Class D amplifier and electronic devices including the same

An electronic device includes a waveform generator, a comparator, and an amplifier. The waveform generator receives a voltage from a power supply to the electronic device and outputs a voltage waveform signal. The comparator compares an input signal and the voltage waveform signal to output a first pulse-width-modulated signal. The amplifier receives the first pulse-width-modulated signal and outputs a second pulse-width-modulated signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 201410438799.2, filed on Aug. 29, 2014, which is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates to electronic devices, and in particular, to electronic devices including a class D amplifier.

BACKGROUND

A class-D amplifier is an electronic amplifier in which the amplifying devices (such as transistors) operate as electronic switches, instead of as linear gain devices as in other amplifiers. Generally, the signal to be amplified is a train of constant amplitude pulses, so the active devices switch rapidly back and forth between a fully conductive and nonconductive state. The analog signal to be amplified is converted to a series of binary waveform by pulse width modulation (PWM), pulse density modulation or other modulation before being applied to the amplifier. After amplification, the output pulse train is converted back to an analog signal by passing through a low pass filter. The class-D amplifier is more efficient than analog amplifiers because it reduces power waste as heat dissipation.

FIG. 1shows a class D amplifier that includes a waveform generator101, a comparator102, a power amplifier circuit103, a first filter circuit104, a power supply105and a signal generator106. The power supply105supplies operating voltage to the power amplifier circuit103. The signal generator106generates a first input signal U1and the waveform generator101outputs a second signal U2. The first and second input signals U1and U2are input to the comparator102which outputs a PWM signal U3. The PWM signal U3goes through the power amplifier circuit103that outputs the amplified PWM signal U4. The amplified PWM signal U4is input to the first filter104to obtain the audio output signal U0. The power of the output signal U0depends on the duty cycle of amplified PWM signal U4and the amplitude of the power supply105to the power amplification circuit103. Thus, when the power supply105fluctuates, the audio output signal U0may fluctuate even when input signals U1and U2remain the same. In short, the fluctuation of the power supply105causes audio distortion of the output signal U0. The users may hear the sound changes abruptly in that case. Thus, there is a need to a class D amplifier that can smooth the output signal U0.

One way to solve the above problem is to introduce a feedback circuit in the class D amplifier. As shown inFIG. 2, the feedback circuit120within the dashed box includes a filter circuit122, a sampling circuit124, and an integrator126. The sampling circuit124takes the PWM signal U4of the power amplifier103and outputs sampled PWM signal U5. The sampled PWM signal U5is filtered by the filter circuit122to receive the signal U6, which passes through the integrator126and accumulates the input signal U1. The integrator126adjusts the amplitude of the input signal U1according to the signal U6. Thus, the output of the waveform generator compares U2with the adjusted input signal U2, thus making the output signal U3and the signal U4changes accordingly, which suppresses undesired change of the power U0. The feedback circuit120, however, includes additional filter circuits after sampling. The feedback circuit120has to filter out the clutter and correct the phase offset of the analog signal, which leads to complex design of the feedback circuit. Further, the feedback circuit120introduces active device such as the integrator126, resulting in an increase in circuit costs.

Thus, there is a need to a class D amplifier that can smooth the output signal U0and reduces the complexity and cost of the feedback circuit.

SUMMARY

In one aspect, an electronic device includes a waveform generator, a comparator, and an amplifier. The waveform generator receives a voltage from a power supply to the electronic device and outputs a voltage waveform signal. The comparator compares an input signal and the voltage waveform signal to output a first pulse-width-modulated signal. The amplifier receives the first pulse-width-modulated signal and outputs a second pulse-width-modulated signal.

In a second aspect, a method is provided for amplifying signal. In the method, a waveform generator in an electronic device receives a voltage from a power supply and outputs a voltage waveform signal. A comparator of the electronic device compares an input signal and the voltage waveform signal to output a first pulse-width-modulated signal. An amplifier of the electronic device receives the first pulse-width-modulated signal and outputs a second pulse-width-modulated signal.

