JPH02234503A - Power amplifier - Google Patents

Abstract

PURPOSE:To keep the linearity at power amplification in an excellent way almost without deteriorating the power efficiency by applying power amplification with a power amplifier circuit of the pulse width modulation(PWM) system at a high output, applying power amplification with a power amplifier circuit having a good linearity at a high output, matching the phases of the both and outputting the result additively. CONSTITUTION:A voice signal Vin from a signal source 21 is inputted to an output system selection circuit 22. The selection circuit 22 compares a voltage level of an input signal with a reference level, selects and operates a 1st system when the input level is the reference level or over and selects and operates a 2nd system when the input level is the reference level or below, and in the case of selecting the 1st system, a voice signal is amplified for the power with a PWM system power amplifier circuit comprising a PWM circuit 23, a pulse amplifier circuit 24 and a low pass filter 25. On the other hand, when the 2nd system is selected, the voice signal is retarded for a prescribed time by a delay circuit 27 and amplified linearly by a linear power amplifier circuit 28. After the power amplifier outputs of both the systems are made unilateral by diodes 26, 29 respectively, added by an adder section 30 and the result is outputted via an output terminal 31.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the invention] (Industrial field of application) The present invention returns to a power amplifier used, for example, in an audio signal modulation amplifier of a medium wave or short wave broadcaster.

(Prior Art) In general, power amplifiers for audio amplification used in modulation amplifiers of broadcasting equipment are required to have good power supply efficiency, so they range from vacuum tube type linear power amplifiers to PWM (pulse width modulation) type power amplifiers. is being transitioned to. This PWM type power amplifier is not only required to have a linear modulation degree of amplitude modulation of the broadcasting device up to 100%, but also required to have linearity from the output voltage Ov. As shown in FIG. 5, the conventional PWM power amplifier converts the straddle signal from the signal source 11 into the PWM circuit! After pulse width modulation in Step 2, power is amplified in a pulse amplifier I3, unnecessary frequency components are removed in a low pass filter I4, and the result is output.

However, in principle, this PWM method has poor linearity at low levels, and the pulse width vs. output voltage characteristic generally becomes as shown in Figure 6, where the pulse width is close to O, it becomes a straight line, It's not.

This non-linearity is so large that it cannot be ignored, and when a sine wave with a negative peak value of Ov is input to this amplifier, for example, distortion as shown in FIG. 7 will occur in the output waveform. If put into practical use as is, it would have the disadvantage of inferior characteristics compared to a power amplifier using a conventional vacuum tube type linear power amplifier.

(Problems to be Solved by the Invention) As described above, the conventional power amplifier using the PWM method has a problem of good power supply efficiency but poor linearity.

The present invention was made to solve the above problems, and an object of the present invention is to provide a power amplifier that can obtain good linearity while minimizing a decrease in power supply efficiency.

[Object of the Invention] (Means for Solving the Problems) In order to achieve the above object, a power amplifier according to the present invention is provided in a first system, and a first power amplifier that amplifies the power of an input signal by a pulse width modulation method. and this first power amplifier circuit.
a first unidirectional means for unidirectionalizing the output of the power amplifying circuit; a second amplifying circuit provided in a second system and linearly amplifying the input signal; and the second amplifying circuit. a second unidirectional means for unidirectionalizing the output of the second system; a delay circuit provided in the second system for delaying and outputting the input signal; and outputting a sum of the output signals of the first and second systems. a first power amplifier circuit of the first system when the level of the input signal is above a reference value, and a second power amplifier circuit of the second system when the level of the input signal is below the reference value; and a selection means for operating.

(Function) The power amplifier with the above configuration is provided with a PWM type first power amplifier circuit in the first system, an amplifier circuit with excellent linearity in the second system, and a non-linearity of the first amplifier circuit. Below the level at which the signal appears conspicuously, the power is amplified in the second system, and above that level, the second system amplifies the power, and the two are added together and output.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 shows its configuration, in which the audio signal Vln from the signal source 21 is input manually to the output system selection circuit 22. This selection circuit 22 compares the voltage level of the input signal with a reference level, selects and operates the first system when the human power level is above the reference level, and selects the second system when it is below the reference level. When the first system is selected here, the audio signal is power amplified by a PWM type power amplification circuit comprising a PWM circuit 23, a Luz amplification circuit 24, and a low-pass filter 25. On the other hand, if the second system is selected,
The audio signal is delayed for a certain period of time by a delay circuit 27 and linearly amplified by a linear power amplification circuit 28. The power amplification output of each system is connected to a diode 26. After being made unidirectional in step 29, the signals are added in addition section 30 and outputted via output terminal 3l.

Specifically, the output system selection circuit 22 may have a configuration shown in FIG. 2 or 3. The circuit shown in FIG. 2 supplies the audio signal V1n to each system as it is, takes out the audio signal Vin from the second system input section, and outputs the audio signal Vin to the comparator 22.
2, and this comparator 222
It is compared with the output level V rar of the pressure source 221. Then, the output of the converter 222 is applied to a switch 223 interposed between the PWM circuit 23 and the pulse amplification circuit 24, and when VIn≦V rer, the switch 223 is closed and P
The configuration is such that the output of the WM circuit 23 is cut off.

