N. A. Shah

Current-mode active-only universal filter

A novel current-mode active-only universal filter based on and employing three DO-CCCIIs and two OAs is introduced. The circuit is fully integrable and programmable, and implements all the five generic filtering functions. The three basic filtering responses LP, BP and HP are implemented simultaneously by the circuit, while AP and notch signals can be realized simply by connecting appropriate node currents. The currents are available at high output impedances, so the synthesized filter can be cascaded without additional buffers to realize higher order filters. The filter performance factors ω 0 and Q are electronically tunable in an orthogonal manner through separate bias currents of the CCCII. The PSPICE simulation was carried out to realize the proposed circuit.

Challenges of CAPTCHA in the accessibility of Indian regional websites

This paper reviews Indian Government guidelines regarding the inclusion of regional content in government websites, compares them to World Wide Web Consortiums (W3C) guidelines for multilingual version and use of CAPTCHA tests and analyzes some Indian Government websites in light of these guidelines. It also analyzes some other non-Indian government websites in terms of multilingual content and use of CAPTCHA tests. It further reports results obtained through several user studies and experiments regarding the use of English and regional CAPTCHA tests on non-English pages of multilingual websites in terms of accuracy and response time.

Analyzing Internet e-mail date-spoofing

Spammers and phishers constantly keep on changing spam structure to circumvent anti-spam procedures and target maximum recipients. Of late, it has been observed that spammers spoof date header of their spam e-mails to keep them on top in the recipients mailbox with an aim to maximize the chances of immediate attention of recipients. This form of spoofing can cause confusion to recipients, create problems in time bound transactions, increase chances of opening spam, worsen the problem of false positive, result in loss of work productivity, render date header field insignificant and would spawn a host of legal issues. This paper reports date-spoofing, analyzes implications of date-spoofed e-mails on some commercial and corporate e-mail servers and surveys e-mail user behavior. It further discusses detection of date-spoofed e-mails to enable forensic examinations of date forged e-mails and presents possible technical solutions to stop date-spoofing.

On the realization of a voltage controlled oscillator

Abstract A new voltage-controlled second-order active-RC oscillator using three grounded capacitors, six resistors, and one second generation current conveyor as an active circuit building block is proposed. The circuit is attractive from the point of view of integrated circuit implementation. The oscillation frequency can be independently adjusted through a single grounded resistor without affecting the condition for sustained oscillation.

Electronically tunable OTA-based all-pass circuit

A simple operational transconductance amplifier (OTA)-based circuit implementing first-order all-pass function is presented. Besides using a single OTA, the circuit employs a grounded capacitor and as many as four resistors. The gain of the circuit is electronically-tunable through transconductance gain of OTA and a grounded resistor, which can be be made voltage dependent. The circuit provides non-interactive tuning of phase and gain without disturbing the realizability condition. The circuit is capable of providing a substantial amount of gain, as the scale factor is a function of two gain-controlling parameters. The circuit is highly stable against temperature variations, since the realizability condition is a function of the resistor ratio.

Operational amplifier-based voltage-controlled oscillator

This paper presents a simple active-R voltage-controlled sinusoidal oscillator circuit which is attractive from the viewpoint of monolithic form of construction. The circuit does not require external capacitors; instead it uses the single-pole roll-off characteristics of the operational amplifier. The oscillation frequency is continuously tunable over a wide range by a single grounded resistor, and is inherently free from the condition of sustained oscillation. The circuit is suitable for IC construction, and does not suffer from the practical limitations encountered in the circuits reported previously. Experimental results agree closely with the theoretical calculations.

Square-Root-Domain Realization of Single-Cell Architecture of Complex TDCNN

Square-root-domain (SRD) CMOS analog realization of a single cell architecture of the complex Temporal Derivative Cellular Neural Networks (TDCNNs) is introduced in this paper. TDCNN initiates time derivative ‘diffusion’ between CNN cells for non-separable spatiotemporal filtering applications, where the input to the CNN is an image that changes over time. The evaluation of the performance of the complex SRD TDCNN cell has been done using the Cadence Orcad software with TSMC 0.18-μm CMOS process model parameters. The provided simulated results confirm the validity of the theory.

Sinh-Domain multiphase sinusoidal oscillator

A Multiphase Sinusoidal Oscillator (MSO) configuration derived by employing appropriate non-linear transconductors which implement lossy integrators in the Sinh-Domain is introduced in this paper. Owing to its companding nature, the oscillator offers the benefits of electronic tuning of the oscillation frequency and the capability for operating in a low-voltage environment. In addition, the condition of oscillation could be electronically adjusted without disturbing the oscillation frequency. This has been achieved by introducing a novel Sinh-Domain lossy integrator topology. The performance of the proposed oscillator has been evaluated through a design example, where a six-phase topology has been simulated by utilizing the Analog Design Environment of the Cadence software.

Versatile voltage-mode universal biquad filter using the operational amplifier pole

A new multifunction voltage-mode biquad filter topology having three inputs and one output is described. The filter consists of a single operational amplifier (OA), a single capacitor, and two resistors and supports LP, BP, HP, AP and Notch filtering signals from the same topology, without requiring additional components besides being devoid of component matching constraints. The filter uses OA pole and has thereby acquired suitability for extended frequency operation. The natural angular frequency ω0 and the Q can be separately tuned. The circuit has low sensitivity figures. PSPICE simulation results are employed to verify the circuit performance.

Universal filters of arbitrary order and type employing square-root-domain technique

Novel Single Input Multiple Output (SIMO) and Multiple Input Single Output (MISO) universal filter topologies of arbitrary order and type are introduced in this paper. The proposed topologies have been realised by employing Square-Root Domain (SRD) technique. An offered benefit of the universal filter topologies is that only grounded capacitors are required for their implementations and the resonant frequency of the filters can be electronically controlled by an appropriate dc current. The proposed universal filters simultaneously offer all the five standard filtering functions i.e. Lowpass (LP), Highpass (HP) and Bandpass (BP), Bandstop (BS) and Allpass (AP) frequency responses. In addition, the SIMO topology is generic in the sense that it can yield four different stable filter configurations. Two design examples are provided in each configuration and the correct operation of the corresponding topologies has been evaluated through the PSPICE software with BSIM 0.35-µm CMOS process model parameters.