Patent ID: 7424120

Claim:
An integrated circuit (IC) chip comprising: a square-wave audio signal generator adapted to generate square-wave signal at an audio frequency; a counter adapted to digitally count from zero to a predetermined number; a register adapted to hold a volume control value; a comparator connected to said counter and connected to said register, said comparator adapted to compare a present count from the counter with the volume control value to produce a modulation signal; and an AND gate, operable in accordance with a switch, said AND gate connected to said square-wave signal generator and connected to said comparator, said AND gate adapted to combine, in a logical AND operation, the square-wave signal with the modulation signal to generate a modulated square-wave signal that is on, when both the square-wave signal and the modulation signal are on, and off when one or both of the square-wave signal and the modulation signal are off, the output signal from the AND gate coupled directly to a single pin of the IC, the single pin being the only volume control coupled to an amplifier subsystem and the only pin needed to send said modulated square-wave signal and the volume control signal to the amplifier subsystem.