TWI454046B - Class ab amplifier and operating method thereof - Google Patents

Description

Class AB amplifier and its operation method

The present invention relates to amplifiers, and more particularly to a class AB amplifier capable of eliminating the need for additional bias circuits.

In general, power amplifiers can be classified into Class A amplifiers, Class B amplifiers, and Class AB amplifiers according to their quiescent operating points. The output stage components of Class A amplifiers are always in the conduction region. Due to their small distortion, good linearity and simple design, they are suitable for applications with small signal levels or low power (such as driving headphones), but their biggest disadvantages. The output efficiency is very low, and the theoretical value does not exceed 50%. Therefore, it is quite power-consuming and because the heat is too large, all parts work at high current and high temperature for a long time, which easily causes problems in stability and life.

As for the Class B amplifier, two outputters are provided to amplify the positive and negative half cycles, respectively, each of which is accurately turned on at 180 degrees (or half cycle) of the input signal. Class B amplifiers have the advantage of high output efficiency and are suitable for the application of high-power amplifier circuits. However, due to the existence of a small non-linear region in the process from the turn-off to the turn-on of the transistor, the signal is distorted. For crossover distortion. Cross-over distortion occurs when one transistor enters an off state, while another transistor enters a conducting state, which is less noticeable when the signal is large, and is easily perceived when the signal is small.

In order to improve the cross-over distortion caused by Class B amplifiers, a Class AB amplifier between Class A amplifiers and Class B amplifiers is proposed. Class AB amplifiers are not as efficient as Class B amplifiers, but are higher in frequency and less distorted than Class A amplifiers, so they are most commonly used as high power amplifiers for audio. Please refer to FIG. 1. FIG. 1 is a circuit diagram of a conventional class AB amplifier. 1, a first input current I _in1 is assumed equal to the second input current I _in2, the gate voltage V _gs of the transistor M33 is equal to the transistor M34 of the gate voltage V _gs, the gate voltage V _gs of transistor M31 Equal to the gate voltage V _gs of the transistor M32, the current ratio between the transistors M31 and M32 is equal to the width to length ratio between the transistors M31 and M32, and the current I _{M32 of the} transistor M32 is equal to the bias current I ₄ , so The current I _{M31 of} the output stage transistor M31 is I ₄ *(W/L) _M31 /(W/L) _M32 . Similarly, the gate voltage V _{gs (M43)} of the transistor _M43 is equal to the gate voltage V _{gs (M44)} of the transistor _M44, and the gate voltage V _{gs (M41)} of the transistor _M41 is equal to the gate voltage V of the transistor M42. _{Gs (M42)} , the current ratio between the transistors M41 and M42 is equal to the width to length ratio between the transistors M41 and M42, and the current I _{M42 of the} transistor M22 is equal to the bias current I ₁ , so that the output stage transistor M41 is obtained. Current I _M41 = I ₁ *(W/L) _M41 /(W/L) _M42 .

2 is a graph showing the relationship between the output voltage and the output current of the output stage transistors M11 and M21 of the class AB amplifier of FIG. 1. When the first input current I _in1 and the second input current I _in2 increase, the current I _{M11 of the} output stage transistor M11 decreases but the current I _{M12 of the} output stage transistor M12 increases; when the first input current I _in1 and the first When the two input currents I _in2 decrease, the current I _{M11 of the} output stage transistor M11 increases but the current I _{M12 of the} output stage transistor M12 decreases.

However, Figure 1 shows, in addition to the bias current source I _1, a conventional class AB amplifier needs to be additionally provided with other bias circuit to work properly, for example, the bias current source I _2, I ₃ and I ₄ Etc., thus resulting in an increase in the cost of the class AB amplifier and a complicated circuit structure.

Accordingly, the present invention proposes a class AB amplifier to solve the above problems encountered in the prior art.

One aspect of the invention is to propose a class AB amplifier. In one embodiment, the class AB amplifier includes an input stage, a current control unit, and an output stage. The input stage includes a first control end and a second control end. The current control unit is coupled to the input stage. The output stages are coupled to the input stage and the current control unit, respectively. The output stage includes a first switch and a second switch. When the first voltage of the first control terminal is lower than the second voltage of the second control terminal, the second current flowing through the second switching switch increases and the first current flowing through the first switching switch does not change; when the first control terminal When the first voltage is greater than the second voltage of the second control terminal, the second current flowing through the second switching switch decreases and the first current flowing through the first switching switch increases.

