JP2013135304A - Balanced wideband amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balanced wideband amplifier that suppresses harmonics in a compact circuit configuration.SOLUTION: A bandpass circuit comprises a pair of series resonance circuits 8a, 8b that become resonant at a frequency 2fwhich is double a low end fof an operating frequency band of a pair of unit amplifiers 4a, 4b, and an N type FET 11 connected in series between the pair of series resonance circuits 8a, 8b. The bandpass circuit is connected between output terminals of the pair of unit amplifiers 4a, 4b.

Description

  The present invention relates to a balanced wideband amplifier having an operating frequency band width of one octave or an operating frequency band width of one octave or more.

In a balanced wideband amplifier having an operating frequency band width of 1 octave or an operating frequency band width of 1 octave or more, a low-frequency end f _L component and a low-frequency end f _L component in the operating frequency band Both components of the frequency 2f _L corresponding to the second harmonic wave are included in the passband of the amplifier itself.
Therefore, when the operating frequency of the balanced broadband amplifier is f _L , a push-pull amplifier composed of a 180 ° power distribution / combination circuit is used when it is necessary to suppress the radiation of the harmonic component of the frequency 2f _L. May be. Alternatively, a filter having a switching function or a variable function may be connected to the outside of the amplifier.

Here, FIG. 3 is a block diagram showing a balanced broadband amplifier disclosed in the following Patent Document 1, and this balanced broadband amplifier is a push-pull amplifier using a 180 ° power combining / distributing circuit (balun). It is.
The push-pull amplifier of FIG. 3, when the frequency of the signal to be amplified is f _L, the output terminal of the pair of units amplifiers constituting the amplifier, become reverse phase component of the frequency f _L from each other, The component of the second harmonic 2f _L of the frequency f _L is in phase.
Therefore, in the 180 ° power combining circuit on the output side, the two components of the frequency f _L are combined and output, but the components of the second harmonic 2f _L cancel each other out of phase and are not output.

FIG. 4 is a configuration diagram showing a balanced broadband amplifier in which a switching filter composed of an SPDT (Single-Pole Dual-Throw) switch is connected to the output side of the broadband amplifier.
In wideband amplifier, a low-frequency end of the operating frequency band when the f _L, since the second harmonic frequency 2f _L frequency f _L is included in the operating frequency band, when amplifying the component of the frequency f _L, twice The radiation of the wave frequency 2f _L cannot be suppressed.
Therefore, in the balanced broadband amplifier of FIG. 4, to connect the SPDT switch to the output end of the wide-band amplifier, the SPDT switch, the transmission line passing the second harmonic frequency 2f _L, the passage of the second harmonic frequency 2f _L The filter to be blocked is switched.
Thereby, when the operating frequency of the broadband amplifier is the frequency f _L , the radiation of the second harmonic 2f _L is suppressed by switching the SPDT switch to the filter side, and when the operating frequency of the broadband amplifier is the second harmonic frequency 2f _L By switching the SPDT switch to the transmission line side, the amplified second harmonic 2f _L component can be passed.

Japanese Patent Laid-Open No. 11-112252 (FIG. 1)

Since the conventional balanced broadband amplifier is configured as described above, the component of the second harmonic 2f _L can be suppressed. However, in the push-pull amplifier, the reflected waves from the pair of unit amplifiers are in phase with each other. Due to the synthesis, there is a problem that the input / output reflection coefficient of the entire amplifier becomes large. In particular, in a wide-band amplifier whose operating frequency band exceeds one octave, it is difficult to keep the reflection coefficient of the unit amplifier small, and this problem tends to become apparent.
Further, SPDT switch, a transmission line which passes the second harmonic frequency 2f _L, in the method for switching a filter for blocking passage of the second harmonic frequency 2f _L, SPDT switch a plurality of SPST (Single-Pole Single- Since it is generally composed of a (Throw) switch, there is a problem in that the circuit size is increased. In addition, there is a problem that the circuit size becomes considerably large in combination with the circuit size of the transmission line and the filter constituting the switching filter.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a balanced broadband amplifier capable of suppressing harmonics with a small circuit configuration.

  The balanced broadband amplifier according to the present invention has a 90 ° hybrid that divides input power having a phase difference of 90 degrees into two, and an operating frequency band that amplifies the input power divided by the 90 ° hybrid into one octave. A pair of unit amplifiers and a 90 ° hybrid that synthesizes the input power amplified by the pair of unit amplifiers, and a pair that is in a resonance state at a frequency twice that of the low end in the operating frequency band of the pair of unit amplifiers. A band-pass circuit composed of a series resonant circuit and a single pole / single throw switch connected in series between a pair of series resonant circuits is connected between the output terminals of a pair of unit amplifiers. It is what you have.

