Nieke Roos
30 October 2020

Harman Kardon’s new Citation Amp boasts 200 watts of Class D amplification per channel, enabled by Axign’s digital feedback audio chip.

Audio control specialist Axign has announced its first A-brand design-win. American home entertainment powerhouse Harman Kardon has integrated the scale-up’s AX5689 chip into its new stereo streaming amplifier. The latest addition to the Citation product line boasts 200 watts of Class D amplification per channel into 4 ohms, controlled by the little piece of silicon from Enschede.

“This is a major milestone for us, a breakthrough even,” states Richard Langezaal, Axign’s sales & marketing director. “Three years ago, we had our own mask set made, taking the big step from prototypes and proofs-of-concept to a design that can be sold. It then takes a while to convince potential customers and get on their shortlist. And once you finally get selected, it takes them another year to make the product and market it. Going to mass production requires a lot of effort and persistence, but we made it.”

Axign AX5689
Credit: Axign

Highly digital

Axign’s AX5689 digital Class D amplifier controller compares the analog signal after the output filter, at the speaker terminals, with the digital input signal. All disturbances in the loop, such as power stage dead times, power supply ripple and non-linearity from the output filter, are directly suppressed thanks to the high digital loop gain. The analog signal at the speaker is converted using a high-performance feedback ADC, which combines a low latency of several nanoseconds, for loop stability, with a high dynamic range up to 120 dB on set level for consumer audio solutions like streaming amplifiers, smart speakers and TV soundbars.

With only the converter’s input stage in the analog domain, the AX5689 is highly digital and consequently has all the accompanying features like programmability, self-learning and robustness. Being highly digital, the chip is insensitive to component tolerances. This allows for high-order loop filters, up to 7th order, enabling a high open-loop gain and steep filtering. The ability to program the transfer function loop makes it easy to change filter characteristics, for example noise shaping from 20 to 40 kHz and vice versa. “The result is a Class A audio performance at Class D efficiency, size and cost,” summarizes Langezaal.


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Custom installations

Powered by the AX5689, the Citation Amp features Harman Kardon’s digital loop amplification. By correcting the natural errors and distortion anomalies that occur in digital amplification, this technology claims to restore audio quality to the way it was meant to be heard. Providing access to over 300 music streaming services, the device can be connected to bookshelf, floor-standing, in-wall or in-ceiling speakers to create a multi-channel wireless surround sound system.

“The Citation Amp is a stand-alone amplifier that connects to a wide range of passive loudspeakers,” explains Langezaal. “It can be used in home entertainment systems, but it’s also targeted at custom installations in homes, restaurants, shopping centers and stadiums, for example. This is a very big market, especially in the US.”

Harman Kardon Citation Amp 01
Thanks to its small footprint – 215 mm wide, 75 mm high and 230 mm deep – the Citation Amp can be unobtrusively and flexibly placed around homes, restaurants, shopping centers and stadiums. Credit: Harman Kardon

Other big names

The design-win with Harmon Kardon, a Samsung subsidiary, is all the more important as it proves that Axign can deliver on its promise. “Customers are all waiting for someone else to take the first step. They all want market evidence,” says Langezaal. “This shows we’re not a one-day fly.”

With its team of 25, Axign is currently planning to expand its relationship with Harman Kardon. In parallel, the Enschede scale-up is gearing up to conquer other top audio brands, leveraging its local representatives in the US and China. Langezaal is confident: “With Harman Kardon on board, other big names are sure to follow.”