Function generators capable of producing sinusoidal, triangular, and rectangular waveforms are commercially available in integrated-circuit form. An example is the 8038, manufactured by Intersil as the ICL8038 and also available from other manufacturers. This versatile circuit is capable of generating the aforementioned waveforms simultaneously (at three separate output terminals) over a frequency range from Hz to 1 MHz. Frequency is determined by externally connected resistor-capacitor combinations and can also be controlled by an external voltage.’ In the latter mode of operation, the generator serves as a voltage-controlled oscillator (VCO). (A VCO is also called a voltage-to-frequency converter.) The 8038 is basically a relaxation oscillator that generates a triangular waveform.
The triangular waveform is converted internally to a rectangular waveform using voltage comparators and a digital-type storage device (flip-flop). Sixteen internal transistors are used to shape the triangular wave into an approximation of a sine wave. Under ideal conditions (using external circuit connections specified in the manufacturer’s literature), the total harmonic distortion of the sine-wave output can be reduced to less than 1%. A pin diagram of the 8038 and identifies the function of each pin. Pins 1 and 12, “sine wave adjust,” are used for connecting external resistors to minimize sine-wave distortion, as previously mentioned. Pins 4 and 5, “duty cycle and frequency adjust,” are used for connecting external resistors that, in conjunction with an external capacitor connected to pin 10, “timing capacitor,” determine the duty cycle and frequency of the outputs. The duty cycle,.[ an output is the time it is high. expressed as a percent of the period of oscillation. For example. a square wave. which is high for one-half of a period and low for the other half. has a 50% duty cycle. Pin R, “FM sweep input.” is the input to which an external voltage may be connected to adjust the frequency of oscillation when the 8038 is operated as a Yeo. (FM refers to frequency modulation: As the input voltage is adjusted. the output frequency changes in direct proportion to the change in voltage.
The simplest possible circuit connections for using the 8038 as a fixed-frequency, 50%-duty-cycle function generator. In the configuration shown, the frequency of oscillation is Manufacturer’s product literature can be consulted for external circuit connections required when the 8038 is used as a VCO and for duty cycles other than 50%.