Audio amplifier turn-off control circuit
AssigneeSGS-Thomson Microelectronics S.A.
InventorsDaniela Nebuloni, Andrea Fassina
Life of this patent
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Abstract
A circuit comprising a transistor which, when supply is turned off, locks the output of the audio amplifier to the supply line, the potential of which is reduced gradually by a filter capacitor, so that the output voltage follows the supply voltage with the same slope, and is so controlled by the filter capacitor, thus eliminating undesired noise ("popping") at the output caused by electric transients in the audio amplifier.
Claims15
A circuit for turn-off control of an audio amplifier supplied by a supply line with a supply voltage, the circuit comprising:
- an input terminal for input of an audio signal;
- an output terminal with an output voltage;
- a first controlled switch element to couple said output terminal to the supply line so as to lock said output voltage to the supply voltage in response to a fall in the supply voltage;
- and
- a control stage for controlling said controlled switch wherein said control stage comprises
- a voltage source generating a reference voltage;
- and
- a comparator having a first input coupled to said voltage source, a second input coupled to the supply line, and a comparator output coupled to a terminal for controlling said controlled switch, said comparator output generating a control signal that closes said controlled switch when the supply voltage reaches a predetermined value with respect to said reference voltage.
A circuit for turn-off control of an audio amplifier supplied by a supply line with a supply voltage, the circuit comprising:
- an input terminal for input of an audio signal;
- an output terminal with an output voltage;
- a first controlled switch element, comprising a transistor, to couple said output terminal to the supply line so as to lock said output voltage to the supply voltage in response to a fall in the supply voltage;
- and
- a control stage for controlling said transistor, said transistor having a first terminal connected to said output terminal of the audio amplifier, a second terminal connected to said input terminal of the audio amplifier, and a control terminal connected to said control stage, said first terminal of said transistor also being connected to a reference potential line via a second switch element controlled by said control stage.
An amplifier control circuit to control an amplifier when power to the amplifier is turned off, the circuit comprising:
- an audio amplifier circuit having an input terminal and an output terminal, said audio amplifier circuit coupled to and receiving power from a supply voltage and providing an output signal at said output terminal;
- a voltage sensing circuit coupled to said supply voltage and generating a transient control voltage in response to a decrease in said supply voltage, said voltage sensing circuit outputting a first control output signal and causing a change in said first control output signal when said transient control voltage falls below a first threshold voltage;
- and
- a control element coupled to said voltage sensing circuit and to said audio amplifier circuit and receiving said first control output signal, said control element entering an active state after said change in said first control output signal, said control element functioning to couple said amplifier circuit output terminal to said supply voltage to cause a reduction in the amplitude of said audio amplifier circuit output signal in a controlled manner.
A method for turn-off control of an audio amplifier having audio input and output terminals and supplied by a supply voltage, the audio output terminal generating an output signal, the method comprising the steps of:
- sensing the supply voltage to detect a decrease in the supply voltage;
- coupling the audio output terminal to the supply voltage by controlling a controlled switch so as to lock the output voltage to the supply voltage in response to a fall in the supply voltage;
- wherein the step of controlling the controlled switch includes performing the steps of:
- generating a reference voltage;
- comparing said reference voltage and the supply voltage;
- and
- generating a control signal that closes said controlled switch when the supply voltage reaches a predetermined value with respect to said reference voltage.
A circuit for turn-off control of an audio amplifier supplied by a supply line with a supply voltage, the circuit comprising:
- an input terminal for input of an audio signal;
- an output terminal with an output voltage;
- and
- a transistor to couple said output terminal to the supply line so as to lock said output voltage to the supply voltage in the event of a fall in the supply voltage said transistor having a first terminal connected to said output terminal of the audio amplifier, a second terminal connected to said input terminal of the audio amplifier, and a control terminal connected to a control stage for controlling said transistor, said first terminal of said transistor also being connected to a reference potential line via a switch element controlled by said control stage.
An amplifier control circuit to control an amplifier when power to the amplifier is turned off, the circuit comprising:
- an audio amplifier circuit having an input terminal and an output terminal, said audio amplifier circuit coupled to and receiving power from a supply voltage and providing an output signal at said output terminal;
- a voltage sensing circuit coupled to said supply voltage and generating a transient control voltage in response to a decrease in said supply voltage, said voltage sensing circuit outputting a first control output signal and causing a change in said first control output signal when said transient control voltage falls below a first threshold voltage;
- a comparator having first and second comparator inputs and a comparator output coupled to said first control output signal, said first comparator input being configured to receive said supply voltage and said second comparator input being configured to receive said transient control voltage wherein said comparator output changes states when said supply voltage is less than said transient control voltage;
- and
- a control element coupled to said voltage sensing circuit and to said audio amplifier circuit and receiving said first control output signal, said control element entering an active state after said change in said first control output signal, said control element functioning to couple said amplifier circuit output terminal to said amplifier circuit input terminal to cause a reduction in the amplitude of said audio amplifier circuit output signal in a controlled manner.
Dependencies are inferred from the claim text.