Devices and methods to control dynamic audio range in boosted audio systems
A controller regulates the voltage delivered to the load and current drawn from the battery in an audio system depending on ripple in the battery voltage which is input to the controller to allocate power for audio playback. Regulation maximizes available headroom while avoiding audio clipping. The effect of internal battery and external parasitic resistance (ESR) on ripple is compensated by an iterative process. ESR is rapidly increased whenever the minimum of the battery voltage input to the controller falls below a clipping threshold and slowly decreased whenever such voltage exceeds such threshold and the audio is under compression. A limiter allocates power to utilize more of the available audio headroom. A de-emphasis filter in each audio signal path compensates for capacitive ripple in the battery voltage input to the controller. As the frequency of the audio input changes, the filter(s) allow frequency-dependent power/current regulation to fill the full audio range without distortion.
1 . An audio system comprising:
a voltage estimator having inputs, a first output, and a second output, wherein the first output of the voltage estimator is configured to provide a voltage that represents an estimate of a voltage input of the audio system based on voltages provided at the inputs of the voltage estimator;
a current regulator having a first input, a second input, and an output, wherein the first input of the current regulator is coupled to the second output of the voltage estimator and the second input of the current regulator is coupled to the first output of the voltage estimator;
a filter disposed in an audio signal path, the filter having an output; and
an audio limiter having a first input coupled to the output of the filter, a second input configured to receive a voltage limit voltage.
2 . The audio system of claim 1 , wherein the audio limiter is configured to control power allocated for audio playback based on the output of the filter, the voltage limit voltage, a load resistance value, and an input power voltage.
3 . The audio system of claim 1 , further comprising:
a boost circuit having a first input configured to receive a device voltage, and a second input configured to receive a current limit voltage; and
an inductor coupled to the first input of the boost circuit, wherein the current limit voltage is configured to limit a peak of a current drawn from a battery via the inductor.
4 . The audio system of claim 3 , further comprising a speaker coupled to an output of the boost circuit.
5 . The audio system of claim 1 , further comprising:
a power threshold calculator having a first input coupled to the first output of the voltage estimator, a second input configured to receive a the current limit voltage, and a third input configured to receive a load resistance value.
6 . The audio system of claim 5 , wherein the power threshold calculator is configured to:
calculate a scaled input power based on the first output of the voltage estimator, a current limit voltage, and a scale factor; and
calculate the voltage limit voltage based on the scaled input power and the load resistance value.
7 . The audio system of claim 6 , wherein the power threshold calculator includes an input power calculator configured to calculate an input power total signal based on the scaled input power.
8 . A method comprising:
measuring an input voltage signal to a controller in each of multiple periods of time to calculate, for each period of time, a maximum value of the input voltage signal (maximum value), an average value of the input voltage signal (average value), and a minimum value of the input voltage signal (minimum value);
outputting, by the controller, an output voltage for each period of time representing an estimate of an actual value of the input voltage signal based on the maximum value for that period of time and an average of multiple maximum values sampled during that period of time;
estimating a resistance for each period of time based on the minimum value for that period of time; and
calculating an output current of the controller for each period of time based on the output voltage for that period of time and the estimated resistance for that period of time.
9 . The method of claim 8 , wherein the output voltage for each period of time is determined based on an intermediate value that is determined based on a difference between the maximum value for that period of time and the average value obtained during that period of time compared to a silence voltage threshold.
10 . The method of claim 9 , wherein, for each period of time, the output voltage is determined based on an average of multiple intermediate values, one from a present period of time and each of the others from a respective previous period of time.
11 . The method of claim 9 , wherein, for each period of time, when the comparison indicates that the difference is less than the silence voltage threshold, the intermediate value is determined to be equal to maximum value obtained during that period of time.
12 . The method of claim 9 , wherein, for each period of time, when the comparison indicates that the difference is greater than or equal to the silence voltage threshold, the intermediate value is maintained the same as in an immediate previous period of time.
13 . The method of claim 8 , wherein the estimating of the resistance for each period of time includes comparing the minimum value for that period of time to a clipping voltage threshold.
14 . The method of claim 13 , wherein, for each period of time, when the comparing indicates that the minimum value is less than the clipping voltage threshold, the estimated resistance is determined to be the sum of the estimated resistance for an immediately previous period of time and a first amount of resistance.
15 . The method of claim 13 , wherein, for each period of time, when the comparing indicates that the minimum value is greater than or equal to the clipping voltage threshold, the method further comprises determining whether a signal is under compression.
16 . The method of claim 15 , wherein, for each period of time,
when it is determined that the signal is under compression, the estimated resistance is determined to be the difference between the estimated resistance for an immediately previous period of time and a second amount of resistance, and
when it determined that the signal is not under compression, the estimated resistance is determined to be the estimated resistance for an immediately previous period of time.
17 . The method of claim 8 , wherein, for each period of time, the output current is calculated to be the difference between the output voltage and a clipping voltage threshold divided by the estimated resistance.
18 . The method of claim 8 , further comprising:
filtering an input audio signal to compensate for capacitive ripple.