JPS5949723B2 - Amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier device for driving a speaker in which the impedance of a connection cord connecting an amplifier and a speaker is reduced and the speaker drive impedance at the input terminal of the speaker is reduced to zero.

In general, it is desired that the output impedance of an acoustic regenerative amplifier is as small as possible in order to sufficiently absorb unnecessary distortion vibrations of a speaker and dampen a voice coil.

However, normally a connection cord is used between the output terminal of the HI-FI amplifier and the speaker input terminal.

The impedance of this connection cord increases the impedance of the amplifier side viewed from the input terminal of the speaker, that is, the voice coil braking impedance.

If you connect the amplifier and speaker with a connection cord of a certain length and compare the signal and its distortion voltage at the amplifier's output terminal and the speaker's input terminal, you will find that the signal voltage is not attenuated at all at the speaker input terminal and is faithful. It was confirmed that even though the signal was being transmitted, a larger distorted voltage was generated at the speaker input terminal.

In other words, the impedance of the connection cord is sufficiently small compared to the impedance of the speaker, so the signal from the amplifier is faithfully transmitted to the speaker input terminal, but the impedance is the same or larger than the output impedance of the amplifier.
This means that the distorted electromotive voltage generated by the speaker is not sufficiently transmitted to the amplifier side.

Therefore, in order to sufficiently reduce the impedance of the connection cord, negative feedback can be applied from the speaker input terminal, but in a normal unimpedance output amplifier, the reference potential point must be at one end of the speaker input terminal, so the input/output In practice, a very inconvenient means must be provided in which a common reference potential line must be brought from the output terminal of the amplifier to the input terminal of the speaker.

The present invention eliminates the above drawbacks, reduces the impedance of the connection cord by adding one connection wire without changing the reference potential point between the input and output in an amplifier with an unbalanced input/output format, and The present invention provides an amplifier device that also makes it possible to reduce the speaker drive impedance at the speaker input terminal to zero (completely constant voltage drive).

In FIG. 1, a main amplifier 10 and a voltage negative feedback circuit 11
constitutes a very general amplifier circuit 12 for driving a speaker.

13 and 14 are output terminals of the amplifier circuit 12, respectively.

In addition to the amplifier circuit 12, the present invention has a transfer characteristic of -A', the reference potential point is common to that of the main amplifier 10, and the input is connected from the output terminal 14 of the amplifier circuit 12 via a connection cord 15. Input terminal 17 of speaker 16 connected to
A feedback connection cord 18 is provided from the reference potential point side of the circuit, and an inverting feedback circuit 19 is provided which is supplied via a feedback terminal 24.

Usually, a connection cord for driving a speaker is a parallel type cord, and its equivalent impedance is represented by a parallel impedance between + and - and a series impedance element that is equal to the parallel impedance between the + and - lines.

However, in normal use, the length of the connection cord 15 is sufficiently short compared to the wavelength of the signal to be handled.

In addition, with respect to the characteristic impedance of the connection cord 15 with a general structure, the output impedance of the amplifier circuit 12 is approximately equal to the short circuit impedance, so the parallel impedance of the connection cord 15 can be sufficiently ignored, and isometrically the series resistance and inductance are As is well known, it is considered to be displayed only in minutes.

Therefore, the currents flowing to the + and - sides of the connection cord 15 are equal in phase and equal to the current flowing through the output terminal 14 of the amplifier circuit 12 and the input terminal 17 of the speaker 16.

It can be seen that an equivalent series impedance R corresponding to one side of the + side-measurement point connection cord is inserted between the output of the amplifier circuit 12 and the input of the speaker 16, respectively.

In FIG. 1, if the voltage generated between the input terminals 17 of the speaker 16 is eL, and the current flowing into the amplifier circuit 12 due to this voltage is it, then the connection cord 15 at the input terminal 17 of the speaker 16 is included. The impedance Zo on the amplifier circuit 12 side is expressed as follows.