  According to the present invention, a pair of series resonant circuits that are in a resonance state at twice the frequency of the low frequency end in the operating frequency band of the pair of unit amplifiers, and a single unit connected in series between the pair of series resonant circuits. Since the band-pass circuit composed of the pole / single throw switch is connected between the output terminals of the pair of unit amplifiers, harmonics can be suppressed with a small circuit configuration. effective.

1 is a configuration diagram illustrating a balanced broadband amplifier according to a first embodiment of the present invention. FIG. 1 is a circuit diagram showing an equivalent circuit of a balanced broadband amplifier according to Embodiment 1 of the present invention. FIG. 1 is a configuration diagram showing a balanced broadband amplifier disclosed in Patent Document 1. FIG. It is a block diagram which shows the balance type wideband amplifier by which the switching type filter which consists of SPDT switches is connected to the output side of the wideband amplifier.

Embodiment 1 FIG.
1 is a block diagram showing a balanced broadband amplifier according to Embodiment 1 of the present invention.
In FIG. 1, a dielectric substrate 1 is a substrate on which a transmission line 2, 90 ° hybrids 3, 5 and unit amplifiers 4a and 4b are formed on the display surface, but the back surface is lined with metal.
The transmission line 2 is made of a metal conductor and is formed on the surface of the dielectric substrate 1.
The 90 ° hybrid 3 is composed of, for example, a Lange coupler, and distributes the power of the input signal whose phase difference is 90 degrees into two, and outputs the distributed signal to the unit amplifiers 4a and 4b.
The distribution terminals of the 90 ° hybrid 3 are connected to the input terminals of the unit amplifiers 4a and 4b. One input terminal is connected to the input terminal of the dielectric substrate 1 through the transmission line 2, and the other input terminal. Is connected to a through hole 7 (a member for electrically connecting the front and back surfaces of the dielectric substrate 1) through a thin film resistor 6.

Unit amplifier 4a is the width of the operating frequency band is one octave or more amplifiers (e.g., if the low-frequency end f _L of the operating frequency band is a 1 GHz, the high-frequency end f _H of the operating frequency band than amplifiers 2 GHz) be The one signal distributed by the 90 ° hybrid 3 is amplified, and the amplified signal is output to the 90 ° hybrid 5 through the transmission line 2.
The unit amplifier 4b is an amplifier having an operating frequency band width of 1 octave or more, amplifies the other signal divided into two by the 90 ° hybrid 3, and sends the amplified signal to the 90 ° hybrid 5 through the transmission line 2. Output.

The 90 ° hybrid 5 is composed of, for example, a Lange coupler, and synthesizes the power of the signals amplified by the pair of unit amplifiers 4a and 4b.
The input terminal of the 90 ° hybrid 5 is connected to the output terminals of the unit amplifiers 4a and 4b. One output terminal is connected to the output terminal of the dielectric substrate 1 through the transmission line 2, and the other output terminal. Is connected to a through hole 7 through a thin film resistor 6.

One end of the series resonance circuit 8a is connected to the output terminal of the unit amplifier 4a, and is in a resonance state at a frequency 2f _L that is twice the low frequency end f _L in the operating frequency band of the unit amplifier 4a. The circuit 8a includes a high-impedance transmission line 9 that operates as an inductor, and an interdigital capacitor 10 formed by facing a comb-shaped conductor pattern.
One end of the series resonance circuit 8b is connected to the output terminal of the unit amplifier 4b, and the other end is connected to the series resonance circuit 8a via the N-type FET 11, and the low frequency end f _L in the operating frequency band of the unit amplifier 4b. The series resonance circuit 8b is a circuit that is in a resonance state at twice the frequency 2f _L , and the series resonance circuit 8b is an interdigital capacitor formed by opposing a high impedance transmission line 9 that operates as an inductor and a comb-shaped conductor pattern. 10.

The N-type FET (field effect transistor) 11 is a switch that operates as an SPST switch (single pole / single throw switch), and is connected in series between the series resonance circuit 8a and the series resonance circuit 8b. , 8b and the N-type FET 11 constitute a band-pass circuit.
When the operating frequency band width of the unit amplifier 4a is 1 octave, one band-pass circuit is connected between the output terminals of the unit amplifiers 4a and 4b, but the operating frequency band width of the unit amplifier 4a. Is one octave or more, a plurality of band-pass circuits are connected in parallel between the output terminals of the unit amplifiers 4a and 4b.
In the example of FIG. 1, two band-pass circuits are connected in parallel between the output terminals of the unit amplifiers 4a and 4b.

