WO2013110221A1

WO2013110221A1 - Vmos power amplifier cancelling distortion and temperature drift via diode

Info

Publication number: WO2013110221A1
Application number: PCT/CN2012/070745
Authority: WO
Inventors: 胡章儒
Original assignee: Hu Zhangru
Priority date: 2012-01-29
Filing date: 2012-01-29
Publication date: 2013-08-01
Also published as: CN102742154A

Abstract

Provided is a circuit for cancelling VMOS transistor audio power amplifier distortion and temperature drift, the circuit comprising complementary S-stage outputted VMOS transistor power amplifiers (Q3, Q4); a series circuit with a resistor (R3) and a forward conduction diode (D1) is added between two G-stages; the series circuit is powered by a constant current source (Q2); the voltage drop at the two terminals of the series circuit provides the two complementary VMOS transistors with a static biased voltage between the G-stage and the S-stage; and simultaneously, the constant current source (Q2) is also the loader of an intermediate amplifier stage. The circuit noticeably reduces the open loop distortion of a VMOS transistor audio power amplifier.

Description

VMOS power amplifier with diode offset distortion and temperature drift The present invention describes a VMOS tube audio power amplifier distortion and temperature drift cancellation method. By using the method of the invention, the open loop distortion of the VM0S tube audio power amplifier can be reduced to an extremely low level. Other partial negative feedback techniques can completely make the sound quality of the transistor amplifier to the extent of the tube amp. The invention also has the function of stabilizing the quiescent current of the VMOS tube, so that the quiescent current of the VMOS tube does not change with the temperature rise and fall surface.

The sound quality of transistor amplifiers has always been a headache. The instrument has a good index of the crystal tube amplifier, but it sounds harsh and harsh. This is because the instrument's measured index is closed-loop, and the human ear hears the sound of the instantaneous open-loop power amplifier, which is a classic interpretation of transient intermodulation distortion. Then, reducing the open-loop distortion will naturally improve the sound quality, which is already the consensus of the industry. The key is to see how to reduce the open-loop distortion. The method of the present invention provides a way to effectively reduce the open-loop distortion. After the actual hearing test of the prototype, the high and medium tones basically reach the level of the single-ended class A power amplifier, and the bass is far better than the tube amp.

The working principle will be described below with reference to the drawings. Q1 in Figure 1 is the intermediate amplifier stage, and Q3 and Q4 are the complementary output poles of a pair of VMOS transistors. Q2 is a constant current source, and Di and R3 are connected in series to provide a static bias voltage for Q3 and Q4. Since the dynamic resistance of the constant current source and the input resistance of the VMOS transistor are both S, the gain of the intermediate amplifier stage is extremely high, and the range of variation of the operating point is also extremely small. The nonlinear distortion is also extremely small. Figure 2 shows an exponential characteristic plot. This picture can represent a lot of natural phenomena. The characteristic curves of the diode and VMOS tube have similar shapes. For a diode, the X axis is the voltage and the Y axis is the current. For the VMOS tube, the X axis is the voltage between the G and S poles, and the Y axis is the current between the D and S poles. If we choose the appropriate coordinate parameters, we can make the characteristic curve of the diode coincide with the characteristic curve of the VMOS tube! This is the theoretical basis of the present invention. Suppose that at some point, the G-pole voltage of Q3 rises. If there is no D1, then the current of Q3 will change as a nonlinear change as shown in 圏2. This nonlinear change is the distortion and now has: m Exist, the positive voltage of D] will also rise. Since the dynamic resistance of the constant current source is not infinite, the current of Di will also be a nonlinear change as shown in Fig. 2. This nonlinear change is also distortion. These two distortions are equal in magnitude and opposite in direction. Therefore, the synthesized output sound is not lost. To illustrate the process of this offset, take the three points A, B, and C on the curve of Figure 2, assuming that the voltage of G pole 1 of Q3 changes from point A to point B, if the line is connected from point A to point C. If you do, it will obviously not pass through point B. This is nonlinear distortion. The problem with this point B is that the larger current ϊί [[the actual is not bigger, that is, the output current should be smaller. Similarly, if this curve is regarded as the characteristic curve of the diode, the voltage of the m positive electrode changes from point A to point B, and the current at point B is supposed to be larger, thereby lowering the G-pole voltage of Q3. At point B, the G-pole voltage of Q3 is supposed to be smaller and actually not smaller. This is good, the distortion of the VMOS tube is that the current at point B becomes smaller, the distortion of the diode is that the voltage at point B becomes larger, and the voltage of this diode becomes larger, which offsets the current that the VMOS tube becomes smaller. The nonlinear distortion of the VMOS tube current is lost. Please note that this is to reduce open loop distortion. If D1 is replaced by two diodes, the series distortion will become very large, which is the cause of overcompensation. This also confirms the rationality of the above analysis on the other hand. Another function of this circuit is to offset the temperature drift, D = the negative temperature coefficient of the voltage drop exactly offsets Q3., Q4 two K VMOS t ^; G, S interelectrode voltage temperature coefficient. For the 'VMOS tube, in the small current state, the same G, S pole voltage, D, S pole current will increase with the temperature rise. The presence of D1 just offsets this temperature drift. As for why a diode can exactly offset the temperature drift of two VMOS tubes, this is determined experimentally. If you want to give a reasonable explanation from the theory, then you can only: put two complementary VMOS Instruction manual