Another aspect of the invention is to propose a class AB amplifier. In one embodiment, the class AB amplifier is coupled between the operating voltage and the ground. The class AB amplifier includes a first control terminal, a second control terminal, a current source, an output terminal, a first switching switch, a second switching switch, a third switching switch, a fourth switching switch, a fifth switching switch, a sixth switching switch, The seventh switch, the eighth switch, the ninth switch, the tenth switch, the eleventh switch, and the twelfth switch.

The working voltage is respectively coupled to the current source, the first switching switch, the third switching switch and the sixth switching switch; the second switching switch, the fifth switching switch, the eighth switching switch, the tenth switching switch and the twelfth switching switch are coupled Connected to the grounding end; the output end is located between the first switching switch and the second switching switch; the fourth switching switch is coupled between the third switching switch and the fifth switching switch; the seventh switching switch is coupled to the sixth switching switch And the eighth switching switch; the ninth switching switch is coupled between the current source and the tenth switching switch; the eleventh switching switch is coupled between the current source and the twelfth switching switch; the first switching switch, the first The third switching switch and the sixth switching switch are coupled to each other in series between the seventh switching switch and the eighth switching switch; the second switching switch is further coupled to the fifth switching switch and the ninth switching switch and the tenth switching switch; The eighth switch is further coupled to the tenth switch, the twelfth switch, and the eleventh switch and the twelfth switch.

When the first voltage of the first control terminal is lower than the second voltage of the second control terminal, the second current flowing through the second switching switch increases and the first current flowing through the first switching switch does not change; when the first control terminal When the first voltage is greater than the second voltage of the second control terminal, the second current flowing through the second switching switch decreases and the first current flowing through the first switching switch increases.

Another aspect of the invention is to propose a method of operating a class AB amplifier. In a specific embodiment, the class AB amplifier includes an input stage and an output stage. The input stage includes a first control end and a second control end, and the output stage includes a first switching switch and a second switching switch. The operation method of the class AB amplifier includes the following steps: (a) detecting and comparing the first voltage of the first control terminal and the second voltage of the second control terminal; (b) if the comparison result of the step (a) is the first control terminal The first voltage is less than the second voltage of the second control terminal, increasing the second current flowing through the second switching switch and maintaining the first current flowing through the first switching switch; (c) comparing the steps (a) The result is that the first voltage of the first control terminal is greater than the second voltage of the second control terminal, reducing the second current flowing through the second switching switch and increasing the first current flowing through the first switching switch.

Compared with the prior art, the class AB amplifier and the method for operating the same according to the present invention can realize the operational characteristics of the class AB amplifier without additionally providing the bias circuits required for the conventional class AB amplifier. It can effectively save the manufacturing cost of the class AB amplifier and make its circuit structure simpler, so as to enhance the market competitiveness of the class AB amplifier.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

A preferred embodiment of the invention is a class AB amplifier. In fact, the class AB amplifier proposed by the present invention is used for power-amplifying an input low-power signal into a high-power signal and outputting it to a device such as a speaker, so that it can be used as an audio low-frequency amplifier or applied to other linearities and efficiencies. Very important design, such as mobile phones, cellular towers or TV transmitters, but not limited to the above applications.

Please refer to FIG. 3. FIG. 3 is a functional block diagram of the class AB amplifier of this embodiment. As shown in FIG. 3, the class AB amplifier 3 is coupled between the operating voltage V _DD and the ground. The class AB amplifier 3 includes a current source I ₁ , an input stage IS, a current control unit CU, and an output stage OS. The current source I ₁ , the current control unit CU and the output stage OS are all coupled to the operating voltage V _DD ; the input stage IS, the current control unit CU and the output stage OS are all coupled to the ground. The current source I _{1 is} coupled to the input stage IS. The current control unit CU is coupled to the input stage IS and the output stage OS. The input stage IS comprises a first control terminal INP and a second control terminal INN. The output stage OS contains an output OUT. In this embodiment, the current source I _{1 is} used to provide a bias current, and the circuits of the input stage IS, the current control unit CU and the output stage OS are all coupled by a plurality of switching switches (for example, transistors), but This is limited to this.

Next, please refer to FIG. 4. FIG. 4 is a detailed circuit diagram of the class AB amplifier 3 of FIG. It should be noted that FIG. 4 is only a specific embodiment of the class AB amplifier 3 of FIG. 3. The circuit structure of the class AB amplifier 3 of the present invention is not limited to this example.

