JP2558965B2 - Wideband DC amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband DC amplifier used in an oscilloscope or the like.

[0002]

2. Description of the Related Art Heretofore, as a wide band DC amplifier of this type, there has been known a structure in which transistors having different conductor characteristics are used in combination in order to obtain an output DC level substantially equal to an arbitrary input DC level.

The conventional wide band DC amplifier will be described below with reference to the drawings. FIG. 2 is a circuit diagram showing the conventional wide band DC amplifier. As shown in FIG.
The input terminal 51 has an NPN transistor 52 and a PN
The bases of P-type transistors 53 are connected, and the connection point between the input terminal 51 and the bases of the transistors 52 and 53 is grounded via a resistor 54. The collector of the transistor 52 is connected to the positive power supply (+ E), and the emitter is connected to the negative power supply (-E) via the resistor 55.
The collector of the transistor 53 is connected to the negative power source (-E), and the emitter is connected to the positive power source (+ E) via the resistor 56. The emitter of the transistor 52 is connected to the base of a PNP type transistor 57, and the transistor 5
The emitter of 3 is connected to the base of an NPN type transistor 58. The collector of the transistor 57 is connected to the negative power source (-E), and the emitter is connected to the positive power source (+ E) via the resistor 59. The collector of the transistor 58 is connected to the positive power supply (+ E), and the emitter is the resistor 60.
Is connected to the negative power source (-E) via. The emitters of the transistors 57 and 58 are connected to the output terminal 63 via the resistors 61 and 62.

In the above structure, when an input signal is applied to the input terminal 51, the in-phase signal component is output to the emitter of the transistor 52, and the in-phase signal component is output to the emitter of the transistor 53. Transistor 52
Is output to the output terminal 63 via the transistor 57. Similarly, the output signal of the transistor 53 is output to the output terminal 63 via the transistor 58. The signal obtained at the output terminal 63 is the transistors 57 and 58.
Output signals are combined and output, and a signal similar to the input signal is obtained.

As described above, two sets of different conductor characteristics for the collector-grounded operation, that is, NPN-type and PNP-type transistors 52 and 53 and PNP-type and NPN-type transistors 57 and 58 are used in combination. By doing so, it is possible to maintain the DC level on the output side at substantially the same value as the DC level on the input side. Therefore, it can be said that the circuit configuration is simple and practical in terms of input and output DC levels and low-frequency signal amplification.

[0006]

Generally, when evaluating a wide band DC amplifier, it is possible to estimate from low frequency to high frequency characteristics by grasping the transmission state of rising and falling waveforms of a high speed pulse signal. Therefore, reproduction fidelity of the input waveform and the output waveform of the high-speed pulse signal is very important in evaluating the wide band DC amplifier. When amplifying a high-speed pulse signal, the above-described conventional collector grounding is often used because it has a simple configuration and can easily obtain the required characteristics.

However, in order to drive the capacitance that is always present in the input and output of the circuit, in order to amplify the pulse signal in the positive direction, that is, the signal changing to the more positive side, the NPN type is seen from the conductor characteristics. A transistor is suitable, and a PNP transistor is suitable for amplifying a signal in the negative direction opposite thereto, that is, a signal changing to a more negative side in terms of conductor characteristics. Therefore, in the circuit configuration of the conventional wide band DC amplifier, transistors having different conductor characteristics are combined, but when the high frequency signal is amplified without utilizing the above characteristics, the circuit configuration is simple but high frequency operation is performed. There was a problem of being restricted in terms of aspects.

The present invention solves such a conventional problem, has a simple circuit configuration, can reduce the input / output DC level difference, and can improve the low-frequency amplification characteristics including DC. Another object of the present invention is to provide a broadband DC amplifier capable of improving high frequency characteristics by taking advantage of transistor conductor characteristics.

[0009]

SUMMARY OF THE INVENTION To achieve the above object, the present invention grounds the collectors of NPN and PNP type transistors having different conductor characteristics, connects each base, and applies an input signal simultaneously. The first amplifier for extracting the output from each emitter and the collectors of NPN and PNP type transistors having different conductor characteristics are grounded,
A second amplifier for applying an input to the base, connecting the respective emitters, and taking out a combined single output, wherein the emitter of each transistor of the first amplifier has a conductor characteristic in the second amplifier. The base of the same transistor is connected via a capacitor, and the emitters of the transistors of the first amplifier are connected via resistors to the bases of the transistors of the second amplifier having different conductor characteristics.

