A 6th-Order 100μA 280MHz Source-Follower-Based Single-loop Continuous-Time Filter

The source follower is a well known basic building block for CMOS design. A capacitively loaded source follower acts as a 1^st-order low- pass filter and exhibits excellent linearity, especially with reduced overdrive voltages. In these source-follower features have been used advantageously in the design of a 2^nd-order (biquadratic) low-pass filter and a 4^th- order filter, which was made by cascading two 2^nd-order cells. We have used this technique to design single-loop high-order source- follower-based continuous-time filters that, like ladder filters, have transfer functions that are insensitive to component variations. An efficient CMOS realization demonstrates the principle an achieves lower power and smaller area than other solutions.