LMV1024 datasheet(11/17 Pages) NSC

11 / 17 page

Application Section

The LMV1024/LMV1026 consist of a pre-amplifier and sigma

delta converter for placement inside an electret condenser

microphone (ECM). The output of the LMV1024/LMV1026 is

a robust digital serial bit stream eliminating the sensitive

low-level analog signals of conventional JFET microphones.

This application section describes, among others, a typical

application, a sensitivity comparison between different ECM

types, stereo operation and layout recommendations on the

ECM PCBs.

TYPICAL APPLICATION

Figure 1 depicts a typical application, where the LMV1024 or

LMV1026 is built inside the ECM canister. This ECM can be

directly connected to a DSP in a digital audio system, like a

baseband chip in a cell phone. Connecting is easy because

of the digital LMV1024/LMV1026 interface. A digital filter in

the DSP or Baseband decimates the audio signal.

BUILT-IN PRE-AMPLIFIER / ADC

The LMV1024/LMV1026 are offered in a space saving small

6-bump micro SMD package in order to fit inside small ECM

canisters. The LMV1024 or LMV1026 IC is placed on the

PCB. This PCB forms the bottom of the microphone, which is

placed in the cell phone.

Figure 3 depicts a cross section of a microphone with the IC

inside the ECM canister. The PCB of the microphone has 4

pads that connects V

DD, Ground, DATA and the CLOCK.

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FIGURE 1. Typical Application

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FIGURE 2. Built-in Pre-Amplifier / ADC

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FIGURE 3. Cross section of a Microphone

LMV1024 Datasheet(PDF) 11 Page - National Semiconductor (TI)