US 6,320,465 B1 · Constant duty-cycle limiting of analog input signal swing in a class-D amplifier

Abstract

A constant limit duty-cycle is established by detecting the equivalent values VDD′ and −VDD″ of the voltages to which the output signal of the amplifier switches or pseudo supplies. An input limiting stage receiving an analog input signal utilizes the pseudo supply values VDD′ and −VDD″ as respective reference values for limiting the voltage swing of the analog signal output to a pre-defined fraction α<1 of such reference values. This avoids using as a reference the real supply voltage values VDD and −VDD, as commonly done. The constant limit duty cycle is substantially independent from fabrication process spreads, temperature, etc., and provides an optimal functioning of the final stage of the amplifier for all working conditions.

Claims32

Dependent claims

A method for limiting duty-cycle in a class-D amplifier comprising:

limiting a maximum amplitude of an analog input signal;
amplifying the amplitude limited analog input signal using an amplifier for providing a digital output signal switching between two voltages, each switched voltage corresponding to a voltage of a respective supply rail of an output power stage of the amplifier less a voltage drop on a respective power device therein, with an average value representing an amplified replica of the amplitude limited analog input signal;
regenerating an amplified analog signal using a low pass filter;
feeding the digital output signal to an input of a threshold limiting circuit for generating a positive threshold voltage and a negative threshold voltage, each threshold voltage corresponding to a pre-defined fraction of the respective switched voltages that the digital output signal switches to;
and
limiting the maximum amplitude of the analog input signal to the positive threshold voltage and the negative threshold voltage.

3 more elements

A class-D amplifier system having a limited duty-cycle comprising:

a limit circuit for limiting a maximum amplitude of an analog input signal, said limit circuit including a first input for receiving the analog input signal, a second input for receiving a positive threshold voltage, and a third input for receiving a negative threshold voltage;
an amplifier stage connected to an output of said limit circuit and comprising an output power stage including high-side and low-side power devices for outputting a digital signal switching between two voltages, each switched voltage corresponding to a voltage of a respective supply rail of the output power stage less a voltage drop on a respective power device, and with an average value representing an amplified replica of an amplitude limited analog input signal;
a low pass filter connected to an output of said amplifier stage;
and
a threshold limiting circuit connected to the output of said amplifier stage for generating the positive threshold voltage and the negative threshold voltage as a pre-established fraction of the respective switching voltages of the digital output signal provided by said amplifier stage.

2 more elements

Dependencies are inferred from the claim text.

Constant duty-cycle limiting of analog input signal swing in a class-D amplifier

Life of this patent

Constant duty-cycle limiting of analog input signal swing in a class-D amplifier

Life of this patent

Abstract

Claims32