A modular and scalable architecture for the realization of high-speed programmable rank-order filters using threshold logic

We present a new scalable architecture for the realization of fully programmable rank order filters (ROF). Capacitive Threshold Logic (CTL) gates are utilized for the implementation of the multi-input programmable majority (voting) functions required in the architecture. The CTL-based realization of the majority gates used in the ROF architecture allows the filter rank as well as the window size to be user-programmable, using a much smaller silicon area, compared to conventional realizations of digital median filters. The proposed filter architecture is completely modular and scalable, and the circuit complexity grows only linearly with maximum window size (m) and with word length (n). A prototype of the proposed filter circuit has been designed and fabricated using double-polysilicon 0.8 μm CMOS technology. Detailed post-layout simulations and test results of the ROF prototype circuit indicate that the new architecture can accommodate sampling clock rates of up to 50 MHz, corresponding to an effective data processing rate of 800 Mb/s for a very large filter with window size 63 and word length of 16 bits.