Resistors R1, R2, R3, and R4 are all 0Ω resistor components. The input terminals (IN+ and IN-) have corresponding sense lines so that the inputs to the device can be terminated on the lines with 50Ω to an oscilloscope. This allows the input signals to be observed with minimal loading and distortion. All input connections are through SMA connectors. If the input signal to the device does not need to be evaluated on an oscilloscope, then R3 and R4 can be left uninstalled. However, the input signal can need to be terminated if the 50Ω setting of the oscilloscope is not connected.

There is an optional resistor pad on the input (R5) side of the device meant for termination of the input signal. R5 can be populated with a 100Ω resistor if applying an unterminated LVDS signal to the board. Alternatively, R5 can be populated with a 50Ω resistor if applying a function generator output that needs a 50Ω termination. One of the inputs can be GND and the board is operating in split supply in this situation. Otherwise the pad can be left unpopulated.

Figure 2-2 Input Side Block Diagram