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 an environmental effect on an electrical load while the electrical load is operating based upon an input signal, comprising:
a first differential amplifier having a first input receiving the input signal and a second input receiving an output of the first differential amplifier, the output of the first differential amplifier driving the electrical load thereby causing the second input to receive a signal representing the input signal and including the environmental effect on the electrical load;
a second differential amplifier having a first input receiving the input signal and a second input receiving an output of the second differential amplifier, the output of the second differential amplifier driving a load having an impedance equal to an impedance of the electrical load, thereby causing the second input to receive a signal representing the input signal; and
a third differential amplifier having a first input receiving the output of the first differential amplifier and a second input receiving the output of the second differential amplifier, thereby producing as an output of the third differential amplifier a signal which is a difference between the input signal and the signal applied to the electrical load by both the input signal and the environmental effect.
2. The circuit of claim 1 wherein the third differential amplifier is an instrumentation amplifier.
3. The circuit of claim 2 wherein the instrumentation amplifier has a third input that receives the output of the instrumentation amplifier and a fourth input that is connected to a ground.
4. 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.
5. A method for determining a signal that is representative of an environmental effect on an electrical load while the electrical load is operating based on an input signal, comprising:
providing the input signal as a first input to a first differential amplifier, a second input of the first differential amplifier receiving an output of the first differential amplifier, the output of the first differential amplifier driving the electrical load thereby causing the second input to receive a signal representing the input signal and including the environmental effect on the electrical load;
providing the input signal as a first input to a second differential amplifier, a second input of the second differential amplifier receiving an output of the second differential amplifier, the output of the second differential amplifier driving a load having an impedance equal to an impedance of the electrical load, thereby causing the second input to receive a signal representing the input signal; and
providing to a third differential amplifier as a first input the output of the first differential amplifier and as a second input the output of the second differential amplifier, thereby producing as an output of the third differential amplifier a signal which is a difference between the input signal and the signal applied to the electrical load by both the input signal and the environmental effect.
6. The method of claim 5 wherein the third differential amplifier is an instrumentation amplifier.
7. The method of claim 6 further comprising providing the output of the instrumentation amplifier as a third input to the instrumentation amplifier and a connecting a fourth input of the instrumentation amplifier to a ground.
8. The method of claim 5 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.