A high-performance full-wave rectifier circuit

A new circuit that enables basic operational amplifiers (op amps) such as the LM741 to produce precise full-wave rectification for frequencies up to and exceeding 100 kHz without waveform distortion is presented. The circuit is based on a standard op amp precise rectifier that is modified by the inclusion of a current conveyor to improve the rectifying process.     

A dual current feedback op amp in CMOS technology

A CMOS circuit configuration implementing a current feedback or transimpedance op amp (CFB op amp) is presented. The architecture of the circuit is derived from similar bipolar CFB op amps. The properties of the CMOS implementation are similar to those of its bipolar counterparts, i.e., a high slew rate and a bandwidth which is independent of the closed-loop gain when the op amp is used with current feedback. Further, it is shown how two CFB op amps can be connected to achieve a non-slew-rate-limited voltage-mode op amp.     

Design for testability of embedded integrated operationalamplifiers

The operational amplifier (op amp) is one of the most encountered analog building blocks. In this paper, the problem of testing an integrated op amp is treated. A new low-cost vectorless test solution, known as oscillation test, is investigated to test the op amp. During the test mode, the op amps are converted to a circuit that oscillates and the oscillation frequency is evaluated to monitor faults. The tolerance band of the oscillation frequency is determined using a Monte Carlo analysis taking into account the nominal tolerance of all important technology and design parameters. Faults in the op amps under test which cause the oscillation frequency to exit the tolerance band can therefore be detected. Some Design for Testability (DfT) rules to rearrange op amps to form oscillators are presented and the related practical problems and limitations are discussed. The oscillation frequency can be easily and precisely evaluated using pure digital circuitry. The simulation and practical implementation results confirm that the presented techniques ensure a high fault coverage with a low area overhead     

A multiplexed switched capacitor filter bank

A technique is introduced which allows several integrator capacitors to be multiplexed onto a single operational amplifier. As a result, the op amp can be shared by several switched capacitor filter channels, drastically reducing the number of op amps required for filter banks. Twenty second-order filters have been implemented in a circuit using only two op amps and 2.5 mm/SUP 2/. The design of this system is presented and its performance is discussed. Some loss of signal energy is shown to occur during the multiplexing operations, which reduces filter Q. Causes of this charge loss are described, and its effects on performance are modeled. The design of the op amp used is presented, which incorporates a new system of input stage biasing and differential to single-ended conversion, as well as other features.     

Simple technique for op amp continuous-time 1 V supply operation

A simple scheme for achieving continuous-time low-voltage operation of op amps is discussed. The scheme involves placing a floating battery in series with one of the op amp input terminals. Simulations and experimental results are presented that verify the proposed scheme with the example of a CMOS op amp that operates from a single 1 V supply and with 0.8 V signal swing     

High-gain microwatt composite cascode op amps

This article discusses the composite cascode stage, both single-ended and differential, operating in the weak inversion or moderate inversion region. The gain of the MOS composite cascode differential stage can exceed 100,000?V/V, a figure that has never been reported in the literature. For low-frequency applications, this configuration can be used to fabricate op amps that have high-gain, low-power and low-nonlinear distortion. Two different architectures, both having two gain stages are reported. The first op amp uses the Widlar architecture to achieve a gain of 117?dB, a power dissipation of 110?µW and uses a compensation capacitor of only 3.5?pF. The second op amp uses a class AB stage for the second and final stage and utilises the parasitic capacitance at the output of the first stage for compensation. This self-compensating op amp has a gain of 110?dB and a power dissipation of 21?µW.     

Macromodeling of integrated circuit operational amplifiers

A macromodel has been developed for integrated circuit (IC) op amps which provides an excellent pin-for-pin representation. The model elements are those which are common to most circuit simulators. The macromodel is a factor of more than six times less complex than the original circuit, and provides simulated circuit responses that have run times which are an order of magnitude faster and less costly in comparison to modeling the op amp at the electronic device level. Expressions for the values of the elements of the macromodel are developed starting from values of typical response characteristics of the op amp. Examples are given for three representative op amps. In addition, the performance of the macromodel in linear and nonlinear systems is presented. For comparison, the simulated circuit performance when modeling at the device level is also demonstrated.     