In another aspect, a system is provided system. The system includes a class-D amplifier directly connected to a power supply. The class-D amplifier includes: a waveform generator and a comparator. The waveform generator receives a voltage from the power supply and outputs a voltage waveform signal. The comparator compares an input signal and the voltage waveform signal to output a first pulse-width-modulated signal. The voltage waveform signal includes a triangular wave signal that serves as a negative feedback control signal to the class-D amplifier.

DETAILED DESCRIPTION OF THE DRAWINGS

The terminology used in the description of the disclosure herein is for the purpose of describing particular examples only and is not intended to be limiting of the disclosure. As used in the description of the disclosure and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “may include,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, operations, elements, components, and/or groups thereof.

FIG. 3is an example schematic structural diagram of an electronic device according to the present disclosure. The electronic device may be a television, a smart phone, a laptop, a tablet, or any other device that includes a speaker and a power supply. The electronic device includes a waveform generator101, a comparator102, a power amplifier circuit103, a first filter circuit104, a power supply105and a signal generator106. The waveform generator101may include an integrated circuit (IC) that produces accurate, high-frequency triangle, sawtooth, sine, square, and pulse waveforms with a few external components. The output frequency may be controlled over a frequency range by an internal voltage reference and an external resistor. The duty cycle may be varied over a wide range by applying a duty control signal, facilitating pulse-width modulation. Frequency modulation and frequency sweeping may be achieved in similar fashion. The duty cycle and frequency controls may be independent.

The comparator102may include an IC that compares two voltages or currents and outputs a signal. The comparator102may include a specialized high-gain differential amplifier circuit. The power amplifier circuit103may be an IC that includes a plurality of pins designated for different input and output signals. The electronic device may include additional components such as speakers, display screens, input modules, etc.

InFIG. 3, the power supply105supplies power to the electronic device. The power supply105also provides an input signal to the sampling circuit202, which samples the input power signal and sends the sampled power signal to the waveform generator101. The sampled power signal may be a voltage signal. In short, the waveform generator101receives the voltage signal from the power supply105to the electronic device and outputs a voltage waveform signal U2to the amplifier102. The signal U2may include a high frequency triangular wave. The waveform generator may101receive the voltage signal directly from the power supply105when the voltage signal is within a preset range. Alternatively, the waveform generator101may receive a sampled voltage signal at least partially related to the voltage signal of the power supply105. The waveform generator101may include a non-sinusoidal waveform generator that generates the voltage waveform signal U2based on the voltage signal. The electronic device may not need to include an integrator. For example, the electronic device may not need an integrator in the feedback control loop.

The comparator102compares an analog input signal U1from the signal generator106and the voltage waveform signal U2to output a first pulse-width-modulated (PWM) signal U3. Note that the PWM signal may also be referred as a pulse-width-modulation signal. For example, the comparator102may compare a high frequency triangular wave U2with the audio input signal U1to generate a series of pulses of which the duty cycle is directly proportional with the instantaneous value of the audio signal. The comparator102may then drive a MOS gate driver which in turn drives a pair of high-power switches to produces an amplified replica of the comparator's PWM signal. An output filter may then remove the high-frequency switching components of the PWM signal and recover the audio information that a speaker can use. The amplifier103receives the first PWM signal U3and outputs a second PWM signal U4.

Here, because the input voltage waveform signal U2is from the power supply, it reflects the fluctuation of the power supply. When the power supply increases, the input voltage waveform signal U2also increase. The first PWM signal U3is partially controlled by the input voltage waveform signal U2. When the input voltage waveform signal U2increases, the first PWM signal U3will have a smaller duty cycle. At the same time, the power supply also supplies operating voltage to the power amplifier circuit103. An increased operating voltage alone may result an increased U4. The smaller duty cycle of U3thus may cancel at least a part of the effect of the increased operating voltage and reduce the undesired fluctuation of the signal U4.

