The MC10115 is a quad differential amplifier designed for use in sensing differential signals over long lines. The base bias supply (VBB) is made available at pin 9 to make the device useful as a Schmitt trigger, or in other applications where a stable reference voltage is necessary. Active current sources provide the MC10115 with excellent common mode noise rejection. If any amplifier in a package is not used, one input of that amplifier must be connected to VBB (pin 9) to prevent upsetting the current source bias network.