Feedback system and method of operating the same

A lock signal generation circuit, comprising:

• an input signal control circuit configured to receive an input signal and two reference signals and output state signals and a code signal for controlling a level of the input signal, the state signals representing a result of comparison of the input signal with the two reference signals, wherein the state signals include an up/down signal and an ambiguous signal;
• a pre-lock signal generator configured to receive the up/down signal, and to output a pre-lock signal to determine a time at which the level of the input signal is to be fixed in response to the up/down signal, wherein the up/down signal represents whether the input signal has a higher or lower level than the two reference signals;
• and
• a signal-processing circuit configured to receive the pre-lock signal and the ambiguous signal, and to output a lock signal to fix the level of the input signal using the ambiguous signal and the pre-lock signal, wherein the ambiguous signal is outputted when the level of the input signal is in between levels of the two reference signals.