Digital microphone assembly with improved frequency response and noise characteristics

A semiconductor die connectable to an output of a capacitive transducer having space-apart electrodes and an acoustic filter with a high pass cut-off frequency, the die comprising:

• a forward signal path including a processing circuit comprising:
• an amplifier configured to amplify or buffer an analog audio signal generated by the transducer when the die is coupled to the transducer;
• an analog-to-digital converter coupled to an output of the amplifier and configured to convert an analog audio signal generated by the transducer to a digital signal when the die is coupled to the transducer;
• a feedback signal path comprising:
• a pulse modulator having an input coupled to the forward signal path and configured to generate a digital control signal based on the digital signal obtained from the forward signal path;
• and
• a current converter having an input coupled to an output of the pulse modulator, the current converter having an output connectable to the first or second electrode of the capacitive transducer, the current converter configured to generate a sequence of variable current pulses based on the digital control signal,
• wherein the variable current pulses suppress frequencies below a second high pass cutoff frequency of the analog audio signal before the analog audio signal is applied to the processing circuit when the die is coupled to the transducer and wherein the second highpass cut-off frequency is at least two octaves higher than the first highpass cut-off frequency.

A method of operating a microphone including a processing circuit and a capacitive transducer having an acoustic filter with a first highpass cut-off frequency, the method comprising:

• a) acoustically filtering and converting sound into a corresponding analog signal using the capacitive transducer;
• b) converting the analog signal to a digital signal using an analog-to-digital converter of the processing circuit upon applying the analog signal to the processing circuit;
• c) generating a pulse modulated control signal based on the digital signal using a pulse modulator of the processing circuit;
• d) generating a sequence of variable current pulses based on the pulse modulated control signal using a current converter of the processing circuit;
• and
• e) suppressing frequencies below a second highpass cutoff frequency of the analog signal before the analog signal is applied to the processing circuit by applying the sequence of variable current pulses to an electrode of the capacitive transducer,
• wherein the second highpass cut-off frequency is at least two octaves higher than the first highpass cut-off frequency.