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Sinusoid generator employs current-controlled conveyors

28 Jan 2016  | Abhirup Lahiri

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Clearly, you can use the gain buffer to vary the frequency of oscillation, which is the area in which this circuit differs from the earlier Design Idea. You can use both current and voltage to control the voltage multiplier. The circuit lets you vary the voltage multiplier by adjusting bias currents IB3 or IB4 (figure 4). For voltage control over K, you can use another circuit simply by using a noninverting op amp and replacing the resistors with MOSFETs working in that triode region. That approach simulates voltage-controlled resistors.


Figure 3: This configuration creates an oscillator from two current-controlled conveyor circuits.


The circuit in figure 2 underwent testing with a PR100N PNP transistor and an NPN NP100N transistor of the bipolar arrays ALA400 and a dc supply of ±3V (Reference 2).


Figure 4: This circuit lets you vary the voltage multiplier by adjusting bias currents IB3 or IB4.


The circuit requires only two current-controlled conveyors, two grounded capacitors, and a voltage multiplier; it requires no floating capacitors and no external resistors, which makes the circuit's power consumption lower than that of RC oscillators. For a conventional bipolar-transconductance operational amplifier, the transconductance, gm, is IB/2VT. Comparing this figure with the equivalent value of IB, the transconductance of the bipolar-transconductance op amp is four times less than that of a dual-output current-controlled conveyor. Thus, the power consumption of the current-controlled-conveyor-based circuit is about four times less per active device than that of the op-amp-based circuit. The sensitivity study shows that SωCK;RX1;RX2;C1;C2=–½; ωc sensitivities are hence less than unity, which is an attractive feature of this circuit. Remember that creating an accurate oscillator model requires modelling equations to be non-linear, and meeting the Barkhausen criteria is a necessary condition for oscillation. Oscillator circuits may latch up and never oscillate even if you satisfy the Barkhausen criteria.
References
1. Lahiri, Abhirup, "Oscillator uses dual-output current-controlled conveyors," EDN, Nov 13, 2008, pg 62.
2. Frey, DR, "Log-domain filtering: an approach to current-mode filtering," Circuits, Devices and Systems, IEE Proceedings G, 1993, Volume 140, pg 406.


About the author
Abhirup Lahiri contributed this article.


This article is a Design Idea selected for re-publication by the editors. It was first published on January 22, 2009 in EDN.com.


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