Older bipolar devices, such as the LM311 and LM319 comparator families, are built on a bipolar junction isolated process. These older processes have larger junction sizes and are robust enough that dedicated ESD protection was not required. Therefore these older devices do not contain dedicated ESD structures and do not have input clamps and rely on device breakdowns when the input is above the supply and the intrinsic body diodes for inputs below the negative supply.

Because these older devices do not have ESD clamping structures, external clamping is required to ensure that the input voltages do not exceed the input specifications.

These devices were also designed for split supply voltages (e.g., ±15 V) applications, with the input signal reference expected to be around mid supply range (e.g., ±1 V). So the valid input range may fall short of the rail by 500 mV to 2 V (not "Rail to Rail" or "Ground Sensing"), limiting the input voltage range.