JPH10145147A - Low-distortion amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-distortion amplifier circuit simple in circuit configuration. SOLUTION: Resonance circuits 3, 6 have a resonance frequency twice an input signal frequency fm, and resonance circuits 4, 7 have a resonance frequency thrice an the frequency fm. A 2nd harmonic component outputted from an amplifier 5 is given to a load circuit 12 through the resonance circuit 6, and a 3rd harmonic component is given to a load circuit 13 via the resonance circuit 7. The load circuit 12 delays the 2nd harmonic component and reflects the delayed component toward the resonance circuit 6, and the load circuit 13 delays the 3rd harmonic component and reflects the delayed component toward the resonance circuit 7. The delay times above are selected so that the harmonic component from the amplifier 5 and the harmonic components returned from the resonance circuits 6, 7 are in opposite phase, and the distortion components are cancelled. Furthermore, the 2nd harmonic component given to an input side of the amplifier 5 is reinjected to the amplifier 5, the resonance circuit 3, and the a circuit 10 and the 3rd harmonic component is reinjected to the amplifier 5 the resonance circuit 4 and the load circuit 11, so that a distortion component generated from the amplifier 5 is minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low distortion amplifier circuit used in a high-frequency (several 100 MHz to several GHz band) transmission system such as a communication system.

[0002]

2. Description of the Related Art In a high-frequency transmission system of several hundred MHz to several GHz, non-linear distortion such as harmonic distortion generated in an amplifier when amplifying a high-frequency signal becomes a problem. A distortion amplifier circuit is used.

Conventionally, as such a low distortion amplifier circuit, there have been a feedforward amplifier circuit and a predistortion amplifier circuit. The feedforward amplifier circuit has a main amplifier and an auxiliary amplifier, a distortion detection loop is provided between the input and output terminals of the main amplifier, and a distortion removal loop using an auxiliary amplifier is provided on the output side of the main amplifier. The distortion component of the main amplifier detected by the detection loop is superimposed on the output signal of the main amplifier via the auxiliary amplifier, and low distortion is realized by adjusting the amplitude and phase of the auxiliary amplifier.

The pre-distortion type amplifier circuit is
Provide a pre-distortion circuit on the input side of the main amplifier,
By distorting an input signal in advance by a pre-distortion circuit and inputting the input signal to a main amplifier, the distortion component generated in the pre-distortion circuit cancels the distortion component generated in the main amplifier.

[0005]

However, the feed-forward type amplifier circuit has a disadvantage that the circuit configuration becomes complicated because the distortion removal loop and the distortion detection loop are provided. Also, in the predistortion type amplifier circuit, since the distortion characteristics of the predistortion circuit and the distortion characteristics of the main amplifier are not completely the same, the configuration of the control circuit of the predistortion circuit is complicated to obtain a sufficient degree of improvement. There were drawbacks.

An object of the present invention is to solve such a conventional problem and to provide a low distortion amplifier circuit having a simple circuit configuration.

[0007]

According to a first aspect of the present invention, there is provided a low distortion amplifier circuit comprising: an amplifier for amplifying an input signal; a first capacitor connected in series; A first resonance circuit comprising a first coil, one end of which is connected to an input terminal of the amplifier, a first load circuit which is connected to the other end of the first resonance circuit, and a second capacitor which is connected in series And a second coil, one end of which is connected to an input terminal of the amplifier.
A second load circuit connected to the other end of the resonance circuit, a third resonance circuit including a third capacitor and a third coil connected in series, one end of which is connected to an output terminal of the amplifier;
A third load circuit connected to the other end of the third resonance circuit, a fourth resonance circuit including a fourth capacitor and a fourth coil connected in series, one end of which is connected to an output terminal of the amplifier; A fourth load circuit connected to the other end of the fourth resonance circuit, wherein a resonance frequency of the first and third resonance circuits is twice the frequency of the input signal frequency, The resonance frequencies of the second and fourth resonance circuits are three times the input signal frequency, and each of the load circuits reflects a signal component passing through the corresponding resonance circuit with a predetermined delay. It is characterized by.

