This paper presents a systematic design methodology for multi-stage feed-forward op-amps used in the active filters of continuous time Σ∆ ADC. This methodology can provide the specifications of each stage in the op-amp (from 2 stages to 4 stages) based on the required ADC specifications and can provide an estimate of the Signal to Noise Ratio (SNR) taking into consideration the effect of the transfer function of the op-amp. This method is then validated on a Lowpass and Bandpass Σ∆ ADCs.