JPS58181304A - Wide band amplifying circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wideband amplifier circuit, and particularly to a balanced amplifier circuit that substantially uniformly amplifies a wideband signal from direct current to ultra-high frequency.

A wideband amplifier circuit is essential for wideband analog measuring instruments such as oscilloscopes. Due to advances in semiconductor device technology,
Although the cutoff frequency (fl) of high-frequency semiconductor elements is increasing year by year, there is a limit to the gain of one semiconductor amplification element. In order to overcome this drawback, the applicant has proposed an amplifier circuit called a so-called f1 doubler (Japanese Patent Publication No. 5
0-26899). This conventional amplifier circuit has a first transistor pair 18.20 and a second transistor pair 22.24 emitter-coupled and a common-base output transistor pair 46.48, the first transistor 18.22 of the first and second transistor pair The second transistor 20.2 supplies a balanced input signal with the base terminal 10.12 as the input terminal 10.12.
Connect the base of 4 to a reference potential source. transistor 18
The emitters of 24 to 24 are resistors 26, 28, 34, 3, respectively.
6 and the collectors are connected to the emitters of a pair of common-base transistors 46 and 48 in phase with each other to perform current addition, and their collectors are connected to the output terminal 5.
The output signal is obtained as 0.52. The emitter of each emitter-coupled transistor pair 18-20 and 22-24 is connected to a resistor/capacitor parallel impedance circuit 30-3.
2.38-40. Since the emitter coupling impedance is sufficiently lower than that of resistors 26, 28, 34, and 36, emitter-collector currents of approximately equal amplitude and opposite polarity flow in transistors 18, 20, and the same goes for transistors 22, 24. . Therefore, even at fT where the input signal frequency increases and the collector-base current ratio, that is, the current gain becomes 1, the output current at the output terminal 50.52, which is the sum of both collector radio waves, is 2, so fT is This can be increased compared to the case of a transistor.

However, the conventional amplifier circuit shown in FIG. 1 uses capacitors 32 and 40 as the emitter-coupled impedance of each emitter-coupled transistor pair 18-20 and 22-24 to improve high-frequency characteristics. It is necessary to provide a connection terminal for this purpose, which creates inductance and makes it difficult to substantially improve high frequency characteristics. Also,
There are drawbacks such as drift due to the temperature dependence of the base-emitter voltage (V) of the transistor used.

Therefore, an object of the present invention is to provide a wideband amplifier circuit which eliminates the emitter coupling capacitor of a so-called fT doubler amplifier circuit and which has excellent wideband amplification characteristics and operational stability.

The present invention is characterized by the structural feature of the so-called fT doubler, namely, the second transistor 20.24 of the first and second transistor pair is of a common base type and has a low input impedance, so that the signal current flowing through the emitter-coupled impedance is substantially reduced. Focusing on the point where all of the current flows to the emitter of each transistor 20.24, one end of the resistor 28.36 is used as a supply point of the additional signal current instead of being directly connected to the power supply. This additional signal current carries the same signal as the input signal to the f1 doubler itself.
The preferred embodiment shown in Figs. 2 and 3 applies the wideband amplifier circuit described below, obtained by amplification by a low-frequency amplifier separate from the main amplifier, to the vertical and horizontal output amplifiers of a wideband oscilloscope. This will be explained based on an example.

First, in FIG. 2, a balanced input signal from a delay line (not shown) of the oscilloscope is input to a delay compensation circuit 8, which will be described later.
The signal is input to the bases of transistors 200 and 202 forming part of the f1 doubler amplifier (main amplifier) 94 through a part of the f1 doubler amplifier (main amplifier) 94 . The bases of transistors 200 and 202 are connected to a positive reference voltage source 2.7 through resistors 204 and 206, respectively. The first transistor 200 and the second transistor 208 constitute a first transistor pair, and the first transistor 202 and the second transistor 210 constitute a first transistor pair.
Together, they constitute a second transistor pair. The bases of both second transistors 208 and 210 are directly connected and further connected to voltage source 207 via a resistor. transistor 20
The emitters of transistors 0 and 208 are coupled to the transistor through resistor 212, and the emitter of first transistor 200 is coupled to resistor 2.
14, etc., to a voltage source 216, and the emitter of the second transistor 208 is connected to a low frequency sub-amplifier 92, which will be described later, via a resistor 218. On the other hand, the emitters of transistors 202 and 210 are coupled to each other via a resistor 220, the emitter of the second transistor 202 is coupled to a voltage source 224 via a resistor 222, etc., and the emitter of the second transistor 21O is coupled to a voltage source 224 via a resistor 226. It is connected to a low frequency amplifier 92 via.

