In the frame of an SMOS follow-on operational mission, a new instrument design is being developed based on the lessons learned from MIRAS, the SMOS payload. To reduce hardware complexity and mass, digital In-phase Quadrature (IQ) demodulation is considered. In this schema, Q components are obtained by delaying one clock of the digitized IF signals instead of using phase quadrature analog mixers. The purpose of this article is to formulate this concept for application to interferometric radiometry, establish the required data processing methods, and provide experimental results.