An automatically calibrated differential amplifier in response to process or environmental variations for use as a comparator in a multilevel signal receiver, comprising: an input stage differential amplifier (130A, 130B, 130C) configured to receive an input differential signal, to differentially amplify the input differential signal to generate an input stage output differential signal, and to have an input stage bias current; and a replica stage differential amplifier comprising: a first amplifier leg; and a second amplifier leg; wherein the first and second amplifier legs, together, are configured to receive a reference differential signal (V ref,p, V ref,n), wherein the reference differential signal is a signal which provides a known output signal at an output of the replica stage differential amplifier under known operating conditions, and differentially amplify the reference differential signal to provide a replica stage output differential signal; and a feedback circuit configured to: receive a differential output of the replica stage differential amplifier; to adjust bias currents of the replica stage in order to maintain a required output in response to the reference differential signal; output a reference current (It) based on the replica stage output differential signal; and copy the reference current to the input stage differential amplifier to enable automatic calibration, wherein a sum of a first amplifier leg current of the first amplifier leg and a second amplifier leg current of the second amplifier leg equals the replica stage bias current and wherein the replica stage bias current and the input stage bias current are based on the reference current. an input stage differential amplifier (130A, 130B, 130C) configured to receive an input differential signal, to differentially amplify the input differential signal to generate an input stage output differential signal, and to have an input stage bias current; and a replica stage differential amplifier comprising: a first amplifier leg; and a second amplifier leg; wherein the first and second amplifier legs, together, are configured to receive a reference differential signal (V ref,p, V ref,n), wherein the reference differential signal is a signal which provides a known output signal at an output of the replica stage differential amplifier under known operating conditions, and differentially amplify the reference differential signal to provide a replica stage output differential signal; and a first amplifier leg; and a second amplifier leg; wherein the first and second amplifier legs, together, are configured to receive a reference differential signal (V ref,p, V ref,n), wherein the reference differential signal is a signal which provides a known output signal at an output of the replica stage differential amplifier under known operating conditions, and differentially amplify the reference differential signal to provide a replica stage output differential signal; and a feedback circuit configured to: receive a differential output of the replica stage differential amplifier; to adjust bias currents of the replica stage in order to maintain a required output in response to the reference differential signal; output a reference current (It) based on the replica stage output differential signal; and copy the reference current to the input stage differential amplifier to enable automatic calibration, receive a differential output of the replica stage differential amplifier; to adjust bias currents of the replica stage in order to maintain a required output in response to the reference differential signal; output a reference current (It) based on the replica stage output differential signal; and copy the reference current to the input stage differential amplifier to enable automatic calibration, wherein a sum of a first amplifier leg current of the first amplifier leg and a second amplifier leg current of the second amplifier leg equals the replica stage bias current and wherein the replica stage bias current and the input stage bias current are based on the reference current.