Abstract: A method and apparatus for generating a low distortion sinusoidal signal with controllable amplitude for use with downhole tools, such as an array laterolog. In preferred embodiment, a signal-generating digital-to-analog converter is provided to produce a sinusoidal or other waveform at full scale. An amplitude-controlling digital-to-analog converter provides a voltage reference for the signal-generating digital-to-analog converter. The tandem combination of two digital-to-analog converters allows the generation of low distortion signals, even at low amplitudes. The amplitude-controlling digital-to-analog converter is provided digital codes by the downhole tool system processor. A high-speed dedicated controller provides digital codes to the signal-generating digital-to-analog converter, which relieves the system processor from the intensive task of providing signal generating codes, thereby freeing processor bandwidth for other system tasks.