A comparator circuit is a device which may compare two voltages (e.g., and/or currents) and which may switch its output to indicate which is larger. The comparator circuit (e.g., a high speed comparator) may use a pre-amplifier circuit (e.g., a first pre-amplifier of an input stage of the comparator circuit) to translate an input common-mode voltage of the pre-amplifier circuit to a level acceptable to stages that follow the pre-amplifier circuit in the comparator circuit. The pre-amplifier circuit may have an instable output common mode voltage when an input common mode to the pre-amplifier circuit varies over a wide range of voltages.
Sometimes, a negative feedback loop may be used. However, the negative feedback loop may require time consuming and/or expensive stability analysis. In addition, undesirable elements in a differential signal path of the pre-amplifier circuit may be introduced. Without any correction, the instable output common mode voltage may vary when the input common mode of the pre-amplifier circuit varies over the wide range of voltages. This may make a design of stages of the comparator circuit which follow the pre-amplifier circuit more difficult.