This paper presents a new electronically tunable universal filter and quadrature oscillator for low frequency biomedical and biosensor applications employing low-voltage differential difference transconductance amplifier (DDTA). The DDTA CMOS structure uses 0.5 V of supply voltage and consumes 277 nW of power. Unlike the previous universal filters, the proposed filter provides many transfer functions of the standard five transfer functions such as low-pass, high-pass, band-pass, band-stop and all-pass with both unity and controlled voltage gains as well as both inverting and non-inverting transfer functions. The natural frequency and the voltage gain of the five standard transfer functions can be controlled electronically. For the band-pass filter, the third intermodulation distortion (IMD 3 ) was 0.37% for 20 mV pp input signal while the output integrated noise was 61.37 µV. The dynamic range (DR) was 53.27 dB for 1% IMD 3 . The quadrature oscillator has electronically and orthogonal control of the condition and frequency of oscillation. The proposed circuit and its applications were designed and verified via Cadence simulator tool using 0.13 µm UMC CMOS technology. Further, the circuit was evaluated by PSPICE simulation and experiment test using commercial OTA LM13700.

This paper presents a new mixed-mode universal filter based on a differential difference transconductance amplifier (DDTA). Unlike the conventional transconductance amplifier (TA), this DDTA has both advantages of the TA and the differential difference amplifier (DDA). The proposed filter can offer four-mode operations of second-order transfer functions into a single topology, namely, voltage-mode (VM), current-mode (CM), transadmittance-mode (TAM), and transimpedance-mode (TIM) transfer functions. Each operation mode offers five standard filtering responses; therefore, at least twenty filtering transfer functions can be obtained. For the filtering transfer functions, the matching conditions for the input and passive component are absent. The natural frequency and the quality factor can be set orthogonally and electronically controlled. The performance of the proposed topology was evaluated by PSPICE simulator using the 0.18 µm CMOS technology from the Taiwan Semiconductor Manufacturing Company (TSMC). The voltage supply was 1.2 V and the power dissipation of the DDTA was 66 µW. The workability of the filter was confirmed through experimental test by DDTA-based LM13600 discrete-component integrated circuits.

This paper presents a new electronically tunable voltage-mode universal filter with four-input one-output employing six simple operational transconductance amplifiers (OTAs), two grounded capacitors and two MOS resistors. The use of grounded passive components is beneficial for integrated circuit implementation. The proposed filter can realize low-pass, band-pass, high-pass, band-stop and all-pass filtering functions without active and passive component-matching conditions and inverting-type input signals requirements. The natural frequency and quality factor can be tuned independently and electronically by adjusting the bias currents. The voltage-mode filter offers the features of high-input impedance and low active and passive sensitivities. The characteristics of the proposed universal filter are verified using PSPICE simulators through 0.35[Formula: see text][Formula: see text]m CMOS process. Experimental results are used to confirm the workability of proposed circuit through LM13600 commercially available OTAs. Also a digitally programmable filter is shown to confirm the advantage of multiple-input universal filter.

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