qlx4600-sl30 Intersil Corporation, qlx4600-sl30 Datasheet - Page 15

• Manufacturer Part Number: qlx4600-sl30
• Description: Quad Lane Extender
• Manufacturer: Intersil Corporation

Control Pin Boost Setting
When register 1 of the QLx4600-SL30 is zero (the default
state on power-up), the voltages at the CP pins are used
to determine the boost level of each channel. For each of
the four channels, k, the [A], [B], and [C] control pins
(CP[k]) are associated with a 3-bit non binary word.
While [A] can take one of two values, ‘LOW’ or ‘HIGH’,
[B] and [C] can take one of three different values: ‘LOW’,
‘MIDDLE’, or ‘HIGH’. This is achieved by changing the
value of a resistor connected between VDD and the CP
pin, which is internally pulled low with a 25kΩ resistor.
Thus, a ‘HIGH’ state is achieved by using a 0Ω resistor,
‘MIDDLE’ is achieved with a 25kΩ resistor, and ‘LOW’ is
achieved with an open resistance. Table 2 defines the
mapping from the 3-bit CP word to the 18 out of 32
possible levels available via the serial interface.
If all four channels are to use the same boost level, then
a minimum number of board resistors can be realized by
tying together like CP[k][A,B,C] pins across all channels
k. For instance, all four CP[k][A] pins can be tied to the
same resistor running to VDD. Consequently, only three
resistors are needed to control the boost of all four
channels. If the CP Pins are tied together and the 25kΩ is
used, the value changes to a 6.25kΩ resistor because the
25kΩ is divided by 4.
Optimal Cable Boost Settings
The settable equalizing filter within the QLx4600 enables
the device to optimally compensate for
frequency-dependent attenuation across a wide variety
of channels, data rates, and encoding schemes. For the
reference channels plotted in Figure 2, Table 3 shows the
optimal boost setting when transmitting a PRBS-7 signal.
The optimal boost setting is defined as the equalizing
filter setting that minimizes the output residual jitter of
the QLx4600. The settings in Table 3 represent the
optimal settings for the QLx4600C across an ambient
temperature range of 0°C to +70°C. The optimal setting
at room temperature (+20°C to +40°C) is generally one
to two settings lower than the values listed in Table 3.
15
QLx4600-SL30
NOTE: Optimal boost settings should be determined on an
application-by-application basis to account for variations in
channel type, loss characteristics, and encoding schemes. The
settings in this table are presented as guidelines to be used as
a starting point for application-specific optimization.
Register Description
The QLx4600-SL30’s internal registers are listed in
Table 4. Register 1 determines whether the CP pins or
register values 2 through 21 are used to set the boost
level. When this register is set, the QLx4600-SL30 uses
registers 2-6, 7-11, 12-16, and 17-21 to set the boost
level of equalizers 1, 2, 3, and 4. When register 1 is not
set, the CP pins are used to determine the boost level for
each equalizer channel. The use of five registers for each
equalizer channel allows all 32 boost levels as candidate
boost levels.
Cable A
Cable B
Cable C
CABLE
TABLE 3. OPTIMAL CABLE BOOST SETTINGS
APPROX. LOSS @
2.5GHZ (DB)
22
27
35
QLx4600-SL30
November 19, 2009
BOOST
10
14
19
FN6981.1