Current mode instrumentation amplifier with rail-to-rail input and output

This paper presents the results from an investigation on the implementation of Current Mode Instrumentation Amplifiers (CMIAs) with rail-to-rail operational amplifiers (op amp) with a gm control circuit. The objective of employing rail-to-rail op amps in the implementation of a CMIA is the improvement of the common-mode operation range. The enhancement of the input common mode range (ICMR) is obtained using op amps with a rail-to-rail input stage followed by a cascode-based output stage. A prototype of the CMIA was implemented in standard 0.6 μm XFAB CMOS technology. Test results showed that the CMIA common mode range was extended but with moderated CMRR. To minimize this issue the amplifier was re-designed and sent to fabrication. Simulations with the components variations included were performed and showed the enhancement of the CMRR can be expected.     

Design techniques for cascoded CMOS op amps with improved PSRR and common-mode input range

Internally compensated CMOS op amps have been widely used in sampled-analog signal processing applications over the past several years. However, the popular two-stage op amp suffers from poor AC power supply rejection to one of the power rails. Two circuits are presented that overcome the power-supply rejection ratio (PSRR) problems of the earlier amplifier: one for virtual ground applications such as switched-capacitor integrators, the other for buffer applications requiring wide common-mode input range. Small signal analysis is developed for the open-loop and PSRR responses of the two amplifiers. In addition, design guidelines are suggested and test results are presented.     

Compact High Gain CMOS Op Amp Design using Comparators

This paper discusses the design of high gain, general purpose op amps. The op amp is based on a novel cascaded design using comparators and with structural simplicity approaching that of digital circuits. Ideally, the design tool presented here can be used to optimize gain and CMRR independent of the other op amp performance parameters. The designed op amp has 140 dB open-loop gain and 43 MHz unity gain frequency (GBW) in Berkeley Spice3f Level-2 simulation. The circuit is implemented using a 2.0 m nwell CMOS process through MOSIS. The op amp is self-biased and requires only power supplies of ±2.5 V. It occupies an area of 113 m×474 m.     

一种折叠共源共栅运算放大器的设计

折叠共源共栅运放结构的运算放大器可以使设计者优化二阶性能指标,这一点在传统的两级运算放大器中是不可能的。特别是共源共栅技术对提高增益、增加PSRR值和在输出端允许自补偿是有很用的。这种灵活性允许在CMOS工艺中发展高性能无缓冲运算放大器。目前,这样的放大器已被广泛用于无线电通信的集成电路中。介绍了一种折叠共源共栅的运算放大器,采用TSMC 0.18混合信号双阱CMOS工艺库,用HSpice W 2005.03进行设计仿真,最后与设计指标进行比较。     

A high precision micropower operational amplifier

An operational amplifier configuration implemented as a true micropower high precision op amp is described. It includes a well controlled and predictable DC biasing network that is insensitive to variations in temperature, supply voltages, and process. Also, it permits single supply operation. Excellent DC precision characteristics, comparable to or better than the very best precision op amps currently available, are realized yet at micropower levels. By simply increasing the biasing currents, a version of this design operates in general purpose applications without any degradation in its high precision characteristics. Thus, the AC performance levels of general purpose op amps are attained at a fraction of supply current. This device is fabricated using a standard bipolar IC process; an ion-implanted JFET is added to simplify biasing.     

Predicting the Effect of Pulsed Ionizing Radiation on Operational Amplifiers

The response of IC operational amplifiers (op amps) to pulsed ionizing irradiation is studied theoretically and experimentally. The major mechanisms of the radiation response are covered. The contributions of main op-amp stages to the output-voltage response are analyzed. The ionization-induced failure of an op amp is traced to its intermediate stages. It is established that the recovery time depends on the type of compensation employed. A block-model approach is proposed as a method for the prediction of transient radiation responses. Ways to define the performance index of an op amp exposed to pulsed ionizing radiation are discussed.     