A low distortion amplifier circuit according to a second aspect of the present invention comprises an amplifier for amplifying an input signal, a first capacitor and a first coil connected in series, and one end is connected to an input terminal of the amplifier. A first resonance circuit, a first resistor for terminating the other end of the first resonance circuit, a second capacitor and a second coil connected in series, and one end connected to an input terminal of the amplifier. The second resonance circuit, and the second resonance circuit
A third resistor terminating the other end of the resonance circuit, a third resonance circuit having a third capacitor and a third coil connected in series, one end of which is connected to an output terminal of the amplifier; A third resistor terminating the other end of the resonance circuit, a fourth resonance circuit including a fourth capacitor and a fourth coil connected in series, one end of which is connected to an output terminal of the amplifier;
A fourth resistor for terminating the other end of the fourth resonance circuit, wherein the resonance frequency of the first and third resonance circuits is twice the frequency of the input signal frequency; The resonance frequency of the fourth resonance circuit is three times the input signal frequency.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment FIG. 1 is a circuit configuration diagram of a high-frequency low distortion amplifier circuit according to a first embodiment of the present invention. The main frequency fm of the input signal of this low distortion amplifier circuit is, for example, 800 [MHz] to 2 [GH].
z], and here fm = 800 [MHz].

The low distortion amplifier circuit shown in FIG. 1 includes an input side protection isolator 1, an input side low pass filter 2, an input side 2 × fm series resonance circuit 3 (first resonance circuit), and an input side 3 × fm. The series resonance circuit 4 (second resonance circuit), the amplifier 5, the output side 2 × fm series resonance circuit 6 (third resonance circuit), and the output side 3 × fm series resonance circuit 7 (fourth resonance circuit) ), The output side low-pass filter 8, the output side protection isolator 9, and the input side 2 × fm series load circuit (Z1) 1.
0 (first load circuit), input side 3 × fm series load circuit (Z2) 11 (second load circuit), and output side 2 × fm series load circuit (Z3) 12 (third load circuit) And the output side 3 × fm series load circuit (Z4) 12 (fourth load circuit)
And

The input side protection isolator 1 has its input terminal connected to the signal input terminal IN, its output terminal connected to the input terminal of the input side low-pass filter 2, and has an input signal vin (fm) having a main frequency fm. To the input side low-pass filter 2 and the input side low-pass filter 2
Of the signal from the terminal to the signal input terminal IN is prevented.
The output-side protection isolator 9 has its input terminal connected to the output terminal of the output-side low-pass filter 8 and its output terminal connected to the signal output terminal OUT, and outputs the output signal of the output-side low-pass filter 8 to the signal output terminal. While transmitting to the OUT side, it prevents the signal from flowing from the signal output terminal OUT.

The input side low-pass filter 2 has an output terminal connected to the input terminal of the amplifier 5, and an input signal v.
Limit the passband of in (fm). The output side low-pass filter 8 has an input terminal connected to the output terminal of the amplifier 5 and limits the pass band of the signal vao appearing at the input terminal.

The amplifier 5 has a signal v appearing at its input terminal.
ai is amplified. When the amplifier 5 amplifies a single-wavelength signal having a frequency fm, a distortion component mainly including a harmonic component having a frequency of 2 × fm and a harmonic component having a frequency of 3 × fm is generated. The low-pass filter 8 alone cannot completely remove it. This distortion component also flows out to the input terminal.

The input side 2 × fm series resonance circuit 3 (hereinafter simply referred to as (2fm) resonance circuit 3) has a capacitor C
1 and a coil L1 connected in series, and one end of the LC series resonance circuit is connected to the input terminal of the amplifier 5. The resonance frequency of the (2fm) resonance circuit 3 is set to 2 × fm, which is twice the main frequency fm of the input signal vin (fm). The input side 2 × fm series resonance circuit 4 (hereinafter simply referred to as “(3fm) resonance circuit 4”) is an LC series resonance circuit in which a capacitor C2 and a coil L2 are connected in series, and one end of which is an amplifier 5 And its resonance frequency is set to 3 × fm.

