Determination of environmental effects on electrical load devices
An improved system and method for reducing the ambient noise experienced by a user listening to an earpiece without the use of a microphone is disclosed. An “ambient noise signal” created by the sound pressure wave of the ambient noise acting on the earpiece transducer is obtained. In some embodiments, the ambient noise signal is inverted and fed back, and the inverted signal is added to the intended audio signal being sent to the earpiece so that the ambient noise is cancelled. In other embodiments, a processor receives the ambient noise signal and predicts the modification to the intended audio signal needed to counteract the ambient noise. The ambient noise signal may be obtained by comparing the actual signal across the earpiece transducer to the intended audio signal, or by detecting variations in the current across the transducer from the current generated to drive the transducer.
1. A circuit for determining a signal that is representative of, and reducing, an environmental effect on an electrical load while the electrical load is operating based on an input signal, comprising:
a current output amplifier configured to output a current and the input signal to the electrical load;
a voltage output amplifier configured to detect variations in current in a resistor connected to the electrical load caused by changes in voltage at the electrical load due to the environmental effect on the electrical load;
a subcircuit configured to amplify the voltage across the resistor in the voltage output amplifier to generate a signal that is representative of the environmental effect and transmit the representative signal to the processor; and
a processor configured to adjust the input signal thereby causing the current output amplifier to alter the current provided to the electrical load to reproduce the input signal while leaving no current flowing through the resistor.
2. The circuit of claim 1 wherein the current amplifier further comprises:
a digital-to-analog converter that converts a digital input signal to an analog input signal;
a differential amplifier that receives and amplifies the analog input signal; and
an output stage that receives the amplified input signal and provides the current and the amplified input signal to the electrical load.
3. The circuit of claim 2 wherein the current amplifier further comprises:
a second output stage that provides a current to a variable resistor, the current to the variable resistor being a fraction of the current that the first output stage provides to the electrical load and the variable resistor having an initial impedance equal to a multiple of the impedance of the electrical load, the multiple being a reciprocal of the fraction.
4. The circuit of claim 3 wherein the processor is further configured to adjust the impedance of the variable resistor when the voltage across the variable resistor changes as a result of a change in the impedance of the electrical load.
5. The circuit of claim 1 wherein the voltage output amplifier further comprises:
a digital-to-analog converter that converts a digital input signal to an analog input signal;
a differential amplifier that receives and amplifies the analog input signal; and wherein
the resistor connects the output of the differential amplifier to the electrical load, thereby allowing any variation in current in the electrical load due to the environmental effect to result in a voltage across the resistor.
6. The circuit of claim 1 wherein the subcircuit further comprises:
a differential amplifier that receives and amplifies the voltage corresponding to any variations in current across the resistor; and
an analog-to-digital converter that converts the amplified voltage to a digital signal and provides the amplified voltage as an input to the processor.
7. The circuit of claim 1 wherein the input signal is an audio signal, the electrical load is an electroacoustic transducer, and the environmental effect is ambient noise acting on the electroacoustic transducer.
8. A method for determining a signal that is representative of, and reducing, an effect of an environmental effect on an electrical load while the electrical load is operating based on an input signal, comprising:
outputting, from a current output amplifier, a current and the input signal to the electrical load;
detecting, by a voltage output amplifier, variations in current in a resistor connected to the electrical load caused by changes in voltage at the electrical load due to the environmental effect on the electrical load;
amplifying, by an amplifier circuit, the voltage across the resistor in the voltage output amplifier to generate a signal that is representative of the environmental effect and transmitting the representative signal to a processor; and
adjusting, by the processor, the input signal thereby causing the current output amplifier to alter the current provided to the electrical load to reproduce the input signal while leaving no current flowing through the resistor.
9. The method of claim 8 wherein outputting, from a current output amplifier, a current and the input signal to the electrical load further comprises:
converting, by a digital-to-analog converter, a digital input signal to an analog input signal;
amplifying, by a differential amplifier, the analog input signal; and
providing, by an output stage that receives the amplified input signal, the current and the amplified input signal to the electrical load.
10. The method of claim 9 wherein outputting, from a current output amplifier, a current and the input signal to the the electrical load, wherein the electrical load is an electroacoustic transducer and wherein the outputting further comprises:
providing, from a second output stage, a current to a variable resistor, the current to the variable resistor being a fraction of the current provided by the first output stage to the electrical load, the variable resistor having an initial impedance equal to a multiple of the impedance of the electrical load, the multiple being a reciprocal of the fraction.
11. The method of claim 10 further comprising, adjusting, by the processor, the impedance of the variable resistor when the voltage across the variable resistor changes as a result of a change in the impedance of the electrical load.
12. The method of claim 8 wherein detecting, by a voltage output amplifier, variations in current in a resistor further comprises:
converting, by a digital-to-analog converter, a digital input signal to an analog input signal;
amplifying, by a differential amplifier, the analog input signal; and
connecting, by the resistor, the output of the differential amplifier to the electrical load, thereby allowing any variation in current in the electrical load due to the environmental effect to result in a voltage across the resistor.
13. The method of claim 8 wherein amplifying, by an amplifier circuit, the voltage across the resistor further comprises:
amplifying, by a differential amplifier, the voltage corresponding to any variations in current across the resistor; and
converting, by an analog-to-digital converter, the amplified voltage to a digital signal and providing the amplified voltage as an input to the processor.
14. The method of claim 8 wherein the input signal is an audio signal, the electrical load is an electroacoustic transducer, and the environmental effect is ambient noise acting on the electroacoustic transducer.