Intersymbol interference (ISI) plays an important role in the performance of continuous time delta-sigma modulators(CT-ΔΣM). Different techniques, such as return-to-zero DAC, ISI-shaping or calibration, were proposed in literature to tackle ISI in CT-ΔΣM. This paper investigates the effect of ISI in the outermost feedback digital-to-analog converter (DAC) for three different DAC structures; a single-bit DAC (SB), a multi-bit DAC (MB) and a FIR DAC. For each case, Monte-Carlo simulations were performed plotting the SFDR and SNDR for different rise/fall time mismatch percentages. The paper shows that DAC element mismatch due to rise and fall time variations in MB-DACs is more severe than ISI. However, for FIR-DAC the contrary is observed, the degradation in the performance due to ISI in FIR-DAC can be as severe as in SB-DACs when all FIR-taps are matched with regards to rise/fall time.