JPS5883413A - Voltage current feedback amplifier - Google Patents

Abstract

PURPOSE:To compensate the deficiency of sound pressure at low frequencies and to suppress the rise in high frequency charactristics, by applying voltage feedback to high frequencies and current feedback to low frequencies. CONSTITUTION:A signal applied to an input terminal 1 is applied to a speaker 4 via an amplifier 2. A voltage at a connecting point of voltage feedback resistors 5, 6 and a voltage at a resistor 8 for load current detection are synthesized at a capacitor 9 and a resistor 10 for feedback synthesis and the result is applied to an inverting input terminal of the amplifier 2. Taking a value of the resistor 10 larger in comparison with a parallel value of the resistors 5, 6 and a value of the resistor 8, voltage feedback is applied at a frequency higher then the frequency determined with the capacitor 9 and the resistor 10 and current feedback is provided at lower frequencies.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage-current feedback amplifier used in an audio power amplifier, etc., in which voltage feedback is applied to the high range and current feedback is applied to the low range. It compensates for the lack of sound pressure in the low range, and suppresses the rise in frequency characteristics in the high range,
Furthermore, the compensation amount near the low resonant frequency of the speaker is prevented from becoming too large.

Speakers for audio users are generally made so that the frequency characteristics of the output sound pressure are as flat as possible for a constant voltage input. For this reason, conventional power amplifiers that drive speakers also generally use voltage feedback, which maintains a constant voltage gain, as shown in FIG. In FIG. 1, 1 is an input terminal, 2 is an amplifying section, 3 is an output terminal on the hot side thereof, 4 is a load speaker, and 6 is a voltage feedback resistor.

In the configuration shown in FIG. 1, the voltage gain of the amplifier is determined by the division ratio of the voltage feedback resistors 6, 6, so its frequency characteristics become flat as shown in FIG. 2a.

However, as shown in Figure 3C, the frequency characteristics of the sound pressure of the speaker for a constant voltage input are as follows:
(hereinafter simply referred to as fo) from the vicinity, 12 dBloa
Because of the rapid attenuation at t, especially when the volume of the speaker box is small, io becomes high, resulting in a low frequency band.

Therefore, in order to increase the sound pressure in the low range, especially in the vicinity of f0, by applying current feedback and using the fact that the impedance of the speaker near f0 increases as shown in Figure 4 d, we can increase the sound pressure in the low range. Conventionally, methods have been proposed to compensate for the shortage.

An example is shown in FIG. In FIG. 6, 7 is the cold side output terminal of the amplifier, and 8 is a load current detection resistor inserted between the cold side output terminal 7 and the ground.

If the value of the load current detection resistor 8 is set sufficiently small with respect to the speaker load resistance value, a signal inversely proportional to the speaker impedance as shown in FIG. 4d is fed back to the inverting input terminal of the amplifier 2. Therefore, the voltage gain of the amplifier has a frequency characteristic as shown in Fig. 2, and the low frequency range is enhanced.

However, since the impedance of a speaker generally increases as the frequency range increases, there is a problem in that the gain of such a current feedback amplifier increases in the high frequency range, as shown in FIG.

Furthermore, since the impedance of the speaker near f0 is several times higher than the impedance in the middle range, there is also the problem that the increase in gain near f0 is too large.

The present invention solves these problems and provides an amplifier that compensates for the lack of sound pressure in the low range of the speaker, suppresses the increase in frequency characteristics in the high range, and further suppresses the amount of compensation near f0 from becoming too large. It provides:

In other words, the present invention uses both voltage feedback and current feedback, and combines both feedback signals using a resistor and a capacitor, so that voltage feedback is applied to high frequencies and current feedback is applied to low frequencies. be.

FIG. 6 shows a first embodiment of the invention. In FIG. 6, 9 and 1o are a feedback signal synthesis capacitor and a resistor, respectively, for synthesizing a voltage feedback signal and a current feedback signal and feeding them back to the inverting input of the amplifier.

Here, if the value of the feedback signal synthesis resistor 10 is set sufficiently large compared to the parallel value of the voltage dividing resistors 6 and 6 and the value of the load current detection resistor 8 (this condition is fully realized), ) Frequency f determined by the time constant of capacitor 9 and resistor 1°
At frequencies higher than c, voltage feedback is applied, and at frequencies lower than fc, current feedback is applied. Therefore, if the ratio of the dividing resistors 6 and 6 is set close to the ratio between the resistance value of the speaker 4 and the load current detection resistor, the frequency characteristics due to voltage feedback in Fig. 6 will be as shown in Fig. 7 e. Therefore, the frequency characteristic due to current feedback becomes as shown in FIG. 7f. The frequency characteristic obtained by combining both feedbacks becomes as shown in FIG. 7q.

