Programmable capacitance scaling scheme based on operational transconductance amplifiers

A new programmable capacitance scaling scheme based on the utilisation of two tunable operational transconductance amplifiers (OTAs) is presented. The capability of the OTAs allows tunable positive/negative capacitance scaling factors. The scheme has been verified with simulations and experimentally using commercial bipolar OTAs and can be implemented in CMOS technology.     

Gain improvement in operational transconductance amplifiers using Graded-Channel SOI nMOSFETS

This paper studies the performance of operational transconductance amplifiers (OTAs) fabricated with Graded-Channel (GC) SOI nMOSFETs and designed to provide high open-loop voltage gain or high gain-bandwidth characteristics. Different design targets were taken in account such as similar power dissipation, transconductance over drain current ratio and die area. Comparisons with OTAs made with conventional SOI nMOSFETs, are performed showing that the GC OTAs presents larger open-loop voltage gain without degrading the phase margin, unit gain frequency and slew rate simultaneously with a significant required die area reduction depending on L_LD/L ratio used. Circuit simulations and experimental results are used to qualify the analysis.     

Improving GBW product on CMOS operational transconductance amplifiers by interleaved feedforward paths

This paper presents two Operational Transconductance Amplifier (OTA) compensation schemes for multistage topologies. The solutions are based on interleaved feedforward paths that cancel a non-dominant pole similarly to the zero nulling resistor technique with the advantage of avoiding resistors. Both schemes are designed in 90 nm CMOS process, the first one obtains 71 dB of DC gain, a gain bandwidth product (GBW) of 720 MHz with 360 μW of power consumption. The second proposed scheme obtains a similar DC gain and doubles the former proposed OTA GBW at the expense of 2.2 mW of power consumption for high speed applications. The compensation schemes are theoretically analyzed and the design guidelines are presented. The results of post layout simulations and corner analysis validate the new solutions.     

Improved common-mode feedback circuit suitable for operational transconductance amplifiers with tuning

A simple modification is proposed for a popular common-mode feedback circuit used in operational amplifiers, such that it can be used in an operational transconductance amplifier (OTA) without leading to significant DC offset caused by the unavoidable tuning of the OTA. Simulation results show that the improved circuit has nearly zero DC offset for the whole tuning range.<>     

Multiple-input single-output universal biquad filter using single output operational transconductance amplifiers

A novel universal biquad filter topology, realized using Operational Transconductance Amplifiers as active elements, is presented in this paper. It offers the benefits of orthogonal adjustment of the resonance frequency and the quality factor of the filter and, also, resistorless realization with grounded capacitors. The attractive characteristic is the requirement of single output Operational Transconductance Amplifies because in this way the implementation of the filter using commercially available discrete component ICs as OTAs is quite facilitated. Comparison with the literature shows that the proposed solution is the most beneficial from the active component count point of view. The behavior of the proposed topology is evaluated trough simulation results, using the OrCAD PSpice simulator, as well as through experimental results using the LM 13700 discrete component IC as Operational Transconductance Amplifier.     

An input stage transconductance reduction technique for high-slew rate operational amplifiers

The use of input stage transconductance reduction as a means of decreasing monolithic op amp die size and increasing slew rate is discussed. A new input stage circuit which provides improved slew rate is presented and compared to earlier techniques.     

A power efficient gain enhancing technique for current mirror operational transconductance amplifiers

In this paper, a power efficient voltage gain enhancing technique is described. This technique is suitable for the amplifiers which use current starving method for gain enhancement (explained in the text). The proposed technique makes use of the current which conventionally goes to ground, through a parallel path. In this paper, the new technique is demonstrated for current mirror type of operational transconductance amplifier (OTA). Simulation results show that gain improves by a factor ~2, while consuming the same power as conventional OTA. The added advantage of this technique is that it does not affect the voltage swing while increasing the gain. Compared to the conventional current starving technique, the proposed technique also improves the noise performance and settling speed of the amplifier. The results are compared with the conventional technique, in terms of gain, settling and noise performance. A comparison of FoM (MHz.pF/mA), with other amplifiers, is given at the end as well.     

An overview of feed-forward design techniques for high-gain wideband operational transconductance amplifiers

In this paper, feed-forward techniques are revised and used for the design of high-frequency operational transconductance amplifiers (OTA). For the same power consumption and similar transistor dimensions, the two- and three-path folded-cascode OTA's present both smaller settling error and faster response as compared to the typical folded-cascode topology.Also, a no-capacitor feed-forward (NCFF) compensation which uses a high-frequency pole-zero doublet to obtain high gain, high GBW and a good phase margin is discussed. The settling-time of the NCFF topology can be faster than that of OTA's with Miller compensation, even if the latter topology uses larger transconductance values. Experimental results for the multi-trajectory OTA's fabricated in the AMI 0.5 μm CMOS process demonstrate the feasibility of the feed-forward schemes.     

Ultra-Low voltage-power DTMOS based full-wave rectifier

In this paper, dynamic threshold MOS (DTMOS) transistor based full-wave rectifier with ultra-low power consumption is presented. The proposed circuit composed of only four NMOS and seven DTMOS transistors when many rectifier circuits consist of passive circuit components such as diodes, resistors and active circuit elements. The layout occupies an active area of 24.6 µm × 65.01 µm and post-layout simulation results performed using Cadence Environment with 0.18 µm TSMC CMOS technology parameters. The rectifier circuit with ±0.2 V DC supply voltages can be operated up to approximately 500 MHz and consumes only 2.83 nW thanks to the DTMOS transistors.     

