For many years, consumer audio engineers have wanted to use power-saving digital Class D amplifiers to replace power-consuming analog Class A / B amplifiers. But so far, two problems have hampered the application of Class D amplifiers: the high EMI radiation generated by the high-frequency switches inherent in traditional Class D amplifier solutions, and the high cost of adding filtering and shielding measures to meet EMI specifications . A few days ago, Silicon laboratories, a high-performance analog and mixed-signal IC manufacturer, launched the Si270x, which is said to be the industry's first 5-watt stereo Class-D amplifier that can effectively reduce EMI in response to the above application bottlenecks.
Currently, in addition to the rapid growth of multiple audio amplifier market segments, another notable trend is the rapid shift from Class A / B amplifiers to Class D amplifiers. Data from Databeans shows that the Class D amplifier market is expected to reach US $ 347 million in 2010, and the compound annual growth rate for the next five years will reach 11%, far exceeding the average growth rate of the audio market.
As the first member of the Silicon Labs Class D amplifier series, the new Si270x amplifier is defined as a product that "changes the game rules of the audio industry." The target market targets consumer audio products that are sensitive to price and noise, including smartphone expansion devices, Desktop radios, TV sound bars and monitors, stereos and battery-powered radios.
The company's audio amplifier product director Rick Beale said that "multi-level EMI reduction technology" will be a key factor to ensure Si270x's market success. Its design philosophy is to suppress the interference of traditional class D amplifiers at the source and make it easier to meet EMI specifications. , More suitable for AM / FM radio and smart phones. It is said that compared to existing Class D amplifier solutions, the Si270x reduces radiated interference by a factor of 10 in the EMI specification band, a factor of 100 in the FM radio band, and a factor of 1,000 in the AM band.
Figure: Si270x amplifier application circuit block diagram.
"The EMI reduction technology that we use the four-level scheme includes: extended PWM to effectively suppress the radiated energy of the broadband switch, so that its radiated energy is less than 1/10 of the original; adjustable noise-free notch, to ensure clear AM signal reception; The adjusted switch conversion makes it easier to meet consistency requirements and FM reception; and on-chip feedback protection to improve audio quality. "Rick added.
In addition, the traditional Class D amplifier generates a lot of EMI radiation in the 900MHz transmission and reception frequency band, which weakens the over-the-air (OTA) transmission and reception signal quality of smart phones and their expansion devices. On the other hand, most expansion platforms currently use analog architectures, which are very susceptible to noise generated by TDMA transmissions. Therefore, the Si270x amplifier uses a smartphone-friendly all-digital architecture, which is not susceptible to interference from radiated noise, and enhances the performance and compatibility of OTA.
To avoid EMI caused by traditional Class D amplifiers, audio engineers often use low-cost but inefficient Class A / B amplifiers, which require larger and more expensive power supplies and heat sinks (some require a 9V or 12V battery configuration) . The Si270x amplifier allows developers to use smaller and lower cost power supplies in portable audio systems, fewer batteries, and no degradation in performance. Rick further explained that compared to systems using Class A / B amplifiers, the Si270x can extend the playback time by 2.5 times and only requires half the number of batteries. For example, using 4 AA alkaline batteries, a Si270x-based consumer audio system can provide up to 8.4 hours of playback time.
To provide a complete consumer audio platform solution for a variety of consumer audio products (such as desktop radios, expansion equipment, stereos, and mini stereo systems), the Si270x Class D amplifier can also be seamlessly connected to the Si473x AM / FM broadcast tuner . It is reported that the Si473x integrates a stereo analog input and an internal analog-to-digital converter and is multiplexed with the radio tuner front-end to support auxiliary analog audio input without the need for an additional external ADC.
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