On the other hand, iL is 1L=(eL-Aei)/(r□+2R)
-・・・・・・・・・(2) However, Aei: Open circuit output voltage of the amplifier circuit 12 A: Voltage gain of the main amplifier 10 ei: Input voltage of the main amplifier 10 ro: Obtained from the output impedance of the main amplifier 10 It will be done.

Now, if the voltage eL appearing at the input terminal 17 of the speaker 16 is caused only by the electromotive force from the speaker 16 side, then
It may be considered as an input signal e520 applied to the amplifier circuit 12.

At this time, the inter-terminal voltage e obtained at the output terminal 14 of the amplifier circuit 12.

is eo=2jtR, and the input voltage of the inverting feedback circuit 19 is -1LR.

However, the input impedance of the inverting feedback circuit 19 is sufficiently larger than the equivalent series impedance of the feedback connecting cord 18 and sufficiently smaller than the parallel impedance of the feedback connecting cord 18 to the ground, so that the voltage transmission loss can be ignored.

Therefore, the input voltage of the main amplifier 10 is e, = −(e L−2iLR)β−i LRA′−
” (3) From equations (1), (2), and (3).

Here, if we set A'=2β ((condition 1)) Zo=(
ro+2R)/(1+Aβ)...(5), and the output impedance Zo of this amplifier circuit 12 is the impedance 2R of the connection cord 15 for driving the speaker 6.
is equal to the reduced output impedance of the voltage negative feedback circuit 11 when voltage negative feedback is applied by including the output impedance of the main amplifier 10.

That is, a result equivalent to the case where voltage negative feedback is applied from the input terminal 17 of the speaker 6 is obtained.

Also, if A' is made very slightly larger than 2β, A'= −+
If set to 2β (condition 2)...
(6)''=1+Aβ, and the impedance 2R of the connection cord 15 of the speaker 6 can be completely canceled.

Furthermore, A' is r.

If /AR is made larger and set to 2 A'-X blindness + i + 2β (condition 3) Zo = 0
・・・・・・・・・・・・・・・
(7), and the speaker 16 can be driven with zero impedance.

In this case, the term r□/AR included in the setting conditions changes depending on the characteristics of the connection cord used, that is, the value of impedance R, so it cannot be set to satisfy all connection cords, but the impedance of the connection cord It is practically possible to set Zo÷0 for an average value of R or a connection code under a certain range of conditions.

In addition, the other constants A, β, and ro are values specific to the amplifier circuit that can be determined approximately constant at the time of designing the amplifier circuit, so the above ((conditions 1 and 2)) can be determined regardless of the connection code. .

Of course, the constants A and β. Since ro is a function of frequency and there is also a change in the phase term, it goes without saying that the value of A' must be set in consideration of the frequency characteristics.

Since the inverting feedback circuit 19 in FIG. 1 inputs the voltage generated between the lines of the connection cord 15 and inverts it, it is necessary to use a wideband transformer or an inverting amplifier.

When using an inverting amplifier, it is desirable that the amplifier has sufficient linearity, but the signal level handled here is much smaller than that handled by the voltage negative feedback circuit 11, and the value of A' is attenuation sufficiently smaller than 1. circuit, an inverting amplifier with sufficient linearity is easily possible.

For example, when comparing the signal voltage ed output from the voltage negative feedback circuit 11 with the signal voltage eA' output from the inversion feedback circuit 19 using numerical values used in a typical amplifier,
Therefore, A=1000 (60dB), β=1/3
0 (-30dB), ro=6Ω, R=0,1Ω, Z,=
In the case of a typical constant of 8Ω, the value of A' in the above ((Condition 3)) also becomes as follows, which shows that an extremely small signal is sufficient.

Therefore, it is possible to realize an inverting feedback circuit 19 with sufficiently good linearity.

A specific embodiment of the present invention will be described in detail below with reference to FIG.

Note that the same parts as in FIG. 1 are given the same reference numerals.

In FIG. 2, the first differential amplifier circuit 20 includes transistors Q1. This is a general differential amplifier circuit used in the first stage of normal power amplification consisting of Q2.

One transistor Q1 of this first differential amplifier circuit 20
The base electrode of the transistor Q2 is used as a signal input, and the other transistor Q2
The base electrode of is used as the input terminal of the voltage negative feedback circuit 11.

