For years, consumer audio engineers have been trying to replace power-hungry analog A/B amplifiers with power-saving digital Class D amplifiers. But so far, two problems have hampered the use of Class D amplifiers: the high EMI emissions generated by high frequency switching inherent in traditional Class D amplifier solutions, and the high cost of adding filtering and shielding measures to meet EMI specifications. . Recently, Silicon Laboratories, a high-performance analog and mixed-signal IC manufacturer, has launched the Si270x, which is said to be the industry's first 5-watt stereo Class D amplifier capable of effectively reducing EMI.
At present, in addition to the rapid growth of multiple audio amplifier segments, another compelling trend is the rapid shift from Class A/B amplifiers to Class D amplifiers. According to data from Databeans, the D-class amplifier market is expected to reach $347 million in 2010, and the compound annual growth rate will reach 11% in the next five years, far exceeding the average growth rate of the audio market.
As the first member of the Silicon Labs Class D amplifier family, the new Si270x amplifier is defined as a product that "changes the rules of the audio industry," targeting the price- and noise-sensitive consumer audio products, including smartphone expansion devices. Desktop radio, TV sound bar and monitor, stereo and battery powered radio.
Rick Beale, director of audio amplifier products at the company, said that "multi-level EMI reduction technology" will be a key factor in ensuring the success of the Si270x. The design philosophy is to suppress the interference of traditional Class D amplifiers from the source, making it easier to comply with EMI specifications. More suitable for AM/FM radios and smartphones. Compared to existing Class D amplifier solutions, the Si270x is reported to reduce radiation interference by a factor of 10 in the EMI specification band, by a factor of 100 in the FM radio band and by a factor of 1000 in the AM band.
Figure: Block diagram of the Si270x amplifier application circuit.
“Our EMI reduction technology using four-level scheme includes: Extended PWM effectively suppresses broadband switching radiant energy, making its radiant energy less than 1/10 of the original; modulable noise-free notch ensures clear AM signal reception; Adjusted switching is easier to meet compliance requirements and FM reception; and on-chip feedback protection to improve audio quality,†adds Rick.
In addition, because the traditional Class D amplifier generates a large amount of EMI radiation in the 900MHz transceiver band, the signal quality of the smartphone and its extended device over-the-air (OTA) is weakened. On the other hand, most of the current extended platforms use analog architectures, which are very susceptible to the noise generated by TDMA emissions. As a result, the Si270x amplifier features a smartphone-friendly all-digital architecture that is less susceptible to radiated noise and enhances OTA performance and compatibility.
To avoid EMI from traditional Class D amplifiers, audio engineers tend to use low-cost, low-efficiency Class A/B amplifiers, which require larger, more expensive power supplies and heat sinks (some require 9V or 12V battery configurations) . The Si270x amplifier allows developers to use smaller and lower cost power supplies in portable audio systems with fewer batteries without sacrificing performance. Rick further explained that the Si270x can extend playback time by a factor of 2.5 compared to systems using A/B amplifiers, and requires only half the battery. For example, with a 4-cell AA alkaline battery, the Si270x-based consumer audio system provides up to 8.4 hours of playback time.
The Si270x Class D amplifier also provides seamless connectivity to Si473x AM/FM broadcast tuners for a complete consumer audio platform solution for a wide range of consumer audio products such as desktop radios, expansion devices, stereos and mini stereo systems. . It is reported that the Si473x integrates a stereo analog input and an internal analog-to-digital converter, and is multiplexed with the front end of the radio tuner to support auxiliary analog audio inputs without the need for an additional external ADC.
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