An amplifier having a high input dynamic range as well as high CMRR and PSRR values and input impedance while using a single supply voltage, includes an input stage with two transistors which are biased by a constant current, preferably of less than 1 microampere, while the collectors of the transistors are kept at fixed reference voltages. The input signal applied between the emitters of the transistors is transferred to the terminals of a first resistor which is supplied with current from a circuit which mirrors the current into a second resistor, from the terminals of which the output signal is taken.The preferred application is for forming interfaces for lambda probes fitted to catalytic converters for motor vehicles.