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Wave Generators Using Constant Current Diodes

IP.com Disclosure Number: IPCOM000075422D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Kochis, RL: AUTHOR

Abstract

An operational amplifier may generate a variety of different waveforms when combined with one or more constant-current diodes, such as Motorola Type 1N5297.

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Wave Generators Using Constant Current Diodes

An operational amplifier may generate a variety of different waveforms when combined with one or more constant-current diodes, such as Motorola Type 1N5297.

In Fig. 1, square waves are converted to triangular waves by placing two opposed constant-current diodes D1 and D2 in the input circuit and providing a feedback capacitor C. The generator is an integrator giving an output approaching a hypothetical triangular shape independent of input amplitude because the diodes supply essentially constant current.

In Fig. 2, the generator is made self-oscillating by positive feedback at the junction of voltage divider R1-R2. With the diode and capacitor positions reversed, both square and triangular waveforms may be obtained from this circuit.

Assume the output is at +V(sat) and that the initial voltage on the capacitor is zero. V1 = V(sat) R1/(R1+R2). The capacitor voltage, Vc, starts charging linearly through the constant-current diodes. As soon as Vc exceeds V1, the voltage across the input terminals changes sign. This small voltage across the input terminals is multiplied by the open-loop gain of the operational amplifier. Consequently, the output switches rapidly to -V(sat). Now the capacitor is discharged at a constant rate through the constant-current diodes. When Vc becomes less than V1 = -V(sat) R1/(R1+R2), the output switches rapidly back to +V(sat). This cycle repeats and produces square waves at V0 and V1. The ampli...