As shown in FIG. 4, the output stage OS further includes a first switch M1 and a second switch M2. The current control unit CU includes a third changeover switch M3, a fourth changeover switch M4, a fifth changeover switch M5, a sixth changeover switch M6, a seventh changeover switch M7, and an eighth changeover switch M8. The input stage IS further includes a ninth changeover switch M9, a tenth changeover switch M10, an eleventh changeover switch M11, and a twelfth changeover switch M12. In this embodiment, the first to the twelfth switch M12 and the twelfth switch M12 disposed in the class AB amplifier 3 are all made of a metal oxide half field effect transistor (MOSFET), but are not limited thereto. In this embodiment, each of the changeover switches M1 M M12 has a first end, a second end, and a third end, wherein the first end is a gate; if the second end is a source, the third end is a drain If the second end is a drain, the third end is the source.

The first switch M1, the third switch M3, and the sixth switch M6 are all coupled to the operating voltage V _DD . The second switch M2, the fifth switch M5, the eighth switch M8, the tenth switch M10, and the twelfth switch M12 are all coupled to the ground.

The output terminal OUT is located between the first changeover switch M1 and the second changeover switch M2. The fourth switch M4 is coupled between the third switch M3 and the fifth switch M5. The seventh switch M7 is coupled between the sixth switch M6 and the eighth switch M8. The ninth switch M9 is coupled between the current source I ₁ and the tenth switch M10. The eleventh switch M11 is coupled between the current source I ₁ and the twelfth switch M12.

The gate of the third switch M3 is coupled to the gates of the first switch M1 and the sixth switch M6, and the gate of the sixth switch M6 is coupled to the drain of the seventh switch M7 and the eighth switch. The source of the M8.

The gate of the second switch M2 and the gate of the fifth switch M5 are coupled to the drain of the ninth switch M9 and the source of the tenth switch M10; the gate of the eighth switch M8, the tenth switch The gate of the switch M10 and the gate of the twelfth switch M12 are both coupled to the drain of the eleventh switch M11 and the source of the twelfth switch M12; the first control terminal INP is coupled to the eleventh switch The switch M11; the second control terminal INN is coupled to the ninth switch M9; the contact P between the fourth switch M4 and the seventh switch M7 is coupled between the fourth switch M4 and the fifth switch M5. Contact Q.

In this embodiment, it is assumed that the first voltage of the first control terminal INP of the input stage IS is V ₁ and the second voltage of the second control terminal INN is V ₂ . When the first voltage V _{1 of the} first control terminal INP is equal to the second voltage V _{2 of the} second control terminal INN, since the gate voltage V _{gs(M2) of the} second switching switch M2 is equal to the gate of the fifth switching switch M5 voltage V _{gs (M5),} the current ratio between the I _M2 of the second switch M2 and the fifth current switch the I _M5 M5 will be equal to the second switch M2, the aspect ratio (W / L) _M2 and the second The ratio between the aspect ratio (W/L) _{M5 of the} five-switch M5, that is, the current I _{M2 of the} second change-over switch _M2 = I _M5 *(W/L) _M2 /(W/L) _M5 .

In addition, when the first voltage V _{1 of the} first control terminal INP is equal to the second voltage V _{2 of the} second control terminal INN, since the gate voltage V _{gs (M12)} of the twelfth switch M12 is equal to the eighth switch M8 The gate voltage V _{gs (M8)} , and the gate voltage V _{gs (M6) of the} sixth switch M6 is equal to the gate voltage V _{gs (M1) of the} first switch M1, and the current I of the twelfth switch M12 the ratio between the eighth switch M8 and _M12 of the current will be equal to the I _M8 twelfth switch M12 of the aspect ratio (W / L) _M12 and the eighth switch M8 of the aspect ratio (W / L) _M8 the ratio between, and the sixth switch M6 _M6 switching current of the I and the I current ratio between the first switching switch M1 _M1 will be equal to the sixth switch M6 aspect ratio (W / L) _M6 first The ratio between the aspect ratio (W/L) _M1 of the switch M1 is calculated, so that the current I _{M1 of the} first changeover switch _M1 = I _M12 *[(W/L) _M8 /(W/L) _M12 can be derived. ]*[(W/L) _M1 /(W/L) _M6 ].

Please refer to FIG. 5. FIG. 5 is a graph showing the relationship between the output voltage and the output current of the first switching switch M1 and the second switching switch M2 of the class AB amplifier 3 of FIG. 5, when the first control terminal INP of the first voltage V ₁ is smaller than the second control terminal INN of the second voltage V _2, since the second switch M2 of gate voltage V _{gs (M2)} increases, The second current I _M2 flowing through the second changeover switch M2 is also increased, and the first current I _M1 flowing through the first changeover switch M1 is also proportional to the current I _M12 flowing through the twelfth switch M12. Therefore, the first current I _M1 does not change much, and can be regarded as unchanged, as shown at K in FIG. 5 .

