Question

In this design problem, your input signal is a mono audio signal that is the output of anelectret condenser microphone. An electret condenser microphone output alwaysincludes a DC offset in addition to the signal itself. Suppose that this microphoneoutputs a signal with a voltage swing of 400 mVpp plus a DC offset of 0.8 V. Thismicrophone output signal needs to be changed before being input to a sensitive audiocircuit. Specifically, it needs to be inverted, amplified, and the DC offset needs to beremoved. Design and build a circuit that will cancel out the DC offset and achievemaximum signal amplification without exceeding the 20 Vpp input limit of the audioequipment. Hint: use superposition.

Answer 1

DC offset is usually undesirable when it causes saturation or change in the operating point of an amplifier. An electrical DC bias will not pass through a transformer; thus a simple isolation transformer can be used to block or remove it, leaving only the AC component on the other side. In signal processing terms, DC offset can be reduced in real-time by a high-pass filter. When one already has the entire waveform, subtracting the mean amplitude from each sample will remove the offset. Often, very low frequencies are called "slowly changing DC" or "baseline wander"

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