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FFX technology description

The FFX class architecture is a digital low-distortion, low-noise PCM-to-PWM converter, based on a new sample reconstruction approach which converts the digital input signal into a differential pulse-width modulated signal at a frequency of 384 KHz and with a time resolution of 100 MHz.
 
   

To avoid distortion and spurious harmonics generation, the audio signal is over-sampled, then linearized and an exact calculation of the intersection between the piecewise linear resulting signal and the up/down carrier signal is performed.

 FFX includes pop free start-up, an STMicroelectronics patented fully-digital pop noise remover. The result is obtained gradually, loading the output capacitor from zero to half the supply with the PWM signal, starting from near 0% duty cycle to 50% duty cycle. ST pop free start-up is thus faster than the traditional resistive partition method.
The FFX modulation scheme can be adapted with the use of software to match portable or home system applications. For home systems, FFX can provide an unrivaled signal to noise ratio and for portable applications FFXcan work either with an output reconstruction filter or in filter-less mode.
   
FFX supports a specific type of modulation, called binary headphone, which delivers a cap-less solution for headphone.
 
FFX based products contain an analog to digital converter and muxing features. The match FFX cell and to keep the overall chain quality unchanged. This step of integration cost, reduce IC count and designed unconstrained form factor products.
 
Comparison between traditional implementation and ST enabled implementation.

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