JP3182735B2 - Low noise distributed amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed amplifier having improved low noise characteristics.

[0002]

2. Description of the Related Art Generally, in a distributed amplifier, the input / output capacity of a transistor and the inductance component of a transmission circuit are determined by the following factors.
Characteristic impedance 50 with very high cutoff frequency
Since the Ω LC transmission circuit is configured, the influence of the input / output capacitance of the transistor is canceled by being taken into this transmission circuit. For this reason, distributed amplifiers are suitable for widening the band, and are widely used in fields requiring wideband amplification, such as optical transmission devices and measuring devices.

FIG. 9 is a diagram showing a configuration of a conventional general distributed amplifier. In this example, a grounded source field effect transistor is used as a unit amplifier element, and four unit circuits (hereinafter, referred to as “sections”) each including a unit amplifier element and a transmission line are connected. Has become.

In FIG. 9, Q1 is a source-grounded field effect transistor, Ti is a transmission line (or inductance element), To is a transmission line (or inductance element),
Ri is the terminating resistance of the input side transmission circuit, and Ro is the terminating resistance of the output side transmission circuit. IN is an input terminal, and OUT is an output terminal.

In FIG. 9, an input-side transmission circuit is formed by the transmission line (or inductance element) Ti and the input capacitance of the transistor Q1, and an output-side transmission circuit is formed by the transmission line (or inductance element) To and the output capacitance of the transistor Q1. Are formed, and resistors Ri and Ro are used in the termination circuit.

Generally, in order to improve the gain characteristics and reflection characteristics of a distributed amplifier over a wide band, the characteristic impedance and the terminating resistance of a transmission circuit are set to 50Ω.

[0007]

However, although the conventional distributed amplifier is suitable for widening the band as described above, it has a drawback that noise characteristics are poor as described below.

FIG. 10 is a diagram showing a low frequency equivalent circuit of the conventional distributed amplifier of FIG. Since the effect of the transmission line is not exhibited at low frequencies, the distributed amplifier is simply a circuit in which four source-grounded transistors Q1 are connected in parallel, and a resistor Ri is connected to the input terminal and a resistor Ro is connected to the output terminal. From FIG. 10, it can be seen that at low frequencies, the noise of the termination resistor Ri is amplified and generated at the output terminal, deteriorating the noise characteristics of the distributed amplifier.

FIG. 11 is a diagram showing a typical example of the characteristics of a conventional distributed amplifier. In FIG. 11, S21 is a gain, S1
1, S22 are input and output reflection coefficients, respectively, and NF is a noise figure. In this characteristic example, the gain S21 is 18 GH
It can be seen that the noise figure NF is degraded at low frequencies, but the noise figure NF is degraded at around 9 GHz, which is almost half of the band, although it is flat near z.

As described above, the conventional distributed amplifier has a disadvantage that the noise figure is large. Therefore, when the conventional distributed amplifier is used in a portion for amplifying a weak signal such as a receiving unit of a communication device,
There is a problem that the reception sensitivity is degraded due to the noise signal.

An object of the present invention is to solve the above-mentioned disadvantages,
An object of the present invention is to provide a distributed amplifier having low noise and wide band characteristics.

[0012]

An object of the present invention is to distribute and connect a plurality of amplifying elements between an input-side transmission circuit and an output-side transmission circuit, and to provide an input on the opposite side of the input-side transmission circuit from the input terminal side. In a distributed amplifier in which a side termination circuit is connected and an output side termination circuit is connected to the output terminal side of the output side transmission circuit opposite to the output terminal side, a gate or a base is connected to the input side termination circuit to the input side transmission circuit. A common-source or common-emitter transistor, a feedback circuit including at least a series resistor connected between the drain or collector of the transistor and the gate or base, and the drain or collector of the transistor and a first power supply terminal. And a first bias circuit including at least a series resistor connected between the first bias circuit and the low noise distributed amplifier.

In the present invention, a second bias circuit including at least a series resistor can be connected between the gate or base of the transistor and a second power supply terminal.

Further, in the present invention, a transmission line or an inductance element can be inserted between the gate or base of the transistor and the input side transmission circuit.

[0015]

According to the present invention, even when a termination impedance of 50 Ω is realized as in the prior art, the noise generated in the termination circuit is reduced as compared with the case of terminating only with a resistor, and a distributed amplifier having a good noise figure is provided. realizable.

[0016]

Embodiments of the present invention will be described below. FIG. 1 is a circuit diagram of a distributed amplifier according to one embodiment. Here, as the amplification element A serving as a unit, a transistor amplifier circuit of various types such as a common source, a common emitter and the like can be used. B is a termination circuit of the input side transmission circuit.

