New CMOS realization of high performance Voltage Differencing Inverting Buffered Amplifier and its filter application

This paper describes a high performance voltage differencing inverting buffered amplifier (VDIBA). The transconductance of the proposed circuit is enhanced by using positive feedback technique with only two extra transistors used in active load. Moreover, the bandwidth of proposed circuit is enhanced by using resistive compensation technique. The performance of proposed VDIBA is demonstrated by detailed frequency analysis. Furthermore, it is shown that the transconductance can be enhanced up to 4.61 mS at biasing current of 300 µA. In addition, a third order low pass filter is given as an application example to confirm the high performance of the proposed VDIBA. The proposed low pass filter operates at natural pole frequency of 15 MHz. The proposed VDIBA and its filter application are implemented using TSMC 90 nm CMOS technology in Cadence virtuoso schematic composer at ±0.6 V supply voltage.     

High-output-impedance current-mode multiphase sinusoidal oscillator employing current differencing transconductance amplifier-based allpass filters

This article presents a multiphase sinusoidal oscillator using current differencing transconductance amplifier (CDTA)-based allpass filters. The oscillation condition and oscillation frequency can be orthogonally controlled. The proposed circuit provides 2n – phase signals (n≥2) that are equally spaced in phase and of equal amplitude. The circuit requires one CDTA, two resistors and one capacitor for each phase and no additional current amplifier. Owing to high-output impedances, the proposed circuit enables easy cascading in current-mode configurations. The effects of the nonidealities of the CDTA-allpass sections were also studied. The results of PSpice simulations are presented, demonstrating their consistency with theoretical assumptions.     

A compact rail-to-rail CMOS buffer amplifier with very low quiescent current

In this work, a very compact, rail-to-rail, high-speed buffer amplifier for liquid crystal display (LCD) applications is proposed. Compared to other buffer amplifiers, the proposed circuit has a very simple architecture, occupies a small number of transistors and also has a large driving capacity with very low quiescent current. It is composed of two complementary differential input stages to provide rail-to-rail driving capacity. The push–pull transistors are directly connected to the differential input stage, and the output is taken from an inverter. The proposed buffer circuit is laid out using Mentor Graphics IC Station layout editor using AMS 0.35 μm process parameters. It is shown by post-layout simulations that the proposed buffer can drive a 1 nF capacitive load within a small settling time under a full voltage swing, while drawing only 1.6 μA quiescent current from a 3.3 V power supply.     

A Novel Resistor-Free Electronically Adjustable Current-Mode Instrumentation Amplifier

In this paper, a novel topology for implementing resistor-free current-mode instrumentation amplifier (CMIA) is presented. Unlike the other previously reported instrumentation amplifiers (IAs), in which input and/or output signals are in voltage domain, the input and output signals in the proposed structure are current signals and signal processing is also completely done in current domain benefiting from the full advantages of current-mode signal processing. Interestingly the CMRR of the proposed topology is wholly determined by only five transistors. Compared to the most of the previously reported IAs in which at least two active elements are used to attain high common-mode rejection ratio (CMRR) resulting in a complicated circuit, the proposed structure enjoys from an extremely simple circuit. It also exhibits low input impedance employing negative feedback principal. Of more interest is that, using simple degenerate current mirrors, the differential-mode gain of the proposed CMIA can be electronically varied by control voltage. This property makes it completely free of resistors. The very low number of transistors used in the structure of the proposed CMIA grants it such desirable properties as low-voltage low-power operation, suitability for integration, wide bandwidth etc. SPICE simulation results using the TSMC 0.18-μm CMOS process model under supply voltage of ±0.8 V show a high CMRR of 91 dB and a low input impedance of 291.5 Ω for the proposed CMIA. Temperature simulation results are also provided, which prove low temperature sensitivity of the proposed CMIA.     

