JPS63263904A - Broad band dc amplifier - Google Patents

Abstract

PURPOSE:To suppress the thermal distortion due to a voltage change in the base-emitter voltage separating the signal line into a high frequency signal line and a low frequency signal line provided with a feedback circuit comprising an operational amplifier between the base and emitter of a transistor(TR) of common emitter connection. CONSTITUTION:A differential input signal given to input terminals 1, 11 is impressed to common emitter TR pairs 15, 16 via Zener diode pairs 3, 12 for level shift. Since the amplifier stage is connected between emitters via a capacitor 14, the DC component is cut off and only the differential signal component of a high frequency is amplified and sent through common base TR pairs 17, 18 of cascode constitution and a differential output of high frequency is obtained at output terminal pairs 19, 20. The low frequency component is fed to a noninverting input of operational amplifier pairs 2, 10, recovered at the emitters of the TR pairs 5, 9 and a differential signal is amplified via an emitter coupled resistor 6.

Description

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

Prior Art FIG. 2 shows the configuration of a conventional vertical output amplifier. In Figure 2, 51.61 is a pair of input terminals, 65.6
Reference numeral 6 denotes a transistor functioning as a high frequency amplifier, and a differential input signal is applied to the bases of transistors 65 and 66. The emitters of the transistors 65, 66 are connected via an emitter-coupled resistor 56 and to a voltage source via resistors 57, 58 of equal resistance. Each collector of transistors 65, 66 is connected to the emitter of a common base transistor 67, 68, each base of transistor 67, 68 is connected to a base bias voltage, and each collector is connected to an appropriate voltage via a load resistor 71, 72. connected to the source. 69.70 is an output terminal.

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

The differential input signal to the input terminals 51.61 is applied to the transistor pair 65.66, the difference signal is amplified via the emitter-coupled resistor 56, transmitted by the transistor pair 67.68, and output to the output terminal 69.70. Provided as a differential output.

Problem to be Solved by the Invention This type of amplifier typically supplies sufficient quiescent current to the output stage of the amplifier 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 emitter-grounded 3rd and 7th stage increases, and heat generation increases.

When an input signal is applied in this state, the operating point of the common emitter stage of the differential configuration changes, and as a result, the power consumption of the grounded emitter stage differs, resulting in a difference in heat generation. This difference in heat generation appears as a difference in voltage between the base and emitter of the common emitter stage, resulting in so-called thermal distortion.

The present invention is intended to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a wideband DC amplifier with a wideband and low thermal distortion.

Means for Solving the Problems In order to achieve the above object, the present invention provides a high frequency signal path having a cascode-connected capacitor-fed, emitter-grounded input stage and a base-grounded output stage, and means for supplying the emitter-grounded DC bias. A low-frequency signal path is provided between the base and emitter of a transistor, which constitutes a feedback circuit using an operational amplifier.

Effects The present invention has the following effects due to the above configuration. In other words, the high-frequency and low-frequency paths are separated, and a feedback circuit using an operational amplifier is installed in the low-frequency path where thermal distortion occurs, so even if a voltage change occurs at the base or emitter, the feedback effect will prevent this change on the output side. No influence appears, and thermal distortion 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 Figure 1, 1 and 11 are a pair of input terminals, 2゜10
are a pair of operational amplifiers with equal characteristics; 3 and 12 are a pair of level-shifting Zener diodes; a differential input signal is applied to the non-inverting input of the operational amplifier 2.10 and one end of the Zener diodes 3 and 120;

5.9 is a pair of transistors with equal characteristics, and the output and inverting input of each operational amplifier 2 and 10 are connected to the transistor pair 5.
, 9 are connected to the bases and emitters of . The emitters of the transistor pair 5, 9 are connected via an emitter-coupled resistor 6 and via resistors 7, 8 whose resistance value is equal to 1/5 to a voltage source.

Reference numerals 15 and 16 designate a pair of transistors that function as high-frequency amplifiers, each emitter of which is connected to the collector of the transistor pair 5 and 9, and a DC bias is applied. transistor pair 1
The emitters of 5.16 are connected through a capacitor 14, the bases of each are connected to a Zener diode pair 3,120 on the other hand and a current source pair 4,13, and the collectors of each are connected to the emitters of a common base transistor pair 17.18. ing. The base of each transistor pair 17.18 is connected to a base bias voltage and the collector of each is connected via a load resistor 21.22 to a suitable voltage source. 19.20 are output terminals.

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

Differential input signals to input terminals 1 and 11 are applied to a pair of common emitter transistors 15 and 16 of a differential amplifier configuration via a pair of Zener diodes 3 and 12 for level shifting. Since this amplification stage has a capacitor 14 interposed between the emitters, the DC component is cut, and only the high frequency difference signal component is amplified and transmitted through a pair of common-base transistors 17 and 1.8 in a cascode configuration, and the output terminal pair is 19.20 is obtained as a high frequency differential output. On the other hand, the low frequency component is applied to the non-inverting inputs of the operational amplifier pair 2 and 10, and a signal with the same amplitude as the input signal is reproduced at the emitters of the transistor pair 5 and 9 due to the feedback effect, and is transmitted through the emitter-coupled resistor 6. The low frequency difference signal is amplified. This signal is passed through transistors 15.17 and 16.18 to output terminal pair 19.2.
0 as a low-frequency differential output, is superimposed on the high-frequency component, and is reproduced as an amplified signal of the differential input signal.

General-purpose operational amplifiers 2 and 1o used in the low frequency path are sufficient; if the loop gain is sufficiently high, changes in base and emitter voltages due to the difference in heat generation between the transistor pair 5 and 9 will not occur on the emitter side. , exhibiting good amplification characteristics.

In this manner, according to this embodiment, the low frequency and high frequency components are amplified separately, and a comprehensively stable broadband DC amplifier is constructed. There is no limit to how thermal distortion can be corrected using external elements, and advanced techniques are required in terms of adjustment, but the present invention with the above configuration eliminates the need for this and solves the problem of thermal distortion. It can be resolved.

Effects of the Invention As described above, according to the present invention, the high frequency and low frequency paths are separated and a feedback circuit using an operational amplifier is provided in the low frequency path where thermal distortion occurs, so that the base and emitter voltages are reduced. Even if a change occurs, this effect does not appear on the output side due to the feedback effect, and thermal distortion can be suppressed over a wide band.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a broadband DC amplifier according to an 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, 3.12...Zena diode for level shift, 4,13...Current source, 2.10
...Operation amplifiers 1, 6...Coupling resistor, 14...Coupling capacitor, 7,8°21, 22...Resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure + VI Figure 2

Claims (1)

[Claims] A high frequency signal path having a cascode-connected capacitor-coupled emitter-grounded input stage and a base-grounded output stage, and a low-frequency signal path comprising a feedback circuit using an operational amplifier between the base and emitter of the transistor that is the emitter-grounded DC bias supply means. A wideband DC amplifier characterized by being equipped with.