A Single-Branch Third-Order Pole–Zero Low-Pass Filter With 0.014- $\hbox{mm}^{2}$ Die Size and 0.8-kHz (1.25-nW) to 0.94-GHz (3.99-mW) Bandwidth–Power Scalability

A single-branch third-order low-pass filter with an ultracompact die size and extensive bandwidth (BW)–power scalability is described. It unifies a source follower , a stackable floating active inductor, and a feedforward capacitor to constitute a transistorized-
$LC$
-ladder topology with a stable pole–zero transfer function over a wide range of tunable BW. Differentially, only eight transistors and five untuned capacitors are required. Fabricated in 0.18-
$\mu\hbox{m}$
CMOS, the prototype occupies 0.014-
$\hbox{mm}^{2}$
die size. By scaling the bias current (and, hence, the power), the flexible BW measures 0.8 kHz at 1.25 nW and 0.94 GHz at 3.99 mW.