Current-mode continuous-time fully-integrated universal filterusing CDBAs

The authors propose a new, fully-integrated universal filter using a current differencing buffered amplifier, a recently introduced active element. It has been shown that the use of the current differencing buffered amplifier in fully-integrated filter design is attractive in that it simplifies the implementation and makes possible the use of a minimum number of grounded capacitors, compared to those using second generation current conveyers and current feedback amplifiers     

Design and analysis of high Transconductance Current Follower Transconductance Amplifier (CFTA) and its applications

In this paper, a single-stage class AB bulk-driven amplifier operating in weak inversion region is proposed. The presented amplifier benefits from an improved high input swing structure using quasi-floating-gate technique. The composite transistors and recycling configuration used at the input stage enable the input differential pair to operate under low supply voltages with larger transconductance as compared to the conventional models at no expense of power budget. The circuit is designed in 0.18 µm CMOS technology and simulation results show 61.5 dB low frequency gain with the gain bandwidth of 30.15 kHz and 55.3 V/ms average slew rate. The total current of 275 nA and 0.6 V supply voltage make the proposed amplifier a suitable choice for ultra-low-power applications.     

Band-pass filter with high quality factor based on current differencing transconductance amplifier and current amplifier

This paper presents second order band-pass filter with high quality factor. Its high quality factor is provided by feedback circuit. The used second order filter is modified so that filters outputs through capacitor can be obtained to high impedance output. Thereby, there is no need the extra active element to obtain filter outputs. Also, the output stage of current differencing transconductance amplifier have only X− terminals instead of X+ and X− terminals. Furthermore, the quality factor of the band-pass filter with feedback circuit is increased by feedback gain consisting of only four transistors. Besides, to examine effects of parasitic elements, non-ideal and sensitivity, the overall structure is investigated deeply. Working conditions and boundaries of the overall structure is also defined. The simulation demonstrates good agreement between the theoretical expectations and simulation results.     

A feedforward excess-phase cancellation technique for integrators

Integrators are useful analogue function blocks. A representative application of integrators is a continuous-time filter on an integrated circuit. Excess phase shift of integrators is one of the most severe problems, because excess phase shift at the unity gain frequency degrades the frequency characteristics of the filters. This paper describes a feedforward excess-phase cancellation technique. The proposed technique is applied to integrators which have feedback with an amplifier. The proposed idea is verified by experiment. It is shown that the excess-phase shift due to the gain-bandwidth product of operational amplifiers is cancelled. The proposed technique is useful for realization of integrated continuous-time filters using integrators because extra capacitors are unnecessary. An integrator with the excess-phase cancellation and a third-order leapfrog filter using the integrator are designed and demonstrated by HSPICE simulation. The integrator has a parasitic pole whose frequency is proportional to the unity gain frequency. The simulation results show that the phase characteristics are improved by the proposed technique over the wide range of the unity gain frequency.     

Electronically controlled high input and low output impedance voltage mode multifunction filter with grounded capacitors

In this study, a three-input single-output voltage-mode biquadratic filter employing voltage differencing differential input buffered amplifier (VD-DIBA) is presented. The proposed filter uses two VD-DIBAs and two grounded capacitors without any external resistors, which is well suited for integrated circuit implementation. The circuit provides five standard transfer functions, namely, low pass, high pass, band pass, notch and all pass filters with electronic control of quality factor and pole frequency. Each transfer function can be selected by suitably selecting input signals via digital method. The filter does not require inverting of the input voltage signal. Moreover, the circuit possesses high input and low output impedances and thus it enables simple voltage-mode cascading. The PSPICE simulation and also experimental results are included, verifying the workability of the proposed filter. The given results agree well with the theoretical anticipation.     

Novel First-Order and Second-Order Current-Mode Filters Using Multiple-Output Operational Transconductance Amplifiers

In this paper, a general structure using dual-output operational transconductance amplifiers (OTAs) is explored to derive new first-order and second-order multi-function filters using OTAs with multiple current outputs and with and without grounded capacitors. Two first-order all-pass filters that have been obtained are presented, together with an analysis of nonidealities of OTAs, viz., finite bandwidth and parasitic output and input resistance and capacitance. Second-order multi-function filters obtained by using OTA-C simulated inductances in the proposed general structure are also presented. The realization of quadrature oscillator using the proposed first-order all-pass networks is also considered. Detailed analysis of nonideal frequency performance of the OTAs as well as finite output and input impedances is presented. SPICE simulation results are also given for the proposed circuits.     

