Feed-forward smart amp protection algorithm has been integrated into TAS5825M for both the excursion and thermal protection of target speakers, which can be presented as Figure 2-4.

Figure 2-4 Smart Amp Algorithm

For excursion protection, a look ahead structure can be applied to make sure the excursion estimation and signal limitation have been completed before the signal is fed to the algorithm output. Figure 2-5 shows the block diagram of the excursion protection algorithm.

Figure 2-5 Smart Amp Excursion Protection Algorithm

As demonstrated in Figure 2-5, the excursion of the speaker’s membrane is estimated firstly with the convolution operation between the audio signals and the derived excursion transfer functions:

Then the excursion is compared with the maximum excursion limit before deciding if protection kicks on. Once the estimated excursion exceeds the limit X_max, the input signal is attenuated to realize the speaker protection, otherwise the input signal passes through unchanged.

Figure 2-6 shows the block diagram of the smart amp thermal protection algorithm. A real-time processing structure is adopted here considering the slow response characteristic of the thermal system.

Figure 2-6 Smart Amp Thermal Protection Algorithm

Firstly, the temperature of the voice coil is estimated with the dissipated power and the thermal model of the speaker, given by:

Then the estimated temperature is compared with the temperature limit of the voice coil, and generate the reference signal to the PI thermal controller. The output of the thermal controller is then sent into the power limit module to attenuate the audio signal when necessary, which keeps the voice coil temperature within the thermal limit.