JPS6130765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier clamp circuit.
In an amplifier that doubles the gain of the other amplifier when one of the connected amplifiers clips, it is possible to suppress distortion that occurs at the joint by smoothly connecting the clip and gain change. purpose. .

The inventors previously filed a patent application No. 54-82970,
In order to increase the output of the amplifier and increase its efficiency, when the output level is within the power supply voltage, the normal BTL is used.
We proposed an amplifier that operates as an amplifier and increases one power supply voltage by following the output level in a range where the level exceeds the power supply voltage.

An example is shown in FIG.

In Figure 1, 1 is a positive phase input terminal, 2 is an amplifier, 3 is a diode, 4 is a capacitor, 5 is a power supply driver, 6 is a negative phase input terminal, 7 is an amplifier, 8 is a diode, 9 is a capacitor, 10 is the power supply drive unit, 1
1 is a load, and 12 is a power supply.

In Figure 1, when the output level is within a certain range below the power supply voltage, amplifiers 2 and 7 are used as normal BTL
Acts as an amplifier, with diodes 3 and 8 respectively.
A power supply voltage is supplied from a power supply 12 through the power supply.

Next, when the output level exceeds the above range, one of the amplifiers 2 and 7 will clip due to the load voltage, but the power supply voltage of the other amplifier will exceed the power supply driver 5.
In addition, since the capacitor 4 or 9 is driven in the positive direction at 10, it is lifted in the positive direction and continues amplification without clipping, reaching the level at which the power supply driver 5 or 10 clips, that is, the power supply 1
It is possible to obtain an output up to twice the voltage of 2.

At this time, at the same time as one amplifier clips in the load direction, the gain of the other amplifier becomes substantially 2.
If it were to double, there should be no distortion in the BTL output.

In the aforementioned Japanese Patent Application No. 54-82970, a circuit as shown in FIG. 2 has already been proposed as a method of obtaining such characteristics.

In Fig. 2, 13 is an input terminal, 14 is an amplifier, 15 is a first amplifier that divides 2 to 5 of the circuit in Fig. 1, and 16, 17, and 18 are input resistances and feedback resistances of the first amplifier, respectively. and a grounding resistor, 19 a second amplifier comprising circuits 7 to 10 of FIG.
0, 21, and 22 are the input resistance, feedback resistance, and grounding resistance of the second amplifier, respectively; 23 is the resistance 24;
an amplifier, 26, which together with 25 constitutes a phase inversion circuit;
27 is a general feedback resistor.

In Figure 2, resistors 16-18, 20-2
2, the values of 24 to 27 are R16, R17, respectively.
By setting R18, R20, R21, R22, R24, R26, and R27, and setting (R17+R18)/R18=R21/R20, amplifiers 15 and 19 can be used in the same way with opposite phases, and further, R26=R27・If R24/R25, the output signals of amplifiers 15 and 19 are fed back in opposite phases by the same amount, so in the end, amplifier 1
A signal corresponding to the voltage between outputs 5 and 19 is fed back.

So, for example, if the output of amplifier 19 is clipped at the negative power supply voltage, there will be no signal fed back through resistor 27, so the total amount of feedback will be halved, and as a result, the gain of amplifier 15 will essentially double. From input terminal 13, amplifiers 15 and 19
The gain between the output ends of is kept constant.

The same applies even if the amplifier 15 clips.

When a sine wave is applied to the input terminal 13 in this way, voltage waveforms as shown in FIG. 3a and b are obtained at the output terminals of the amplifiers 15 and 19, and when they are combined, the amplifier Between the output terminals 15 and 19, an output signal corresponding to the original sine wave is obtained.

However, in the configuration shown in FIG. 2, the feedback amount when the clip level is above the clip level is half of the feedback amount when the clip level is below the clip level, but since the gain of the amplifier 14 is finite, this feedback amount is Due to the change, the gain from the input terminal 13 to the output terminals of the amplifiers 15 and 19 changes to some extent, which causes a problem in that it appears as distortion.

In order to solve the above problems, the present invention adds a clamp circuit to such an amplifier, and the clamp circuit eliminates gain change and suppresses distortion.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 4, 11 to 27 correspond to the same numbers in FIG. 2, and 26 to 31 are clamp diodes and resistors.

In Figure 4, the value of the resistor 31 is set as R31, and the conditions of R16=R20, R31/R22=R20/R21 R31+R22=R18 are satisfied in addition to the above-mentioned condition (R17+R18)/R18=R21/R20. When each resistance value is set, clamp circuits 29 to 31 and resistors 16 to
The operation in which the output of one amplifier is clamped in the negative direction and the gain of the other amplifier is doubled at the same time with only the first and second amplifiers 15 and 19 including 18, 20 and 22 will be described below. establish

First, when the output voltage of the pre-stage amplifier 14 moves in the negative direction, the diode 29 does not conduct until a certain level, so the positive phase input terminal of the first amplifier 15 moves following the pre-stage output voltage, and the second The negative phase input terminal of the amplifier 19 is at ground potential. Then, when the previous stage output voltage reaches the conduction level of the diode 29,
Since the diode 29 is conductive, the first amplifier 1
5 is level clamped, and at the same time, the resistor 16 is connected to the input resistor 2 of the second amplifier 29.
0 in parallel, the gain of the second amplifier 19 is doubled.

