Audio signal output control device that suppresses pop sound
View Patent ↗The potential of a smoothing capacitor for a speaker is smoothly changed by controlling the potential with use of a PWM signal and switching between outputting the PWM signal and an actual audio signal, thereby suppressing a pop sound. The scale of circuitry is reduced and cost is lowered by implementing a PWM circuit in a one-chip microcontroller. Noise is eliminated by outputting a pulse that has been divided in the PWM signal generation stage.
1. A control apparatus for playing back audio by outputting an audio signal to a speaker, the control apparatus comprising:
a generation unit configured to, before output of the audio signal, generate a pulse signal composed of a plurality of pulses, and output the generated pulse signal to a smoothing capacitor for the speaker; and
a switch unit configured to switch between the audio signal and the pulse signal, wherein a duty ratio of each of the pulses is smaller the earlier the pulse exists on a time axis, and is larger the later the pulse exists on the time axis,
wherein the generation unit includes:
a counter configured to perform count processing according to a reference clock of the control apparatus, and
a PWM circuit configured to generate each of the pulses by modulating a width of the pulse in accordance with a digital value output by the counter,
said control apparatus further comprising:
a dividing unit configured to divide the digital value in each count cycle of the counter into a plurality of values, and output each of the values obtained by the dividing to the PWM circuit,
wherein each of the pulses in the pulse signal has a duty ratio in accordance with a different one of the values obtained by the dividing in the count cycle of the counter.
2. The control apparatus of claim 1 , wherein when the digital value cannot be evenly divided by a predetermined number, the dividing unit unevenly divides the digital value and selectively outputs values obtained by the uneven division to the PWM circuit.
3. The control apparatus of claim 2 , wherein when at least a value m and a value n, being mutually different values, are obtained by the uneven division, the dividing unit adjusts a timing according to which each of the values m and n is output to the PWM circuit.
4. An integrated circuit for playing back audio by outputting an audio signal to a speaker, the integrated circuit comprising:
a generation unit configured to, before output of the audio signal, generate a pulse signal composed of a plurality of pulses, and output the generated pulse signal to a smoothing capacitor for the speaker; and
a switch unit configured to switch between the audio signal and the pulse signal, wherein a duty ratio of each of the pulses is smaller the earlier the pulse exists on a time axis, and is larger the later the pulse exists on the time axis,
wherein the generation unit includes:
a counter configured to perform count processing according to a reference clock of the integrated circuit, and
a PWM circuit configured to generate each of the pulses by modulating a width of the pulse in accordance with a digital value output by the counter,
said integrated circuit further comprising:
a dividing unit configured to divide the digital value in each count cycle of the counter into a plurality of values, and output each of the values obtained by the dividing to the PWM circuit,
wherein each of the pulses in the pulse signal has a duty ratio in accordance with a different one of the values obtained by the dividing in the count cycle of the counter.