The electrode 13 is connected to the N-type FET 11 via a thin film resistor 12 (a resistor having a high resistance value that prevents leakage of a high-frequency component to be amplified), and supplies a control voltage to the N-type FET 11.
In the balanced broadband amplifier shown in FIG. 1, the bias circuit is not shown because the bias voltage is applied to the unit amplifiers 4a and 4b from the outside of the dielectric substrate 1.

Next, the operation will be described.
The balanced broadband amplifier of FIG. 1 is composed of unit amplifiers 4a and 4b, 90 ° hybrids 3 and 5 and the like, and these components all have an operating frequency bandwidth of 1 octave or more. Therefore, the entire amplifier also has an operating frequency bandwidth of one octave or more.

In the first embodiment, on the output side of unit amplifiers 4a and 4b constituting a balanced amplifier, a pair of series resonant circuits 8a and 8b composed of a high impedance transmission line 9 and an interdigital capacitor 10, and an SPST switch 2 and an electrode 13 for applying a control voltage to the N-type FET 11, and an equivalent circuit thereof is as shown in FIG.
The operation of the balanced broadband amplifier will be described below based on the equivalent circuit shown in FIG.

The general advantage of balanced broadband amplifiers is that the input / output reflection coefficient seen from the input / output terminals of the entire amplifier can be reduced.
As an example, when looking at the input side of the unit amplifiers 4a and 4b, the signal input from the input terminal is divided into two by the 90 ° hybrid 3 with a phase difference of 90 ° and input to the unit amplifiers 4a and 4b, and the reflection thereof. The waves are input again to the 90 ° hybrid 3, but these reflected waves are connected to the through hole 7 via the thin film resistor 6 to which the resistor Zo is connected among the 90 ° hybrid 3 terminals. Are output in the same phase with each other and synthesized. The input terminals of the dielectric substrate 1 are output in opposite phases with each other and cancel each other.
Therefore, the resistance Zo is the 90 ° hybrid 3 input impedance (usually 50Ω), and one end thereof is electrically grounded, so that the reflected wave is absorbed by the resistance Zo, and the input reflection coefficient seen by the entire amplifier is sufficient. Can be small.
The output side reflection coefficient of the entire amplifier can be reduced by the same operation principle.

Next, another advantage (harmonic suppression function) of the balanced broadband amplifier according to the first embodiment will be described.
Since the balanced broadband amplifier of FIG. 1 has an operating frequency bandwidth of one octave or more as described above, a frequency 2f _{L that} is twice the low frequency end f _L in the operating frequency band is It is difficult to suppress harmonics that are included in the operating band and are generally required when operating a balanced broadband amplifier (particularly, it is difficult to suppress the second harmonic with a relatively high power level).

In the first embodiment, a pair of series resonance circuits 8a and 8b are provided on the output side of the unit amplifiers 4a and 4b in order to suppress only the component of the frequency 2f _L while amplifying and passing the component of the frequency f _L. (L1 and C1 series resonance circuit) and the N-type FET 11 are connected.
If a signal of frequency f _L is input from the input terminal of the entire amplifier at a phase angle of 0 °, the phase angle of the component of frequency f _L at the input terminals of the unit amplifiers 4a and 4b is 0 ° and −90 °, respectively. At the output terminals of the unit amplifiers 4a and 4b, the components of the amplified frequency f _L become phase angles of 0 ° and −90 °, respectively (the passing phase shift amount of the unit amplifier is considered to be 0 °).

On the other hand, the unit amplifier 4a, the nonlinearity of 4b, the unit amplifier 4a, the output terminal of the 4b, but the component of the frequency 2f _L occurs, the phase angle are each 0 °, -180 °, and the frequency f _L Twice the component.
Therefore, the circuit symmetry plane shown in FIG. 2 has an electrically shorting plane for the component of the frequency 2f _L, the series resonant circuit 8a shown in FIG. 2, the resonant frequency of 8b as 2f _L, on state N-type FET11 By setting (the electrode 13 applies a positive control voltage to the N-type FET 11), both the points A and B in FIG. 2 become electrical short-circuit points at the frequency 2f _L.
For this reason, the component of the frequency 2f _L is totally reflected at the points A and B, and is not output to the output terminal of the entire amplifier.

Since the impedance of the series resonant circuits 8a and 8b is sufficiently large if the frequency is f _L , the influence of the series resonant circuits 8a and 8b can be ignored at points A and B in FIG. The component of f _L is output to the output terminal of the entire amplifier with almost no loss.
At this time, even if the input frequency to the amplifier becomes somewhat higher than f _L , the point A and the point B are close to an electrical short circuit at the frequency of the second harmonic, so that a constant second harmonic It is possible to exhibit suppression characteristics.

