This paper presents an efficient way to implement an interpolation filter in a 20bit Σ-Δ DAC with an oversampling ratio of 128.A multistage structure is used to reduce the complexity of filter coefficients and the finite word length effect.A novel method based on mixed-radix number representation is proposed to realize a poly-phase multiplier-free half-band subfilter with a high resolution.This approach reduces the complexity of the control system and saves chip area dramatically.The IC is realized in a standard 0.13μm CMOS process and the interpolation filter occupies less than 0.63mm2.This realization has desirable properties of regularity with simple hardware devices which are suitable for VLSI and can be applied to many other high resolution data converters.