Similarly, when the power supply decreases, the input voltage waveform signal U2also decrease. The decrease of the input voltage waveform signal U2will cause the first PWM signal U3to have a greater duty cycle. At the same time, the power supply also supplies operating voltage to the power amplifier circuit103. A decreased operating voltage alone may result a decreased U4. The greater duty cycle of U3thus may cancel at least a part of the effect of the decreased operating voltage and reduce the undesired fluctuation of the signal U4. In other words, the combination effect of the power supply on the comparator102and the amplifier103has an effect of a feedback circuit with less hardware components and much less cost.

FIG. 4is an example block diagram of a class D amplifier according to the present disclosure. The class D amplifier further includes a filter104that removes the high-frequency switching components of the second PWM signal U4and recovers the analog signal information. The analog input signal may be an audio signal or other type of analog signals. The filter104may include a low pass filter that that passes signals with a frequency lower than a certain cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The amount of attenuation for each frequency depends on the filter design. The filter104may include a band pass filter that passes frequencies within a certain range and attenuates frequencies outside that range. The filter104may include other types of filters if necessary. The class D amplifier may be implemented in a single IC. In that case, the IC may include all the above components inFIG. 4in a single chip. The IC may include a power supply pin that is internally connected to the waveform generator in the chip.

FIG. 5is an example block diagram of a class D amplifier according to the present disclosure. The D amplifier includes a sampling circuit202. The sampling circuit202includes: a second filter circuit203and a voltage dividing circuit204.

The second filter circuit203receives an input from the power supply105. The second filter circuit203outputs a signal to the voltage dividing circuit204. The voltage dividing circuit204outputs a voltage signal to the input terminal of the waveform generator101. The second filter circuit203filters the power supply signal from the power supply105while the voltage divider circuit204divides the filtered voltage signal from the second filer circuit203.

The second filter circuit203may include: a first resistor unit301and a capacitor unit302. The voltage dividing circuit204may include: a second resistor unit303and a third resistor unit304. It should be understood that the sampling circuit202inFIG. 5is only for illustration purpose. A first end of the first resistor unit301is connected to the power supply105and a second end of the first resistor unit301is connected to the first end of the second resistor unit303. The first end of the capacitor unit302is connected to the second end of the first resistor unit301. The second end of the capacitor unit302is connected to ground. The second end of the second resistor unit303is connected to a first input of the waveform generator101. The first end of the third resistor304is connected to of the second end of the second resistor unit303. A second end of the second resistor unit303is connected to the ground.

The sampling circuit202may include additional circuitry components. The sampling circuit202may be implemented using other alternative circuitry.

FIG. 6is an example block diagram of a sampling circuit of a class D amplifier. The class D amplifier includes a waveform generator101, which may be a non-sinusoidal waveform generator that generates a non-sinusoidal waveform. For example, the non-sinusoidal waveform generator maybe a triangular wave generator that generates a triangular wave. Alternatively, the non-sinusoidal waveform generator may be a sawtooth wave generator that generates a sawtooth wave. InFIG. 6, the waveform generator101includes two operational amplifiers T1and T2, three resistors R1, R2, and R3, and a capacitor C1.

InFIG. 6, the class D amplifier further includes: a second filter circuit203and a voltage dividing circuit204. The second filter circuit203may include a resistor-capacitor circuit (RC circuit), which may also be called as a RC filter. The RC filter203shown inFIG. 6is a first order RC circuit that includes one resistor R3and one capacitor C2, which is the simplest type of RC circuit. The filter circuit203may include additional circuitry components and be implemented differently. The voltage dividing circuit204includes two resistors R5and R6connected in series, with the input voltage applied across the two resistors and the output voltage emerging from the connection between them. Here, the second filter circuit203and a voltage dividing circuit204work together as the sampling circuit. The input of the sampling circuit is the voltage supply VCC while the output voltage of the sampling circuit is Vref.

