JPH07176986A - Distribution balun - Google Patents

Abstract

PURPOSE:To eliminate a signal loss, to improve the matching of input output and to attain the operation over a broad band by applying distribution amplification to an input signal and providing an output at 1st and 2nd output terminals while the phase is deviated by a specific angle. CONSTITUTION:When an input terminal 12 connects to ground in terms of high frequency and a signal is allowed to input from an input terminal 11, signals whose phase is deviated by 180 deg. are outputted to output terminals 01, 02. The gain of the respective signals is halved to a gain when transistors(TRs) X1, X2 are regarded as common source TRs. Since the total sum of current flowing to the TRs X1, X2 is kept always constant, the voltage whose amplitude is a half of a voltage amplitude to the input terminal 11 is applied between a source terminal S and a gate terminal G of the TRs X1, X2 at a phase difference of 180 deg. and the voltage is amplified by the TRs X1, X2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed balun (balanced-unbalanced conversion circuit) having a wide band frequency characteristic.

[0002]

2. Description of the Related Art Conventionally, as a balun, one using a passive element such as a quarter wavelength line has been widely used. However, since this type of balun has a narrow band, it is not suitable for a device such as a receiver for optical transmission or a measuring device that requires a wide band frequency characteristic.

Therefore, as a method of constructing a wide band balun, a distributed amplification type balun combining a source grounded transistor and a gate grounded transistor has been conventionally proposed (for example, AMPavio and RH Halladay, "A Distrib").
uted Double-Balanced Dual-Gate FETMixer "IEEE GaAs
IC Symposium Digest pp.177-180 1988).

FIG. 7 is a circuit diagram showing the outline of the configuration of this type of distributed amplification type balun in the case of four sections. Here, the section means a unit circuit (circuit of the transistors Q1 and Q2) of active elements connected to each other by a line. In FIG. 7, IN is an input terminal, OUT1, O
UT2 is an output terminal that outputs signals that are 180 degrees out of phase with each other, Ti is a transmission line (or an inductance element) that constitutes an input side filter circuit (transmission circuit), Q1 is a source-grounded transistor, Q2 is a gate-grounded transistor,
To1 and To2 are transmission lines (or inductance elements) forming the output side filter circuit (transmission circuit), Ri and R
o1 and Ro2 are terminating resistors forming a terminating circuit.

Generally, in the distributed amplification type configuration, the input / output capacitance of the transistor and the inductance component of the transmission line constitute an LC delay line having a very high cutoff frequency, so that the input / output capacitance of the transistor is not affected. , It is canceled by being taken into this delay line.
Therefore, the distributed amplification type configuration is suitable for widening the band, and even the conventional balun of FIG. 7 using the same can obtain frequency characteristics in a wider band than that of the balun using the passive element.

[0006]

However, in the conventional distributed balun shown in FIG. 7, as described below,
It is difficult to obtain gain and the loss of the signal is large,
Further, it has a drawback that input matching is poor.

FIGS. 8, 9 and 10 are circuit diagrams for explaining the drawbacks of the conventional distributed balun. FIG. 8 is a diagram showing a configuration of a distributed amplifier using a commonly used 4-section source-grounded transistor having a gain. 9 is a diagram showing an equivalent circuit of the input part of the distributed amplifier of FIG. 8, and a tenth diagram is an equivalent circuit of the input part of the distributed balun of FIG. In the figure, Cgs is the transistor input capacitance (gate-source capacitance), and gm is the transconductance of the transistor.

The input portion equivalent circuit of FIG. 10 is greatly different from the input portion equivalent circuit of FIG. 9 in that the input resistance 1 / gm of the grounded-gate transistor Q2 is added as a pure resistance component. Since this resistance component 1 / gm is connected in parallel with the terminating resistor Ri (normally 50Ω), it lowers the input impedance of the entire circuit and deteriorates the matching of the inputs. This causes a reduction in the component applied to the input, which causes a reduction in the gain of the entire circuit.

The gain Gv and the input impedance Zi at a low frequency are shown below by the normal distributed amplifier of FIG. 8 and the conventional distributed balun of FIG. Distributed amplifier of grounded source transistor Q1: Gv = n.gm.Zo / 2 .. (1) Zi = Ri = Zo .. (2) Distributed balun: Gv = n.gm.Zo / (2 + n.gm.Zo) ··· (3) Zi = 1 / (n · gm + 1 / Zo) ··· (4) where n is the number of sections and Zo is 50Ω. Further, since the normal termination resistor Ri is equal to Zo in order to widen the band, Ri = Zi is set.

