Continuous-time active-RC Filters Research Articles

GENERAL STRUCTURE OF INTEGRATOR-BASED CONTINUOUS-TIME ACTIVE-RC FILTER AND APPLICATIONS

In the paper, a general structure of integrator-based continuous-time Active-RC filter is presented. More specifically, filter structures containing inverting amplifiers and passive feedback network are considered. The structure is analyzed using matrix description. The extensions of the model that take into account finite DC gain and finite bandwidth of operational amplifiers as well as other non-ideal effects are presented. The matrix-based approach is formulated especially for efficient use in computer analysis and design of Active-RC filters. An application example of the proposed approach to obtain OPAMP specifications for 3rd order low-pass Chebyshev filter for Analog Front End for VDSL is given. In this paper, we consider a general Active-RC filter topology suitable for computer-aided analysis, design and optimization of Active-RC filters. The structure is not the most general one, since it is restricted to filter topologies containing only inverting amplifiers (especially integrators) and RC feedback network.

Correlated double sampling technique for continuous-time filters

A correlated double sampling technique, applicable to continuous-time active-RC filters, is proposed. It provides suppression of DC offset and 1/f noise, and performs gain boosting and level shifting for the opamps used. A biquad lowpass filter is described to demonstrate the application of the technique.

Continuous-time active-RC filter model for computer-aided design and optimization

A general circuit model is presented for integrator-based continuous-time active-RC filters, consisting of inverting amplifiers and a passive feedback network. The structure is analyzed using a matrix description and the explicit transfer-function formula is given for the general case. Extensions of the model are given that take into account finite dc gain and bandwidth of operational amplifiers, as well as other nonideal effects. Noise analysis of the active-RC filters is performed in a general setting. The matrix-based approach is formulated especially for the efficient use in computer-aided analysis and design of active-RC filters. As illustrations, a few application examples of the proposed approach are given.

Jump phenomenon in an OTA simulated LC circuit

Commercially available discrete operational transconductance amplifiers (OTAs) in current use possess a limited differential input voltage range. This requires that corresponding continuous-time active RC filters operate with small input voltages in order to avoid the appearance of nonlinear behaviour of the overall circuit. Since this leads to reduced signal-to-noise ratios this active element is used mainly in integrated continuous-time active filter design. The nonlinear operation of circuits using discrete elements, with the active elements being OTAs, is studied here both theoretically and experimentally by means of the jump phenomenon. This phenomenon appears in many experimental circuits and should be a cause of concern for those who intend to use OTAs in discrete active RC filter design.

Active-MOSFET-C single-amplifier biquadratic filters for video frequencies

The authors show how continuous-time active-RC filters can be implemented in CMOS by replacing all resistors by MOSFETs operating in the linear region. As an example, a 24 MHz active MOSFET-C single-amplifier biquadratic lowpass filter with a pole-Q of 3 implemented in a 0.6 /spl mu/m CMOS process is discussed. By comparing measurements of a test chip, simulations and calculations, the following conclusion is reached. As long as the specifications for frequency, pole-Q, spurious-free dynamic range and supply voltage lie within certain limits, then active-MOSFET-C single-amplifier biquads (MOSFET-C SABs) are preferable; with respect to chip size and power consumption, compared to multi-amplifier biquads, e.g. integrator-connected biquads. Above these limits, the latter must be used.

A monolithic data acquisition channel

A monolithic data acquisition channel has been fabricated using a double level polysilicon NMOS process. The channel consists of a switched-capacitor filter, a continuous-time active RC filter, and a successive approximation analog-to-digital converter. The IC is in the form of a parts kit for a data acquisition channel so that each functional component can be characterized independently. Stitch bonds are used to connect the elements together to form the complete monolithic channel. Each element is implemented with a symmetric, fully differential structure. The measured dynamic range of the channel is 86.1 dB when using ± 5 V supplies.

A Monolithic Data Acquisition Channel

A monolithic data acquisition channel has been fabricated using a double level polysilicon NMOS process. The channel consists of a switched-capacitor filter, a continuous-time active RC filter, and a successive approximation analog-to digital converter. The IC is in the form of a parts kit for a data acquisition channel so that each functional component can be characterized independently. Stitch bonds are used to connect the elements together to form the complete monolithic channel. Each element is implemented with a symmetric, fully differential structure. The measured dynamic range of the channel is 86.1 dB when using +- 5 V supplies.