Similarly, the output side 2 × fm series resonance circuit 6
(Hereinafter, simply referred to as (2fm) resonance circuit 6) is an LC series resonance circuit in which a capacitor C3 and a coil L3 are connected in series, and one end thereof is connected to the output terminal of the amplifier 5. The resonance frequency of the 2fm resonance circuit 6 is
(2fm) It is set to 2 × fm which is the same as that of the resonance circuit 3. The output side 3 × fm series resonance circuit 7 (hereinafter simply referred to as (3fm) resonance circuit 7) is connected to a capacitor C4
And a coil L4 connected in series, one end of which is connected to the output terminal of the amplifier 5 and whose resonance frequency is the same as that of the (3fm) resonance circuit 4.
fm.

The input side 2 × fm series load circuit 10 (hereinafter referred to as “the load circuit 10”)
(Hereinafter simply referred to as (2fm) load circuit 10) is (2f
m) The component of the signal vai that is connected to the resonance circuit 3 and passed through the resonance circuit 3 (2fm), that is, the input signal v
A distortion component mainly including a second harmonic component of in (fm) is reflected after being delayed for a predetermined time. This delay time can be adjusted. By changing the impedance of the (2fm) load circuit 10, the equivalent Q of the (2fm) resonance circuit 3 can be adjusted. Here, the equivalent Q of the (2fm) resonance circuit 3 indicates the Q of the resonance circuit constituted by the impedance up to the reflection end of the (2fm) resonance circuit 3 and the (2fm) load circuit 10.

The input side 3 × fm series load circuit 11 (hereinafter referred to as the
(Notated simply as (3fm) load circuit 11) is (3f
m) The component of the signal vai that is connected to the resonance circuit 4 and (3fm) has passed through the resonance circuit 4, that is, the input signal v
The distortion component mainly including the third harmonic component of in (fm) is reflected after being delayed for a predetermined time. This delay time can be adjusted. By changing the impedance of the (3fm) load circuit 11, the equivalent Q of the (3fm) resonance circuit 4 can be adjusted.

Output side 2 × fm series load circuit 12
(Noted simply as (2fm) load circuit 12) is (2f
m) is connected to the resonance circuit 6 and (2fm) reflects a component of the signal vao passing through the resonance circuit 6, that is, a distortion component mainly including a second harmonic component, with a predetermined delay.
This delay time can be adjusted. In addition, this (2f
m) By changing the impedance of the load circuit 12, (2fm) the equivalent Q of the resonance circuit 6 can be adjusted.

Output side 3 × fm series load circuit 13
(Notated simply as (3fm) load circuit 13) is (3f
m) is connected to the resonance circuit 7 and (3fm) reflects a component of the signal vao passing through the resonance circuit 13, that is, a distortion component mainly including a third harmonic component, with a delay for a predetermined time. This delay time can be adjusted. By changing the impedance of the (3fm) load circuit 13, the equivalent Q of the (3fm) resonance circuit 7 can be adjusted.

Next, the operation of the low distortion amplifier circuit shown in FIG. 1 will be described. The input signal vin (fm) is input to the amplifier 5 via the input isolator 1 and the input low-pass filter 2, and the amplifier 5 amplifies the input signal. At this time, the output signal vai of the amplifier 5 includes a distortion component mainly including the second harmonic component and the third harmonic component of the input signal vin (fm).

On the output side of the amplifier 5, the distortion component mainly including the above-mentioned double harmonic component passes through the (2 fm) resonance circuit 6 and is input to the (2 fm) load circuit 12, and the above-mentioned third harmonic component The distortion component mainly including the wave component passes through the (3 fm) resonance circuit 7 and is input to the (3 fm) load circuit 13.