Electronically tunable voltage-mode quadrature oscillator based on high performance CCCDBA

This paper presents a new electronically tunable voltage-mode quadrature oscillator using two high performance current controlled current differencing buffered amplifiers (CCCDBA), two capacitors and single resistor, all of them are grounded which is advantageous for monolithic integration. The condition of oscillation and the frequency of oscillation are independent and can be controlled by two separate bias currents. The output voltages are obtained at the terminals with almost zero internal impedances, thus there is no need to use any buffering devices. The MOS structure of the CCCDBA presented in this paper is of a high performance and ensures precision, large dynamic range, wide bandwidth and has the capability to drive a load with very low resistance. Non-ideal analysis of the proposed oscillator is provided and PSpice simulation results using the 0.18 μm n-well CMOS technology from TSMC are included to verify the correct functionality of the proposed circuit.     

An in-probe receiver amplifier with 3 dB noise figure and 50 dB dynamic range for medical ultrasound imaging using CMUTs

This paper presents the design and measurements of an in-probe receiver amplifier for ultrasound imaging applications using a capacitive micromachined ultrasonic transducer (CMUT). In such applications, the noise and the dynamic range play very important roles, as the former dictates the minimum input signal level and the latter defines the maximum input signal level that can be applied to a system. This work concentrates on both of these specifications. The amplifier consists of a transimpedance amplifier followed by a voltage gain stage implemented using a current feedback amplifier. It is designed and fabricated using a 180 nm CMOS process. A noise figure of 3 dB is measured for a CMUT model with 10–30 MHz frequency range. The amplifier shows a dynamic range of 50 dB with 0.8 % total harmonic distortion for the full scale input current of 7 µA peak-to-peak.     

A high input impedance buffer amplifier using bipolar transistors

The input impedance of conventional emitter follower circuits is limited due to the finite value of the passive emitter resistance, shunting effect of biasing resistors and that of intrinsic collector to base feedback admittance and also to the fall in current amplification factor at low operating currents. Further, the input admittance is frequency dependent because the device parameters involved therein are themselves frequency dependent. However, the shunt positive feedback incorporated in such circuits minimizes the shunting effect of the biasing network and also that of the intrinsic feedback admittance. The simulation of negative capacitance across the input terminals nullifies the effect of the presence of the otherwise positive capacity. This technique extends the bandwidth over which the input impedance remains constant. A typical buffer amplifier circuit employing five conventional epitaxial planar bipolar silicon transistors has been described in the present communication. The input impedance of which is found to be constant over a frequency range of 10 HZ to 2 KHz and its magnitude is about 25MΩ.     

Charge pump with reduced current mismatch for reference spur minimization in PLLs

In this article, a charge pump circuit featuring minimal mismatch between its up and down currents is proposed. In conventional charge pumps, where error amplifiers are used in feedback, the factor that hinders exact current matching is the offset voltage of the error amplifier. In the proposed design, the input offset voltage is computed and additional current delivering/comsuming branch is implemented to supplement for the error current. The new charge pump requires a few error amplifiers and a dynamic comparator for its operation. Simulations considering process variations show current mismatch of less than 20 nA even at the worst case event. The proposed charge pump has been utilized in PLL circuits to reduce reference spurs and simulations of these PLLs show remarkable spur reduction.     

New strategies to improve offset and the speed–accuracy–power tradeoff in CMOS amplifiers

Four continuous-time strategies to improve the speed–accuracy–power tradeoff in CMOS amplifiers by using low-power offset-compensation circuits are presented. The offset contribution at the output voltage is extracted and used to modify the DC component of the input voltage or the value of the active load, through low frequency feedback loops, which are realized using two transistors operating in weak inversion and a small capacitor. Because these circuits do not affect the bandwidth and allow using small transistors, the power consumption is greatly reduced with respect to an uncompensated amplifier of the same speed and offset behavior. The proposed strategies present reduced costs in area, power consumption and complexity, and a decrease in the low frequency noise contributions. MonteCarlo, HSPICE simulations results of common source, class AB and fully differential amplifiers, and experimental results of a class AB amplifier, all implemented in a 0.5-μm CMOS technology are shown. Statistical analyses of these strategies are also presented. Improvements up to 99.74% and 398.6% in the offset and the power consumption are respectively observed.     