Further, the peak of f0 is also suppressed lower than in the case where only voltage feedback is used, which is limited by the frequency characteristic e due to voltage feedback. And 8f0 where fo becomes high
Since the level of the frequency characteristic e due to voltage feedback at is high, the peak of the synthesized frequency characteristic q is high, and f
It can be seen that the lower o is, the lower the peak of the synthesized frequency characteristic q becomes.

Therefore, by making the feedback signal synthesis resistor 10 a variable resistor, the degree of the peak in fo can be set as desired by changing the resistance value.

According to the present invention, even when the feedback signal synthesis resistor is made variable in this way, the ratio of voltage feedback and current feedback before and after fo does not change. Depending on the type of speakers to be combined, the user's preferences, etc., it may be more convenient to use only voltage feedback. Furthermore, since the load current detection resistor 8 also results in a loss of output power, it is desirable to short-circuit it when current feedback is not used.

FIG. 8 shows a second embodiment of the present invention that achieves the above requirements in a very simple manner. This embodiment uses a switch 11. When used as a voltage-current feedback amplifier, the switch 11 is switched to the side of the feedback signal synthesis resistor 1o shown in FIG. It is designed so that it can be switched to the side. In this way, the voltage feedback amplifier and the voltage/current feedback amplifier can be switched simply by switching the switch 11.

Note that when the switch 11 as shown in FIG. 8 is used, when the switch 11 is switched to the ground side, the load on the feedback signal synthesis capacitor 9 is released, so the feedback signal synthesis capacitor 9 and the 1 degree resistor are It has the advantage of being unaffected.

In the above embodiment, the synthesized feedback signal is directly fed back to the inverting input of the amplifier 20, but even if it is fed back through the sound quality adjustment circuit 12 as shown in FIG. The present invention is effective.

Also, if the amplifier output is open, or if the switch 11
In order to solve the problem that the DC component is no longer fed back when the voltage is switched to the ground side, and that the feedback of the DC component is not sufficient even when used as a normal voltage/current feedback amplifier, we have developed the following. As shown in Fig. 9, the present invention is effective even when DC component feedback circuits 13 to 16 are added. Although the feedback signal is supplied to the feedback signal combining resistor 1o via a switch, the present generator F11 is also effective even if the signal from the load current detecting resistor 8 is further divided into resistors and supplied.

As described above, the present invention applies voltage feedback to the high range and current feedback to the low range, so when driving a speaker, the sound pressure is insufficient in the low range. can be compensated for, suppressing an increase in the high frequency characteristic in the case of only current feedback, and further suppressing the amount of compensation from becoming too large near the low frequency resonance frequency of the speaker.

In addition, by adding a switch, it is possible to easily switch between voltage and current feedback and voltage feedback, and when switching only to voltage feedback, it is not affected by the feedback signal synthesis capacitor and resistor, and the load current detection resistor An excellent effect can be obtained in that there is no loss of output power due to

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional voltage feedback amplifier, and Figure 2 is a circuit diagram of a conventional voltage feedback amplifier.
Figure 3 is a frequency characteristic diagram of a typical speaker, Figure 4 is a frequency characteristic diagram of the impedance of a typical speaker, and Figure 6 is a diagram of a conventional current feedback amplifier. 6 is a circuit diagram of the first embodiment of the present invention, FIG. 7 is a frequency characteristic diagram of the embodiment of FIG. 6, FIG. 8 is a circuit diagram of the second embodiment of the present invention, FIG. 9 is a circuit diagram of the fourth embodiment of the present invention. 1...Input end, 2...Amplification section, 3
...Hot side output end of amplifier section, 4...Speaker, 6゜6...Resistance divider circuit, 7...
...Cold side output terminal of the amplifier section, 8...--Load current detection resistor, 9...Capacitor for feedback signal synthesis, 10...Resistance for feedback signal synthesis, 11...・・・
・・Switch, 12・−°・Sound quality adjustment circuit, 13~16
...DC component feedback circuit 0 Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Figure 6 Figure 8 Figure 9

Claims (1)

[Scope of Claims] (1) An amplifier section, a resistance divider circuit that divides the output voltage of the amplifier section, and a load current detection resistor inserted between the cold side output terminal of the amplifier section and the output terminal; a feedback signal synthesis capacitor connected to the resistor divider circuit, and a feedback signal synthesis capacitor having one end connected to the cold side output end and the other end connected to the other end of the feedback signal synthesis capacitor. A voltage/current feedback amplifier 0 (2) comprising a resistor and configured to feed back a signal at a connection point 'of the feedback signal synthesis capacitor and the feedback signal synthesis resistor to the input side of the amplification section. The voltage-current feedback amplifier according to claim 1, further comprising a switch that switches and connects the cold side output end to the ground side and the feedback signal synthesis resistor side. (3) Scope of the Claims In claim 1, A voltage-current feedback amplifier characterized in that the division ratio of the resistance divider circuit is set to a value close to the ratio of the load resistance and the load current detection resistor.