The (2fm) load circuit 12 delays the second harmonic component and reflects it to the (2fm) resonance circuit 6. The delay time at this time is such that the second harmonic component is output to the output terminal of the amplifier 5. After that, the time required to return to the output terminal of the amplifier 5 again is set to 1 / (2 × 2 × fm). The (3fm) load circuit 13 delays the third harmonic component and reflects it to the (3fm) resonance circuit 7. The delay time at this time is such that the third harmonic component is output to the output terminal of the amplifier 5. Is set so that the time required to return to the output terminal of the amplifier 5 again becomes 1 / (2 × 3 × fm).

As a result, at the output terminal of the amplifier 5, the opposite phase component of the second harmonic component of the distortion component output from the amplifier 5 is injected from the (2fm) resonance circuit 6, and
The opposite harmonic component of the higher harmonic component is injected from the (3fm) resonance circuit 7, and the distortion component output from the amplifier 5 is canceled.

On the input side of the amplifier 5, the signal v
The distortion component mainly including the second harmonic component included in ai is (2f
m) The distortion component mainly including the third harmonic component included in the signal vai is input to the load circuit 10 after passing through the resonance circuit 3 (2fm), and passes through the (3fm) resonance circuit 4 to load (3fm). Input to the circuit 11.

The (2fm) load circuit 10 delays the second harmonic component and reflects it to the (2fm) resonance circuit 3, and the (3fm) load circuit 11 delays the third harmonic component. (3fm) and is reflected by the resonance circuit 4. (2fm)
The distortion components reflected by the load circuit 10 and the (3fm) load circuit 11 are again input to the amplifier 5 via the (2fm) resonance circuit 3 and the (3fm) resonance circuit 4, and the amplifier 5 amplifies the distortion component. At this time, the delay time of the (2fm) load circuit 10 and the (3fm) load circuit 11 is such that, when the (2fm) resonance circuit 6 and the (3fm) resonance circuit 7 are separated, the distortion component included in the output signal of the amplifier 5 is Set to be the smallest. That is, the amplification output of the distortion component re-injected into the amplifier 5 is set so as to cancel the distortion component generated in the amplifier 5 by the amplification of the input signal vin (fm).

As described above, according to the first embodiment,
A circuit in which a resonance circuit having a resonance frequency of 2 × fm and a load circuit for delay reflection are connected in series to the input side and the output side of the amplifier 5, respectively, and a resonance circuit having a resonance frequency of 3 × fm and a load for delay reflection. Provide a circuit in series with the circuit,
The 2nd and 3rd harmonic components output from the amplifier 5 are inverted in phase and returned to the output terminal of the amplifier 5, and the 2nd and 3rd harmonic components appearing at the input terminal of the amplifier 5 are output. Is reinjected into the amplifier 5, the distortion component of the amplifier 5 can be removed with a simple circuit configuration that does not use a feedback circuit such as a pre-distortion circuit and a distortion removal loop.

Second Embodiment FIG. 2 is a circuit configuration diagram of a high-frequency low-distortion amplifier circuit according to a second embodiment of the present invention. The main frequency fm of the input signal of this low distortion amplifier circuit is, for example, 800 [MHz] to 2 [GH].
z], and here fm = 800 [MHz].

The low distortion amplifier circuit shown in FIG. 2 includes an input-side protection isolator 1, an input-side low-pass filter 2, and (2 ×
fm) resonance circuit 3, (3 × fm) resonance circuit 4, amplifier 5, (2 × fm) resonance circuit 6, (3 × fm) resonance circuit 7, output-side low-pass filter 8, output side It has a protection isolator 9 and terminating resistors R1 to R4 (first to fourth resistors).

That is, the low distortion amplifier circuit shown in FIG.
At (2fm) load circuits 10, 12, and (3fm)
fm) The load circuits 11 and 13 are removed, and at the input side of the amplifier 5, (2fm) the resonance circuit 3 is terminated with the resistor R1, (3fm) the resonance circuit 4 is terminated with the resistor R2, and at the output side of the amplifier 5. , (2fm) resonance circuit 6 is terminated by a resistor R3, and (3fm) resonance circuit 7 is terminated by a resistor R4. The resistance values of the resistors R1 to R4 are, for example, 5
0 [Ω]. However, the effect of removing the distortion component is the first
Lower than the embodiment.