On the other hand, the circuit shown in FIG. 3 has an audio signal V in the second system.
ln is supplied as is, and is supplied to the PWM circuit 23 via a precompensation amplifier circuit 224 to the first system. FIG. 4 shows the input/output characteristics of the human voice signal Vln with the gain at low level input lowered by the precompensation amplifier circuit 224. The configuration shown in FIG. 3 has a more complex circuit than the configuration shown in FIG. 2, but the connection between the system outputs can be made smooth later.

Furthermore, if the output of the linear power amplifier circuit 28 is not shut off during high-level input, there will be a disadvantage in terms of power supply efficiency. As the design suppresses the voltage to the minimum required to obtain a straight line, the linear power amplifier circuit 28 saturates when a high level input occurs, and the output voltage of the second system is lower than the output voltage of the first system. This is equivalent to automatically cutting off the direct ITfS force amplification circuit 28 by the diode 29 for making the output unidirectional. Regarding the interruption of these linear power amplifier circuits 28, there is no difference whether the output system selection circuit is the one shown in FIG. 2 or the one shown in FIG.

The delay circuit 27 is used to match each phase of the first system output and the second system output in the adder 30, and when the delay time of each circuit other than the low-pass filter 25 is short enough to be ignored (usually For example, a small-signal low-pass filter (for example, an active filter, an LC filter, etc.) having the same transfer function as the low-pass filter 25 may be assembled. Further, it may be omitted if the phase difference between each system is small enough to not cause a problem.

The linear power amplifier circuit 28 has excellent linearity at low level inputs, can supply the necessary power, and can be any type of circuit as long as the resulting reduction in power supply efficiency is within an acceptable range. good. Unidirectional diode 28.
29 is for preventing the output of one system from entering the other system via the adder 30, and as mentioned above, the diode 29 cuts off the output of the linear power amplifier circuit 28 during high-level human power. It has both functions. however,
The use of diodes is not mandatory; for example, in applications where voltage drop across diodes is a problem, there is no problem in replacing them with active elements such as transistors, thyristors, and FETs that are controlled on and off by audio input voltage.

Although it is conceivable that the adding section 30 adds up each system using a transformer or the like, the purpose can be sufficiently achieved with a wired OR circuit simply connecting lines as shown in FIG.

That is, in the above circuit, a well-designed PWM
Even in this type of power amplification circuit, nonlinearity becomes noticeable when the duty ratio falls below 10%. This portion is a small portion, less than 1% of the total output, when considered as electric power. Good linearity can be obtained by amplifying the output power of this portion using another linear power amplification circuit 28 without performing power amplification using the main PWM method. Also,
Even if the power efficiency of this linear power amplifier circuit 28 is conservatively estimated at 50% and this ti-line power amplifier circuit 28 always takes over 1% of the total output power, the overall power supply efficiency will decrease by 1% or less. fits in. In reality, the time that a PWM power amplifier circuit operates with a duty ratio of 10% or less is:
Since this is extremely small in audio signal amplification, it can be said that there is almost no decrease in overall power supply efficiency.

Therefore, the power amplifier with the above configuration performs power amplification using a PWM type power amplification circuit when the output is high, and a power amplification circuit with good linearity when the output is low, and performs phase matching between the two to output a summed output. Therefore, linearity during power amplification can be maintained well with almost no reduction in power supply efficiency. It goes without saying that the present invention is not limited to the embodiments described above, and may be modified in various ways without changing the gist thereof.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a power amplifier that can obtain good linearity while minimizing a decrease in power supply efficiency.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing the overall configuration of an embodiment of a power amplifier according to the present invention, and FIGS. 2 and 3 are block circuit diagrams showing the specific configuration of an output system selection circuit of the same embodiment, respectively. , Figure 4 shows the PW when using the circuit shown in Figure 3.
FIG. 5 is a block circuit diagram showing the configuration of a PWM power amplifier; FIG. 6 is a diagram showing the PWM pulse width vs. output voltage characteristic of the power amplifier shown in FIG. 5. , FIG. 7 is a waveform diagram showing how distortion occurs near OV when a sine wave signal is input to the power amplifier having the characteristics shown in FIG. 2l... Signal source, 22... Output system selection circuit, 22
1 converter, 222... reference voltage source, 223...
- Switch, 23...PWM circuit, 24...Pulse amplification circuit, 25...Low pass filter, 26. 29
...Unidirectional diode, 28...Delay circuit, 2
9... Linear power amplifier circuit, 80... Addition section, 3l.
...Output terminal, Vln...Audio signal.

Claims (1)

[Claims] a first power amplification circuit provided in the first system and amplifying power of an input signal using a pulse width modulation method; and first unidirectionalization means for unidirectionalizing the output of the first power amplification circuit; a second amplifier circuit provided in a second system and linearly amplifying the input signal; a second unidirectional means for unidirectionalizing the output of the second amplifier circuit; a delay circuit which is provided in the system and delays and outputs the input signal; an adder circuit which adds and outputs each output signal of the first and second systems; and when the level of the input signal is equal to or higher than a reference value, the first
A power amplifier comprising a selection means for substantially operating a first power amplifying circuit of the second system when the first power amplifying circuit of the system is equal to or less than a reference value.