Next, when the output voltage of the preamplifier 14 moves in the positive direction, the diode 30 does not conduct until a certain level, so the negative phase input terminal of the first amplifier 15 moves following the preamplifier output voltage, and the The positive phase input terminal of the second amplifier 19 is at ground potential. and,
When the pre-stage output voltage reaches the conduction level of the diode 30, the diode 30 becomes conductive, so the pre-stage output voltage is connected to the positive phase input of the second amplifier 19 through the resistor
The voltage divided by 1 and 22 is applied, but the gain of the second amplifier output due to this circuit is [R22/(R31+R22)]・[(R20+R21)/
R20]=R21/R20 cancels out the gain -R21/R20 due to the path from the input resistor 20 and becomes zero, so the second amplifier is clamped here.

At this time, since the resistors 31 and 22 are connected in parallel with the resistor 18, the gain of the first amplifier 15 is doubled.

Furthermore, by setting the output levels of the first and second amplifiers clamped by the above-mentioned clamp circuits just before the clip levels caused by their respective power supply voltages, it is possible to achieve this without substantially impairing the power supply utilization rate. , effective clamping and stretching operations are performed.

In reality, since there is a series resistance component in the diodes 29 and 30, errors will be reduced if the values of the resistors 16 and 31 are corrected to be smaller by that amount. Also, even if the diode 30 becomes conductive and the resistors 31 and 22 are connected in parallel to the resistor 18, strictly speaking, the gain of the first amplifier will not double, but will be slightly lower than double, so the resistor 17,1
If the value of 8 is set a little larger, the error will be smaller.

In the embodiment shown in FIG. 4, the positive side of the power supply voltage of the first and second amplifiers is raised, but in the opposite case, the polarities of the diodes 29 and 30 may be switched. .

As described above, according to the present invention, the clamp circuit clamps one of the first and second amplifiers and at the same time doubles the gain of the other one, so that the total amount of feedback increases before the clamp. and will not change later, so that distortion can be sufficiently suppressed.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a conventional example, FIG. 3 is an operation explanatory diagram of the conventional example, and FIG. 4 is a circuit diagram of an embodiment of the present invention. 3, 8...Diode, 4,9...Capacitor, 12...Power supply, 14...Previous stage, 15...First stage
amplifier, 16... first input resistor, 17... first feedback resistor, 18... first grounding resistor, 19...
...Second amplifier, 20...Second input resistor, 21
...Second feedback resistance, 22...Second grounding resistance,
23, 24, 25... Phase inversion circuit, 26, 27
... Adder circuit, 29 ... First diode, 30
...Second diode, 31...Clamp resistor.

Claims (1)

[Claims] 1. A front stage, a positive phase input terminal, a negative phase input terminal, and an output terminal, and a first input resistor is connected between the output terminal of the front stage and the positive phase input terminal, A first amplifier having a first feedback resistor connected between the output terminal and the negative phase input terminal, and a first grounding resistor connected between the negative phase input terminal and the ground; It has a negative phase input terminal and an output terminal, a second input resistor is connected between the output stage of the preceding stage and the negative phase input terminal, and a second feedback resistor is connected between the output terminal and the negative phase input terminal. a second amplifier to which a resistor is connected and a second grounding resistor connected between the positive-sequence power terminal and ground; a phase inversion circuit for inverting the output voltage of the second amplifier; and an output of the phase inversion circuit. voltage and the output voltage of the first amplifier and the first
and an adder circuit that adds the output voltages of the first and second amplifiers and feeds it back to the input terminal of the first stage amplifier, and the output is taken out between the output terminals of the first and second amplifiers. 1st
between the positive phase input terminal of the amplifier and the negative phase input terminal of the amplifier, and between the negative phase input terminal of the first amplifier and the positive phase input terminal of the second amplifier, respectively. An amplifier clamp circuit consisting of connected diodes. 2. The amplifier clamp circuit according to claim 1, characterized in that a clamp resistor is connected in series to the second diode. 3. The amplifier clamp circuit according to claim 1, characterized in that the clamp level by the clamp circuit is set near the clip level controlled by the power supply voltages of the first and second amplifiers. 4 In claim 2, the values of the first input resistance and the second input resistance are set to be approximately equal, and the sum of the clamp resistance and the second grounding resistance and the value of the first grounding resistance are set to be approximately equal. The amplifier clamp circuit is further characterized in that the ratio of the second input resistance to the second feedback resistance and the ratio of the clamp resistance to the second grounding resistance are set to be approximately equal. 5 In claim 4, the series resistance component of the first diode is included in the first input resistance,
A clamp circuit for an amplifier, characterized in that a series resistance component of a second diode is included in the clamp resistance. 6 In claim 4, the first and second amplifiers are supplied with a power supply voltage from a positive or negative power supply via a diode, and
In a range where the output voltage of the amplifier exceeds a certain level near the power supply voltage, by driving the other end of the capacitor whose one end is connected to the connection point between the first and second amplifiers and the diode. ,
An amplifier clamp circuit configured to increase the power supply voltage at the connection point.