JPH0695609B2 - Wideband DC amplifier - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband DC amplifier used for driving a cathode ray tube (CRT) of an oscilloscope, and more particularly for driving a vertical deflection plate.

2. Prior Art FIG. 2 shows the configuration of a conventional vertical output amplifier. In FIG. 2, 51 and 61 are a pair of input terminals, and 65 and 66 are transistors which act as high frequency amplification, and a differential input signal is applied to the bases of the transistors 65 and 66. Transistor 65,66
The emitter of is connected through an emitter-coupled resistor 56,
In addition, it is connected to the voltage source via resistors 57 and 58 having the same resistance value. The collectors of the transistors 65 and 66 are connected to the emitters of the base-grounded transistors 67 and 68, the bases of the transistors 67 and 68 are connected to the base bias voltage, and the collectors are connected to appropriate voltages via the load resistors 71 and 72. Connected to the source. 69 and 70 are output terminals.

Next, the operation of the above conventional example will be described.

The differential input signals to the input terminals 51 and 61 are transistor pairs 65 and 66.
Applied to the output terminal 69, the difference signal is amplified through the emitter-coupled resistor 56 and transmitted by the transistor pair 67, 68.
Given to 70 as a differential output.

The problem to be solved by the invention is that an amplifier of this kind normally supplies sufficient quiescent current to the output stage of the amplifier in order to charge the capacitance of the deflection plate for the highest frequency and maximum amplitude of the applied input signal. There is a need. For this reason, the power consumption in the grounded-emitter stage is large and the heat generation is large. When an input signal is applied in this state, the operating point of the differential grounded-emitter stage changes, so that the power consumption of the transistors 65 and 66 in the grounded-emitter stage is different, resulting in a difference in heat generation. This heat generation difference appears as a difference between the base-emitter voltage of the grounded-emitter stage and a so-called thermal distortion. For example, a transistor
When the heat generation of 65 is larger than that of the transistor 66, the base-emitter forward voltage of the transistor 65 decreases and the base-emitter forward voltage of the transistor 66 increases. This voltage difference appears at the output stage. That is, when this phenomenon is viewed on the tube surface of the oscilloscope, it takes several tens of seconds for the bright line to gradually move and stabilize after the step signal is input, which has a problem of affecting the measurement accuracy.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a broadband DC amplifier with a wide band and less thermal distortion.

In order to achieve the above object, the present invention has a high frequency signal path having a cascode-connected capacitor-coupled grounded-emitter input stage and a grounded-base output stage, and a transistor which is a grounded DC bias supply means. A low-frequency signal path that constitutes a feedback circuit by an operational amplifier is provided between the base and the emitter.

Action The present invention has the following actions due to the above configuration. In other words, the high-frequency and low-frequency paths are separated and the feedback circuit with operational amplifiers is provided in the low-frequency path where thermal distortion occurs. No influence appears, and thermal strain can be suppressed.

Examples Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, reference numerals 1 and 11 are a pair of input terminals, 2 and 10 are a pair of operational amplifiers having the same characteristics, 3 and 12 are a pair of level shift zener diodes, and differential input signals are operational amplifiers 2 and 10.
Applied to the non-inverting input of and the ends of the zener diodes 3 and 12. 5 and 9 are a pair of transistors with the same characteristics, and the output and inverting input of each operational amplifier 2 and 10 are a transistor pair.
Connected to the bases and emitters of 5,9. The emitters of the pair of transistors 5 and 9 are connected to each other via the emitter coupling resistor 6 and to the voltage source via the resistors 7 and 8 having the same resistance value. 15 and 16 are a pair of transistors that act as high frequency amplification.
Nine collectors are connected and a DC bias is applied.
The emitters of the transistor pair 15 and 16 are connected via a capacitor 14, each base is connected to one of the zener diode pair 3 and 12 and the current source pair 4 and 13, and each collector is the emitter of the grounded base transistor pair 17 and 18. It is connected to the. The bases of transistor pairs 17, 18 are connected to the base bias voltage, and the collectors are connected through load resistors 21, 22 to a suitable voltage source. 19, 20 are output terminals.

Next, the operation of the above embodiment will be described.

The differential input signal to the input terminals 1 and 11 is applied to the grounded-emitter transistor pair 15 and 16 in the differential amplifier configuration via the level shift zener diode pair 3 and 12. Since this amplification stage has the capacitor 14 between the emitters, the direct current component is cut, only the high frequency difference signal component is amplified, transmitted by the base grounded transistor pair 17, 18 in the cascode configuration, and the output terminal pair 19, Obtained as a high frequency differential output to 20. On the other hand, the low frequency component is added to the non-inverting input of the operational amplifier pair 2 and 10, and a signal having the same amplitude as the input signal is reproduced at the emitters of the transistor pair 5 and 9 by the feedback action, and via the emitter coupling resistor 6. The low frequency difference signal is amplified. This signal passes through transistors 15, 17, 16 and 18 and outputs 1 pair
It is obtained as a low-frequency differential output at 9, 20 and superposed with the high-frequency component, and reproduced as an amplified signal of the differential input signal.

It is sufficient that the operational amplifiers 2 and 10 used for the low-frequency path are versatile, and if the loop gain is sufficiently high, the transistor pair
The base and emitter voltages do not change on the emitter side due to the heat generation difference between 5 and 9, and show good amplification characteristics.

As described above, according to the present embodiment, the low-frequency component and the high-frequency component are separately amplified to form a comprehensively stable wide-band DC amplifier. There is no limit to correcting thermal distortion with an external element, and a sophisticated technique is required in terms of adjustment as well, but according to the present invention having the above configuration, this is not required,
The problem of thermal distortion can be solved.

EFFECTS OF THE INVENTION As described above, according to the present invention, the high-frequency and low-frequency paths are separately configured, and the feedback circuit of the operational amplifier is provided in the low-frequency path where thermal distortion occurs. Even if a change occurs, this effect does not appear due to the feedback effect on the output side, and thermal distortion can be suppressed in a wide band.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a wide band DC amplifier in one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional amplifier. 1,11… Input terminal, 5,9,15,16,17,18… Transistor, 3,1
2 ... Zener diode for level shift, 4,13 ... Current source,
2, 10 ... Operational amplifier, 6 ... Coupling resistor, 14 ... Coupling capacitor, 7, 8, 21, 22 ... Resistor.

Claims (1)

[Claims] 1. A high-frequency differential amplifier path having a cascode-connected capacitor-coupled common-grounded input stage and a common-grounded output stage, and the emitters of the first and second transistors are resistance-coupled to each other. In the amplifier whose collector is connected to the emitter of the grounded-emitter input stage, a buffer amplifier is formed by an operational amplifier between the bases and the emitters of the first and second transistors, and the non-inverting input terminal of the operational amplifier is formed. A wide band DC amplifier, wherein a differential signal is applied to the base of the grounded-emitter input stage via a level shift means.