In the presence of narrowband interference (NBI), detection of weak wideband signals faces foremost challenges in analog-to-digital conversion (ADC), due to the dynamic range problem encountered when the weak signal cannot be amplified adequately to achieve sufficient quantization accuracy. Building on a parallel frequency-domain sampling structure for ADCs, this letter derives a new quantization bit allocation scheme that effectively removes strong NBI. Frequency bins hosting NBIs are allocated with no quantization bits. Optimal rules for symbol detection and quantization bit allocation are derived by jointly minimizing the mean square error of the decoding output.