REALIZATION OF A 1-V ACTIVE-FILTER USING A LINEARIZATION TECHNIQUE EMPLOYING PLURALITY OF EMITTER-COUPLED PAIRS

A low-voltage (1 V), low-power (100-mu-W), and low-frequency (9 kHz) fifth-order fully integrated active low-pass filter (LPF) using a bipolar technology is described. Novel highly linear transconductors consisting of N emitter-coupled pairs were designed for low-voltage operation. The linear input range is expanded to about 100 mV(p-p) at 1% error with N = 4, which is about twice that of the conventional linearization technique. The filter is basically a gyrator-capacitor type, in which gyrators are implemented by using the linearized transconductors. Large time constants were realized with very low current (540 nA/transconductor) owing to the high transconductance-to-operating-current ratio of the linearized transconductors. Measured results show a passband ripple of 1.5 dB, a minimum stopband rejection of 70 dB, and a dynamic range of 56 dB, despite a very high nominal impedance (400 k-OMEGA). Practical limitations of this approach are also discussed, such as the sensitivity of the linearized transconductors against process variations, noise, and frequency limitations.