JPH0253307A - Low frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To extract an output signal voltage over the maximum rated power voltage of an operational amplifier by connecting a voltage neutral level of bipolar power supplies to an input terminal so as to deflect the level in phase with an input signal. CONSTITUTION:Since a positive constant current circuit 16 comprising a current mirror circuit gives a prescribed current to a Zener diode 17 independently of a level of a voltage neutral point 15, the level of an emitter of a transistor(TR) 18 is always kept positive from the voltage neutral point 15 by a Zener voltage and the level of an emitter of a relevant TR is always kept negative from the voltage neutral point 15 by a Zener voltage. Therefore, a power source voltage of the OP amplifier 14 is hold constant for a neutral potential. On the other hand, since the neutral point level is given to an input terminal 11, the level is deflected in the same phase and the same amplitude as those of the input signal and an input voltage within the power supply voltage of the operational amplifier 14 only is always applied to the input terminal of the operational amplifier 14. Thus, an output voltage over the maximum rated power voltage of the operational amplifier is obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a low frequency amplification circuit.

2. Description of the Related Art In recent years, operational amplifiers (hereinafter referred to as OP amplifiers) have become very inexpensive, and there are many examples of low frequency amplification circuits using them.

An example of the conventional low frequency amplification circuit mentioned above will be described below with reference to one drawing.

FIG. 6 shows a low frequency amplification circuit using a conventional OP amplifier. In this example, a voltage follower circuit with a voltage gain of OdB will be described.

1 is the input terminal of this circuit, 3 is the output terminal, and 4.6 are the 10 and - power supply terminals of the OP amplifier, respectively. The inverting input terminal of the OP amplifier e is connected to the output terminal of the OP amplifier 6 (l), and a negative feedback of 10% is applied, so the output terminal 3 is always in phase with the input signal, with the same oscillation. An output signal appears.

Problems to be Solved by the Invention However, in the above-mentioned simple configuration, the maximum rated power supply voltage of the OP amplifier is about ±18 to ±257, so adding an input signal voltage higher than this will also result in a higher output. It is also not possible to extract the signal voltage.

In view of the above-mentioned problems, the present invention uses a general OP amplifier and adopts a configuration that can output an output signal voltage higher than the maximum rated power supply voltage. This provides a low frequency amplification 1flA circuit.

Means for Solving the Problems In order to solve the above problems, the low frequency amplifier circuit of the present invention is composed of an OP amplifier and a starting voltage power supply circuit with a floating voltage midpoint as a power supply for the OP amplifier. , ± the voltage midpoint of the constant voltage power supply is read directly to the input terminal.

Effect of the present invention With the above-described configuration, the input voltage and the output voltage of the OP amplifier are applied to the power supply terminal of the OP amplifier by amplifying the voltage midpoints of the ± constant voltage power supplies of the OP amplifier in the same phase with the input signal. By adjusting the output voltage to within the power supply voltage, it is possible to obtain an output voltage that is higher than the maximum rated power supply voltage of the OP amplifier. @Circuit can be realized.

Embodiment 1 A low frequency amplifier circuit according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an example in which a voltage 7-orer circuit is used as the low frequency amplifier circuit according to the first embodiment of the present invention.

In the figure, 11 is an input terminal, and 12 is an output terminal.

13 is a starting voltage power supply circuit with a floating voltage midpoint, and 14 is an OP amplifier. A voltage midpoint 16 of the starting voltage power supply circuit 13 is connected to the input terminal 11 .

The operation of the low frequency amplification circuit configured as described above will be explained below with reference to FIG.

16 is a constant current circuit on the + side using a current mirror circuit,
A constant current is passed through the Zener diode 17 regardless of the potential at the voltage midpoint 16. Therefore transistor 1
The emitter of 8 is always kept well above the voltage midpoint 15 by the Zener voltage.

Similarly, the constant voltage circuit 19 on the negative side is always maintained negative by the amount of Zener voltage below the voltage midpoint 16.

Therefore, the power supply voltage of the op amp 14 is kept constant with respect to the midpoint potential. On the other hand, since the midpoint potential is connected to the input terminal 11, it is the input signal.

It moves in the same phase and in the same root. Therefore, only an input voltage within the power supply voltage of the KOP amplifier 14 is normally applied to the input terminal of the OP amplifier 14. However, in the case of a voltage follower circuit, the output voltage of the 0P77 circuit also moves equal to the input voltage, so the output voltage is within the power supply voltage of the OP amplifier 14.

As described above, according to this embodiment, the OP amplifier and the power supply for the OP amplifier are constructed from a running voltage power supply circuit whose midpoint is floating, and by connecting the voltage midpoint of the running voltage power supply to the input terminal. As long as the withstand voltage of the transistor used in the starting voltage power supply allows, it is possible to obtain an output voltage that is higher than the maximum rated power supply voltage of the OP amplifier, and an input voltage that is higher than the maximum rated input voltage of the OP amplifier.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a low frequency amplification circuit showing a second embodiment of the present invention.

In the figure, 21 is a starting voltage power supply with a floating midpoint, 22 is an operational amplifier, and 1 or more have the same configuration as in FIG. 1. The difference from the configuration shown in FIG. 1 is that an output circuit 23 including a single-end push-pull connected output transistor is provided at the next stage of the oP amplifier output.

The operation of the low frequency amplifier circuit configured as described above will be described below.

