Operational Transconductance Amplifier-capacitor Research Articles

A Bootstrapped Pseudo Resistor by Reusing OTA-C Filter for Neural Signal Processing

In integrated neural signal monitoring systems, pseudo resistor (PR) is widely used to form very large time constant filters, due to its large impedance within an acceptable die area. However, its linearity (the dependency of the resistance to applied voltage) and impedance are limited by the nonlinear MOS transistors in weak inversion, and suffers from process, voltage and temperature (PVT) variations. In this brief, a PR bootstrapped by reusing the operational transconductance amplifier-capacitor (OTA-C) filter is presented, it substantially increases the impedance and linearity to dynamically support lower frequency neural signal applications. It has no need for extra bias scheme on the gate or bulk, which decreases the circuit complexity, die area and power consumption. The proposed circuit implemented in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process occupies an area of 0.026 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the impedance of the bootstrapped PR is approximately 94 G <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> , and the high-pass cut-off frequency is reduced to 0.5 mHz.

Analysis and Experimental Validation of Large-Signal Linearization for Low-Power Complex OTA-C Filters

This paper presents a second-order complex baseband operational transconductance amplifier-capacitor (OTA-C) filter design for wireless receivers. It employs a novel adaptive biasing circuit for large-signal linearization that extends the filter’s usable signal swing range. An analysis of this linearization technique provides insights into its underlying concepts to assist the design process. The method is demonstrated with the first experimental evaluation of a second-order complex baseband filter prototype having a center frequency of 2 MHz and a bandwidth of 850 KHz. Fabricated in a standard 130nm CMOS technology, the filter prototype measurement results show a gain of 35.1 dB and an image rejection ratio of 39.7 dB while operation from a supply voltage of 0.95 V and consuming 0.13 mA. This design advances the low-power bandpass filter state-of-the-art by having an in-band and out-of-band SFDR of 62 dB and 64 dB respectively due to the use of the large-signal linearization approach.

Low-Voltage OTA-C Filter With an Area- and Power-Efficient OTA for Biosignal Sensor Applications.

This paper presents a systematic method for decreasing the amount of transconductors used by an operational transconductance amplifier-capacitor (OTA-C) filter to decrease the power consumption and the active area. An OTA with a local-feedback linearized technique and a transconductance booster is proposed based on the presented method. The proposed OTA combines current division with source degeneration to enhance linearity and implement low transconductance. This topology enables the proposed OTA to drive multiple integration capacitors without an additional output stage. The OTA-based circuit realizes low power consumption by operating under a weak inversion at a supply voltage of 1 V. Thus, a fifth-order ladder-type low-pass Butterworth OTA-C filter is implemented for the acquisition of electrocardiograph signals. The proposed method is validated using a prototype fabricated through a 1P6M 0.18-μm CMOS process. Results show that in ECG signal acquisition, the proposed filter has a signal bandwidth located within 250Hz, a dynamic range of 61.2dB, and a power consumption of 41nW to achieve a figure-of-merit of 5.4 × 10-13. The active area of the filter is 0.24mm2.

Design of a new low power MISO multi-mode universal biquad OTA-C filter

ABSTRACTIn this article, a new low-power multiple-input, single-output (MISO) multi-mode universal biquad operational transconductance amplifier-capacitor (OTA-C) filter with a minimum number of active and passive components is proposed. The proposed filter employs three OTAs, one inverter and two grounded capacitors. The proposed filter can realise all filter frequency responses including low-pass (LP), band-pass (BP), high-pass (HP), band-stop (BS) and all-pass (AP) in all operation modes including voltage, current, tranasresistance and transconductance modes using the same topology. Furthermore, sensitivity analysis is done which shows that the proposed filter has a low sensitivity to the values of the active and passive elements. The proposed filter is simulated in HSPICE using 0.18 µm CMOS technology. The HSPICE simulation results demonstrate that the proposed filter consumes only 35 μW at 2.5 MHz from a ±0.5 V supply voltage, while all of the transistors are biased in strong inversion region. Also, the simulation results are in a close agreement with the theoretical analysis which is done in MATLAB. Furthermore, the process, voltage and temperature variation simulations are done to study the effect of non-idealities on the performance of the proposed filter. It is shown that the simulation results justify a 4.8%, 0.8% and 20% variations of the centre frequency for process, voltage and temperature, respectively. Finally, Monte-Carlo, noise and transient simulations are done to justify the good performance of the proposed filter performance.