However, the second harmonic frequency range that can be cut off by the series resonant circuits 8a and 8b is limited to some extent.
In the first embodiment, another series resonance circuit 8a, 8b (series resonance circuit of L2, C2) shown in FIG. 2 is used in order to suppress the second harmonic frequency that cannot be handled by the series resonance circuits 8a, 8b. And N-type FET 11 are connected.
The series resonant circuit 8a, the 8b (L2, C2 series resonance circuit), and the series resonant frequency is set to a higher frequency 2f _L 'than 2f _L, the principle similar to the operation described above, the input frequency to the amplifier It is possible to suppress the frequency component of the second harmonic 2f _L 'when is _{L L} (> f _L ).

For example, the operating frequency bandwidth of the wideband amplifier 1: in the case of 3 (Teiikitan f _L, Koikitan 3f _L), it can be considered that a 2f _L '≒ 3f _L.
In the first embodiment, when the frequency to be amplified input to the amplifier is 2f _L or 2f _L ′ instead of the above-described f _L or f _L ′, the series resonant circuits 8a and 8b ( The N-type FET 11 of the L1 and C1 series resonance circuit or the L2 and C2 series resonance circuit) is turned off so that the series resonance circuits 8a and 8b have almost no influence at the frequency 2f _L or 2f _L ′.
As a result, it is possible to configure a high-gain wideband amplifier that has no unnecessary internal loss at the frequency 2f _L or 2f _L ′.

Note that the passband circuit composed of the series resonance circuits 8a and 8b (L1, C1 series resonance circuit or L2, C2 series resonance circuit) and the N-type FET 11 is located at the points A and B in FIG. Instead, it is conceivable to connect to the output terminal of the entire balance amplifier (at the position of point C in FIG. 2).
However, in this case, when the N-type FET 11 is turned off, the voltage applied to the N-type FET 11 becomes larger than that in the case of the first embodiment. There arises a problem that there is an increased possibility of communication quality deterioration due to an increase in distortion signal components.
By adopting the configuration of the first embodiment, it is possible to reduce those possibilities.

  In this way, in a balanced broadband amplifier composed of 90 ° hybrids 3 and 5 and unit amplifiers 4a and 4b and having an operating frequency band width of 1 octave or more, a pair of series resonances between the output terminals of the unit amplifiers 4a and 4b. By connecting the circuits 8a and 8b and the passband circuit composed of the N-type FET 11 and appropriately switching the N-type FET 11 in accordance with the signal frequency to be amplified, the input / output reflection coefficient is reduced over a wide band. Even when the harmonic of the frequency of the target signal is included in the amplification band of the amplifier itself, the harmonic can be suppressed.

  In the present invention, any constituent element of the embodiment can be modified or any constituent element of the embodiment can be omitted within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 Dielectric board | substrate, 2 Transmission line, 3,5 90 degree hybrid, 4a, 4b Unit amplifier, 6 Thin film resistor, 7 Through hole, 8a, 8b Series resonance circuit, 9 High impedance transmission line, 10 Interdigital capacitor, 11 N-type FET (single pole / single throw switch), 12 thin film resistors, 13 electrodes.

Claims (2)

A 90 ° hybrid that splits input power with a phase difference of 90 degrees into two, a pair of unit amplifiers that have an operating frequency band width of 1 octave for amplifying the input power split into two by the 90 ° hybrid, and the pair In a balanced wideband amplifier comprising a 90 ° hybrid that synthesizes input power amplified by unit amplifiers of
A pair of series resonant circuits that resonate at a frequency twice the lower end in the operating frequency band of the pair of unit amplifiers, and a single pole / single throw connected in series between the pair of series resonant circuits A balanced wideband amplifier characterized in that a band-pass circuit composed of a switch is connected between the output terminals of the pair of unit amplifiers. A 90 ° hybrid that divides input power with a phase difference of 90 degrees into two, a pair of unit amplifiers that have an operating frequency band width of 1 octave or more for amplifying the input power divided into two by the 90 ° hybrid, and In a balanced wideband amplifier comprising a 90 ° hybrid that synthesizes input power amplified by a pair of unit amplifiers,
A pair of series resonant circuits that resonate at a frequency twice the lower end in the operating frequency band of the pair of unit amplifiers, and a single pole / single throw connected in series between the pair of series resonant circuits A balanced broadband amplifier characterized in that a plurality of band-pass circuits composed of switches are connected in parallel between the output terminals of the pair of unit amplifiers.

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