From the above equation (1), it can be seen that in the ordinary distributed amplifier, the gain Gv increases in proportion to the transconductance gm of the transistor Q1 and the number of sections n. On the other hand, in the distributed balun, the input resistance 1 / gm of the grounded-gate transistor Q2 in each section is equal to the termination resistance Ri.
And the input impedance Zi becomes low,
The gain is reduced accordingly. Therefore, as in equation (3),
Basically, the gain cannot be set to 1 or more even if n and gm increase.

Further, in the normal distributed amplifier, the input impedance is matched with the terminating resistance to achieve the input matching as shown in the expression (2), but in the distributed balun, the gate is grounded as shown in the expression (4). Input resistance of transistor Q2 1 / gm
Is parallel to the terminating resistor Ri, the input impedance becomes low, and the matching deteriorates.

FIG. 11 shows the experimental result of the frequency characteristic of the distributed balun. In the figure, S21 is a gain from the input terminal IN to the output terminal OUT1, S31 is a gain from the input terminal IN to the output terminal OUT2, S11 is a reflection coefficient of the input terminal IN, and S22 is a reflection coefficient of the output terminal OUT1.

From this figure, the gains S21 and S31 are -4d.
It can be seen that the signal loss is about B. Also,
The reflection coefficient S11 needs to be at least -10 dB or less to secure good matching with the signal source.
It can be seen that the distributed balun is deteriorated to -4 dB at a low frequency and does not become -10 dB even at a high frequency, which shows a problem.

These drawbacks of conventional distributed baluns require the use of a combination of wide band amplifiers to compensate for the loss when using distributed baluns, or attenuators to improve their integrity, etc. It has caused various problems in application such as needing to be placed in front.

It is an object of the present invention to solve the above problems and provide a distributed balun that has no signal loss, has good input / output matching, and operates in a wide band.

[0016]

[Means for Solving the Problems] First to achieve the above object
Of the present invention, the first input terminal of each of a plurality of 2-input 2-output differential amplifier circuits is connected via a plurality of transmission lines or inductance elements to form a first transmission circuit. Ground the second input terminal of each of the circuits at high frequencies,
Each of the first output terminals of the differential amplifier circuit is connected via a plurality of transmission lines or inductance elements to form a second transmission circuit, and each of the second output terminals of the differential amplifier circuit has a plurality of second output terminals. A distributed balun, which is connected through individual transmission lines or inductance elements to form a third transmission circuit,
One terminal of the first transmission circuit is an input terminal, one terminal of the second transmission circuit is a first output terminal, and one output terminal of the third transmission circuit is a second output terminal. The other terminal of each of the first, second and third transmission circuits is connected to a terminating circuit, and the input signal input to the input terminal is distributed-amplified to obtain the first and second signals. It is configured as a distributed balun, which is characterized in that the phases are shifted by 180 degrees from each other and output to the output terminals.

A second aspect of the present invention for achieving the above object is to connect a first input terminal of each of a plurality of 2-input 2-output differential amplifier circuits via a plurality of transmission lines or inductance elements. And a second input terminal of each of the differential amplifier circuits is connected via a plurality of transmission lines or inductance elements to form a second transmission circuit. One output terminal is connected via a plurality of transmission lines or inductance elements to form a third transmission circuit, and each second output terminal of the differential amplifier circuit is connected via a plurality of transmission lines or inductance elements. A distributed balun connected as a fourth transmission circuit by using one terminal of the first transmission circuit as a first input terminal and the second transmission circuit.
One terminal of the transmission circuit is used as a second input terminal, and one output terminal of the third transmission circuit is used as a first output terminal,
One output terminal of the fourth transmission circuit is used as a second output terminal, and the other terminal of each of the first, second, third, and fourth transmission circuits is connected to a termination circuit, The first,
One of the second input terminals is connected to a terminating circuit, and an input signal input to the other is distributed-amplified and output to the first and second output terminals with their phases shifted by 180 degrees from each other. It was constructed as a distributed balun.

[0018]

In the present invention, since the differential amplifier circuit is used as the amplifying element and the grounded-gate transistor is not used, there is no problem of deterioration of input matching or reduction of gain due to the grounded-gate transistor. Therefore, good input / output matching and operation without signal loss are possible over a wide frequency range.

