What Is a LVDS Transceiver?
A low-voltage differential signaling (LVDS) transceiver is a signaling transmitter/receiver that uses a low voltage with differential signaling to attain high bit rates. The LVDS transceiver drives twisted copper wires, which are low cost and very common. Differential signaling is preferred because of its high immunity to external electrical noise and surges.
The purpose of a LVDS transceiver is to interconnect circuits or equipment via a reliable data communications link. Without an LVDS transceiver, alternative solutions may either be more expensive or more complicated to use. A typical LVDS transceiver may convey high-speed serial line or even a parallel bus to other locations more than 49 feet (15 m) away. LVDS is a system used by several data communication standards, such as the Telecommunications Industry Association/Electronic Industries Alliance-644 (TIA/EIA-644).
Using a LVDS transceiver is a logical choice when the digital cabling length for an application limits the data speed. Non-differential signaling is very common for short-length data connection. In this scheme, the digital voltages range from 0 to about +5 volts direct current (VDC). A low-speed parallel data cable for printers may be limited to 39.4 inches (1 m) in length, but when the data cable is longer, the “electrical” capacitance is higher, and high capacitance increases the signal rise and fall times resulting in limited data speeds. LVDS solves the capacitance limitation by using current-driven transmitters that compensate for much of the capacitance in the data line.
The voltage difference across the differential mode receiver input, which is less than 1 V, accounts mostly for the high-speed feature of LVDS transceivers. Less current in less time will be needed to reverse the voltage differential for every data bit reversal if the needed change in voltage is low. With less than 1 V difference in the receiver inputs all the time, the protection circuitry against voltage surges from external sources is greatly simplified.
When choosing a LVDS transceiver, circuit developers usually prefer an integrated circuit (IC) LVDS transceiver, which is designed to accept single-ended digital signals such as transistor-transistor logic (TTL) signals. Single-ended levels are single polarity, such as 0 V and +5 VDC. When a TTL bus has to be connected to more than a few meters away, a parallel-to-serial-to-parallel (PSP) IC is available. For instance, when transmitting and receiving an 8-bit bus, a clock signal that is about eight times the data bus clocking rate is applied to the PSP. Instead of a connector with more than 8 pins, the LVDS transceiver serial connector will just need one or two bidirectional pair of data lines, depending on the design.
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