Shu-Hui Tu

Analytical Synthesis of Current-Mode High-Order Single-Ended-Input OTA and Equal-Capacitor Elliptic Filter Structures With the Minimum Number of Components

None of the previously reported third-order and fourth-order operational transconductance amplifier and capacitor (OTA-C) elliptic filter structures use the minimum number of active and passive components. After an innovative algebraic decomposition for a complicated transfer function, i.e., a new analytical synthesis method, a current-mode odd-nth-order and a current-mode even-nth-order OTA-C elliptic filter structure having the following advantages are presented: 1) all the OTAs have single-ended inputs; 2) all the capacitors are grounded; 3) the minimum active and passive components are used. An equal-capacitance-type structure is designed taking into account the difficulty of precisely fabricating capacitances in integrated circuits. Although the above three advantages lead to the lowest total parasitics and to the most precise output response, the small deviations (such as the 3.5159% error in fp) of the four parameters of the new third-order OTA-C elliptic filter can be drastically reduced (for example, to 0.1553% error in fp) by only slightly tuning the four transconductances, but fixing the ratio of the given three capacitances, and without adding any other active and passive components. H-spice high-pass and low-pass simulations with 0.35-mum process are provided to demonstrate the theoretical results.

Novel versatile insensitive universal current-mode biquad employing two second-generation current conveyors

A new universal current-mode biquad with two inputs and three outputs or three inputs and two outputs using only two second-generation current conveyors and four grounded/virtual-grounded passive elements is proposed. The proposed circuit has the following advantages: simultaneous realization of five generic current-mode filter signals from the same configuration; no requirements of any cancellation constraints; employment of two grounded capacitors ideal for integrated circuit implementation; employment of two grounded/virtually grounded resistors suitable for voltage control; orthogonal adjustment of ω0/Q and ω0 through two separate grounded/virtually-grounded resistors; high output impedance good for cascadability for the current-mode circuits; and low active and passive sensitivities.

New building block: multiplication-mode current conveyor

A new building block called the multiplication-mode current conveyor (MMCC) is proposed here. The structure consists of a differential voltage current conveyor (DVCC) and a folded Gilbert cell without any other auxiliary circuits. Based on the MMCC, a four-quadrant analogue multiplier is designed in TSMC 0.35 mum CMOS 2P4M processes with power supply plusmn 1.65 V. HSPICE post-layout simulation results show that the maximum DC operating range is plusmn 200 mV, the loading range is from 1 to 10 kOmega, the bandwidth is about 90 MHz, the total harmonic distortion (THD) is 0.85 , the power consumption is 1.08 mW and the chip area without pads is 0.48 times 0.36 mm 2 . The new square summer and analogue divider applications employing MMCCs are also presented.

OTA-C Arbitrary-Phase-Shift Oscillators

This paper exhibits the generation of an operational transconductance amplifier and capacitor (OTA-C) arbitraryphase-shift sinusoidal oscillator (APSO) for an order n ≥ 3 for various advanced applications. A new nth-order quadrature oscillator (QO) is obtained via the algebraic quadrature manipulations of an oscillatory characteristic equation. Based on a phase shift transformation from a quadrature, an APSO is then generated by superposing OTAs with required +/- transconductance(s) in parallel with some grounded capacitor(s) on the QO. For eliminating nonideal and parasitic effects to improve phase accuracy, phase compensation schemes are proposed. A new native amplitude control exploiting the nonlinearity of all employed OTAs of the APSO is presented as well to lead to rather low THD and a lower variation of THD with respect to amplitude enlargement. A fourth-order APSO is demonstrated and simulated using Hspice with a 0.35-μm process for validation. In addition, its real application to a polyphase rectifier is improved. Finally, an experiment using LM13700s shows favorable potential of APSOs.

Low sensitivity single-ended-input OTA and grounded capacitor elliptic filter structure with the minimum components

After an innovative algebraic decomposition of a transfer function, a current-mode odd-order operational transconductance amplifier and capacitor (OTA-C) elliptic filter structure is proposed with the following advantages: (i) all single-ended-input OTAs; (ii) all grounded capacitors; (iii) the minimum of active and passive components; (iv) one grounded capacitor at each internal node; (v) low sensitivities. Hspice simulation with a 0.35 /spl mu/m process for a current-mode third-order OTA-C elliptic low pass filter, employing four single-ended-input OTAs and three grounded capacitors, validates the theoretical predictions.

Design of Odd nth-order elliptic High-Pass Filters Employing OTRAs

Two new analytical synthesis methods are proposed for synthesising an nth odd-order elliptic high-pass (HP) filter using operational trans-resistance amplifiers (OTRAs). The analytical synthesis scheme is based on the assumption of infinite trans-resistance R m for the OTRA. The H-spice simulations of the realised elliptic third-order HP filters show that the realisation using less number of OTRAs has a performance better than that which uses more number of OTRAs, as is to be expected in view of the assumption that R m is infinite, when in fact it is finite in practice. However, it is shown that by slightly adjusting a single resistor, the amplitude–frequency response can be made close to the theoretical response.