GS9064 データシートの表示（PDF） - Gennum -> Semtech

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GS9064

SD SDI Adaptive Cable Equalizer

Gennum -> Semtech 

3. DETAILED DESCRIPTION

The GS9064 is a high speed bipolar IC designed to

equalize SD serial digital signals. The device can typically

equalize 350 meters of Belden 1694A cable at 270Mb/s.

Powered from a single +3.3V or -3.3V power supply, the

device consumes approximately 240mW of power.

3.1 SERIAL DIGITAL INPUT

The SD serial digital input signal may be connected to the

input pins (SDI/SDI) in either a differential or single ended

configuration. AC coupling of the inputs is recommended,

as the SDI and SDI inputs are internally biased at

approximately +1.8 volts.

3.2 AUTOMATIC CABLE EQUALIZATION

The input signal passes through a variable gain equalizing

stage whose frequency response closely matches the

inverse of the cable loss characteristic. In addition, the vari-

ation of the frequency response with control voltage imitates

the variation of the inverse cable loss characteristic with

cable length.

The edge energy of the equalized signal is monitored by a

detector circuit which produces an error signal

corresponding to the difference between the desired edge

energy and the actual edge energy. This error signal is

integrated by both an internal and an external AGC filter

capacitor providing a steady control voltage for the gain

stage. As the frequency response of the gain stage is

automatically varied by the application of negative

feedback, the edge energy of the equalized signal is kept

at a constant level which is representative of the original

edge energy at the transmitter.

The equalized signal is also DC restored, effectively restor-

ing the logic threshold of the equalized signal to its correct

level independent of shifts due to AC coupling. The digital

output signals have a nominal voltage of 750mVpp differen-

tial, or 375mVpp single ended when terminated with 50Ω as

shown below in Figure 13.

SDO

SDO

50 50

+187.5mV

VCM = 2.925V

typical

-187.5mV

+187.5mV

VCM = 2.925V

typical

-187.5mV

3.3 CABLE LENGTH INDICATION & CARRIER

DETECT/MUTE

The GS9064 incorporates an analog cable length indicator

(CLI) output and a programmable threshold output mute

(MCLADJ). In addition, a multi-function CD/MUTE pin allows

control of the GS9064 MUTE functionality for SD inputs.

3.3.1 Cable Length Indicator

The voltage output of the CLI pin is a representation of the

amount of cable present at the inputs of the device. Figure

8 shows the CLI voltage versus cable length (signal

strength). At 270Mb/s with no cable length and 800mV input

signal levels, the CLI output voltage is approximately 2.5V.

As the cable length is increased, the CLI voltage

decreases, thereby providing an approximate correlation

between the CLI voltage and cable length

3.3.2 Programmable Mute Threshold

A voltage programmable mute threshold (MCLADJ) is

included to allow muting of the GS9064 output when a

selected cable length is reached. This feature allows the

device to distinguish between low amplitude SDI signals

and noise at its input.

Figure 10 shows the relationship between the voltage

applied to the MCLADJ pin and the input cable length

accepted by the GS9064. For consistent accurate results

this may need to be calibrated for each device. The

MCLADJ pin may be left unconnected for applications

where output muting is not required.

This feature has been 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 actually present. The use of a Carrier Detect function with

a fixed internal reference does not solve this problem since

the signal to noise ratio on the circuit board could be

significantly less than the default signal detection level set

by the on-chip reference.

NOTE: MCLADJ and CLI are only recommended for data

rates up to 360 Mb/s.

3.3.3 Carrier Detect/Mute

Applying a HIGH INPUT to the CD/Mute pin forces the

GS9064 outputs to a muted condition. See the DC Electrical

Characteristics table for voltage levels. In this condition the

outputs are latched to the last logic level present at the

output to avoid signal crosstalk.

Applying a LOW INPUT to the CD/Mute pin will force the

GS9064 outputs to remain active regardless of input cable

length or the voltage applied to the MCLADJ pin. See the DC

Electrical Characteristics table for voltage levels.

Figure 13 Typical Output Voltage Levels

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