Audio amplifier

Claim 2

An audio amplifier for amplifying an input signal thereto comprising an amplifier circuit (27) having an amplification device and a variable operating point; characterized in that said amplifier further comprises a delay circuit (24) for delaying the input signal; a power supply circuit (29) capable of changing a supply voltage to said amplifier circuit (27); and a control circuit (30) for detecting a level of said input signal to output a control signal corresponding to said level, and changing the operating point of said amplifier circuit (27) and an output voltage of said power supply circuit (29), in response to a level change of said input signal.

Claim 3

An audio amplifier according to claim 1, wherein said input signal is a digital input signal, and said amplifier further comprises a first digital-to-analog converter (25) connected between said delay circuit (24) and said amplifier circuit (27).

Claim 4

An audio amplifier according to claim 2, wherein said control circuit (30) comprises: a second digital-to-analog converter (31) for converting said digital input signal into an analog signal a peak-detecting circuit (32) for detecting a peak value of an output signal of said second digital-to-­analog converter (31); and a discrimination circuit (33) for comparing an output signal of said peak-detecting circuit (32) with a preset value to generate a control signal by which said operation point and an output voltage of said power supply circuit are changed.

Claim 5

An audio amplifier according to claim 1, wherein said amplifier circuit has a variable bias circuit (27b).

Claim 6

An audio amplifier for amplifying an input signal thereto comprising an amplifier circuit (27) having an amplification device and a variable operating point; characterized in that said amplifier further comprises a delay circuit (24) for delaying an input signal to be amplified; a power supply circuit (29) capable of changing a supply voltage to said amplifier circuit; a first peak-detecting circuit (42) for detecting a level of said input signal; a second peak-detecting circuit (43) for detecting a level of an input signal to a level adjuster (26) which adjusts a level of an input signal to said amplifier circuit (27); a third peak-detecting circuit (44) for detecting a level of an output signal of said amplifier circuit; a dividing circuit (51) for dividing an output signal of said third peak-detecting circuit (44) by an output signal of said second peak-detecting circuit (43); and a multiplying circuit (52) for multiplying an output signal of said dividing circuit by an output signal of said first peak-detecting circuit (42); whereby the operating point of said amplifier circuit and said supply voltage of said power supply circuit are changed in response to an output signal of said multiplying circuit.

Claim 7

An audio amplifier for amplifying an input signal thereto comprising an amplifier circuit (27) having an amplification device and a variable operating point; characterized in that said amplifier further comprises a delay circuit (24) for delaying an input signal to be amplified; a power supply circuit (29) capable of changing a supply voltage to said amplifier circuit; a first peak-detecting circuit (42) for detecting a level of said input signal; a second peak-detecting circuit (43) for detecting a level of an input signal to a level adjuster (26) which adjusts a level of an input signal to said amplifier circuit (27); a third peak-detecting circuit (44) for detecting a level of an output signal of said amplifier circuit; a dividing circuit (51) for dividing an output signal of said third peak-detecting circuit (44) by an output signal of said second peak-detecting circuit (43); and a multiplying circuit (52) for multiplying an output signal of said dividing circuit by an output signal of said first peak-detecting circuit (42); whereby the operating point of said amplifier circuit and said supply voltage of said power supply circuit are changed in response to an output signal of said multiplying circuit.

Claim 8

An audio amplifier according to claim 5, wherein said input signal is a digital input signal, and said amplifier further comprises: a first digital-to-analog converter (25) for converting an output signal of said delay circuit; and a second digital-to-analog converter (41) for converting said digital input signal into an analog

Claim 9

An audio amplifier for amplifying an input signal thereto comprising an amplifier circuit (27) having an amplification device and a variable operating point; characterized in that said amplifier further comprises a delay circuit for delaying said input signal to be amplified; a power supply circuit (29) capable of changing a supply voltage to said amplifier circuit; a first peak-detecting circuit (42) for detecting a level of said input signal; a second peak-detecting circuit (43) for detecting a level of an input signal to a level adjuster (26) which adjusts a level of an input signal to said amplifier circuit; a third peak-detecting circuit (44) for detecting a level of an output signal of said amplifier circuit; a dividing circuit (51) for dividing an output signal of said third peak-detecting circuit (44) by an output signal of said second peak-detecting circuit(43); a multiplying circuit (52) for multiplying an output signal of said dividing circuit (51) by an output signal of said first peak-detecting circuit; and a gate circuit (48) for switching between an output signal of said multiplying circuit (52) and an output signal of said first peak-detecting circuit (42); whereby the operating point of said amplifier circuit and said supply voltage of said power supply circuit are changed in response to an output signal of said multiplying circuit (52) when an output signal of said peak-detecting circuits (43) becomes larger than a predetermined level, whereas the operating point of said amplifier circuit (27) and said supply voltage of said power supply circuit are changed in respone to an output signal of said first peak-detect circuit (42) when an output signal of said second peak-detecting circuits (43) becomes smaller than the predetermined level.

Claim 10

An audio amplifier for amplifying an input signal thereto comprising an amplifier circuit (27) having an amplification device and a variable operating point; characterized in that said amplifier further comprises a delay circuit for delaying said input signal to be amplified; a power supply circuit (29) capable of changing a supply voltage to said amplifier circuit; a first peak-detecting circuit (42) for detecting a level of said input signal; a second peak-detecting circuit (43) for detecting a level of an input signal to a level adjuster (26) which adjusts a level of an input signal to said amplifier circuit; a third peak-detecting circuit (44) for detecting a level of an output signal of said amplifier circuit; a dividing circuit (51) for dividing an output signal of said third peak-detecting circuit (44) by an output signal of said second peak-detecting circuit(43); a multiplying circuit (52) for multiplying an output signal of said dividing circuit (51) by an output signal of said first peak-detecting circuit; and a gate circuit (48) for switching between an output signal of said multiplying circuit (52) and an output signal of said first peak-detecting circuit (42); whereby the operating point of said amplifier circuit and said supply voltage of said power supply circuit are changed in response to an output signal of said multiplying circuit (52) when an output signal of said peak-detecting circuits (43) becomes larger than a predetermined level, whereas the operating point of said amplifier circuit (27) and said supply voltage of said power supply circuit are changed in respone to an output signal of said first peak-detect circuit (42) when an output signal of said second peak-detecting circuits (43) becomes smaller than the predetermined level.