As described above, according to the second embodiment,
By simply terminating the resonance circuits having the resonance frequencies of 2 × fm and 3 × fm with a simple resistor, the distortion component of the amplifier 5 can be reduced with the circuit configuration simpler than that of the first embodiment (the first embodiment). Less than).

[0031]

As described above, according to the low distortion amplifier circuit of the first aspect, the second harmonic component and the third harmonic component output from the amplifier are inverted in phase and returned to the output terminal of the amplifier. By reinjecting the 2nd and 3rd harmonic components appearing at the input terminal of the amplifier into the amplifier, the circuit configuration is simple and stable without using a feedback circuit such as a pre-distortion circuit and a distortion removal loop. This has the effect of realizing a low distortion amplifier circuit having excellent characteristics.

According to the low distortion amplifier circuit of the second aspect, the circuit configuration can be further simplified by simply terminating the resonance circuit with a resistor.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a high-frequency low distortion amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a high-frequency low distortion amplifier circuit according to a second embodiment of the present invention.

[Explanation of symbols]

1 input side protection isolator, 2 input side low pass filter, 3 input side 2 × fm series resonance circuit, 4 input side 3
× fm series resonance circuit, 5 amplifiers, 6 output side 2 × fm
Series resonance circuit, 7 output 3 × fm series resonance circuit, 8
Output low-pass filter, 9 output protection isolator, 10 input 2 × fm series load circuit, 11 input 3 × fm series load circuit, 12 output 2 × fm series load circuit, 13 output side 3 × fm series load circuit , C1 to C4
Capacitor, L1-L4 coil, R1-R4 termination resistor

Claims (2)

[Claims] An amplifier for amplifying an input signal; a first resonance circuit including a first capacitor and a first coil connected in series, one end of which is connected to an input terminal of the amplifier; A first load circuit connected to the other end of the resonance circuit, a second resonance circuit including a second capacitor and a second coil connected in series, one end of which is connected to an input terminal of the amplifier; A second load circuit connected to the other end of the second resonance circuit, a third resonance circuit including a third capacitor and a third coil connected in series, one end of which is connected to an output terminal of the amplifier; A third load circuit connected to the other end of the third resonance circuit, a fourth resonance circuit including a fourth capacitor and a fourth coil connected in series, one end of which is connected to an output terminal of the amplifier; Connect to the other end of the fourth resonance circuit The load frequency of the first and third resonance circuits is twice the frequency of the input signal frequency, and the resonance frequency of the second and fourth resonance circuits is A low distortion amplifier circuit having a frequency three times as high as an input signal frequency, wherein each of the load circuits reflects a signal component having passed through a corresponding resonance circuit with a delay of a predetermined time. 2. An amplifier for amplifying an input signal, a first resonance circuit comprising a first capacitor and a first coil connected in series, one end of which is connected to an input terminal of the amplifier; A first resistor that terminates the other end of the resonance circuit, a second resonance circuit that includes a second capacitor and a second coil connected in series, and has one end connected to an input terminal of the amplifier; A second resistor for terminating the other end of the resonance circuit, a third resonance circuit including a third capacitor and a third coil connected in series, one end of which is connected to an output terminal of the amplifier; A third resistor for terminating the other end of the resonance circuit, a fourth resonance circuit including a fourth capacitor and a fourth coil connected in series, one end of which is connected to an output terminal of the amplifier; A fourth resistor that terminates the other end of the resonance circuit of The resonance frequency of the first and third resonance circuits is twice the frequency of the input signal, and the resonance frequency of the second and fourth resonance circuits is three times the frequency of the input signal. Low distortion amplifier circuit characterized by having a frequency of