[0010]

Therefore, according to the present invention, since two sets of collector-grounded amplifiers are formed by combining NPN and PNP type transistors having different conductor characteristics from each other, all the DC signal components given from the input terminal can be obtained. Transmit,
The difference between the input and output DC level can be reduced. Further, by connecting the transistors having the same conductor characteristic in the two sets of amplifiers via the capacitor, the conductor characteristic of the transistor can be utilized.

[0011]

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

FIG. 1 is a circuit diagram showing a wide band DC amplifier according to an embodiment of the present invention. As shown in FIG. 1, an NPN transistor 4 is connected to an input terminal 1 through resistors 2 and 3.
And the respective bases of the PNP type transistor 5 are connected. The connection point between the input terminal 1 and the resistors 2 and 3 is grounded via the resistor 6, and the base of the transistor 5 is connected via the resistor 7 between the positive power source (+ E) and the negative power source (-E). 8 is connected. The collector of the transistor 4 is connected to the positive power supply (+ E), and the emitter is connected to the negative power supply (-E) via the resistor 9. The collector of the transistor 5 is connected to the negative power supply (-E), and the emitter is connected to the positive power supply (+ E) via the resistor 10. NPN
-Type transistor 4 has NPN with the same conductor characteristics as the emitter
Of the PNP type transistor 5 is connected to the base of the PNP type transistor 11 via a capacitor 12 and a resistor 13. The emitter of the PNP type transistor 5 is connected to a PNP type transistor 14 having the same conductor characteristics via a capacitor 15 and a resistor 16. The emitter of the NPN transistor 4 has a resistor 17 at the base of the PNP transistor 14 having different conductor characteristics.
The emitter of the PNP transistor 5 is connected to the base of the NPN transistor 11 having different conductor characteristics via the resistor 18. The collector of the transistor 11 is connected to the positive power supply (+ E), and the emitter is connected to the negative power supply (-E) via the resistor 19.
The collector of the transistor 14 is connected to the negative power supply (-E), and the emitter is connected to the positive power supply (+ E) via the resistor 20. The emitters of the transistors 11 and 14 are connected to the output terminal 23 via the resistors 21 and 22. A first amplifier including the NPN type transistor 4 and the PNP type transistor 5 is configured, and a second amplifier including the NPN type transistor 11 and the PNP type transistor 14 is configured.

The operation of the above arrangement will be described below. When a signal is applied to input terminal 1, NP
A signal is given to the base of the N-type transistor 4, and is output from the emitter of the N-type transistor 4 to the base of the collector-grounded PNP-type transistor 14 through the resistor 17. As a result, a signal is output from the emitter of the transistor 14 to the output terminal 23. Since all paths of the signal, that is, the input terminal 1 to the output terminal 23 via the resistor 17 are all directly coupled, all input signal components from the given direct current are transmitted. Further, since the NPN type transistor 4 and the PNP type transistor 14 are combined,
Although the DC voltage changes in the middle of the input DC level, the DC level from the input terminal 1 to the output terminal 23 is almost the same as the input, and the difference is very small. On the other hand, when a signal is applied to the input terminal 1 as described above, P
A signal is given to the base of the NP type transistor 5, and is output from the emitter of the NP type transistor 5 to the base of the collector-grounded NPN type transistor 11 through the resistor 18. As a result, a signal is transmitted from the emitter of the transistor 11 to the output terminal 23. Also in this case, the DC level from the input terminal 1 to the output terminal 23 is almost the same as the input for the same reason as above.

As described above, in amplifying a low-frequency signal including direct current, it is possible to effectively operate with a simple circuit configuration.

Next, the flow of the high frequency signal passing through the transistors 4, 14, 5 and 11 when the capacitors 12 and 15 are not used will be described.

