Design Article
The current differencing transconductance amplifier (CDTA)
Jun Xu and Chunhua Wang
1/28/2013 12:36 PM EST
Editor’s note: Most modern designs have been using voltage mode elements like op-amps for implementation of various electronic circuits. These elements are used widely due to their small sizes and good performance. With the demand for portable battery powered equipment increasing, designers have begun to look into different architectures to fit these demanding designs. This issue is not easily solved with voltage mode elements since the voltage supply if reduced will cause problems with realizing good, fully-functional circuits. Instead, current mode (CM) elements are now being considered for the same circuits and these issues can then be addressed.
The Current Differencing Transconductance Amplifier (CDTA) is the active element operating in current-mode and can be applied to various circuits such as comparators, second order high pass, second order low pass, second order band pass filters.
This article outlines a design method for CDTA-based resistor-less current-mode full balanced nth-order leapfrog ladder filter is presented. Second, circuit device’s parameters confirmation for actual design are analyzed in detail. Further, PSpice simulation for an actual 6th-order butterworth filter is conducted, and the result verifies the validity of the proposed circuits.A new method for design of resistorless current-mode full balanced nth-order leapfrog ladder filter using CDTA as active component is proposed in the paper. The proposed circuit, which adopts only n active components and n grounded capacitors, can realize n-order filter’s function and shares simple configuration, low power consumption. It contains minimum component and doesn’t use any resistor.
The proposed filter can be applied in many fields: for instance, RF transmitter/receiver, phase-locked loop FM demodulator, wireless communication and instrumentation. In order to demonstrate the validity of the proposed circuit, PSpice simulation for actual 6th-order butterworth filter is conducted, and the result has good agreement with the theoretical analysis.
Next: Introduction
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atemp
1/29/2013 4:29 PM EST
Yes, yes, all very well. But until somebody starts sampling and shipping actual chips that are practical, repeatable, and stable, with lots of competition and drop-in equivalents, CDTAs will join current conveyors and "perfect" OTAs in being purely SPICE or lab curiosities--- impractical and irrelevant. The LM13600/LM13700 are the most-used non-opamp topology, and then they are slow, noisy, tempco-ridden beasties sorely in need of an update after three DECADES of deployment.
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steve.taranovich
1/30/2013 1:06 PM EST
Sounds like process engineers have their work cut out!
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