8.2.3 Application Curves

Table 3 lists the performance of the preamplifier circuit in Figure 60. The total power supply current of the circuit is a combination of the 600 µA consumed by the microphone element itself and the 650 µA power-supply current of the OPA1692. Figure 61 shows the frequency response of the circuit. Comparing the output signal level of the microphone for a 1-Pa input signal level to the A-weighted noise of the preamplifier circuit and microphone determines the SNR of the circuit. For a 1-Pa input sound level, the microphone produces a 14.13 mV_RMS signal. The microphone has an SNR of 80 dB, which results in a RMS noise voltage of 1.41 µV_RMS. The input-referred A-weighted noise voltage of the preamplifier circuit is 600.6 nV_RMS. The microphone and preamplifier noise must be combined as a root sum of squares, which results in a total RMS noise voltage of 1.53 µV_RMS and a total circuit SNR of 79.3 dB. By selecting the OPA1692 for this design, this circuit achieves a high level of performance with low power consumption.

Figure 61. Frequency Response of the Low-Noise Preamplifier for 3-Wire Electret Microphones