JP2573782Y2 - Broadband 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 wide-band amplifier, and more particularly to a wide-band amplifier suitable for use as a vertical-axis input amplifier of an oscilloscope. The present invention relates to widening the bandwidth of a vertical axis amplifier or the like of an oscilloscope. SUMMARY OF THE INVENTION In view of the above points, the present invention aims to improve the DC drift characteristics and compensate for the fluctuation of the operating point due to a temperature change, thereby widening the band.

[0002]

2. Description of the Related Art A circuit in which a temperature drift is improved by using a dual FET will be described with reference to FIG. In the figure, 1
Is a terminal to which an input signal is applied. The signal applied to this terminal 1 is output from an output terminal 3 through a field effect transistor (hereinafter referred to as FET) 2 constituting a source follower. Here, the FET 4 is an FET that compensates for a bias variation due to a temperature change of the FET 2. If the thermal characteristics of FET2 and FET4 do not match, drift due to temperature change cannot be completely corrected. Regarding the high frequency characteristics, between the gate and the drain of the FET 2 and between the gate and the drain
It is difficult to obtain a constant gain up to a high frequency due to capacitance between sources. In addition, since the impedance of the FET 4 to the negative power supply is capacitive, it is a loss factor in a high frequency range.
Therefore, a conventional technique with improved DC stability will be described with reference to FIG. In the figure, a signal applied to an input terminal 5 is divided by a capacitor 6 into a low frequency component and a high frequency component. In this case, the low frequency amplification is performed by the operational amplifier 8. Here, since the gain of the operational amplifier 8 has a very large value, for example, 100 dB, the dual F shown in FIG.
It is possible to obtain much better DC stability than the ET circuit. The high frequency amplification is performed by a source follower using the FET 7.

[0003]

[Problems to be solved by the invention]
There is a disadvantage that the high frequency characteristics are deteriorated due to the feedback capacitance and the capacitive impedance of the bias stabilizing circuit. In order to solve these drawbacks, the present invention avoids the capacitive impedance of the bias stabilization circuit, compensates for the high frequency characteristics, reduces the DC drift, and, in addition to the conventional technique, stabilizes the drift due to the bias fluctuation by the independent circuit. The aim is to obtain a broadband amplifier.

[0004]

FIG. 1 is a view showing the present invention. In order to achieve the above-mentioned object, the present invention aims at avoiding a temperature drift of an FET by amplifying a DC region by an operational amplifier 8. In addition, with respect to the deterioration of the high-frequency characteristics, the frequency band at which the frequency characteristics start to fall is provided with an AC bypass circuit 9, passed through a source follower, and added to a subsequent stage by a grounded base circuit 10 to improve the frequency band. Things.

[0005]

The operation of the present invention will be described. Operational amplifier 8
Since the gain of the DC amplifier constituted by the above is extremely large in the DC region, the output accurately follows the input. Therefore, the drift due to the temperature change can be determined by the performance of the operational amplifier 8. In addition, since the grounded base circuit 10 has a high impedance for both the emitter and the collector, the DC range from the operational amplifier 8 and the high range from the AC bypass circuit 9 can be efficiently added.

[0006]

FIG. 1 shows an embodiment of the broadband amplifier according to the present invention. In the figure, 5 is an input terminal to which an input signal is applied, 6 is a DC cut capacitor, and 7 is an FET. The FET 7 constitutes a source follower circuit which is AC-coupled to the input terminal 5 via a capacitor 6. Reference numeral 8 denotes a DC amplifier DC-coupled to the input terminal 5, and reference numeral 9 denotes a series circuit of a variable capacitance element and a resistor, which forms an AC bypass circuit. Reference numeral 10 denotes a common-base amplifier including a transistor 11, and reference numeral 12 denotes an output transistor to which a signal of the common-base amplifier 10 is applied to a base, which constitutes an emitter follower. Reference numeral 13 denotes a negative feedback path connecting the emitter of the output transistor 12 and the inverting input terminal (-) of the DC amplifier 8. Hereinafter, this operation will be described. The input signal applied to the input terminal 5 is applied to the operational amplifier 8 in the DC region by the DC cut capacitor 6 and to the F component in the AC region.
ET 7 and the AC bypass circuit 9. The AC bypass circuit can adjust the amount of addition to the output by varying the capacitance with a series of a variable capacitance element and a resistor. On the other hand, the DC region amplified by the operational amplifier 8 is applied to the grounded base amplifier 10 together with the AC bypass. The output of the grounded base amplifier 10 is added with a correction in a DC range and a high range, and is added on the input side of the output transistor 12. Here, since the emitter and the collector of the common base amplifier 10 have high impedance, addition is possible.
The feature of the present invention is that the temperature drift performance is
It is determined by the ability. FET7 is limited by DC characteristics
Because it is released, you can choose a variety with a large gm
It is advantageous for high frequency characteristics. Gate Dore
Between the gate and the source
Output drop is added to the output from the source follower
That can be compensated. Furthermore, in this embodiment,
High-frequency characteristics due to gm change due to degree
Therefore, it can be corrected.

[0007]

By determining the DC characteristics by the performance of the operational amplifier, it is possible to select a high gmFET which is disadvantageous in terms of DC for the FET, which is advantageous in terms of high frequency, and can realize a wide band. In addition, there is a problem with the conventional technology regarding high frequency characteristics.
The attenuation due to the gate-source capacitance was
This can be avoided by adding a high frequency component to the side.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the present invention.

FIG. 2 is a circuit diagram of a conventional technique.

FIG. 3 is a circuit diagram of a conventional technique. 7 FET 8 Operational amplifier 9 AC bypass circuit 10 Base ground circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 1/42 H03F 3/50 H03F 3/68

Claims (1)

(57) [Scope of request for utility model registration] A DC cut means connected in series between an input terminal and a source follower FET;
T, an operational amplifier DC-coupled to the input terminal, a means for adding the output of the source follower FET and the output of the operational amplifier, and a bypass for a high-frequency signal connecting the gate electrode of the source follower FET and the input of the adding means. Broadband amplifier consisting of circuits.