JPS598083B2 - bidirectional amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bidirectional amplifier that is stable in operation and capable of amplifying transmitted signals in both directions with a uniform gain.

A known bidirectional amplifier is intended for two-wire baseband transmission of audio signals, and is described in Ogata et al., "Carrier Telephone Part 2," published by the Institute of Electronics and Communication Engineers, p. 52 (published in 1972), or J.
．． L. Negative by Merrill et al.
Impedance TelephoneRepea
ter'', B.S.T.J., 33, 5, p. 1070 (Sept., 1954), etc., it was constructed based on the principle of canceling line impedance by a negative impedance converter.

In other words, a Wheatstone bridge is constructed using a negative impedance of an open stable type or a short circuit stable type, and two of its six independent branches are connected to two sides of the lines on both sides when viewed from the insertion position of the bidirectional amplifier. When the terminal impedance is taken as the terminal impedance, the amplification gain due to inserting the bidirectional amplifier configured between the two sides into the line can be adjusted between O dB and infinite dog dB by appropriately selecting the value of the above negative impedance. In principle, it was possible to set it arbitrarily.

However, this known bidirectional amplifier cannot avoid the influence of operational instability peculiar to negative impedance, and depending on the characteristics of the line impedance, it may oscillate and fail to perform normal amplification. In order to avoid such an oscillation phenomenon, the amplification gain must be significantly reduced.

Because it is difficult to achieve ideal negative impedance at high frequencies, the range of application of known bidirectional amplifiers is limited to low frequencies such as the audio signal band, and it is difficult to apply them to wideband carrier systems. It also had the disadvantage of being extremely difficult.

In order to eliminate these drawbacks, the present invention combines a pair of summing amplifier circuits and six passive impedances or their equivalent circuits without using a negative impedance converter.
For two signals that share the same line and are to be transmitted in opposite directions, one
This is a configuration of two-way amplifiers.

The drawings will be explained in detail below.

The figure shows an embodiment of a bidirectional amplifier according to the present invention, with 1
and 2 are signal input/output terminals, 3 and 4 are branch points for branching the signals of terminals 1 and 2, respectively, 5 and 6 are each summing amplifier circuits, 1 is an output terminal of the amplifier circuit 5, 8 and 9 are summing terminals, respectively. The input terminals of the amplifier circuit 50 are input terminals whose signs of transfer coefficients from these input terminals to the output terminal 7 via the amplifier circuit 5 are opposite, 10 is the output terminal of the amplifier circuit 6, and 11 and 12 are the respective amplification terminals. input terminals of the amplifier circuit 6 whose transfer coefficients reaching the output terminal 10 via the circuit 6 have opposite signs;
13, 14, 15, 16, 17, and 18 are passive impedance circuits, respectively, and branch point 3 is connected to circuits 13 and 16.
The branch point 4 is connected to the output terminal 7 and the input terminal 11 through circuits 15 and 14, respectively, and the circuit 17 is connected between the terminals 7 and 12, and the terminal 9 A circuit 18 is connected between the circuits 1 and 10, respectively.

These passive impedance circuits 13 to 18 are l-terminal pair circuits in which the real part of the impedance is non-negative, and are constructed using coils, capacitors, and resistors.

Furthermore, the summing amplifier circuits 5 and 6 have input terminals with a ground potential of almost zero and an output impedance of zero, and their transfer coefficient is expressed by the transfer impedance, which is the ratio of the output voltage and the input current. .

Therefore, these summing amplifier circuits have two types of input terminals with opposite signs of transfer impedance.

It goes without saying that a summing amplifier circuit that satisfies these conditions can be easily realized using one or more so-called operational amplifiers or circuits equivalent thereto.

Next, the operation of this bidirectional amplifier will be explained.

First, a signal input to the input/output terminal 1 is branched at a branch point 3 into two components passing through either the circuit 13 or 16.

Of these, the component passing through the circuit 13 is amplified by the amplifier circuit 5 and output to the input/output terminal 2 via the circuit 15.

Since the output impedance of the amplifier circuit 6 seen from the output terminal 10 is zero, the remaining components passing through the circuit 16 are short-circuited at the output terminal 10 and do not pass through the circuits 14, 17, and 18.

Further, the component of the signal inputted to the above-mentioned input/output terminal 1 and passed through the circuit 13 is outputted to the input/output terminal 2 and reaches the input terminal 11 via the circuit 14 at the same time.

On the other hand, the same component as the signal that has reached this input terminal 11 is branched at the output terminal 7 and reaches the input terminal 12 via the circuit 18 .

As a result of these two components being differentially amplified in the amplifier circuit 6, only extremely small amounts appear at the output terminal 10.

Therefore, unnecessary signal components that are input to input/output terminal 1 and return to input/output terminal 1 via amplifier circuits 5, 6, and circuit 16 are ignored compared to the signals that were originally input to input/output terminal 1. can do.

Since this bidirectional amplifier is constructed symmetrically with respect to a signal input to input/output terminal 1 and another signal input to input/output terminal 2, the same logic as described above is applied to input/output terminal 2. This also holds true for other signals.

That is, another signal input to the input/output terminal 2 is branched at a branch point 4, the component passing through the circuit 15 is short-circuited at the output terminal T, and the component passing through the circuit 14 after branching is amplified by the amplifier circuit 6. , are output to the input/output terminal 1 via the circuit 16.

Some of the components that have passed through this circuit 16 branch off at branch point 3 and reach input terminal 8 via circuit 13, but they also branch off at output terminal 10 and reach input terminal 9 via circuit 17. As a result of being differentially amplified by the amplifier circuit 5 together with the input components, the unnecessary signal components that return to the input/output terminal 2 via the circuits 6, 5, and 15 are the same as those originally input to the input/output terminal 2. It can be ignored compared to signals.

