A 0.02 mm$^{2}$ 59.2 dB SFDR 4th-Order SC LPF With 0.5-to-10 MHz Bandwidth Scalability Exploiting a Recycling SC-Buffer Biquad
This paper reports a switched-capacitor (SC)-buffer Biquad that can be recycled efficiently as an ultra-compact low-pass filter (LPF) in nanoscale CMOS. It incorporates only passive-SC networks and open-loop unity-gain buffers; both are friendlier to technology downscaling than most conventional Biquads that use high-gain amplifiers and closed-loop negative feedback. Complex-pole pairs with independent Q factors are recursively realized in one clock period, while ensuring low crosstalk effect between the formations of each pole. Nonlinearity and parasitic effects are inherently low due to no internal gain. The fabricated 65 nm CMOS prototype is a 1x-recycling SC-buffer Biquad that is equivalent to a 4th-order Butterworth LPF with 75% buffer utilization. It occupies a die size of only 0.02 mm2 and exhibits 20x bandwidth tunability (0.5 to 10 MHz), linear with the clock rate. At 10 MHz bandwidth, the in-band IIP3 is +17.6 dBm and input-referred noise is 19.5 nV/ √Hz; they correspond to 59.2 dB SFDR and 0.013 fJ figure-of-merit which are favorably comparable with the recent art. The 1 dB compression point (P1dB) conforms to the out-of-band blocker profile of the LTE standard at a 20 dB front-end gain.