A sigma – delta modulator is used in a variety of applications. One application is that of a A/D converter. In order to understand the operation in a intuitive way ( and the sigma -delta A/D is not a circuit open to intuitive understanding), a behavioral model can be very, very helpful. Recently a first order sigma – delta modulator was modeled and its operation was understood. Interested parties can contact us at the website located at http://www,signalpro.biz. A complete PSPICE behavioral model is available for experimentation.