The collectors of transistors 200 and 210 are both connected to node 228, and the collectors of transistors 202 and 208 are both connected to node 230. Furthermore, connection point 2
28 and 230 are output terminals of the fT doubler amplifier 94.

Next, the low frequency amplifier 92 will be explained. This amplifier 92 supplies a portion of the balanced input signal obtained from the above-mentioned delay line via the input terminals 84 and 86 to the inductors 300 to 31 forming the delay line compensation circuit 88 and the low-pass filter.
0 to operational amplifier 312 via 0. The delay line compensation circuit 88, which includes a resistor, a capacitor, and an inductor, is a circuit that cancels the delay line loss of the input signal due to the skin effect of the delay line and attenuates the low frequency portion of the input signal. Diodes 314 and 316 serve as dynamic inputs for f1 doubler amplifier 94 and output amplifier 98, also of the fT doubler type.
This is provided to limit the amplitude of the output (ie, correction signal) of the amplifier 92 that exceeds the range, and to improve recovery from overdrive of the vertical axis circuit. Operational amplifier 312
The output signal converted into a single-ended signal at
It is added to a variable low-pass filter 96 for frequency characteristic adjustment consisting of 0 to 330 filters (each having a different time constant). The outputs of variable resistor 318. and 210 emitters. The variable capacitor 338 is for adjusting the output signal (correction signal) of the amplifier 92 together with the variable resistor 318 and the variable resistors of the 80 circuit networks 320 to 330, and the thermistor 340 is for adjusting the output signal (correction signal) of the amplifier 92. accompanying transistor 3
Amplifier 92 based on self-heating of junction resistance in 34.336
This is to compensate for the gain fluctuation of the output signal. Note that the correction signal from the low frequency amplifier 92 at the emitters of the second transistors 208 and 210 is of opposite polarity to the input signal to the first transistors 200 and 202.

Thus, the low frequency amplifier 92 prevents the high frequency signal from being shunted through the inductor to the f1 doubler amplifier 94 and the variable resistor 318.80 network 320-33.
0 variable resistor and variable capacitor 338,
The balance correction signal is sent to the transistor 2 of the f□ doubler amplifier 94.
In addition to the 08,210 emitter. Therefore, the low frequency amplifier 92 reduces only the low frequency (including DC) gain of the f doubler amplifier 94 without affecting the high frequency operation of the f doubler amplifier 94, thereby reducing the frequency characteristics of the output signal of the fT doubler amplifier 94. (Actually, considering the frequency characteristics of another fT doubler amplifier 98 provided after the fT doubler amplifier 94, the frequency characteristics of the output signals from the output terminals 102 and 104) are smoothed out to higher frequencies than when the amplifier 92 is not used. It can be used as a burden. Therefore, the coupling capacitor between the emitters of the transistor pair of the fT doubler amplifier 94 can be eliminated, making it suitable for integrated circuit implementation. Also,
By using operational amplifiers 312, 332, thermistor 340, etc., a broadband amplifier circuit with extremely stable operating characteristics can be obtained.

In addition, in FIG. 2, another f
Although a T-doubler amplifier 98 is provided, its operation is similar to that of the fT-doubler amplifier 94 described above, so a description thereof will be omitted. Circuit 100 provides a bias voltage and a second
This is to partially clamp the level of the DC common-mode component of the output of the circuit shown in the figure. The output of amplifier 98 is at terminal 102
and 104 to the vertical deflection means of the CRT of the oscilloscope. The other circuit parts in FIG. 2 are not directly related to the present invention, and therefore their explanation will be omitted. Note that the amplifier shown in FIG. 2 has a frequency bandwidth of about IGHz.

The wideband amplifier circuit shown in FIG. 3 is composed of a wideband main amplifier consisting of an f1 doubler type input stage amplifier 500 and an output stage amplifier 502, and a low frequency amplifier 114 that compensates for changes in the gain of the main amplifier due to changes in ambient temperature. , input terminal 1
A balanced input signal, such as a sweep signal, is received via 06 and 108 from the horizontal axis circuit of the oscilloscope. The input stage amplifier 500 has an fT doubler amplifier 110, and this fT doubler amplifier 110 has a first transistor pair (400, 4
08) and second transistor pair (402°410), resistor 404.406.412.414.418.420
, 422 and 4 (26, etc.), amplifies the balanced signal input to the base of each first transistor 400 and 402, and approximately doubles fT in the case of one transistor pair, as described above. The emitters of each second transistor 408 and 410 are interconnected and connected to the low frequency amplifier 114 via resistors 418 and 422, respectively.The output of the fT doubler amplifier 110 is an amplifier for the first and a connection point 42 where the collectors of the second transistor pair are connected so that the phases of the output signals are in phase.
8 and 430. The operation of the f1 doubler amplifier 110 is similar to the operation of the f1 doubler amplifier 94 in FIG. 2, so a description thereof will be omitted. The balanced output of the input stage amplifier 500 is a transistor pair 43443 whose emitters are directly connected.
6 and a transistor pair 438 whose emitters are also directly connected
, 440 and a diode pair 433, 435, and a T transformer resistor 432 to control the gain before being supplied to the output stage amplifier 502.