24.25 is a bias resistor S26 is a bias circuit, 27
is a single-ended push-pull connected output transistor circuit, and 28 is an output terminal.

The output current of the OP amplifier is multiplied by the current increase factor of the 5IEPP output circuit and output from the output terminal. Therefore, the output current can be as large as the 5xpp circuit allows.

As described above, the maximum output current of a single circuit can be increased by providing an output circuit with a single-end push-pull connected output transistor at the next stage of the OP amplifier output, and the output impedance can also be reduced. can do.

A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a low frequency amplifier circuit showing a third embodiment of the present invention.

In the figure, numeral 31 has the same structure as in FIG. The difference from the configuration shown in FIG. 1 is that an attenuator 32 is provided in the feedback circuit from the output terminal.

Regarding the low frequency amplifier configured as above.

The operation will be explained below.

If the attenuation factor of the attenuator 32 is β, the voltage gain of one circuit is 1/β times. When voltage Ma1 is applied to the input terminal, an output voltage of Mai/β appears at the output terminal. On the other hand, the potential of the OP amplifier's power supply with respect to the ground is given by the output voltage of the constant voltage power supply being v2.

Since the voltage midpoint is set by my i, it becomes my + vz. Now, if we ignore the V□ of the transistor, what are the conditions under which the signal output does not clip the voltage?

My/β≦Ma1 + v2 It is. Also, the above formula is the output voltage ma. If you rewrite it as.

Ma. = My i/β that's why.

Ma0≦βma. +vz becomes.

Therefore, one circuit can have a voltage gain within the range that satisfies the above conditions.

As described above, by providing an attenuator in the feedback circuit from the output terminal, a single circuit can have a voltage gain.

A fourth embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows a low frequency amplifier circuit showing a fourth embodiment of the present invention.

In the figure, numeral 41 has the same structure as in FIG. 1. The difference from the configuration shown in FIG. 1 is that a simple buffer 42 is provided between the input terminal and the voltage midpoint of the starting voltage power source with the midpoint floating.

The operation of the low frequency amplifier circuit configured as described above will be explained below.

In the configuration shown in FIG. 1, since the input impedance at the voltage midpoint is relatively low, the input impedance as a low frequency amplification circuit cannot be increased. Therefore, the input impedance can be increased by connecting the voltage midpoint to the input terminal via a buffer.

As described above, the input impedance can be increased by providing the buffer between the input terminal and the midpoint of the starting voltage power supply with the midpoint floating.

In the first embodiment, the starting voltage power supply 13 with the voltage midpoint floating uses a constant current circuit based on a current mirror circuit, and uses a Zener diode as the reference voltage element. Voltage power supply 413 may have other configurations.

Further, in the second embodiment, the output circuit 23 having a single-ended push-connected output transistor includes a transistor in a bias circuit.

In addition, although a bipolar medium transistor was used as the output transistor, the output circuit 23 equipped with a single-ended push-pull connected output transistor requires other elements such as a diode and other configurations in the bias circuit, and the output transistor is a MOS- Other configurations such as a field element such as FIET and a three-stage Darlington connection may also be used.

Further, in the fourth embodiment, the buffer 42 uses a complementary biporter transistor.

Also, a diode was used in the bias circuit.

The buffer 42 is MOS-FICT, junction type FIT, etc.
It's still a bias circuit, but it uses other elements such as transistors,
Other configurations may also be used.

Also, the second. Third. The fourth embodiment may be appropriately combined with the first embodiment.

Effects of the Invention As described above, the present invention is composed of an OP amplifier and a running voltage power supply circuit whose midpoint is floating as a power supply for the OP amplifier, and the voltage midpoint of the ± constant voltage power supply is connected to the input terminal. In some cases, the output voltage may exceed the maximum rated power supply voltage of the OP amplifier.

It is possible to realize a low frequency amplifier 11III circuit having a set input that is higher than the maximum rated common mode input voltage of the OP amplifier.

[Brief explanation of the drawing]

1 is a circuit diagram of a low frequency amplifier circuit according to a first embodiment of the present invention, FIG. 2 is a circuit diagram of a low frequency amplifier circuit according to a second embodiment of the present invention, and FIG. 3 is a circuit diagram of a low frequency amplifier circuit according to a second embodiment of the present invention. FIG. 4 is a circuit diagram of three low frequency amplifier circuits in the fourth embodiment of the present invention, and FIG. 6 is a circuit diagram of the low frequency amplifier circuit in the fourth embodiment of the present invention.
The figure is a circuit diagram of a conventional low frequency amplifier. 11...Input terminal, 12...Output terminal, 13
...Starting voltage power supply circuit, 14...OP amplifier, 15...Voltage midpoint. Name of agent Patent attorney Shigetaka Awano and one other person No. 1 Fig. 3 Fig. 1/-Jinriki legitimate child 11-Ichimika Tatsuyoshi 13- Dosei no Kite-wa 57 + Mendori/4-- OP amplifier f5 -'Mr. E. Diagram

Claims (1)

[Claims] It consists of an operational amplifier and a ± constant voltage power supply circuit whose midpoint is floating as the power supply for this operational amplifier.By connecting the voltage midpoint of the ±constant voltage power supply to the input terminal, the ±constant voltage power supply can be input. A low frequency amplification circuit characterized by making the amplitude in phase with the signal.