Single Active Element Based Capacitance Multipliers for Speech Processing and Ultrasound Applications

This study presents a detailed evaluation of two capacitance multiplier configurations with a focus on noise optimization in second order low pass filters. The proposed multipliers are based on MO-VDTA (Multi Output Voltage Differencing Transconductance Amplifier) and MO-CDTA (Multi Output Current Differencing Transconductance Amplifier) architectures. In the MO-VDTA based design, the multiplication factor ranges from 120 to 750 (CB= 1pF), controlled by the bias current IB. The designed filter provides a tunable cut-off frequency ranging from 2 kHz to 12.4 kHz (CB= 1pF). In additon, the MO-CDTA based structure enables the multiplication factor ‘k’ to be adjusted between 400 and 1250 (CB= 2pF) by varying the gate-source voltage (VGS) of an external PMOS transistor connected to the Z terminal. This configuration is used in a low pass filter with a tunable cut-off frequency between 23.6 kHz and 91 kHz (CB= 2pF), suitable for ultrasound applications. Additionally, this study includes a comprehensive noise analysis of both capacitance multiplier based filters, demonstrating their effectiveness in low frequency and biomedical signal processing environments.