SCAS901D September 2010 – November 2017 CDCLVD1212
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The CDCLVD1212 is a low additive jitter universal to LVDS fan-out buffer with 2 selectable inputs. The small package, low output skew, and low additive jitter make for a flexible device in demanding applications.
The CDCLVD1212 shown in Figure 16 is configured to select two inputs: a 156.25-MHz LVDS clock from the backplane, or a secondary 156.25-MHz LVCMOS 2.5-V oscillator. The LVDS clock is AC-coupled and biased using the integrated reference voltage generator. A resistor divider is used to set the threshold voltage correctly for the LVCMOS clock. 0.1-µF capacitors are used to reduce noise on both VAC_REF and SECREF_N. Either input signal can be then fanned out to desired devices, as shown. The configuration example is driving 4 LVDS receivers in a line card application with the following properties:
See Input Termination for proper input terminations, dependent on single-ended or differential inputs.
See LVDS Output Termination for output termination schemes depending on the receiver application.
Unused outputs can be left floating.
In this example, the PHY, ASIC, and FPGA or CPU require different schemes. Power supply filtering and bypassing is critical for low-noise applications.
See Power Supply Recommendations for recommended filtering techniques. A reference layout is provided in Low-Additive Jitter, Twelve LVDS Outputs Clock Buffer Evaluation Board (SCAU045).
The CDCLVD12xx's low additive noise is shown in this line card application. The low noise 156.25-MHz source with 67-fs RMS jitter drives the CDCLVD12xx, resulting in 80-fs RMS when integrated from 12 kHz to 20 MHz. The resultant additive jitter is a low 44-fs RMS for this configuration.
|Reference signal is low-noise Rohde & Schwarz SMA100A|