Advances in Reversed Nested Miller Compensation

The use of two frequency compensation schemes for three-stage operational transconductance amplifiers, namely the reversed nested Miller compensation with nulling resistor (RN-MCNR) and reversed active feedback frequency compensation (RAFFC), is presented in this paper. The techniques are based on the basic RNMC and show an inherent advantage over traditional compensation strategies, especially for heavy capacitive loads. Moreover, they are implemented without entailing extra transistors, thus saving circuit complexity and power consumption. A well-defined design procedure, introducing phase margin as main design parameter, is also developed for each solution. To verify the effectiveness of the techniques, two amplifiers have been fabricated in a standard 0.5-mum CMOS process. Experimental measurements are found in good agreement with theoretical analysis and show an improvement in small-signal and large-signal amplifier performances. Finally, an analytical comparison with the nonreversed counterparts topologies, which shows the superiority of the proposed solutions, is also included.     

Resistorless realization of current-mode first-order allpass filter using current differencing transconductance amplifiers

This paper presents a realization of a current-mode first-order allpass filter using two current differencing transconductance amplifiers (CDTAs) as the active components and one virtually grounded capacitor as the only passive component. The proposed filer requires no external resistor and is electronically adjustable by varying the external bias current of the CDTA. No component-matching constraints are required. The circuit realizes both inverting and non-inverting types of allpass filters, and also exhibits high-output impedances, which are easy cascading in the current-mode operation. As an application of the proposed CDTA-based allpass section, a current-mode quadrature oscillator is realized. PSPICE simulation results are given to confirm the theoretical analysis.     

New topology for implementing bandpass,bandstop and allpass filters with CFAs

In this brief, a new filter topology based on current feedback amplifiers is presented and compared with its operational amplifier counterpart. The circuits arising from the new topology have the important advantage that access to the Z node of the current feedback amplifier is not required, as is the case with many existing current feedback amplifier filter circuits. The operation and requirements for each of the filters are described. Theoretical results and circuit limitations are discussed and verified with experimental results. In one experiment a bandpass filter with a calculated Q and centre frequency of 20 and 158.53 kHz, respectively was built using the OPA2607 dual CFAs IC. Measured results yielded a Q of 20.153 at a centre frequency of 148.62 kHz showing close agreement with theory.     

A 0.7 to 3 GHz wireless receiver front end in 65-nm CMOS with an LNA linearized by positive feedback

This paper presents a wireless receiver front-end intended for cellular applications implemented in a 65 nm CMOS technology. The circuit features a low noise amplifier (LNA), quadrature passive mixers, and a frequency divider generating 25 % duty cycle quadrature local oscillator (LO) signals. A complementary common-gate LNA is used, and to meet the stringent linearity requirements it employs positive feedback with transistors biased in the sub-threshold region, resulting in cancellation of the third order non-linearity. The mixers are also linearized, using a baseband to LO bootstrap circuit. Measurements of the front-end show about 3.5 dB improvement in out-of-band IIP3 at optimum bias of the positive feedback devices in the LNA, resulting in an out-of-band IIP3 of 10 dBm. With a frequency range from 0.7 to 3 GHz the receiver front-end covers most important cellular bands, with an input return loss above 9 dB and a voltage gain exceeding 16 dB for all bias settings. The circuit consumes 4.38 mA from a 1.5 V supply.     

Realization of multiple-output biquadratic filters using current differencing buffered amplifiers

In this paper, multiple-output multifunctional biquadratic filters using current differencing buffered amplifiers (CDBAs) as active elements are presented. The proposed circuit configuration is mainly composed of the CDBA-based cross-coupled feedback configuration and the simple CDBA-based voltage substractor. By an appropriate choice of virtually grounded passive components, the configuration can simultaneously realize lowpass, highpass, bandpass, bandstop and allpass voltage transfer functions, all at low resistance outputs. The natural angular frequency and the quality factor can orthogonally controllable. Experimental results verifying the theoretical analysis are also given.