FIGS. 2A to 2D are diagrams showing various examples of the configuration of the termination circuit B. FIG. (A) to (d) in FIG.
And VD and VG are power supply terminals.
First, the termination circuit of FIG.
A feedback circuit B1 is connected between the drain and the gate of the first circuit, and a first bias circuit B2 is connected between the drain and the power supply terminal VD.
Are connected. The termination circuit of (b)
(A) In addition to the configuration of the termination circuit, a second bias circuit B3 is connected between the gate of the transistor Q2 and the power supply terminal VG.
Are connected. The termination circuit of (c) is
The transmission circuit (or inductance element) T1 is connected to the input path to the gate in the terminal circuit of FIG. The termination circuit of (d) is configured by connecting a transmission line (or an inductance element) T1 to the input path to the gate in the termination circuit of (b).

FIG. 3A is a diagram showing a specific circuit of the feedback circuit B1, and FIG. 3B is a diagram showing a specific circuit of the first bias circuit B2 and the second bias circuit B3. In the figure, g
Is a connection terminal to the gate of the transistor Q2, and d is a connection terminal to the drain. T2 and T3 are transmission lines (or inductance elements), R2 to R4 are resistors, and C2 and C3 are capacitors. The circuits B1 to B3 have a configuration including a transmission line (or an inductance element), a resistor, and a capacitor, but may have a configuration including at least the series resistors R2 and R3.

FIG. 4 shows a conventional grounded source transistor Q1 as a conventional amplifier element A and a termination circuit B.
2 uses the circuit shown in FIG. In particular, here, only the resistor R2 is used as the feedback circuit B1, and only the resistor R3 is used as the first bias circuit B2.

The operation will be described with reference to the circuit shown in FIG. In order to derive the impedance Z when viewing the termination circuit B from the point a in FIG. 4 and the noise voltage nz at the point a, FIG. 5 shows an equivalent circuit for the noise of the termination circuit B, and FIG. showed that. 5 and 6, gm is the transconductance of the transistor Q2, Cm
gs is the gate-source capacitance of the transistor Q2, id
n is a noise current source of the transistor Q2, and en2 is a resistor R2.
A noise voltage source of En3 indicates a noise voltage source of R3.

When the impedance Z and the noise voltage nz of the terminal circuit B at a low frequency are obtained from these equivalent circuits, they are as follows. Where k is Boltzmann's constant, T is temperature, and P is a parameter of the noise current of the transistor.
This P is approximately 1. Z = (R2 / R3 + 1) / gm (1) nz = [4 · k · T · (Z / R3 + P) / gm] ^1/2 = (4 · k · T · Zeff) ^1/2 ·· ( 2) Here, Zeff = (Z / R3 + P) / gm.

On the other hand, the impedance Z and the noise voltage nz of the terminating resistor Ri of the conventional distributed amplifier shown in FIG. 9 are as follows. Z = Ri (3) enz = (4kT Ri) 1/2 (4)

In the distributed amplification of the present invention, when the impedance is set to the same value of 50Ω, the noise voltage of the termination circuit B of the present invention is smaller than the noise voltage of the termination resistor Ri of the conventional distributed amplifier. It is improved compared to.

Here, as a numerical example, the transistor Q2
G having a gate width of 100 μm and a gate length of 0.3 μm
When the MAsFET of aAs is used, gm is usually 40 m.
S, and if R2 = 300Ω and R3 = 100Ω,
The impedance Z of the termination circuit B of the present invention is 50Ω,
At this time, Zeff in equation (2) is 40Ω or less. on the other hand,
Since Ri = 50Ω in the conventional terminating resistor, a comparison of Equations (2) and (4) shows that the present invention has a lower noise voltage.

In the termination circuit B of the present invention, the gate-source capacitance Cgs of the transistor Q2 is added. However, the capacitance Cgs does not affect the frequency characteristics.
Broadband characteristics can be obtained as in the case of a conventional distributed amplifier.

The reason is that the signal component reflected at the point a due to the influence of the capacitance Cgs reaches the output terminal OUT through the input / output transmission circuit, but the signal from the point a to the output terminal OUT is distributed in the distributed amplifier. Since there is a phase difference due to the sum of the different transmission paths, they cancel each other out, and the number of signals reaching the output terminal OUT is extremely small. Therefore, there is no effect on the output signal of the capacitance Cgs,
Therefore, the gain does not affect the frequency characteristics.