The G-pole of the tube is considered to be a very thin layer of conductor, and connected together. The conductive channels of the two complementary VMOS tubes form a PN junction. This PN junction & 3⁄4 temperature coefficient and the temperature coefficient of the common diode PN junction Just equal.

In the figure, V!. is that the constant current source composed of Q2 uses TL431, and the voltage drop on the E pole of Q2 is fed back to the reference voltage terminal of TL431, and the voltage drop of Q2's BE junction is reduced after being heated. As the current flowing through R2 increases, the voltage at the reference voltage of the TL431 increases, the voltage at the output of the TL431 decreases, and the voltage at the B pole of Q2 decreases, suppressing the R2 current [3⁄4 increase. Similarly, the principle of the TL431 in suppressing Q2 noise is also similar. It can be seen that this can achieve lower noise, more stable current, better thermal stability, and higher dynamic resistance for the intermediate amplifier stage. If a triode is used instead of the TL431 to form a constant current source, the thermal stability is not satisfactory. If the constant current source cannot be stabilized, then the bias voltage formed by the current flowing through Di and R3 cannot be stabilized, and the distortion cancellation effect of D1 is not met.

In the existing VMOS tube power amplifier, a triode is used instead of the position of the TL431 in Fig. 1, and the current stability and noise performance of the transistor Q2 are poor. In use, the unstable surface of the constant current source can easily cause the VMOS tube current to burn out. In the existing VMOS tube power amplifier, in the circuit that supplies the bias voltage to the VMOS tube, there is no D1, and it is easy to cause the VMOS tube current to be too large and burned. At the same time, the distortion of the VMOS tube is also large.

The specific implementation of the present invention is easy to accomplish and is a common common component. D1 should be close to Q3 or Q4 in the installed position for better thermal coupling. It should be noted that in order to achieve the sound quality of the tube, it is also necessary to: 3⁄4 into the local negative feedback technique, reduce the gain of each stage, and reduce the negative feedback of the large loop.

Claims

: ί, A distortion cancellation circuit of a VMOS tube power amplifier, characterized in that: a complementary S-pole output VM0S tube power amplifier, a circuit in which a resistor and a forward-conducting diode are connected in series between two G-poles, a series circuit Powered by a constant current source, the voltage drop across the series circuit provides a static bias voltage between the G and S poles for the two complementary VM0S tubes. The constant current source is also the load of the intermediate amplifier stage.

2. A temperature drift canceling circuit for a VMOS tube power amplifier, characterized in that: the series circuit of claim 1 uses a forward conducting diode to cancel the voltage between the G and S poles of two complementary VMOS tubes The temperature drift.

3. As claimed! The constant current source circuit is characterized in that: TL431 is used to provide a constant voltage, and the constant voltage is applied to the B pole of the triode, the E pole of the triode is connected to the reference voltage end of the TL431, and the current limiting resistor is connected in the E pole loop to adjust the constant The current of the current source, the C pole of the triode is connected to the G pole of the VMOS tube, the other complementary VMOS tube G is connected to the output end of the intermediate amplifier stage, and the complementary voltage of the two complementary VMOS tubes is connected to the resistor, the constant current source It is also the load of the intermediate amplification stage.