch, controlled impedance traces

should be used. The pullup resistors should be placed at

the end of the output traces as they terminate the trace in

its characteristic impedance (75

Ω).

Fig. 13

0

1

2

3

4

5

50

100

150

200

250

300

350

400

450

500

CABLE LENGTH (m)

0

CD_ADJ

CONTROL RANGE

SDI

GS9024

SDI

75

Ω

37.5

Ω

75

Ω

10nF

10nF

75

Ω

SDO

SDO

GS9024

75

Ω

75

Ω