Impedance circuit 13, 14, 15, 16, 17, 1
The impedances of 8 are respectively a, A, b, B, e
) Let it be E.

Furthermore, the transfer impedance of the amplifier circuit 5 from the input terminals 8 and 9 to the output terminal 7 is -f, , f, respectively, and the transfer impedance of the amplifier circuit 6 from the input terminals 11 and 12 to the output terminal 10 is -f2, respectively. Let it be f2.

In addition, the insertion gain due to inserting this bidirectional amplifier into the line may be G12 for the signal transmitted to terminal 1 or terminal 2.
, G21 for the signal transmitted from terminal 2 to terminal 1, and the impedances of the lines connected to terminals 1 and 2 being r and R, respectively. According to Kirchhoff's law, G12,
G21 is given by the following formula.

? μ1, μ21, β12, β21, θ,2, θ2,
are μ12 = r1/a1p21 = f2/A, respectively?
12-A/e-θ12, β2-a/E-θ21.

μ1, μ2. are the amplification gains by 5 and 6, respectively, β12,
β2 represents the differential loss caused by the amplifier circuits 6 and 5, respectively, θ12,
θ21 represents the branch loss at branch points 4 and 3, respectively.

Therefore, in each right-hand denominator of equations (1) and (2), μ12
The quantity T, .mu.2.beta.1.beta.2 -T, represents the one-round gain of the closed loop including the amplifier circuits 5 and 6, that is, the so-called feedback ratio.

According to Nyquist's stability criterion, when this complex vector T changes the real frequency from zero to infinity,
The bidirectional amplifier shown in the figure always operates stably under the condition that it does not go around the critical point T=1 on the complex plane of T.

Such a condition is μ1.

Alternatively, this can be achieved by shaping the frequency characteristics of μ2, selecting each passive impedance constituting β12 and β2, etc.

That is, the bidirectional amplifier in this figure operates as a negative feedback amplifier for both transmission directions from terminal 1 to terminal 2 and from terminal 2 to terminal 1.

Therefore GI2 or G2. It is easy to train a dog to do this.

In addition, the input impedance seen from terminals 1 and 2 is Z1, respectively.
, Z2, zl and z2 are given by the following equations.

Z1= aB/ (a 10B) (3
)Z2-Ab/(A+b) (4) Formula (1)
, (2) each represents a parallel connection of two passive impedances, it is extremely easy to match Z1z2 to the line impedances r and H of each line.

Note that the signal supplied from the terminal 10 to the amplifier circuit 5 may be supplied not only to the input terminal 9 but also to intermediate stages when the amplifier circuit 5 has a multi-stage configuration.

Then, for example, a variable resistor in the circuit 18 is adjusted so that the voltage reaching the terminal 8 from the output terminal 10 through the circuits 16 and 13 and the voltage reaching the terminal 9 through the circuit 18 are canceled out. The remaining adjustment is carried out by the amplifier circuit 5.
The level of the signal at terminal 10 supplied to the intermediate stage can be adjusted to achieve as complete cancellation as possible.

Similarly, a signal may be supplied from the terminal 7 to the intermediate stage of the amplifier circuit 6.

Also, even if the above negation is not completely performed in the upper eido,
Since each signal is subjected to negative feedback amplification, oscillation does not occur, and the point is that other signals are sufficiently suppressed compared to the input signal.

As explained above, according to the bidirectional amplifier of the present invention, it is possible to realize an extremely high amplification gain that is impossible with known bidirectional amplifiers, and at the same time, it operates extremely stably.

Furthermore, since impedance matching to the line is easy, the influence of reflected waves at the input and output ends can be ignored.

Furthermore, since this bidirectional amplifier is constructed from only one terminal-pair passive impedance and a summing amplifier circuit, which are easy to implement, it can handle frequencies ranging from low frequencies such as the audio signal band to high frequencies such as the television signal band and the ultra-multi-carrier band. Bidirectional amplification can be achieved over a wide frequency range.

Therefore, according to the present invention, not only two-wire baseband transmission of audio signals, which was the field of application of conventional bidirectional amplifiers, but also two-wire two-way baseband transmission of television signals and coaxial cables as a transmission medium can be achieved. Ultra-multiplexed two-way transmission has also become possible, and the economical effects such as halving the line cost are great.
New communication services can be provided.

[Brief explanation of drawings]

The figure is a circuit configuration diagram showing an embodiment of a bidirectional amplifier according to the present invention. 1, 2: Signal input/output terminal, 3, 4: Signal branch point, 5, 6
: Addition amplifier circuit, 7: Output terminal of amplifier circuit 5, 8, 9:
Amplification circuit 50 input terminal, 10: output terminal of amplifier circuit 6,
11, 12: amplifier circuit 60 input terminal, 13-18: passive impedance.

Claims (1)

[Claims] 1 A first summing amplifier circuit that amplifies a signal input to the first terminal and outputs it to the second terminal, and a second summing amplifier circuit that amplifies another signal input to the second terminal and outputs it to the first terminal. a summing amplifier circuit; and a first summing amplifier circuit connected to apply an input proportional to the output of the first summing amplifier circuit to the second summing amplifier circuit.
an impedance circuit; and a second impedance circuit connected to apply an input proportional to the output of the second summing amplifier circuit to the first summing amplifier circuit;
The first and second terminals are connected to the first and second terminals so that the signal inputted to the terminal and outputted to the second terminal, and the signal inputted to the second terminal and outputted to the first terminal are negative feedback amplified.
A bidirectional amplifier characterized in that the gain of the summing amplifier circuit and the impedance of the first and second impedance circuits are selected.