FIGS. 7 and 8 show the experimental results of the characteristics of the distributed amplifier of the present invention shown in FIG. FIG. 7 shows a change in frequency of the impedance of the termination circuit B from 0 to 30 GHz on a Smith chart. It can be seen from FIG. 7 that the impedance is approximately 50Ω at low frequencies.

FIG. 8 shows gain S21, noise figure NF, input,
FIG. 9 is a diagram illustrating frequency characteristics of output reflection coefficients S11 and S22. When the noise figure of FIG. 8 is compared with the conventional result of FIG. 11, it can be seen that the noise figure is improved, and particularly at a low frequency, a large improvement of about 1 dB is seen. It can also be seen that the frequency and characteristics of the gain S21 are comparable to those of a conventional distributed amplifier.

From the above, it can be seen that the distributed amplifier according to the present invention can obtain lower noise characteristics as compared with the conventional one.
Further, it can be seen that a wide band characteristic of the gain can be obtained as in the related art.

Although the termination circuit B has been described as a circuit shown in FIG. 4, the same effect can be obtained by using any of the configurations of the termination circuits shown in FIGS. A similar effect can be obtained without depending on the number of sections constituting the distributed amplifier. Further, in the above description, a case where a field-effect transistor is used as a transistor has been described. However, a bipolar transistor can be used instead. In this case, the transistor circuit has a common emitter.

[0031]

As described above, according to the present invention, it is possible to realize a distributed amplifier with low noise and wide band characteristics, so that it is possible to increase the sensitivity and speed of a communication transmission device and an electrical measurement device. There are advantages.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a low noise distributed amplifier according to an embodiment of the present invention.

FIG. 2 is a diagram showing each example of an input-side termination circuit according to an embodiment of the present invention.

FIG. 3 is a specific circuit diagram of a feedback circuit and first and second bias circuits constituting a termination circuit in FIG. 2;

FIG. 4 is a circuit diagram of a low noise distribution amplifier according to the present embodiment to which a specific termination circuit is connected.

5 is a diagram showing an equivalent circuit with respect to noise of a termination circuit of the low noise distribution amplifier of FIG.

6 is a diagram showing an equivalent circuit for a signal of a termination circuit of the low noise distribution amplifier of FIG.

FIG. 7 is a Smith chart showing a frequency change of the impedance of the termination circuit of the low noise distribution amplifier of FIG. 4 from 0 to 30 GHz.

FIG. 8 is a diagram illustrating frequency characteristics of gain, noise figure, and reflection coefficient of the distributed amplifier of FIG. 4;

FIG. 9 is a circuit diagram of a conventional distributed amplifier.

10 is a diagram showing an equivalent circuit at a low frequency of the conventional distributed amplifier of FIG. 9;

11 is a diagram illustrating frequency characteristics of gain, noise figure, and reflection coefficient of the conventional distributed amplifier of FIG. 9;

[Explanation of symbols]

Ri, Ro: terminal resistance, Q1, Q2: grounded source field effect transistor, Ti, To, T1 to T4: transmission line (or inductance element), S21: gain, S11:
Input reflection coefficient, S22: Output reflection coefficient, NF: Noise figure, A: Amplifier element, B: Termination circuit, B1: Feedback circuit, B
2: a first bias circuit, B3: a second bias circuit,
VD, VG: power supply terminal, Cgs: gate-source capacitance of transistor, gm: transconductance of transistor, en2: noise voltage source by resistor R2, en3: noise voltage source by resistor R3, idn: noise current source of transistor.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-205458 (JP, A) JP-A-5-251962 (JP, A) German Patent Application Publication No. 4123437 (DE, A1) (58) Search Field (Int.Cl. ⁷ , DB name) H03F 3/60

Claims (3)

(57) [Claims] A plurality of amplifying elements distributedly connected between an input side transmission circuit and an output side transmission circuit; an input side termination circuit connected to a side of the input side transmission circuit opposite to an input terminal side; In a distributed amplifier having an output-side termination circuit connected to the output terminal side of the transmission circuit opposite to the output-side termination circuit, the input-side termination circuit is connected to a source-grounded or emitter-grounded transistor whose gate or base is connected to the input-side transmission circuit; A feedback circuit including at least a series resistor connected between the drain or collector of the transistor and the gate or base, and at least a series resistor connected between the drain or collector of the transistor and a first power supply terminal. A low noise distributed amplifier comprising a first bias circuit including the first bias circuit. 2. The low noise distribution amplifier according to claim 1, wherein a second bias circuit including at least a series resistor is connected between said gate or base of said transistor and a second power supply terminal. . 3. A transmission line or an inductance element is inserted between the gate or the base of the transistor and the input-side transmission circuit.
2. The low noise distribution amplifier according to 1.