When a high-speed pulse signal is applied to the input terminal 1 in the transmission system including the NPN-type transistor 4 and the PNP-type transistor 14, the NPN-type transistor 4 outputs a signal in the positive direction as described above, that is, When it changes to a more positive side, it operates favorably from the viewpoint of the conductor characteristics, but the PNP transistor 14 in the next stage has a signal direction which is unfavorable from the viewpoint of high frequency operation. The configuration is not suitable.
In the case of a negative direction signal, the transistor 4 is an NPN.
However, the transistor 14 is of the PNP type and has a preferable signal direction, but the overall configuration is not good. On the other hand, in the transmission system including the PNP-type transistor 5 and the NPN-type transistor 11, the PNP-type transistor 5 is a conductor when the applied signal changes to the negative direction signal, that is, to the minus side, as described above. Although it operates favorably in view of the characteristics, the NPN transistor 11 in the next stage has a signal direction that is unfavorable in terms of high-frequency operation, so that the overall configuration is not suitable for amplifying a high-speed pulse signal. Further, when the signal is a positive direction signal, since the transistor 5 is of the PNP type, the operation becomes unfavorable, and the transistor 11 becomes N-type.
Since it is a PN type, it is a preferable operation direction, but the overall configuration is not good.

As described above, in the configuration in which the capacitors 12 and 15 are not used, the goodness of the transistor conductor characteristics cannot be positively utilized in the positive and negative amplification of the high-speed pulse as a whole. The limitation of the combination of transistor conductor characteristics due to the circuit configuration is improved by using the capacitors 12 and 15, and the high frequency characteristics are improved, which will be described below. In order to realize the required high-speed pulse / high-frequency characteristics, focusing only on the system that amplifies high-frequency components, NPN transistor 4
Is transmitted to the base of the NPN transistor 11 via the capacitor 12. This is because when the grounded collector is used for the purpose of amplifying a high-speed pulse signal as described above, a positive direction signal, that is, a signal changing to a more positive side is transmitted by an NPN transistor as a conductor characteristic. Therefore, this transistor 4
The amplification paths of 11 and 11 satisfy the condition. On the other hand, the output of the PNP transistor 5 is the capacitor 1
5 to the base of a PNP type transistor 14. As described above, the PNP-type transistor is suitable for amplifying a signal in the negative direction, that is, a signal changing to the negative side.
The amplification paths of 14 and 14 satisfy the conditions.

In summary of the above, the capacitors 12 and 15
In the high-frequency signal / high-speed pulse amplification, the transistor conductors are connected by the paths of the NPN transistors 4 and 11 for a positive direction signal and the paths of the PNP transistors 5 and 14 for a negative direction signal. The circuit configuration takes advantage of the characteristics, and the high frequency characteristics can be improved. At the same time, it means that the high frequency component is amplified regardless of the operation of the DC conversion, and an output DC level value substantially the same as that can be obtained from any input DC level.
The gain between the input and the output is divided into a low frequency gain determined by the resistors 17 and 18 and a high frequency gain determined by the capacitors 12 and 15, respectively. , 14 and the output terminal 23 in which the emitters are combined, the configuration is simple and a comprehensive wide band DC amplifier can be realized.

A resistor 1 in series with the capacitors 12 and 15
Reference numerals 3 and 16 are used to correct high frequency components and suppress unnecessary oscillation.

[0020]

As described above, according to the present invention, two sets of collector-grounded amplifiers are constructed by combining NPN and PNP type transistors having different conductor characteristics from each other, that is, from the entire signal path, that is, from the input terminal. Considering the output terminals as well, since all are configured by direct coupling, it is possible to transmit all the DC signal components given from the input terminals and reduce the input / output DC level difference. Therefore, it is possible to improve low-frequency amplification characteristics including direct current. Further, by connecting the transistors having the same conductor characteristic in the two sets of amplifiers via the capacitor, the conductor characteristic of the transistor can be utilized. Therefore,
High frequency characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a wide band DC amplifier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional wide band DC amplifier.

[Explanation of symbols]

 1 Input terminal 4 NPN type transistor 5 PNP type transistor 11 NPN type transistor 12 Capacitor 14 PNP type transistor 15 Capacitor 23 Output terminal

Claims (1)

(57) [Claims] 1. A first transistor in which the collectors of transistors having different conductor characteristics are grounded, the respective bases are connected to apply an input signal at the same time, and respective outputs are taken out from the respective emitters.
And a second amplifier in which the collectors of transistors having different conductor characteristics are grounded, an input is applied to the base, each emitter is connected, and a combined single output is taken out. The emitter of each transistor of the amplifier is connected to the base of the transistor having the same conductor characteristic in the second amplifier via a capacitor, and the emitter of each transistor of the first amplifier is connected to the second amplifier.
Wide-band DC amplifier connected to the bases of transistors with different conductor characteristics in the amplifier of the above through a resistor.