Feedback microphones encoder modulators, signal generators, mixers, amplifiers, summing nodes
A noise-cancelling system includes headset for generating a feedback signal for noise-cancellation in response to sound externally generated from the headset. The noise-cancellation feedback signal can also be described as a noise-cancellation “feed-forward” signal. An encoded microphone signal is generated in response to the first feedback signal. An audio generator can be used to generate a noise-cancellation signal in response to the encoded microphone signal and to generate an electronic audio signal in response to the encoded microphone signal and a first output audio signal. An audio connector is provided to couple the encoded microphone signal from the headset to the audio generator and to couple the first electronic audio signal to the headset.
1. Encoder circuitry comprising:
A. first modulator circuitry having an analog, feedback microphone input and an analog output;
B. first signal generator circuitry providing a first ultrasonic carrier frequency signal and having an analog output;
C. first mixer circuitry having an analog input connected to the analog output of the first modulator circuitry, an analog input connected to the analog output of the first signal generator circuitry, and an analog output;
D. first amplifier circuitry having an analog input connected to the analog output of the first mixer circuitry and an analog output;
E. second modulator circuitry having an analog, feedback microphone input and an analog output;
F. second signal generator circuitry providing a second ultrasonic carrier frequency signal having a frequency different from the frequency of the first ultrasonic carrier frequency signal and having an analog output;
G. second mixer circuitry having an analog input connected to the analog output of the second modulator circuitry, an analog input connected to the analog output of the second signal generator circuitry, and an analog output;
H. second amplifier circuitry having an analog input connected to the analog output of the second mixer circuitry and an analog output;
I. a first summing node having a first input coupled to the analog output of the first amplifier circuitry, a second input coupled to the analog output of the second amplifier circuitry, and an output; and
J. a second summing node having a third microphone input, a second input coupled to the output of the first summing node, and an output.
2. The encoder circuitry of claim 1 including a headset having a speaker, a feedback microphone mounted on the headset proximate the speaker, and an audio microphone, the feedback microphone having an analog feedback microphone output coupled to the analog, feedback microphone input, the audio microphone having an analog output coupled with the analog output of the first amplifier circuitry.
3. The encoder circuitry of claim 2 including a jack having a speaker terminal and a microphone terminal, the speaker having an input that is coupled to the speaker terminal through a lead, and the audio microphone and the analog output of the first amplifier circuitry being coupled to the microphone terminal through respective leads.
4. The encoder circuitry of claim 1 in which the first and second modulator circuitry are baseband modulator circuitry.