AS1156/AS1154
Data Sheet - Detailed Description
8 Detailed Description
LVDS Interface
The LVDS interface standard is a signaling method intended for point-to-point communication over a controlled-imped-
ance medium as defined by the ANSI/TIA/EIA-644 and IEEE 1596.3 standards. The LVDS standard uses a lower volt-
age swing than other common communication standards, achieving higher data rates with reduced power
consumption while reducing EMI emissions and system susceptibility to noise.
The AS1156/AS1154 is an 800Mbps single/dual differential LVDS driver that is designed for high-speed, point-to-point,
low-power applications. This device accepts LVTTL/LVCMOS input levels and translates them to LVDS output signals.
The AS1156/AS1154 generates a 2.5mA to 4.5mA output current using a current-steering configuration. This current
steering approach induces less ground bounce and no shoot-through current, enhancing noise margin and system
speed performance. The driver outputs are short-circuit current limited, and enter a high-impedance state when the
device is not powered or is disabled.
The current-steering architecture of the AS1156/AS1154 requires a resistive load to terminate the signal and complete
the transmission loop. Because the device switches current and not voltage, the actual output voltage swing is deter-
mined by the value of the termination resistor at the input of an LVDS receiver (AS1157, AS1158). Logic states are
determined by the direction of current flow through the termination resistor.
With a typical 3.7mA output current, the AS1156/AS1154 produces an output voltage of 370mV when driving a 100Ω
load.
Termination
Because the AS1156/AS1154 is a current-steering device, no output voltage will be generated without a termination
resistor. The termination resistors should match the differential impedance of the transmission line. Output voltage lev-
els depend upon the value of the termination resistor.
The AS1156/AS1154 is optimized for point-to-point interface with 100Ω termination resistors at the receiver inputs. Ter-
mination resistance values may range between 90 and132Ω, depending on the characteristic impedance of the trans-
mission medium.
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