| 摘要 |
PROBLEM TO BE SOLVED: To finely control sound volume of a loudspeaker by simplified and low cost speaker structure, when a driving coil of the loudspeaker such as an electromagnetic coupling speaker is driven by a digital audio signal. SOLUTION: A primary coil of a speaker unit 10, being an electromagnetic coupling speaker, consists of fifteen coils 1A to 1N, 1P, and the coils 1A to 1N, 1P correspond to each bit, except MSB of 16 bit digital audio signal Dp from a serial-parallel converter 220 respectively. Coil-driving circuits 40A to 40N, 40P are constituted by bridging constant current sources 41A to 41N, 41P, four FETs 51 to 54 for each of the constant current sources, corresponding coils 1A to 1N, 1P, and electric current Ia of the constant-current sources 41A to 41N, 41P is supplied to the coils 1A to 1N, 1P. The electric current Ia of the constant-current sources 41A to 41N, 41P are commonly controlled by changing voltage Vc, by adjusting a variable resistor 92. |
