OBUFDS

OBUFDS stands for Output Buffer Differential Signaling. It is a digital I/O primitive used in many FPGA families to generate a true differential output from a single-ended input. The primitive produces two outputs, O and OB, which are complementary. When the input I is asserted, O is driven as a logic high and OB as a logic low, and when I is deasserted, O goes low and OB goes high. This creates a differential pair suitable for LVDS or other differential receivers.

OBUFDS is typically used to drive external differential signaling networks, such as LVDS lines, backplanes, or high-speed data links. It is often paired with a differential input buffer (IBUFDS) on the receiving end, enabling full single-ended-to-differential and differential-to-single-ended signaling paths within a design. The device provides configuration options through IO standards and termination to meet signal integrity requirements.

Common configurable aspects include the IO standard (for example LVDS, RSDS, or other differential standards), drive strength and slew rate, and, in some devices, internal differential termination (DIFF_TERM) to match the characteristic impedance of the transmission line. The O and OB outputs are physically separate pins on the FPGA package, representing the non-inverted and inverted sides of the differential pair, respectively.

In practice, OBUFDS is instantiated in Verilog or VHDL with a single input signal I and two outputs O and OB. For example, an OBUFDS instantiation connects I to O and OB, and assigns the appropriate differential pins, with the chosen IO standard and termination settings applied.