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National Semiconductor Improves Audio Quality in Consumer Products with New Microphone Technology

Digital Voice Technology Integrates Digital Output Into Existing Microphones

The manufacturer says...

ChipCenter's Paul O'Shea says . . .

Achieving another first in consumer microphone electronics, National Semiconductor Corporation announced technology that puts digital voice quality directly inside electret condenser microphones (ECMs). Previously, the large size and high cost associated with this effort kept manufacturers from implementing digital voice technology in consumer products. National overcame the size-and-cost barrier by putting the digital modulation and gain inside the microphone to dramatically improve sound quality. By integrating several components and simplifying routing, National's "digital voice in a mic" technology reduces the overall system cost and enables the smallest possible form factor. "Today's announcement furthers National's amplifier strategy of providing leading-edge innovation in signal conditioning," said Erroll Dietz, product line director for National Semiconductor's amplifier products group. "With mixed-signal capability so small that it fits inside existing ECMs, this technology is the next step in integrating digital voice directly inside microphones." The introduction of National's digital voice technology follows the company's recent announcement of its analog "amp in a mic" products, the LMV1012 and the LMV1014. These products transformed the market by replacing the decades-old junction field-effect transistor (JFET), dramatically improving audio performance and sensitivity in 2- and 3-wire ECMs. Integrating the digital output into the microphone is the next step in amplifier technology, delivering the world's first digital-output capability to enable built-in gain inside 4-wire ECMs. Applications using this technology are microphones in mobile handsets, PDAs, and other portable-microphone applications. "National brings digital sound quality to consumer communications and computing," said Dietz. "To achieve this goal, we're partnering with major microphone suppliers to facilitate digital ECMs, and we intend to release customized products utilizing this technology by the end of the year." Integrating the digital output into the microphone improves the signal integrity for ease of design with regard to RF immunity. The end products developed using National's digital voice technology will be less sensitive to noise for ease of implementation, resulting in faster design-cycle times. With digital modulation integrated into the ECM, the baseband partition is now optimized for better audio performance, consumer features, and lower overall system cost. National Semiconductor Corp. Design Support Group Phone: 800-272-9959 Web: www.national.com

The footprint for the microphone canister is well-defined for products like cell-phone handsets. The microphone in the canister will probably be available this way for a long time. However, by putting mixed-signal, gain, and digital modulation in the microphone, National Semiconductor expects that designers will be able to remove analog components from the canister. Presently, many companies are changing the analog signal to digital in an ASIC, which is downstream from where it is now. However, with this digital design the microphone can be placed anywhere. It means you don't have to route the signals in a special way, you also don't have to use special plastics or acoustics to shape the noise, and that means increasing the gain is no longer as important. Using digital output you can expect the RF immunity to be reduced, and that means the amount of shielding needed will also be reduced. This product from National is going to give customers a chance to look at this design situation a little differently, and perhaps get designers to think about dis-integrating the design. That's a particularly foreign idea because the job of many designers is to integrate as much as possible. However, every time something is integrated, one part of the signal, gain, drive, buffering, or filtering gets squeezed out. Integrating is like a water balloon—when you have one part under control, another pops out. But there is always some part of the analog that doesn't make the step into the next generation. The digital microphone may change when a designer looks for a microphone in the design cycle mainly because it can be manipulated and offers more control. This announcement is really about telling the world that National Semi has created the IC and expects to be in production with this second-order sigma-delta modulator IC in four to five months. However, the company is not naming it because they expect customers will want to customize it with something like a specific clock rate, or certain power consumption. Like the hamburger-chain commercial, you can have it designed your way. So there won't be just one digital microphone handset because there will be too many requests tailored to different markets. This digital microphone product offers a digital formatting output that doesn't require the customer to buy a lot of code, and it is in a standard footprint. That's a smart move for the first step of this design. Initially, National is trying to make the job of the audio-baseband designer easier by making it digital more quickly. National also wants to educate the designer about the uses of digital. If you have digital coming out of the diaphragm in this canister, the digital signal can be used for many applications such as voice recognition, perhaps even voice security. The first-generation product will use four wires. There were customers who used two-wire designs for JFETs, but now that National put the ICs in the canister, the connections can be the same as those for any amplifier, which is up to eight connections. However, for now the company is starting with what the industry knows best, and then migrating as the industry requests it. National says that with digital modulation integrated into the ECM, the baseband partition is now optimized for better audio performance. The present designs don't do anything with the signal from the canister to the baseband. National thinks the DSP baseband companies probably won't like cutting out the CODEC and allowing it to go to the canister. This electrotet condenser microphone (ECM) allows customers to start breaking up their costs. So a few baseband customers of the DSP baseband manufacturers will probably ask why they are paying the baseband manufacturer when they could be paying only the microphone maker. The biggest resistance to this design will be users saying that they already have the CODEC modulation in their baseband and they don't want to pay for it twice. It means that these customers need to decide if they want the better signal to noise at the canister that this ECM offers. National also is telling customers that they can improve on RF immunity, gain, signal to noise, and sensitivity at the canister. Additionally, customers may not need the present modulation scheme inside the baseband anymore. It's a bold step, but it is worth thinking about. White Paper

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