Texas Instruments Stellaris LM3S1968, Руководство пользователя

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Stellaris® LM3S1968 Evaluation Board
January 6, 2010 15
Other Peripherals
Speaker
The LM3S1968 evaluation board's speaker circuit can be used in either tone or waveform mode.
The quick-start application uses tone mode.
In tone mode, the LM3S1968 microcontroller's PWM module directly generates tones within the
audible frequency range. The width of the pulses determines the volume. If only one PWM signal
(PWM2 or PWM3) is used, the non-PWM signal should be configured as a general-purpose
output. For increased speaker volume, PWM2 and PWM3 can be configured as complementary
drive signals. In tone mode, be careful to avoid large DC currents in the speaker.
Waveform mode uses two high-frequency PWM signals to drive a MOSFET H-bridge with an
output filter. This circuit is essentially a Class-D amplifier. The symmetrical 2nd order low-pass L-C
filter has a cut-off frequency of approximately 33 kHz. The microcontroller's PWM module should
be configured with a PWM frequency of at least 100 kHz. Using 500 kHz improves audio quality