Buffers and line drivers are integrated circuit devices that isolate the input circuit from the output circuit. This reduces the load seen by the input circuit and enables signals to be sent on PCB or cables over longer distances with higher fan-out. Fan out is a description of the number of typical inputs an output is driving. Each input adds a capacitive load on the driving amplifier. As the capacitance gets higher, the peak current required to transition the voltage from one level to another gets higher. If this gets higher than the output can handle or the slope of the signal level changes gets too low, the circuit performance is compromised. Over and above this, the output may become overloaded, unstable or damaged. It is common to find buffers in clock trees on PCBs where low noise and high-speed logic signals are important. Buffers are also found in bus applications and in applications where digital I/O of a system is too weak to drive a load. Buffers also typically exhibit better ESD and latch up protection than the I/O directly on the microcontroller and are thus used to isolate and protect devices.

Line drivers are a special type of buffer that includes the ability to drive a transmission line or cable that may be quite long. They also may adapt the input logic format to the specific line driving standard. An example of this is an eSATA Redriver. These devices extend the distance supported by the SATA standard by buffering the differential current mode logic (CML) signals on their input and re-transmitting them as a corrected and compensated CML signal output. They incorporate an equalizer, a filter that compensates for the loss and distortion of a signal on a physical medium (cable or PCB traces) to enable the correct signal shape to be ultimately presented to the receiver.

Some buffers and line drivers convert from logic signal inputs to a high-speed serial output. The input may be a parallel bus to meet the high-speed data requirements.  Cable drivers tend to output differential serial data signals at a standard that supports very high-speed data transfer on cable. This is particular true of high definition, and ultra high definition video systems. These can require more than 12GHz serial data streams sent over hundreds of meters of copper cable. CML is used in these applications because differential pairs of transistors require very little voltage swing to switch and so can operate much faster than voltage-oriented alternatives. This standard is used in interface standards like SDI and HDMI.

Some drivers also incorporate translation between the PCB trace impedance and the cable characteristic impedance. There is a special category of driver that also performs a process called reclocking where the data clock is recovered from the signal, a new clean clock is phase locked to this signal and the  data is re-transmitted with clean clocking. This compensates for Jitter introduced in the path. Jitter is phase noise introduced onto the signal by system noise and by attenuation effects in the physical medium.