Abstract: The detailed analysis of a highspeed optical analogtodigital (A/D) converter consisting of an array of coplanar waveguide (CPW) travelingwave interferometric modulators on xcut LiNbO3 substrate has been performed. The development of this kind of optical A/D converters is described. The relation of smallsignal bandwidth, impedance, microwave attenuation parameters and drive power to the trapezoidal CPW electrode parameters including the electrode thickness, the buffer layer thickness to the edge inclination of the central electrode and ground planes β1,βg by coformal mapping are analyzed. When the electrode thickness is 3μm and β1=βg=10°，the bandwidth of 4bit A/D converter is 7.3GHz and the requirement of drive power is 6.7W. The numerical results show that it is feasible to design a highspeed A/D converter using travelingwave interferometric modulator with moderate resolution.