9.2.2.2 Threshold

The LVDS Standard (ANSI/TIA/EIA-644) specifies a maximum threshold of ±100 mV for the LVDS receiver. The DSLVDS1048 supports an enhanced threshold region of −100 mV to 0 V. This is useful for fail-safe biasing. The threshold region is shown in the Voltage Transfer Curve (VTC) in Figure 20. The typical DSLVDS1048 LVDS receiver switches at about −35 mV.

In the following example, this would be 60 mV of Differential Noise Margin (+25 mV − (−35 mV)). With the enhanced threshold region of −100 mV to 0 V, this small external fail-safe biasing of +25 mV (with respect to
0 V) gives a DNM of a comfortable 60 mV. With the standard threshold region of ±100 mV, the external fail-safe biasing would need to be +25 mV with respect to +100 mV or +125 mV, giving a DNM of 160 mV which is stronger fail-safe biasing than is necessary for the DSLVDS1048. If more DNM is required, then a stronger fail-safe bias point can be set by changing resistor values.

Figure 20. VTC of the DSLVDS1048 LVDS Receiver