A Power-Efficient Reconfigurable OTA-C Filter for Low-Frequency Biomedical Applications

A power-efficient operational-transconductance-amplifier-capacitor (OTA-C) filter for biomedical applications is presented with detailed noise analysis. This filter consists of a cascade of biquadratic sections, each of which is configured via a serial-peripheral-interface circuit embedded with non-volatile memories to provide low pass or bandpass response. All filter parameters, including the gains, natural frequency, and quality factor, are orthogonally adjustable by programming charges on floating-gate bias transistors. The reconfigurable biquadratic section is composed of four power-efficient linearized OTAs. Each OTA consists of complementary hextuple-diffusor-quadruple-differential-pairs (HDQDPs) and a floating-gate common-mode feedback scheme. A developed computer algorithm for transistor dimension optimization is adopted to extend the input linear range of the HDQDP based on nonlinearity cancellation. A prototype chip is designed and fabricated in a $0.35~ \mu {\mathrm{ m}}$ CMOS process to demonstrate reconfigurability and performance of the proposed filter. Each biquadratic section occupies $0.12{\mathrm{ mm}}^{2}$ with a frequency tuning range more than five decades. Measured spurious-free dynamic ranges (SFDR) at the low pass and bandpass outputs from one of the biquadratic sections are 52.6 and 54.55 dB, respectively, when the natural frequency is programmed at 2 kHz with power consumption of 107.2 nW. A fourth-order Chebyshev low pass and an eighth-order Butterworth bandpass responses are implemented with characterized SFDRs of 50.43 and 48.3 dB, respectively.

Designing an Inverter-based Operational Transconductance Amplifier-capacitor Filter with Low Power Consumption for Biomedical Applications

The operational transconductance amplifier-capacitor (OTA-C) filter is one of the best structures for implementing continuous-time filters. It is particularly important to design a universal OTA-C filter capable of generating the desired filter response via a single structure, thus reducing the filter circuit power consumption as well as noise and the occupied space on the electronic chip. In this study, an inverter-based universal OTA-C filter with very low power consumption and acceptable noise was designed with applications in bioelectric and biomedical equipment for recording biomedical signals. The very low power consumption of the proposed filter was achieved through introducing bias in subthreshold MOSFET transistors. The proposed filter is also capable of simultaneously receiving favorable low-, band-, and high-pass filter responses. The performance of the proposed filter was simulated and analyzed via HSPICE software (level 49) and 180 nm complementary metal-oxide-semiconductor technology. The rate of power consumption and noise obtained from simulations are 7.1 nW and 10.18 nA, respectively, so this filter has reduced noise as well as power consumption. The proposed universal OTA-C filter was designed based on the minimum number of transconductance blocks and an inverter circuit by three transconductance blocks (OTA).

Current-mode operational transconductance amplifier-capacitor biquad filter structures based on Tarmy–Ghausi Active-RC filter and second-order digital all-pass filters

The Tarmy-Ghausi (TG) active resistor-capacitor (RC) filters using op-amps and its modification by Moschytz are well known to active RC filter designers. These use first-order all-pass networks in a negative feedback loop. New current-mode universal operational transconductance amplifier-capacitor (OTA-C) biquad filters based on the TG active RC filter are considered here. These are based on a recently proposed OTA-C based first-order all-pass network. Three different feedback arrangements are investigated in the proposed filter structure so as to reduce the pole-Q sensitivity. The proposed biquad filters are shown to implement all different types of filters like low-pass, high-pass, band-pass, symmetric notch, all-pass, low-pass notch and high-pass notch. The synthesis of the general biquad is carried out in a novel way by invoking the analogy with direct-form digital filter structures. The special case of all-pass filter realisation derived from the proposed universal filter needs additional hardware for realising the feed-forward coefficients. Hence alternative OTA-C based all-pass filter implementations based on Mitra-Hirano and Gray-Markel second-order digital filter structures are derived in which the coefficients that are used to realise the denominator are shared in the realisation of numerator also. All the proposed circuits are compared with the other structures available in the literature. The simulation results of the proposed circuits are also presented.

