AS1153/55
Data Sheet - Detailed Description
8 Detailed Description
The AS1155/58 and AS1153/57 are 260Mbps, single/dual-channel LVDS receivers intended for high-speed, point-to-
point, low-power applications. Each independent channel accepts and converts an LVDS input to an LVTTL/LVCMOS
output. The devices are capable of detecting differential signals from 100mV to 1V within an input voltage range of 0 to
2.4V.
The 250 to 450mV differential output of an LVDS driver is nominally centered around 1.25V. Due to the receiver input
voltage range, a ±1V voltage shift in the signal relative to the receiver is allowed. Thus, a difference in ground refer-
ences of the transmitter and the receiver, as well as the common mode effect of coupled noise, can be tolerated.
LVDS Interface
The LVDS Interface Standard is a signaling method defined 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, resulting in higher data rates, reduced power consumption
and EMI emissions, and less susceptibility to noise.
The devices fully comply with the LVDS standard input voltage range of 0 to +2.4V referenced to receiver ground.
The AS1157/58 has an integrated termination resistors connected internally across each receiver input. This internal
termination saves board space, eases layout, and reduces stub length compared to an external termination resistor. In
other words, the transmission line is terminated on the IC.
Failsafe Circuit
The devices contain an integrated Failsafe circuit to prevent noise at inputs that are open, undriven and terminated, or
undriven and shorted.
Open or undriven terminated input conditions can occur if there is a cable failure or when the LVDS driver outputs are
high impedance. A short condition also can occur because of a cable failure. The Failsafe circuit of the AS1153/55 and
AS1157/58 automatically sets the output high if any of these conditions are true.
The Failsafe input circuit (see Figure 18) samples the input common-mode voltage and compares it to VCC - 0.3V
(nominal). If the input is driven to levels specified in the LVDS standards, the input common-mode voltage is less than
VCC - 0.3V and the Failsafe circuit is not activated. If the inputs are open, undriven and shorted, or undriven and paral-
lel terminated, there is no input current. In this case, a pullup resistor in the Failsafe circuit pulls both inputs above VCC
- 0.3V, activating the Failsafe circuit and thus forcing the device output high.
Figure 18. Failsafe Input Circuit
VCC
VCC
RIN2
RIN2
VCC - 0.3V
VCC - 0.3V
INx+
INx+
RIN1
RIN1
RDIFF
RIN1
OUTx
OUTx
RIN1
INx-
INx-
AS1153/55
AS1157/58
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