Micropower CMOS GM-C filters for speech signal processing

In this paper, CMOS implementations of two low-voltage, micropower 5th-order elliptic low-pass GM-C filters are presented. Both of the 5th-order elliptic low-pass GM-C filters operate at a supply voltage of 3V. Their tunable cutoff frequencies are from 3 Hz to 600 Hz and from 140 Hz to 3.5 KHz, respectively. The Operational Transconductance Amplifier (OTA) in these GM-C filter design is implemented by a low-voltage voltage-to-current converter (V-I converter) working in the weak-inversion region. The transconductance can be tuned by DC currents or DC voltage. This V-I converter can also be used as a basic building block to construct low-voltage, micropower analog VLSI signal processing systems. These filters provide a practical means for implementing very large time constants on-chip allowing single-chip solutions at very low frequencies. They can be applied in speech processing systems and other very low frequency applications.