Class D amplifier
A class D amplifier for audio and an audio system including the class D amplifier are provided. The class D amplifier is configured to be operable in an open loop mode, be operable in a closed loop mode, and switch between the open loop mode and the closed loop mode. A method of controlling a class D amplifier is also provided.
1 . A class D amplifier for audio, wherein the class D amplifier is configured to:
be operable in an open loop mode;
be operable in a closed loop mode; and
switch between the open loop mode and the closed loop mode, wherein the class D amplifier comprises:
a controller configured to control the switching of the class D amplifier between the open loop mode and closed loop mode; and
a digital modulator configured to receive a modulator input signal,
wherein:
the digital modulator is configured to operate as a pulse-density modulator arranged to provide a constant width pulse signal whilst the class D amplifier is operating in the open loop mode; and/or
the digital modulator is configured to operate as a pulse-width modulator arranged to provide a varying pulse width signal whilst the class D amplifier is operating in the closed loop mode.
2 . The class D amplifier of claim 1 , wherein;
the controller is configured to provide a communication signal to the digital modulator, the communication signal comprising information on whether the class D amplifier is operating in the open loop mode or the closed loop mode; and
the digital modulator is configured to operate as the pulse-density modulator or the pulse-width modulator depending on a mode of the class D amplifier as indicated by the communication signal.
3 . The class D amplifier of claim 2 , wherein the digital modulator comprises:
a noise shaper arranged to receive the modulator input signal and to quantize the modulator input signal from a first word length to a second word length, thereby providing a quantized noise shaper output.
4 . The class D amplifier of claim 3 , wherein the noise shaper comprises:
a sigma-delta modulator.
5 . The class D amplifier of claim 4 , wherein the first word length comprises 24 bits.
6 . The class D amplifier of claim 5 , wherein the second word length comprises 7 bits.
7 . The class D amplifier of claim 6 , wherein the digital modulator comprises:
a pulse modulator arranged to receive the quantized noise shaper output and invert the quantized noise shaper output then subsequentially splitting the inverted quantized noise shaper output, thereby providing the digital modulator a first bi-level output signal and a second bi-level output signal.
8 . The class D amplifier of claim 7 , wherein the controller comprises:
a detector that monitors a property of the class D amplifier; and wherein
the controller determines a control of switching of the digital modulator between the open loop mode and closed loop mode based on the property monitored by the detector.
9 . The class D amplifier of claim 8 , further comprising:
a h-bridge switching element arranged to receive the first bi-level output signal and the second bi-level output signal and provide an error signal.
10 . The class D amplifier of claim 9 , further comprising:
an analog-to-digital converter arranged to receive an error signal from the h-bridge switching element and provide a digital error feedback signal.
11 . The class D amplifier of claim 10 , wherein the analog-to-digital converter comprises:
a sigma-delta analog-to-digital converter.
12 . The class D amplifier of claim 11 , further comprising:
a selectively enabling loop filter configured to receive the digital error feedback signal from the analog-to-digital converter and provide a loop signal to the digital modulator.
13 . The class D amplifier of claim 12 , wherein the controller is configured to transmit a control signal to the loop filter, thereby selectively enabling the loop filter and controlling the switching of the class D amplifier from the open loop mode to the closed loop mode or the switching of the class D amplifier from the closed loop mode to the open loop mode.
14 . The class D amplifier of claim 12 , wherein the property comprises:
a first threshold value of a class D amplifier input signal, and/or;
a pulse collision of the class D amplifier input signal; and
a quanta differential determined, at least in part, from the modulator input signal and the quantized noise shaper output.
15 . The class D amplifier of claim 14 , wherein the controller sends a first control signal to the loop filter in response to the detector detecting a first the property of the modulator input signal, wherein the first control signal disables transmission of the modulator input signal, thereby transitioning the digital modulator from the open loop mode to the closed loop mode.
16 . The class D amplifier of claim 15 , wherein the response to the detector detecting the property of the modulator input signal occurs over a predetermined period.
17 . The class D amplifier of claim 16 , wherein the controller comprises:
a clock to record a timer of operation in the closed loop mode and wherein:
the controller sends a second control signal to the digital modulator to switch the digital modulator from the closed loop mode to the open loop mode in response to the timer recording a predetermined closing time.
18 . An audio system comprising a class D amplifier, wherein the class D amplifier is configured to:
be operable in an open loop mode;
be operable in a closed loop mode; and
switch between the open loop mode and the closed loop mode, wherein the class D amplifier comprises:
a controller configured to control the switching of the class D amplifier between the open loop mode and closed loop mode; and
a digital modulator configured to receive a modulator input signal, wherein:
the digital modulator is configured to operate as a pulse-density modulator arranged to provide a constant width pulse signal whilst the class D amplifier is operating in the open loop mode; and/or
the digital modulator is configured to operate as a pulse-width modulator arranged to provide a varying pulse width signal whilst the class D amplifier is operating in the closed loop mode.
19 . The audio system of claim 18 , comprising a headphones or a speaker.
20 . A method of controlling a class D amplifier being operable in an open loop mode and a closed loop mode, the method comprising:
switching from the closed loop mode to the open loop mode; and/or
switching from the open loop mode to the closed loop mode, wherein the class D amplifier comprises:
a controller configured to control the switching of the class D amplifier between the open loop mode and closed loop mode; and
a digital modulator configured to receive a modulator input signal, wherein:
the digital modulator is configured to operate as a pulse-density modulator arranged to provide a constant width pulse signal whilst the class D amplifier is operating in the open loop mode; and/or
the digital modulator is configured to operate as a pulse-width modulator arranged to provide a varying pulse width signal whilst the class D amplifier is operating in the closed loop mode.