August 15, 1997

Gates provide low-cost sine-wave generator

Adolfo Mondragon, Philips Components, Juarez, Mexico

One of the troubleshooting tests required for telephone/data twisted-pair copper lines is the determination of the attenuation factor. The test uses frequencies of 300 to 4000 Hz to plot the attenuation performance. Because many central-distribution lines are in locations where power lines are unavailable, a battery-powered generator is desirable for the testing. The circuit in Figure 1 runs from 6 to 9V dry-cell batteries. It uses a 74C04 logic circuit in analog mode, as opposed to the IC's usual digital operation. The circuit uses the classical configuration of comparator and integrator in closed-loop operation to produce square and rectangular waves.

IC_1A and IC_1B are the comparators; IC_1C serves as the integrator. Red LEDs D₃ and D₄ round off the triangular wave to simulate a sinusoidal signal. IC_1D, whose gain is 1.2, also rounds off the triangular wave. Red LEDs D₁ and D₂ serve as 1.5V regulators to keep the frequency and amplitude stable with battery variations. IC_1E and IC_1F amplify the signal to a 0-dBm level into a 600 ohm load. (DI #2066)

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