The output stage amplifier 502 includes a first transistor pair (600,
608) and a second transistor pair (602, 610),
Resistor 604.606.612.614.618.62
0.622, 626, etc., and their collectors are connected so that the phases of the output signals are in phase relationship 628
and f doubler amplifier 112 obtained from 630 and a base junction tank width amplifier (consisting of transistors 640 and 642, etc.). The operation of the fT doubler amplifier 112 is similar to the operation of the fT doubler amplifier 94 in FIG. 2, so a description thereof will be omitted. A common base transistor amplifier consisting of transistors 640 and 642 is for summing and amplifying the output of f1 doubler amplifier 112.

Low frequency amplifier 114 transfers a portion of the input signal applied to input terminals 106 and 108 to inductors 650 and 6, respectively.
52 and is amplified by transistors 654 and 656 and applied to the non-inverting and inverting input terminals of operational amplifier 658. On the other hand, part of the output of the collectors of the transistors 64°0 and 642 of the output stage amplifier 502 is passed through the low-pass filter and the resistor 66.
0.662 and is applied to the non-inverting and inverting input terminals of operational amplifier 658 along with the collector outputs of transistors 654 and 656. The balanced signals amplified by the operational amplifier 658 are respectively f and the second one of the doubler amplifier 110.
added to the emitters of transistors 408 and 410. As a result, the low frequency gain of the f-r doubler amplifiers 500 and 502 is reduced, and the gain change of the broadband amplifier circuit due to changes in ambient temperature is compensated for. That is, when the outputs from the output terminals 116 and 118 of the circuit shown in FIG. do. Note that the output of the output stage amplifier 502 drives the horizontal deflection means of the CRT via the output terminals 116 and l18.

In this way, the wideband amplifier circuit shown in FIG. 3 also has a main amplifier and a low-frequency sub-amplifier, and provides negative feedback to the output of the output stage amplifier 502 to improve the frequency characteristics of the main amplifier and change the gain due to temperature changes. By compensating and stabilizing the operation, it is possible to amplify the human power input substantially uniformly over a wide band.

As is clear from the explanation below, the present invention has the high frequency characteristics of an f□ tabular amplifier, is stable in operation in a low frequency region including direct current, and is capable of connecting a capacitor between the emitters of a pair of transistors. Therefore, a wideband amplifier circuit having flat frequency characteristics from low frequencies to extremely high frequencies can be obtained.

[Brief explanation of drawings]

FIG. M1 is a circuit diagram of a conventional doubler amplifier, and FIGS. 2 and 3 are embodiments of a broadband amplifier circuit according to the present invention. 92: Low frequency amplifier 94: Main amplifier (fT doubler amplifier) 96: Frequency characteristic adjustment variable filter 114: Low frequency amplifier 200.202: First transistor (208).210: Second transistor 300 to 310: Inductor 650. 652: Inductor patent applicant Tektronix Incorporated Representative Patent attorney Toshiaki Morisaki 10

Claims (4)

[Claims] (1) It has two pairs of transistors each consisting of a first and a second transistor whose emitters are coupled via a coupling resistor, and a balanced input signal is applied to the base of each first transistor, and the emitter is connected to a desired power source via a resistor i. a main amplifier, the bases of each second transistor being interconnected, and the collectors of the first transistor of one transistor pair and the second transistor of the other transistor pair being connected to the pair of output terminals in an in-phase relationship; and a low frequency amplifier that receives the balanced input signal and supplies an output to the emitter of each second transistor of the two transistor pairs. (2) The wide band according to claim 1, wherein the low frequency amplifier receives the input signal through an inductor and prevents the high frequency signal from being shunted to the base of the first transistor of the two transistor pairs. Amplification circuit. (3) The wideband amplifier circuit according to claim 1 or 2, wherein the low frequency amplifier includes a variable filter for adjusting frequency characteristics. (4) The wideband amplifier circuit according to claim 1, wherein negative feedback is applied to the L low frequency amplifier from the output sides of the two transistor pairs.