Programmable – Filters Using Floating-Gate Operational Transconductance Amplifiers

We present programmable, fully differential – second-order sections (SOS) showing tunability over a wide range of frequencies. The SOSs use floating-gate operational transconductance amplifiers (FG-OTAs) to realize tunability. We present two FG programmable OTAs. The OTAs have a pFET input stage and employ current mirror topology. An FG common-mode feedback (CMFB) circuit as well as a conventional CMFB circuit is described for use with these OTAs. Their performance is compared. Expressions are derived for the differential and common-mode frequency response of the OTAs. Typical simulation and experimental results are shown for prototypes fabricated in a 0.5m CMOS process available through MOSIS. The prototypes operate from a single 3.3-V supply with typical bias currents in the 10–100-nA range. We present experimental results showing frequency-and -tuning for a low-pass SOS (LPSOS) and a bandpass SOS (BPSOS) designed using these FG-OTAs also fabricated in a 0.5m CMOS process. Measured 1-dB compression for LPSOS and BPSOS are 15 and 11 dBm, respectively.