Further, the transistors Q3 and Q4 constitute a similar second differential amplifier circuit 21, and the collector electrode of one transistor Q3 is the collector electrode of the transistor Q1, and the collector electrode of the other transistor Q4 is the same as the transistor Q3.
The two collector electrodes are commonly connected to each other.

A first differential amplifier circuit 20 including the transistors Q□ and Q2 and the transistor Q3. The output of the second differential amplifier circuit 21 based on Q4 is connected in parallel, and the transistor
2, the input of the base electrode of transistor Q3 is inverted.

Therefore, in contrast to FIG. 1, in contrast to the voltage negative feedback circuit 11 coupled to the base electrode of the transistor Q2, the inverting feedback circuit 19 is coupled to the base electrode of the transistor Q4, thereby achieving an inversion effect. do.

Further, the network of the inverting feedback circuit 19 is connected to the resistor r1.
Although we have shown a resistor divider circuit using r2, as mentioned above, it is of course possible to use an impedance network with frequency characteristics in order to satisfy the setting conditions over a wide band, and this should be changed based on the design requirements. It is.

Furthermore, the terminating resistor r at the input terminal of the inverting feedback circuit 19 is used to optimize the terminal impedance to an appropriately low impedance in order to eliminate voltage transmission loss due to the grounding capacitance when a shielded wire is used as the feedback connection cord 18, for example. is necessary.

Furthermore, it goes without saying that the base electrode of the transistor Q3 of the second differential amplifier circuit 21 may be directly grounded, but as shown in the figure, the base electrode of the transistor Q3 of the voltage negative feedback circuit 11 may be connected to a bypassed point. By grounding, only the DC component is generated by the second differential amplifier circuit 21, which has the effect of further improving the DC stability of the entire amplifier device.

As described above, in the embodiment shown in FIG. 2, if no inverting feedback is applied, that is, if no feedback connection is made from the reference potential point side of the input terminal 17 of the speaker 16, it will not work simply like a conventional amplifier device. it is obvious.

Next, another embodiment of the present invention will be described with reference to FIG.

In the embodiment of FIG. 2, in contrast to negative feedback of the voltage applied to the base electrode of transistor Q2, inverted feedback is achieved by applying the voltage to the base electrode of transistor Q1.

However, since the impedance of the input signal source causes fluctuations in the feedback constant, it is impossible to set the conditions fixedly.

As a result, in FIG. 3, after the buffer amplifier 23 is provided between the base electrode and the input terminal of the transistor Q5 to make the impedance of the input signal source to the base circuit of the transistor Q5 constant, the feedback terminal 23 is connected to the base circuit of the transistor Q5. It has been established.

In this case, the feedback circuit constants may be configured assuming that the output of the loose lid amplifier 23 is grounded at its output impedance for the inverted feedback signal.

The above embodiments of the present invention have been explained by applying it to a device that drives a speaker, but the impedance removal effect of the connection cord can also be applied to an amplifier that must be driven at a constant voltage according to an input signal, such as a servo amplifier that drives a motor. As a result, a higher performance servo system can be realized.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the principle of the amplifying device of the present invention, Figure 2 is a circuit diagram showing one embodiment of the present invention, and Figure 3 is a circuit diagram showing another embodiment of the present invention. . 13...Input terminal, 14...Output terminal, 24...Feedback terminal, 18...Connection cord.

Claims (1)

[Claims] 1. One end of the input terminal of the input circuit of the amplifier circuit and one end of the output terminal of this amplifier circuit have an input terminal connected to a common ground, and the other end of the output terminal is connected to the input or intermediate amplification stage. In an amplifier device in which voltage negative feedback is inserted and connected, a feedback input terminal is provided that provides positive feedback with respect to the polarity of the output voltage of the amplifier circuit, and a connection cord is connected to the load from one end and the other end of the output terminal, respectively. By connecting a connection cord different from each of the connection cords from the ground side terminal of the load to the feedback input terminal, driving impedance can be reduced at the load end. Amplifying device.