Realization of Tunable Pole-Q Current-Mode OTA-C Universal Filter

A realization of a current-mode operational transconductance amplifier-capacitor (OTA-C) universal filter with tunable pole-Q is proposed. A biquadratic band-reject function is used as the initial synthesis function based on three integrator blocks. Consequently, the proposed filter uses a total of three multiple-output OTAs and three grounded capacitors. Five types of transfer functions, namely, low-pass, high-pass, band-pass, band-reject, and all-pass responses, can be obtained without changing the circuit topology. The pole-Q (Q0) and the pole-frequency (ω0) parameters are independently tuned. The Q0 and ω0 parameters are electronically tuned by adjusting the transconductance gains of the OTAs. Furthermore, Q0 can be tuned by varying the capacitor manually without affecting ω0. SPICE simulation results of the proposed filter are presented.

Programmable feedforward linearized CMOS OTA for fully differential continuous‐time filter design

AbstractIn this paper, a feedforward linearization method for programmable CMOS operational transconductance amplifier (OTA) is described. The proposed circuit technique is developed using simple source‐coupled differential pair transconductors, a feedback‐loop amplifier for self‐adjusting transcoductance (gm) and a linear reference resistor (R). As a result, an efficient linearization of a transfer characteristic of the OTA is obtained. SPICE simulations show that for 0.35µm AMS CMOS process with a single +3V power supply, total harmonic distortion at 1 Vpp and temperature range from −30 to +90°C is less than −49.3 dB in comparison with −35.8 dB without linearization. Moreover, the input voltage range of linear operation is increased. Power consumption of the linearized OTA circuit is 0.86 mW. Finally, the OTA is used to design a third‐order elliptic low‐pass filter in high‐frequency range. The cut‐off frequency of the operational transconductance amplifier‐capacitor (OTA‐C) filter is tunable in the range of 322.6 kHz–10 MHz using the feedforward linearized OTAs with the digitally programmable current mirrors. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Compact sub-hertz ota-c filter design with interface-trap charge pump

Single-ended and differential operational transconductance amplifier (OTA) configurations are biased with MOSFET interface-trap charge-pumping (ITCP) current generators to achieve very low transconductances for tunable sub-hertz operational transconductance amplifier-capacitor (OTA-C) filter implementation. This paper reviews the basics of ITCP current generation and presents the transconductors and the OTA-C filter configurations based on these transconductors. One of the filters is a low-pass with an experimentally determined lowest cutoff frequency of 0.18 Hz, and the other is a fully differential bandpass with individually tunable lower and upper cutoff frequencies measured down to 0.3 Hz. The former has one 15-pF filter capacitor, and measures 0.0346 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whereas the latter contains four such capacitors and occupies 0.188 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> silicon. Experimental evaluation also includes offset, harmonic distortion, and noise performance.

Two-stage high swing fully integrated tunablequadrature sine oscillator

A new fully integrated two-stage operational transconductance amplifier-capacitor (OTA-C) sine oscillator circuit configuration using a 0.5 μm CMOS digital process is described. A simple linear impedance analysis is presented to predict the amplitude and distortion of oscillation. The accuracy of this approach is examined by comparing calculated, simulated and measured results. Transconductance tuning keeps the startup condition satisfied within the frequency range from 2 to 11 MHz.

Universal current-mode OTA-C biquad with the minimum components

A universal current mode operational transconductance amplifier-capacitor (OTA-C) biquad with three inputs and four outputs employing the minimum of components: only two OTAs and only two grounded capacitors is presented. The proposed circuit offers the following advantageous features: realization of low-pass, bandpass, high-pass, notch; and all-pass signals from the same simple configuration, employment of two grounded capacitors ideal for integration and low-sensitivity performance.

A current-mode testable design of operational transconductance amplifier-capacitor filters

Analog filters are important building blocks of many communication and instrumentation systems. However, similar to other analog circuits, testing an analog filter is a difficult problem. In recent years, this problem has become even more difficult because of the increase of circuit complexity. Operational transconductance amplifier-capacitor (OTA-C) filters are especially useful in video applications such as HDTV. In this paper, we first present the design of an OTA-C low-pass filter with a passband from 0 to 4.5 MHz. We then propose a current-mode method for the error detection of this filter. By comparing the current consumed by the circuit under test (CUT) and the current converted from the voltage levels of the CUT, abnormal function of circuit components can be concurrently detected. This technique has been applied to the OTA-C filter and a testable design is obtained. Experimental results show that our design has the following advantages: (1) easy to design and implement; (2) high accuracy in error detection; (3) little impact on the circuit performance of the filter; and (4) high error-detection speed. From an actual layout, we find that the area overhead is about 25% and only one extra pin is needed.