InFIG. 6, Vo represents the output voltage of the operational amplifier T1, where the operational amplifier T1includes a maximum output voltage Vo Hand the minimum output voltage VoL. Vout represents the output voltage of the operational amplifier T2, which is the output voltage of the triangular waveform generator101. The operational amplifier T2has a maximum output voltage VoutH and a minimum output voltages VoutL.

The output voltage Vout of the triangular waveform generator101depends on the input Vref of the operational amplifier T1on the inverting terminal. From the characteristics of the operational amplifier, when two input terminals of the operational amplifier T1have the same input voltages, the output of the operational amplifier T2may reach its maximum or minimum VoutH or VoutL.

For example, in the first situation, when the output of the operational amplifier T1is at a high level, it may continuously charge to C1and the output voltage of the operational amplifier T2is reduced to the lowest point. As a result, the non-inverting input of the operational amplifier T1and the inverting input terminal of the operational amplifier T1have equal input voltages.

In the second situation, when the output of the operational amplifier T1is at a low level, it may continuously discharge the capacitor C1and the output voltage of the operational amplifier T2is increased to the highest point. As a result, the non-inverting input of the operational amplifier T1and the inverting input terminal of the operational amplifier T1have equal input voltages.

Thus, combining equations 1 and 2, VoutH and VoutL may be determined according to the following two equations. In Equation 3 and Equation 4, the resistances of the two resistors R2and R3are predetermined, the maximum and minimum output voltage VoH and VoL are predetermined. Thus, so long as the input voltage Vref changes, the output voltage of the operational amplifier T2will change accordingly. Specifically, when Vref increases, VoutH and VoutL increase; when Vref becomes decreases, VoutH and VoutL also decrease. Thus, the output of the triangular waveform generator101and the voltage of the power supply VCC are a positively correlated. In other words, if the power supply voltage fluctuates, the output voltage will follow the amplitude of the triangular waveform generator101and change accordingly.

FIG. 1is an example diagram that illustrates the output change of a waveform generator. InFIG. 7, the magnitude of the output voltage changes. Here, as shown by the solid line, the maximum value of the amplitude of Vout is A before Vref increase. As Vref increases, the output voltage Vout of the triangular waveform generator101, which is shown using the broken line, also increases. The maximum value of the amplitude A′ is greater than A.

FIG. 8is an example diagram that illustrates the output change a class D amplifier according to the present disclosure. Waveform401shows the output waveform of the triangular waveform generator waveform101, which is adjusted by the sampling circuit202. Waveform402represents original waveform of the triangular waveform generator output waveform101, which is not adjusted by the sampling circuit202. Waveform403shows a waveform of an analog signal such as an audio input signal. Waveform404shows the waveform of the output signal U3of the comparator102. Waveform405shows the power amplifier circuit103of the output signal U4.

In the above embodiments, when the power supply VCC becomes larger, the voltage Vref output from the sampling circuit also becomes larger, i.e., the signal Vref at the inverting input terminal of the operational amplifier T1becomes larger. From Equations 3 and 4, when Vref becomes larger, the output voltage of the operational amplifier T2becomes larger. Thus, the output voltage of the triangular waveform generator becomes larger. As can be seen fromFIG. 8, the waveform from the waveform of the waveform402becomes waveform401, where the amplitude of the triangular wave becomes large. The comparator102compares the audio input signal and the increased triangular signal. The duty ratio of the first PWM output signal U3will be smaller. The magnitude of the output PWM signal U4increases while the duty cycle of the second PWM signal U4decreases following the duty cycle of the first PWM output signal U3. Thus, the output of the PWM power amplifier circuit may be stabilized because the increased amplitude and the smaller duty cycle may cancel at least a part of each other, which achieves the effect of negative feedback. Therefore, the final power of the output signal U0does not fluctuate following the fluctuation of the supply voltage VCC. The stability of the output power ensures the quality of the audio output signal.

