| 摘要 |
A switched power supply 904 provides a supply voltage to a power amplifier 106 and a dither block 906 dithers its switching frequency, based on either the input signal, a volume input to a preamplifier 118 (fig 17), or a combination of them. The frequency dither may increase with the signal amplitude and volume, be turned off at low levels, and be controlled by an envelope detector 902. Dither block 906 generates a randomized frequency clock signal. The switched power supply can be a dual mode level shifting charge pump using a flying capacitor (fig 19b, Cf) supplying bipolar voltages that are each either equal to or a fraction of a supply voltage. The amplifier volume and signal magnitude may also be used to adjust: the switching frequency of the switched supply (fig 8); whether low or high on-state resistance switching MOSFETS (Fig 11, 550,552) having different relative widths are selected for the power supply; and the bias applied to amplifier components (fig 14) such as a digital to analogue converter 116, preamplifier 118 or power amplifier 118. The amplifier can implemented as an integrated circuit and be used in portable and in-car audio devices such as MP3 players, mobile phones and televisions. |
