OTA-Based Logarithmic Circuit for Arbitrary Input Signal and Its Application
Abstract : In this paper, a new design procedure has been proposed for realization of logarithmic function via three phases: 1) differentiation; 2) division; and 3) integration for any arbitrary analog signal. All the basic building blocks, i.e., differentiator, divider, and integrator, are realized by operational transconductance amplifier, a current mode device. Realization of exponential, power law, and hyperbolic function as the design examples claims that the proposed synthesis procedure has the potential to design a log-based nonlinear system in a systematic and hierarchical manner. The performance of all the proposed circuits has been verified with SPICE simulation.
? The possibility exists that they may go into oscillation or become unstable if you are not careful and ignore the margins.
? A variety of special-purpose op amps and op amp derivatives now exist for the designer's convenience.
? Moderate power devices exist that have been designed for line drivers and audio applications.
? This variation is used when a potential greater than the input is desired, such as deriving a 15 V supply from an existing 5 V source.
? Although four op amps may sound like a large number of devices, remember that a variety of quad op amp packages exist, indicating that the actual physical layout may be quite small.
? Design of logarithmic and exponential circuit for any arbitrary input signal remains a serious problem.
? Excellent contributions are reported of nonlinear circuits dealing with particular important nonlinear problems.
? In this paper, rather than try to tackle a specific problem, we focus our attention on a general approach dealing with nonlinear basic building blocks using OTA’S as the main active elements.
? The slopes and breakpoints are voltage programmable, which gives an additional flexibility in the function approximation design problem.
• The proposed multipliers are of the transconductance type, the outputs must be converted into voltages for use as the inputs to subsequent multipliers.
• The proposed OTA-based building blocks can be incorporated in a CAD software to fully exploit their functionality and versatility.
• Current mirrors are widely used for biasing purposes and as active loads. Active loads offer the advantage of producing higher gains than ordinary resistive loads.
• To help reduce these problems, a number of circuits have been specially optimized for comparator purposes.
? The actual OTA circuit implementation, where an optional diode and voltage source have been added at the OTA to improve the high-frequency performance of the circuit.
? We show that the operational transconductance amplifier (OTA), as the active element in basic bnilding blocks, can be efficiently used for programmable nonlinear continuous-time function synthesis.
? The linearized OTA used to synthesize the different nonlinear analog functions is reported elsewhere.
? The equivalent circuit of the OTA when used as a two-terminal resistive element to simulate a grounded load resistance.
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