DS99R105_13 Datasheet, PDF (19/29 Pages) Texas Instruments – DS99R105/DS99R106 3-40MHz DC-Balanced 24-Bit LVDS Serializer and Deserializer

DS99R105, DS99R106
www.ti.com
SNLS242D – MARCH 2007 – REVISED APRIL 2013
LIVE LINK INSERTION
The Serializer and Deserializer devices support live pluggable applications. The “Hot Inserted” operation on the
serial interface does not disrupt communication data on the active data lines. The automatic receiver lock to
random data “plug & go” live insertion capability allows the DS99R106 to attain lock to the active data stream
during a live insertion event.
PCB LAYOUT AND POWER SYSTEM CONSIDERATIONS
Circuit board layout and stack-up for the LVDS SERDES devices should be designed to provide low-noise power
feed to the device. Good layout practice will also separate high frequency or high-level inputs and outputs to
minimize unwanted stray noise pickup, feedback and interference. Power system performance may be greatly
improved by using thin dielectrics (2 to 4 mils) for power / ground sandwiches. This arrangement provides plane
capacitance for the PCB power system with low-inductance parasitics, which has proven especially effective at
high frequencies, and makes the value and placement of external bypass capacitors less critical. External bypass
capacitors should include both RF ceramic and tantalum electrolytic types. RF capacitors may use values in the
range of 0.01 uF to 0.1 uF. Tantalum capacitors may be in the 2.2 uF to 10 uF range. Voltage rating of the
tantalum capacitors should be at least 5X the power supply voltage being used.
Surface mount capacitors are recommended due to their smaller parasitics. When using multiple capacitors per
supply pin, locate the smaller value closer to the pin. A large bulk capacitor is recommend at the point of power
entry. This is typically in the 50uF to 100uF range and will smooth low frequency switching noise. It is
recommended to connect power and ground pins directly to the power and ground planes with bypass capacitors
connected to the plane with via on both ends of the capacitor. Connecting power or ground pins to an external
bypass capacitor will increase the inductance of the path.
A small body size X7R chip capacitor, such as 0603, is recommended for external bypass. Its small body size
reduces the parasitic inductance of the capacitor. The user must pay attention to the resonance frequency of
these external bypass capacitors, usually in the range of 20-30 MHz range. To provide effective bypassing,
multiple capacitors are often used to achieve low impedance between the supply rails over the frequency of
interest. At high frequency, it is also a common practice to use two vias from power and ground pins to the
planes, reducing the impedance at high frequency.
Some devices provide separate power and ground pins for different portions of the circuit. This is done to isolate
switching noise effects between different sections of the circuit. Separate planes on the PCB are typically not
required. Pin Description tables typically provide guidance on which circuit blocks are connected to which power
pin pairs. In some cases, an external filter many be used to provide clean power to sensitive circuits such as
PLLs.
Use at least a four layer board with a power and ground plane. Locate LVCMOS (LVTTL) signals away from the
LVDS lines to prevent coupling from the LVCMOS lines to the LVDS lines. Closely-coupled differential lines of
100 Ohms are typically recommended for LVDS interconnect. The closely coupled lines help to ensure that
coupled noise will appear as common-mode and thus is rejected by the receivers. The tightly coupled lines will
also radiate less.
Termination of the LVDS interconnect is required. For point-to-point applications, termination should be located at
both ends of the devices. Nominal value is 100 Ohms to match the line’s differential impedance. Place the
resistor as close to the transmitter DOUT± outputs and receiver RIN± inputs as possible to minimize the resulting
stub between the termination resistor and device.
LVDS INTERCONNECT GUIDELINES
See AN-1108 (SNLA008) and AN-905 (SNLA035) for full details.
• Use 100Ω coupled differential pairs
• Use the S/2S/3S rule in spacings
– S = space between the pair
– 2S = space between pairs
– 3S = space to LVCMOS/LVTTL signal
• Minimize the number of VIA
• Use differential connectors when operating above 500Mbps line speed
• Maintain balance of the traces
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Product Folder Links: DS99R105 DS99R106
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