An operating point elimination technique for weak-inversion log-domain filters with multiple operating points

When converting conventional BJT-based log domain filters to the CMOS equivalent, operated in the weak inversion region, it has been shown that there can be unwanted DC operating points. This paper presents a simple technique for eliminating such operating points once they have been identified. An example of the elimination of unwanted states is presented, and this technique is verified both by simulation and also by the measurement of a solid-state version of the corrected filter