Claims
- 1. A power amplifier in a personal computer having a screen, a CPU and associated electronics and storage media generating heat within a confined environment, wherein the power amplifier is responsive to the CPU to drive a pair of loudspeakers, the power amplifier comprising:a sawtooth generator configured to generate a periodic, non-symmetric ramp signal with an amplitude that varies with the voltage level of a power supply; a level shifting circuit configured to receive an input audio signal and to center the input audio signal about the halfway point between the peak to peak voltage of the periodic, non-symmetric ramp signal generated by the sawtooth generator; a comparator configured to receive the ramp signal and to produce a pulse width modulated signal with pulse widths determined by amplitude comparisons of an output of the level shifting circuit to the ramp signal; a driving circuit configured to receive the pulse width modulated signal and to output control signals; and a switching bridge network configured to receive the control signals and to produce an amplified version of the pulse width modulated signal, wherein the amplified version of the pulse width modulated signal is thereafter filtered to be an amplified version of the input audio signal which is provided to the pair of loudspeakers contained within the personal computer.
- 2. The power amplifier of claim 1, wherein the personal computer is a notebook form computer.
- 3. The power amplifier of claim 1, wherein the personal computer is a desktop computer.
- 4. The power amplifier of claim 1, wherein the power amplifier is a class D switching amplifier.
- 5. The power amplifier of claim 4, wherein the personal computer is battery powered providing a voltage level, the gain of the power amplifier being insensitive to variations in the voltage level.
- 6. The power amplifier of claim 5, wherein the variations are short term and long term, wherein the gain of the power amplifier is substantially insensitive to variations in the voltage level.
- 7. The power amplifier of claim 6, wherein the power amplifier is fabricated on one integrated circuit chip.
- 8. The power amplifier of claim 1, wherein said comparator has hysteresis.
- 9. The power amplifier of claim 1, wherein a period of said periodic non-symmetric ramp signal comprises a first ramp portion having a first slope and a second ramp portion having a second slope, and wherein a duration of said first ramp portion is at least 90% of said period.
- 10. An audio amplifier which drives a speaker in response to a CPU in a portable device, the audio amplifier comprising:a sawtooth generator configured to output a non-symmetric periodic signal with slopes and voltage maxima that vary with a power supply voltage; a level shifting circuit configured to receive an input audio signal and to shift the level of the input audio signal in response to variations in the power supply voltage; a comparator configured to compare outputs from the sawtooth generator and the level shifting circuit to generate a pulse width modulated signal with a pulse width proportional to the amplitude of the input audio signal; a driving circuit configured to receive the pulse width modulated signal and to generate control signals; and a switching bridge network configured to receive the control signals and to produce an amplified version of the pulse width modulated signal which is filtered to be an amplified version of the input audio signal.
- 11. The audio amplifier of claim 10, wherein the audio amplifier delivers the amplified version of the input audio signal to the speaker housed within the portable device.
- 12. The audio amplifier of claim 10, wherein the non-symmetric periodic signal is divided into two parts, a rising part and a falling part, with one of the parts having a duty cycle greater than 90%.
- 13. The audio amplifier of claim 10, wherein the level shifting circuit shifts the level of the input audio signal to reference a halfway point between the peak to peak voltage of the non-symmetric periodic signal.
- 14. The audio amplifier of claim 10, wherein the comparator has hysteresis.
- 15. The audio amplifier of claim 10, wherein the portable device operates on battery power which varies over time.
Parent Case Info
This application is a divisional of U.S. patent application Ser. No. 08/899,445, filed on Jul. 23, 1997, now U.S. Pat. No. 5,982,231.
US Referenced Citations (12)
Non-Patent Literature Citations (3)
Entry |
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Harris Corporation, APP Note Harris Intelligent Power, Class-D Audio II Evaluation Board (HIP4080AEVAL2), No. AN9525.2, Mar. 1996. |
Harris Corporation, APP Note Harris Intelligent Power, HIP4080A, 80V High Frequency H-Bridge Driver, No. AN9404.1, Mar. 1995. |