A robust feedforward compensation scheme for multistage operational transconductance amplifiers with no Miller capacitors

A multistage operational transconductance amplifier with a feedforward compensation scheme which does not use Miller capacitors is introduced. The compensation scheme uses the positive phase shift of left-half-plane (LHP) zeroes caused by the feedforward path to cancel the negative phase shift of poles to achieve a good phase margin. A two-stage path increases further the low frequency gain while a feedforward single-stage amplifier makes the circuit faster. The amplifier bandwidth is not compromised by the absence of the traditional pole-splitting effect of Miller compensation, resulting in a high-gain wideband amplifier. The capacitors of a capacitive amplifier using the proposed techniques can be varied more than a decade without significant settling time degradation. Experimental results for a prototype fabricated in an AMI 0.5-/spl mu/m CMOS process show DC gain of around 90 dB and a 1% settling time of 15 ns for a load capacitor of 12 pF. The power supply used is /spl plusmn/1.25 V.     

Electronically tunable high-input impedance voltage-mode universal biquadratic filter based on simple CMOS OTAs

This paper describes a new electronically tunable three inputs and single output voltage-mode universal biquadratic filter based on simple CMOS operational transconductance amplifiers (OTAs) and grounded capacitors. The proposed configuration provides lowpass, highpass, bandpass, bandstop and allpass voltage responses at a high impedance input terminal, which enable easy cascadability. Additionally, the circuit parameters ω_o${\omega }_o$ and Q   can be set orthogonally by adjusting the transconductances and grounded capacitors. The filter also offers an independent electronic control of parameters ω_o${\omega }_o$ by adjusting the transconductance through the bias current/voltage of the OTA. For realizing all the filter responses, no critical component matching condition is required, and all the incremental parameter sensitivities are low. PSPICE simulation results are performed to confirm the theoretical analysis.     

A novel CMOS operational transconductance amplifier based on a mobility compensation technique

This brief describes a new linear operational transconductance amplifier (OTA) and its application to a ninth-order Bessel filter. To improve the linearity of the OTA, we employ a mobility compensation circuit which combines the transistors operating in the triode and the subthreshold regions. The proposed technique enhances the linearity of the transconductance without loss of the input swing range. The proposed OTA shows /spl plusmn/0.5% Gm variation and the total harmonic distortion of less than - 60-dB over the input range of /spl plusmn/0.8-V. The ninth-order Bessel filter employing the proposed OTA has been implemented in a 0.35-/spl mu/m n-well CMOS process under 3.3-V supply voltage. It shows the cutoff frequency of 8 MHz and the power consumption of 65 mW.     

Realization of current-mode fully integrated full-wave rectifier

In this paper, a new fully integrated high frequency current-mode full-wave rectifiers are presented. The proposed circuits rectify the input signals without diode, so the output signal confronts zero-crossing distortions because of the diode characteristics have been solved with this rectifier even in high frequencies. While the current rectifier has dual output, the voltage rectifier has one output. The presented circuits have a vastly superior zero crossing performance, good linearity, minimum number of transistors, wide frequency range, and they are suitable for monolithic integrated implementation. The performances of the proposed circuits are investigated through LTSpice. Monte-Carlo and Noise analyses have also been performed to show the effectiveness of the proposed circuits.     

一种小型化电调功分器设计

该文提出了一种等功分电调功分器。该功分器基于传输线变换技术进行设计,利用变容二极管调节功分器的中心频率,实现了从900～1050MHz的中心频率调节范围,在可调范围内实现S11小于-20dB。S21、S31大于-3．2dB,S23小于-22dB。该功分器具有尺寸小,偏置电路简单的优点。     

A new low-power current-mode MOS only versatile precision rectifier

In this paper, a new low-power versatile current-mode rectifier is proposed. As a salient feature, the proposed rectifier provides two positive half-wave, two inverting negative half-wave or two full-wave outputs from the same configuration. The proposed circuit employs only a dual-output second-generation current conveyor (DO-CCII) and a core rectifying circuit consisting of twelve MOS transistors. The input and output signals are current. Favorably, by adding two additional transistors, the proposed rectifier can also rectify voltage signals with electronic tuning capability. The simple and MOS only structure of the proposed circuit is highly attractive from integration point of view. In spite of providing multiple outputs at the same time, the proposed rectifier enjoys low power consumption. PSPICE simulations using 0.18 μm CMOS parameters and supply voltage of ±0.9 V demonstrate a precise operation and good temperature stability.     

一种小型化电调正交耦合器

该文提出了一种3dB正交电调耦合器。该耦合器基于传输线变换技术进行设计,利用变容二极管调节3dB正交耦合器的中心频率,实现了从1.8~2.8GHz的中心频率调节范围,在可调范围内实现S11优于-15dB,S31大于-4.4dB,直通和耦合端的相位差为90±5°。该耦合器具有结构紧凑,偏置电路简单的优点。     

High input impedance voltage-mode universal biquadratic filter using two OTAs and one CCII

A three-input and single-output voltage-mode universal biquadratic filter with high input impedance, using only two operational transconductance amplifiers (OTAs), one plus-type second-generation current conveyor (CCII) and two capacitors, is presented. The proposed circuit can realize all the standard filter responses, that is, highpass, bandpass, lowpass, notch and allpass filters, from the same configuration. The proposed circuit has no requirements for component matching conditions.     

Current-mode KHN filter employing current differencing transconductance amplifiers

This study proposes a current mode (CM) Kerwin–Huelsman–Newcomb (KHN) filter employing only two current differencing transconductance amplifiers (CDTA) and two grounded capacitors. It is concluded that the circuit described here offers a simpler and more economical alternative to other CM KHN filters reported previously in literature.