High-gain gaas mesfet op amp

A gain enhancement technique for GaAs MESFET op amps is presented. It uses positive feedback to cancel the output conductance between the driver and active load transistors in a common-source amplifier configuration. An op amp using this technique was implemented in a 1-µm non-self-aligned GaAs MESFET process. The op amp exhibited a dc gain of 60 dB and a unity-gain frequency of 840 MHz.Please address all correspondence to C.A.T. Salama.     

Operational amplifier with 1-V rail-to-rail multipath-driven outputstage

A bipolar operational amplifier (op amp) with a rail-to-rail multipath-driven output stage that operates at supply voltages down to 1 V is presented. The bandwidth of this output stage is as high as possible, viz, equal to that of one of the output transistors, loaded by the output capacitance. The output voltage can reach both supply rails within 100 mV and the output current is ±15 mA. The op amp is designed to be loaded by a 100-pF capacitor and the unity-gain bandwidth is 3.4 MHz at a 60° phase margin. The voltage gain is 117 dB and the CMRR is 100 dB. The frequency behavior of the multipath-driven (MPD) topology has an improved performance when compared to that of previously presented low-voltage output stages. A figure of merit F_M for low-voltage op amps has been defined as the bandwidth-power ratio     

High-frequency active filter design using monolithic nullors

A monolithic building block suitable for high-frequency RC active filter implementation is described. The transconductance-type device is fabricated using standard bipolar technology, and its performance is shown to be superior to corresponding voltage operational amplifiers (op amps) at frequencies above 20 kHz. It is also shown that high quality simulated inductance and frequency dependent negative resistance elements can be implemented at higher frequencies than is possible using standard bipolar op amps.     

The response of 741 op amps to very short pulses

A 741 op amp behaves like a monostable multivibrator when very short pulses are applied to the noninverting input terminal. It is shown that perturbations on the power supply lines or at the output of the amplifier will directly or indirectly have the same effect on the op amp.     

High performance op amps in a 40V BiCMOS process and their applications

This paper describes the design of three high-performance op amps in a 40V BiCMOS technology. The first circuit is a low-noise op amp with MOS inputs. A thermal noise level as low as with a 1/f noise corner frequency of 100 Hz is achieved. For applications that can tolerate a lower input impedance, a more economical bipolar input low-noise op amp has been designed, yielding an even better noise performance for source impedances up to 20 k. The third circuit is an internally compensated high-gain-bandwidth (GBW=15 MHz) op amp that can drive loads from 0 to 20 pF. A fourth-order low-pass switched-capacitor filter making use of the latter op amp is discussed next. Finally the applications of this 40V BiCMOS process are illustrated.     

A macromodel for integrated all-MOS operational amplifiers

A macromodel for integrated all-MOS operational amplifiers is developed with reference to circuits where the settling behavior of the op amps is of particular concern. Expressions for the values of the elements of the macromodel are obtained from typical measured characteristics. It is shown that the proposed macromodel can satisfactorily predict both small-signal and large-signal behavior of the op amps.     

Computer-Aided Analysis of RFI Effects in Operational Amplifiers

The modified Ebers-Moll model is used to predict RFI effects in the 741 operational amplifier (op amp)-a bipolar linear integrated circuit (IC). RFI susceptibility predictions for RF incident upon the op-amp input terminals are made using a complete model, a macromodel, and a voltage-offset model. Both the batch-mode computer program SPICE 2 and the commercial interactive computer program ISPICE are used. The three sets of calculated results are essentially identical and agree within 4 dB with experimental results measured at 220 MHz. A threshold cannot be given for the RF power level at which a 741 op amp is susceptible to RFI. The level depends upon the op-amp circuit application. For op-amp circuits designed to amplify input signals in the 0.1-to 1.0-V range, RF power levels as large as -15 to + 5 dBm may be required to cause RHI susceptibility problems. For op-amp circuits designed to amplify input signals in the 1-to 10-mV range, RF power levels as low as -55 to -35 dBm may cause RHI susceptibility problems.