[0019]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a diagram showing a differential amplifier circuit which is a unit circuit constituting a distributed balun. The distributed balun of the first embodiment is shown in FIG.
As shown in FIG. 4, this is a distributed amplification type circuit in which one input terminal of this differential amplifier circuit is grounded in high frequency and the unit circuit is used as the unit circuit.

1 and 2, X1 and X2 are amplifying transistors of the differential amplifier circuit, X3 is a transistor for a constant current source, S is a source terminal of the transistor, G is a gate terminal of the transistor, and I1 and I2 are I1 and I2. Two input terminals of the differential amplifier circuit, O1 and O2 are two output terminals of the same differential amplifier circuit, Ro1 and Ro2 are terminating resistors that configure the output side terminating circuit, and To1 and To2 are output side transmissions. A transmission line (or an inductance element) that forms a circuit, and Ti is a transmission line (or an inductance element) that forms a transmission circuit on the input side. Although an example of four sections is shown here, the number of sections is arbitrary.

In the structure of the present invention, the differential amplifier circuit is used as the unit circuit. This differential amplifier circuit has the following features. In FIG. 1, one input terminal I
When 2 is grounded at a high frequency and a signal is input from the other input terminal I1, signals output from the output terminals O1 and O2 are 180 degrees out of phase with each other. Moreover, the gain of each signal is half of the gain when the transistors X1 and X2 are regarded as source-grounded transistors.

The reason why the gain is halved is that in the differential amplifier circuit of FIG. 1, the sum of the currents flowing through the transistors X1 and X2 is always kept constant by the transistor X3 for the constant current source. This is because a half of the voltage amplitude applied to the input terminal I1 is applied between the source terminal S and the gate terminal G of X2 with a phase difference of 180 degrees, and this is amplified by the transistors X1 and X2.

The equivalent circuit of the input section of the differential amplifier circuit is the same as the source-grounded transistor, and in the configuration example of FIG. 1, the input capacitance of the transistor X1 can be seen from the input terminal I1.

In the distributed balun of the present invention, since the differential amplifier circuit is used as the unit circuit shown in FIG. 1, the equivalent capacitance of the input section is the same as that of the distributed amplifier using the source-grounded transistor shown in FIG. In the same manner, the input section does not have a pure resistance as in the case of using the grounded-gate transistor, and there is no deterioration in gain or input matching due to this. Further, the transistors X1 and X2 have the same amplifying action as the source-grounded transistor.

Therefore, the gain Gv and the input impedance Zi at the low frequency are as follows, like the distributed amplifier using the source-grounded transistor. Gv = n · gm · Zo / 4 ··· (5) Zi = Ri = Zo ··· (6) Note that the gain of the equation (5) is 1 / value less than that of the equation (1).
2, which is due to the action of the constant current source transistor X3 of the differential amplifier circuit as described above.
From this expression (5), it is understood that the balun of the present invention increases the gain Gv in proportion to the number of sections n and the transconductance gm of the transistor. Further, since the input impedance Zi matches the value of the termination resistor Ri (normally 50Ω), good input matching can be obtained.

FIG. 3 shows the experimental results of the distributed balun of the first embodiment shown in FIG. The symbols in the figure are the same as those shown in FIG. From this figure, the gain S2
1, S31 is about 5 dB in the frequency range of 0 to 50 GHz
It can be seen that the input reflection coefficient S11 is -10 dB or less, and good input matching is ensured.
From these results, it can be seen that the gain and the input matching are superior to those of the conventional distributed balun shown by the characteristics of FIG.

FIGS. 4, 5 and 6 are diagrams showing the circuits of the distributed baluns according to the second to fourth embodiments of the present invention. First, the distributed balun of FIG. 4 of the second embodiment is the transistor X.
The difference from the distributed balun of the first embodiment shown in FIG. 2 is that transmission lines (or inductance elements) Td1 and Td2 are inserted into the drain terminals of X1 and X2.

The distributed balun of FIG. 5 of the third embodiment does not ground the input terminal I2 of the differential amplifier circuit which constitutes the unit circuit in terms of high frequency, but the transmission line (or the input line I2 between the input terminals I2 of the unit circuit). Inductance element) Ti2 is connected to make the distributed balun 2 inputs (IN1, IN2), and the termination resistor Ri
1 and Ri2 are different. The distribution balun of FIG. 6 of the fourth embodiment is a combination of the configurations of FIG. 4 and FIG.