7-decade tuning range CMOS OTA-C sinusoidal VCO

A new operational transconductance amplifier-capacitor (OTA-C) based sinusoidal voltage-controlled oscillator (VCO) has been designed and fabricated, the oscillation frequency of which can be tuned from 74 mHz to 1 MHz. The VCO uses a new OTA whose transconductance is adjusted by using a set of special current mirrors. These current mirrors operate in weak inversion and their gain can be controlled continuously through a gate voltage over many decades. This is the first report of such a wide tuning range for CMOS sinusoidal oscillators. Experimental results are provided.

Evolutional searching for circuit structures

A new method based on a genetic algorithm is presented to search for graphs representing structures of circuits with a given transfer function. Operational transconductance amplifier-capacitor filters consisting of lossy and lossless integrators have been taken as an example.

Design and evaluation of a high-precision, fully tunable OTA-C bandpass filter implemented in GaAs MESFET technology

A second-order bandpass filter employing the operational transconductance amplifier-capacitor (OTA-C) method and featuring independent tuning of center frequency and Q is described. The filter, which is realized in 0.5-/spl mu/m GaAs MESFET technology, is intended for use in high-precision, continuous-time (CT) IF bandpass filtering applications requiring both accurate amplitude and group delay responses. The filter center frequency is tunable in the range 12-50 MHz, Q is tunable in the range 4-60, and a transfer function accuracy of the order of 1% is achieved throughout the tuning range. Active area is 1 mm/sup 2/ and static power consumption is 230 mW. >

New linearly tunable CMOS-compatible OTA-C oscillators with non-interacting controls

Operational transconductance amplifier capacitor (OTA-C) sinusoidal oscillators have attracted considerable attention recently because they offer several advantages over conventional op-amp-based oscillators, as well as because in conjunction with CMOS OTAs, they lead to the evolution of fully integrated oscillators in CMOS technology. The purpose of this paper is two-fold: first to present three new canonic (employing only two capacitors) four-OTA-C sinusoidal oscillator circuits possessing the capability of providing independent linear control of the frequency of oscillation, and then to describe an approach to converting these structures into CMOS VCOs, which requires a reduced number of components as compared to the CMOS OTA-based approaches used earlier. The validity of the proposed formulations has been confirmed by SPICE simulation results.

Generation, design and tuning of OTA-C high-frequency sinusoidal oscillators

A systematic approach to derive practical CMOS sinusoidal oscillators is presented. A general topology is given to implement sinusoidal oscillators by using operational transconductance amplifier capacitor (OTA-C) techniques. To illustrate the proposed approach five different structures are presented from this general topology and analysed, taking into account the CMOS OTAs dominant non-idealities. Building blocks are presented for amplitude control, both by automatic gain control (AGC) schemes and by limitation schemes. Experimental results from 3 μm and 2 μm CMOS (MOSIS) prototypes showing oscillation frequencies up to 69 MHz are included. The amplitudes can be adjusted between 1 V peak-to-peak and 100 mV peak-to-peak. Total harmonic distortions (THD) from 2.8% down to 0.2% have been experimentally measured in the laboratory. A frequency tuning loop for these structures is introduced that provides a precise, temperature and parasitic independent frequency-to-voltage relationship. Experimental results for the tuning loop are presented.

CMOS OTA-C high-frequency sinusoidal oscillators

Several topology families are given to implement practical CMOS sinusoidal oscillators by using operational transconductance amplifier-capacitor (OTA-C) techniques. Design techniques are proposed taking into account the CMOS OTA's dominant nonidealities. Building blocks are presented for amplitude control, both by automatic gain control (AGC) schemes and by limitation schemes. Experimental results from 3- and 2- mu m CMOS (MOSIS) prototypes that exhibit oscillation frequencies of up to 69 MHz are obtained. The amplitudes can be adjusted between 1 V peak to peak and 100 mV peak to peak. Total harmonic distortions from 2.8% down to 0.2% have been measured experimentally. >

Operational Transconductance Amplifier Capacitor Networks for Higher Order Filters and Oscillators

A generalized synthesis procedure of higher order OTA-C networks is presented. The general circuit configuration proposed can realize LP, HP and AP characteristics after inserting capacitors at the appropriate points. From the admittance matrix derived, the transfer functions are also obtained in terms of the capacitances of the network and transconductances of OTAs.