When the first voltage V _{1 of the} first control terminal INP is greater than the second voltage V _{2 of the} second control terminal INN, the gate voltage V _{gs(M2) of the} second switching switch M2 is reduced, so that the second switching is performed. The second current I _{M2 of the} switch M2 is reduced. It should be noted that, because the capability of the third switch M3 is greater than the fifth switch M5, the voltage V _P of the contact P between the fourth switch M4 and the seventh switch M7 is increased, resulting in the seventh switch. M7 is turned off, so that the gate voltage V _{gs (M1) of the} first changeover switch M1 is increased, so that the first current flowing through the first changeover switch M1 also increases, as shown at J in FIG.

In summary, since the circuit of the class AB amplifier 3 is composed of a plurality of switching switches M1 to M12, the bias current sources I ₂ and I ₃ additionally provided by the conventional class AB amplifier 1 shown in FIG. 1 can be omitted. The bias circuit of I ₄ can effectively save the cost of the class AB amplifier and make its circuit structure simpler.

Another preferred embodiment of the present invention is a class AB amplifier operating method. In effect, the Class AB amplifier operates to operate a Class AB amplifier that is coupled between the operating voltage and the ground. The class AB amplifier includes a current source, an input stage, a current control unit, and an output stage, wherein the input stage includes a first control end and a second control end, and the output stage includes a first switching switch and a second switching switch. The current source, the current control unit and the output stage are all coupled to the working voltage; the input stage, the current control unit and the output stage are all coupled to the ground. The current source is coupled to the input stage. The current control unit is coupled to the input stage and the output stage. The output stage contains the output. In this embodiment, the circuits of the input stage, the current control unit, and the output stage are all coupled to each other by a plurality of switching switches (for example, transistors), but are not limited thereto.

Please refer to FIG. 6. FIG. 6 is a flowchart of a method for operating a class AB amplifier of this embodiment. As shown in FIG. 6, first, the method performs step S10, detecting and comparing the first voltage of the first control end and the second voltage of the second control end. If the comparison result in step S10 is that the first voltage of the first control terminal is smaller than the second voltage of the second control terminal, the method performs step S12, increasing the second current flowing through the second switching switch and maintaining the flow through the first switching switch. The first current is unchanged; if the comparison result of step S10 is that the first voltage of the first control terminal is greater than the second voltage of the second control terminal, the method performs step S14 to reduce the second current flowing through the second switch The first current flowing through the first switch is increased.

Compared with the prior art, the class AB amplifier and the method for operating the same according to the present invention can realize the operational characteristics of the class AB amplifier without additionally providing the bias circuits required for the conventional class AB amplifier. It can effectively save the manufacturing cost of the class AB amplifier and make its circuit structure simpler, so as to enhance the market competitiveness of the class AB amplifier.

The features and spirits of the present invention are more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents within the scope of the invention as claimed.

S10~S14. . . Process step

I _in1 . . . First input current

I _in2 . . . Second input current

M1~M12, M31~M34, M41~M44. . . Transistor

V _INN , V _INP . . . Input voltage

P, Q. . . Circuit contact

I ₁ , I ₂ , I ₃ , I ₄ . . . Bias current source

V _OUT . . . The output voltage

V _DD . . . Operating Voltage

I _OUT . . . Output current

3. . . Class AB amplifier

IS. . . Input stage

CU. . . Current control unit

OS. . . Output stage

INP. . . First control terminal

INN. . . Second control terminal

OUT. . . Output

J. . . Current increase in the curve

K. . . The constant current in the curve

FIG. 1 is a circuit diagram of a conventional class AB amplifier.

2 is a graph showing the relationship between the output voltage and the output current of the output stage transistors M31 and M41 of the class AB amplifier of FIG. 1.

3 is a functional block diagram of a class AB amplifier in accordance with a preferred embodiment of the present invention.

4 is a detailed circuit diagram of the class AB amplifier of FIG. 3.

FIG. 5 is a graph showing the relationship between the output voltage and the output current of the output stage transistors M1 and M2 of the class AB amplifier of FIG. 4.

6 is a flow chart showing a method of operating a class AB amplifier according to another embodiment of the present invention.