In the distributed balun circuits of the third and fourth embodiments shown in FIGS. 5 and 6, one of the input terminals IN1 and IN2 is terminated and a signal is input to the other input terminal IN1.
Between the output terminals OUT1 and OUT2 or the input terminal IN
2 and the output terminals OUT1 and OUT2 can be used as a balun, and the same effect as the distributed balun of the first embodiment described in FIG. 2 can be obtained.

In the above example, the case where the field effect transistor is used as the transistor has been described, but the same effect can be obtained even when the bipolar transistor is used.

[0031]

As described above, according to the present invention, it is possible to realize a distributed balun having no signal loss, good input / output matching, and wide band frequency characteristics. There is an advantage that the performance of the electrical measuring device can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a differential amplifier circuit that constitutes a unit circuit of a distributed balun according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of the distributed balun according to the first embodiment of the present invention.

FIG. 3 is a frequency characteristic diagram of the distributed balun of FIG.

FIG. 4 is a circuit diagram of a distributed balun according to a second embodiment.

FIG. 5 is a circuit diagram of a distributed balun according to a third embodiment.

FIG. 6 is a circuit diagram of a distributed balun according to a fourth embodiment.

FIG. 7 is a circuit diagram of a conventional distributed balun.

FIG. 8 is a circuit diagram of a conventional distributed amplifier using a typical source-grounded transistor.

9 is an equivalent circuit diagram of an input unit of the distributed amplifier of FIG.

10 is an equivalent circuit diagram of an input unit of the distributed balun of FIG.

11 is a frequency characteristic diagram of the distributed balun of FIG.

[Explanation of symbols]

IN, IN1, IN2: input terminals, OUT1, OUT
2: output terminal, Q1: grounded source transistor, Q2:
Grounded-gate transistor, Ri, Ri1, Ri2: R
o, Ro1, Ro2: termination resistors, Ti, Ti1, Ti
2, To, To1, To2, Td1, Td2: Transmission line (or inductance element), Cgs: Gate-source capacitance of transistor, gm: Transconductance of transistor, S21, S31: Gain, S11, S12:
Reflection coefficient, I1, I2: Input terminal of differential amplifier circuit, O
1, O2: output terminal of differential amplifier circuit, X1, X2: transistor of differential amplifier circuit, X3: transistor for constant current source of differential amplifier circuit, G: gate terminal, S: source terminal.

Claims (2)

[Claims] 1. A differential transmission circuit comprising the first input terminal of each of a plurality of 2-input 2-output differential amplifier circuits connected through a plurality of transmission lines or inductance elements to form a first transmission circuit. A second transmission circuit in which each second input terminal of the amplifier circuit is grounded in high frequency, and each first output terminal of the differential amplifier circuit is connected through a plurality of transmission lines or inductance elements. A distributed balun, in which the second output terminal of each of the differential amplifier circuits is connected via a plurality of transmission lines or inductance elements to form a third transmission circuit, the first transmission circuit One terminal is an input terminal, one terminal of the second transmission circuit is a first output terminal, and one output terminal of the third transmission circuit is a second output terminal. The other terminal of each of the second and third transmission circuits is used for termination. A distributed balun, which is connected to a path and which distributedly amplifies an input signal input to the input terminal and outputs the input signal to the first and second output terminals with a phase shift of 180 degrees from each other. 2. A differential transmission circuit comprising: a plurality of two-input two-output differential amplifier circuits having first input terminals connected to each other through a plurality of transmission lines or inductance elements to form a first transmission circuit; Each second input terminal of the amplification circuit is connected through a plurality of transmission lines or inductance elements to form a second transmission circuit, and each first output terminal of the differential amplification circuit is transmitted to a plurality of transmission lines. A third transmission circuit is formed by connecting via a line or an inductance element to each of the second transmission circuits of the differential amplification circuit.
Is a distributed balun, which is a fourth transmission circuit in which the output terminals of the first transmission circuit are connected through a plurality of transmission lines or inductance elements, and one terminal of the first transmission circuit is a first input terminal, One terminal of the second transmission circuit is a second input terminal, one output terminal of the third transmission circuit is a first output terminal, and one output terminal of the fourth transmission circuit is a first output terminal. 2 output terminals, and the other terminal of each of the first, second, third and fourth transmission circuits is connected to a termination circuit, and one of the first and second input terminals is terminated. Connected to a circuit for input, and distributedly amplifying the input signal input to the other, and
A distributed balun, which outputs to the second output terminal with a phase difference of 180 degrees from each other.