Performance testing was conducted and verified by Bascom H. King a consultant in the audio industry. Measurement results are made possible by JamTech's innovative sub-ranging PWM digital amplifier architecture that inherently avoids the fundamental distortion mechanism of traditional Class D amplifiers. This new category of digital amplifier faithfully reproduces ultra-low level audio signals, resulting in exceptional audio clarity, warmth and detail reminiscent of early tube analog amplifiers.
JamTech's digital amplifier performance testing resulted in measurements of less than +/-3dB deviation from absolute linearity over a range from 0 to 108 dBFS (dB relative to Full Scale), or the equivalent of 18 bits. This is compared to a typical range of 72-78dB (12-13 bits) for traditional analog PWM Class D amplifiers and 84-90dB (14-15 bits) for delta-sigma PWM digital amplifiers. Range of linearity as measured by the Deviation from Absolute Linearity (DAL) test is an important metric of fidelity for digital amplifiers by indicating ability to accurately reproduce the low level tones and harmonics that give audio its richness, detail, and clarity. Standard CD quality audio is specified at 96dB or 16 bits of resolution, and is considered the minimum acceptable performance level for true audio fidelity.
In addition, performance testing measured spectral noise floor measurements of -150 dBFS, which is seven times smaller than the smallest reproducible audio signal. Traditional Class D and digital amplifiers typically have a spectral noise floor between 100-105 dBFS, making it impossible to discern low level audio from the noise. Full enjoyment of the small signal detail requires a sufficiently low spectral noise floor so as not to detract from the desired audio signals.
"The ability to reproduce silence or small sounds is every bit, if not more, as important to audio fidelity as the ability to create loud sounds. High inherent instantaneous accuracy enables sub-ranging PWM digital amplifiers to accurately reproduce extremely fine audio detail," said Herbie Kirn, JamTech chief technology officer.
Sub-ranging PWM as employed in JamTech's digital amplifiers is a patented bi-level digital to pulse-width conversion technique that drives the output stage with significantly higher precision than traditional single level modulation schemes. Sub-ranging is a technique previously used in data converters that divides the input data into the sum of a large and small signal component that are subsequently converted separately and recombined in the output drive stage. This direct digital parallel conversion technique achieves high precision and fidelity by avoiding the non-linearity caused by pulse width timing resolution limitations of silicon technology. This benefits digital amplifiers by extending usable operating range beyond 100 dB and reducing zero crossing distortion by a factor greater than 250.
JamTech's initial product, the JM2020, is currently sampling and is targeted to the digital TV market. Featuring a monolithic design integrating both the modulator and power stage into a single chip, the JM2020 delivers best in class audio fidelity at a price comparable to traditional Class D amplifiers and newer delta-sigma PWM digital amplifiers. JamTech's next generation sub-ranging PWM digital amplifier will be available for sampling in the fourth quarter and features even better fidelity with more than 20-watts of output power.
"Sub-ranging PWM delivers great fidelity without the costly complexity and audio coloration associated with delta-sigma modulators and DSPs," explained Rick Beale, JamTech's vice president of marketing and business development. "With JamTech digital amplifiers, customers can enjoy the cost and efficiency benefits of digital without compromising audio fidelity."
Because digital amplifiers enable a crystal clear audio experience, small signal performance has become a requirement. JamTech has made available a measurement testing report that maintains the DAL metric as important for assessing true fidelity over the operating range of a digital amplifier by determining at what input signal level the output amplitude no longer faithfully tracks the input amplitude. As a demanding test traditionally used for characterizing high performance audio digital to analog conversion systems, it typically will reveal problems at much lower input signal amplitudes than the standard -60dBFS probe tone test.
For more information on the JamTech product line, visit www.jam-tech.com. To download the full measurement testing report, visit http://www.jam-tech.com/support/library/downloads/ JamTech_WP_Digital_Amplifier_Testing.pdf. (Due to its length, this URL may need to be copied/pasted into your Internet browser's address field. Remove the extra space if one exists.)
About JamTech
JamTech is a fabless, mixed signal semiconductor company with innovative and scalable digitized power audio technology focused on creating System Interface Chips for audio-centric consumer electronics, including flat panel TVs, computers and portable media players. JamTech invented and pioneered True Fidelity(R) sub-ranging PWM digital amplifiers featuring the audio fidelity of analog, the power efficiency of Class D and the scalability of digital. The company has over 23 patents issued and 17 pending. With headquarters in Austin, Texas and Singapore, JamTech ICs are sold through its direct sales force and international distributors. More information is available at http://www.jam-tech.com.
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