To eliminate the noise above the band of interest a low pass

decimation filter is implemented in the baseband chip or

DSP. The resulting frequency spectrum contains only the

frequency components left within the band of interest. Figure

8 depicts the frequency spectrum after filtering.

STEREO OPERATION

The LMV1024 and the LMV1026 are designed to operate

together in a stereo solution with two microphones. One

microphone will have a LMV1024 built-in and the other will

have a LMV1026 built-in. These two microphones share the

same interface lines to minimize wiring (Figure 9).

Both microphones produce valid data in only one half of a

clock cycle to allow the two microphones to operate on the

same I/O lines (Data and Clock). To avoid overlap between

the drivers of the microphones, one microphone always

goes into a high impedance state before the second micro-

phone starts driving the data-line. The LMV1024 is positive

edge triggered while the LMV1026 is negative edge trig-

gered. The timing between the two microphones is shown in

Figure 10. For exact timing values, please see the Electrical

Characteristics table.

LAYOUT CONSIDERATIONS

To obtain the best possible performance from the micro-

phone, special care needs to be taken for the design of the

PCB. Especially the V

nected to the high impedance electret element. It is essential

to isolate and shield the V

the digital signal traces (DATA and CLOCK). This needs to

be done to avoid any switching noise coupling directly into

the input of the IC. An example of a PCB layout is given in

Figure 11. The microphone PCB has two capacitors. One

capacitor (100 nF) is connected to the reference pin of the

LMV1024/LMV1026. The other capacitor (10 nF) is used as

decoupling for high frequencies on the supply. No capacitors

should be placed on the data output of the LMV1024/

LMV1026 since it will only load the output driver and would

degrade the performance. This is opposite to the regular

analog phantom biased microphones, where capacitors are

needed to improve RFI.

20133461

FIGURE 7. Frequency Spectrum

20133473

FIGURE 8. Frequency Spectrum after Filtering

20133425

FIGURE 9. Stereo Application

20133429

FIGURE 10. Timing

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