Similarly, when the power supply VCC becomes smaller, the voltage Vref output from the sampling circuit also becomes smaller, i.e., the signal Vref at the inverting input terminal of the operational amplifier T1becomes smaller. From Equations 3 and 4, when Vref becomes smaller, the output voltage of the operational amplifier T2becomes smaller. Thus, the output voltage of the triangular waveform generator becomes smaller. The comparator102compares the audio input signal and the decreased triangular signal. The duty ratio of the first PWM output signal U3will be larger. The magnitude of the output PWM signal U4decreases while the duty cycle of the second PWM signal U4increases following the duty cycle of the first PWM output signal U3. Thus, the output of the PWM power amplifier circuit may be stabilized because the decreased amplitude and the larger duty cycle may cancel at least a part of each other, which achieves the effect of negative feedback. Therefore, the final power of the output signal U0does not fluctuate much following the fluctuation of the supply voltage VCC. The stability of the output power ensures the quality of the audio output signal.

Compared with the prior art, the feedback circuit of the embodiments of the present disclosure filters the direct current signal generated by the power supply and reduces the output fluctuations because of the fluctuations in the DC signal. The embodiments do not need converting the PWM output signal to an analog signal. The embodiments do not need a phase shift conversion or a superimposition of the audio input signal and the feedback signal. The electronic device does not need an integrator in a feedback loop to the class-D amplifier as in the prior arts. In other words, the electronic device or electronic system does not need an integrator in a feedback loop that generates the negative feedback control signal. Thus, the present embodiments of the disclosure provide a simple feedback circuit design, without complex filter circuit. Further, there is no need to add the active devices, effectively reducing the design complexity of the feedback circuit. Thus, the cost of the feedback circuit is much less while the effect of the feedback circuit is almost the same.

FIG. 9is an example flowchart of a method according to embodiments of the present disclosure. In act510, a waveform generator in an electronic device receives a voltage signal from a power supply and outputs a voltage waveform signal. The voltage waveform signal may include a triangular wave signal that serves as a negative feedback control signal to the electronic device.

In act520, a comparator of the electronic device compares an analog signal and the voltage waveform signal to output a first PWM signal. In act560, the comparator decreases a duty cycle of the first PWM signal when the voltage signal from the power supply increases. In act570, the comparator increases a duty cycle of the first PWM signal when the voltage signal from the power supply decreases.

In act530, an amplifier of the electronic device receives the first PWM signal. In act540, the amplifier outputs a second PWM signal. The magnitude of the second PWM signal may be controlled at least partially by the amplitude of the power supply105shown inFIGS. 3-5. The duty ratio of the second PWM signal may be controlled at least partially by the duty ratio of the first PWM signal.

In act550, a filter circuit of the electronic device receives the second pulse-width-modulated signal from the amplifier and outputs an amplified analog signal. The electronic device may include a second filter circuit that receives an input from the power supply and outputs a filtered power supply signal to a voltage divider circuit.

Note that each of the above resistor unit, the capacitor unit may be a combination of one or more circuit devices to achieve similar effects. For example, the resistance unit may include any of the above at least one resistor, the resistor unit may include at least two resistors, where the resistors may be connected in parallel within a resistors unit, and may also be connected in series. The resistance of the resistor may be fixed or may be changing. The capacitor unit may include at least one capacitor, when the capacitor unit includes at least two capacitors, the capacitors may be connected in parallel within a capacitor unit, and may also be connected in series, and the capacitance of the capacitor can be fixed or may be varied.

The present disclosure provides a novel electronic device that can smooth the output signal and reduces the complexity and cost of the feedback circuit by connecting the power supply directly to the waveform generator of the electronic device.

The above descriptions are merely preferred embodiments of the present disclosure, but not intended to limit the scope of the present disclosure. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present disclosure should fall within the scope of the present disclosure.