M1~M12. . . Transistor

INN, INP. . . Input voltage

P, Q. . . Circuit contact

I ₁ . . . Battery

V _DD . . . Operating Voltage

3. . . Class AB amplifier

IS. . . Input stage

CU. . . Current control unit

OS. . . Output stage

INP. . . First control terminal

INN. . . Second control terminal

OUT. . . Output

Claims (11)

A class AB amplifier includes: an input stage including a first control end and a second control end; a current control unit coupled to the input stage; and an output stage coupled to the input stage and the current control a unit, the output stage includes a first switch and a second switch; wherein, when the first voltage of the first control terminal is less than the second voltage of the second control terminal, the second switch is performed a second current of the switch is increased and the first current flowing through the first switching switch is constant; when the first voltage of the first control terminal is greater than the second voltage of the second control terminal, flowing through the The second current of the second switch is decreased and the first current flowing through the first switch is increased. The class AB amplifier of claim 1, wherein the input stage, the current control unit, and the output stage are coupled between an operating voltage and a ground. The class AB amplifier of claim 2, further comprising: a current source coupled between the input stage and the operating voltage. The class AB amplifier of claim 2, wherein the current control unit comprises a third switch, a fourth switch, a fifth switch, a sixth switch, a seventh switch, and An eighth switching switch, the third switching switch and the sixth switching switch are respectively coupled to the working voltage, and the fifth switching switch and the eighth switching switch are respectively coupled to the grounding end, the fourth switching switch coupling The third switching switch is coupled between the third switching switch and the fifth switching switch, and the seventh switching switch is coupled between the sixth switching switch and the eighth switching switch. The class AB amplifier of claim 2, wherein the output stage further includes an output, the first switch is coupled between the operating voltage and the output, and the second switch is coupled to The output is between the ground and the ground. The class AB amplifier of claim 3, wherein the input stage further comprises a ninth switch, a tenth switch, an eleventh switch, and a twelfth switch, the ninth switch The switch is coupled between the current source and the first control terminal, and the tenth switch is coupled between the ninth switch and the ground, the eleventh switch is coupled to the current source and the second control end The twelfth switch is coupled between the eleventh switch and the ground. The class AB of claim 4, wherein the first end of the third switch is coupled to the first end of the first switch and the first end of the sixth switch, the sixth The first end of the switch is coupled to the second end of the seventh switch and the third end of the eighth switch. The class AB amplifier of claim 6, wherein the first end of the second switch and the first end of the fifth switch are coupled to the second end of the ninth switch and the tenth Switch the third end of the switch. The class AB amplifier of claim 6, wherein the first end of the eighth switch, the first end of the tenth switch, and the first end of the twelfth switch are coupled to the first The second end of the eleventh switch and the third end of the twelfth switch. A class AB amplifier is coupled between an operating voltage and a ground. The class AB amplifier includes: a first control terminal; a second control terminal; a current source; an output terminal; and a first switching switch a second switching switch, a third switching switch, a fourth switching switch, a fifth switching switch, a sixth switching switch, a seventh switching switch, an eighth switching switch, a ninth switching switch, and a a tenth switch, an eleventh switch, and a twelfth switch; wherein the operating voltage is coupled to the current source, the first switch, the third switch, and the sixth switch; The second switch, the fifth switch, the eighth switch, the tenth switch, and the twelfth switch are all coupled to the ground; the output is located at the first switch and the second The fourth switching switch is coupled between the third switching switch and the fifth switching switch; the seventh switching switch is coupled between the sixth switching switch and the eighth switching switch; Ninth switch The first switching switch is coupled between the current source and the twelfth switching switch; the first switching switch, the third switching switch, and the first switching switch are coupled between the current source and the tenth switching switch; The sixth switching switch is coupled to the seventh switching switch and the eighth switching switch in series; the second switching switch is further coupled to the fifth switching switch and the ninth switching switch and the tenth switching switch The eighth switching switch is further coupled to the tenth switching switch, the twelfth switching switch, and the eleventh switching switch and the twelfth switching switch; wherein, when the first control terminal is When the first voltage is less than the second voltage of the second control terminal, the second current flowing through one of the second switching switches is increased and the first current flowing through one of the first switching switches is unchanged; when the first control When the first voltage of the terminal is greater than the second voltage of the second control terminal, the second current flowing through the second switching switch decreases and the first current flowing through the first switching switch increases. A class AB amplifier operating method for operating a class AB amplifier, the class AB amplifier comprising an input stage and an output stage, the input stage comprising a first control end and a second control end, the output stage comprising a a switching switch and a second switching switch, the class AB amplifier operating method comprises the following steps: (a) comparing a first voltage of the first control terminal with a second voltage of the second control terminal; (b) if The comparison result of the step (a) is that the first voltage of the first control terminal is smaller than the second voltage of the second control terminal, and the second current flowing through one of the second switching switches is increased and maintained through the first The first current of the switch is unchanged; and (c) if the comparison result of the step (a) is that the first voltage of the first control terminal is greater than the second voltage of the second control terminal, the reduction flows through the first The second current of the switch is switched and the first current flowing through the first switch is increased.