JP2509781B2 - High frequency negative feedback 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 high frequency negative feedback amplifier provided with a negative feedback circuit for reducing intermodulation distortion and stabilizing gain.

[0002]

2. Description of the Related Art First, a conventional high frequency negative feedback amplifier will be described with reference to FIG.

IN is an input end of a signal, and the signal input from here is applied to an amplifier 72 through a band pass filter 71. The signal amplified by the amplifier 72 is output from the output terminal OUT.

Reference numeral 73 surrounded by a dotted line is a feedback circuit,
The feedback circuit 73 is coupled to the output side of the amplifier 72, and a part of the output is fed back to the input side of the bandpass filter 71. Here, the transfer function of the amplifier 72 is A, and the feedback circuit 7
3, each transfer function of the bandpass filter 71 is B,
If C is set, the following relationship is obtained.

A = a × exp (−jτ _a Δω) (1) B = b × exp (−jτ _b Δω) (2) C = c / (1 + jTΔω) (3) The feedback circuit The transfer function C of 73 includes the characteristics of the input and output couplers.

In the above equations, a ... Gain at the center frequency of the amplifier 72, b ... Insertion loss at the center frequency of the feedback circuit 73, c ... Insertion loss at the center frequency of the bandpass filter 71, τ _a . Group delay time of amplifier 72, τ _b ... Feedback circuit 7
Group delay time of 3, T ... time constant of the band pass filter 71,
Δω is a deviation from the center frequency.

Here, assuming that the bandwidth in which the in-band ripple of the band pass filter 71 is 3 dB or less is B _W , T = 1 / πB _W (4)

With the above relationship, the output voltage e0 is
It can be expressed as follows.

E 0 = (AC / 1 + ABC) · e _i + ( _1/1 + ABC) · e _im (5) Here, e _{i is the} input voltage, e _im is the distortion voltage generated from the amplifier.

From the equation (5), the gain of the amplifier is (AC / 1
+ ABC) times, and the distortion voltage is (1/1 + AB)
C) It is doubled.

When the open loop gain ABC is _GL , the stability of the high frequency negative feedback amplifier is determined by the open loop gain _GL . Then, the phase margin θ indicating the stability of the high frequency negative feedback amplifier can be expressed by the following equation (6).

Θ = 180 ° − | φ (ω _c ) | (6) where ω _c ... | ABC | = 1, where φ (ω) ... Angle (ABC).

[0013]

In the high frequency negative feedback amplifier, in order to stabilize the operation, a band pass filter is connected to the input side of the amplifier and the pass phase deviation is within ± 90 ° within the band. I am trying to become.

In order to prevent oscillation from occurring due to the presence of the feedback circuit, a one-stage series resonance circuit including an inductor L and a capacitor C as shown in FIG. 8 is used as a bandpass filter.

For example, as shown in FIG. 8, a bandpass filter is composed of an inductor L and a capacitor C and has a center frequency F0.
When = 1 GHz and bandwidth B _W = 10 MHz, the insertion loss characteristic of the band pass filter is as shown in FIG.

In FIG. 9, the horizontal axis represents frequency (GHz) and the vertical axis represents insertion loss (dB).

When the transfer function of the band pass filter at that time is displayed in polar coordinates, it becomes as shown in FIG. 10 (a). Here, the gain of the amplifier shown in equation (1) is 48 dB and equation (2). The loss of the feedback circuit is 30 dB, the sum of the group delay times τ _a and τ _b of the amplifier and the feedback circuit τ _a + τ _b = 3n
S, and using the bandpass filter having the characteristics shown in (a) of FIG. 9 or FIG. 10, when the open loop gain G _L is 0 dB, that is, the loss of the bandpass filter represented by the formula (3) is When the bandwidth becomes 18 dB, if the 3 dB bandwidth B _W with respect to the bandwidth of the band pass filter at that time is defined as the ratio band, the band pass filter having the characteristic of FIG.
12%.

At this time, in order to prevent oscillation of the high frequency negative feedback amplifier, if the phase margin is 45 °, the high frequency negative feedback in which the bandpass filter of the one-stage series resonance circuit is connected to the input side of the amplifier as described above. In the amplifier, the amount of improvement in distortion within the bandwidth B _W is unidirectional as shown in FIG. 11A, and the bandwidth is narrow.

In FIG. 11, the horizontal axis represents frequency (GHz),
The vertical axis is the distortion improvement amount (dB).

When the distortion improvement amount characteristic is unidirectional, in order to widen the distortion improvement amount band while maintaining the phase margin, the group delay time of the amplifier must be reduced.

It is an object of the present invention to provide a stable high-frequency negative feedback amplifier which can increase the ratio band of the bandpass filter, widen the band of distortion improvement amount, or increase the group delay time distribution to the amplifier. And

[0022]

According to the present invention, a high frequency amplifier, a bandpass filter connected in series to the input side of the amplifier, and feedback from the output side of the amplifier to the input side of the bandpass filter. In a high-frequency negative feedback amplifier including a feedback circuit, the bandpass filter is configured by connecting a plurality of series resonance circuits including an inductor, a capacitor, and a resistor in parallel, and a plurality of the bandpass filters are configured. Of the series resonance circuit has a plurality of resonance frequencies.

A high frequency negative amplifier comprising a high frequency amplifier, a band pass filter connected in parallel to the input side of the amplifier, and a feedback circuit for feeding back from the output side of the amplifier to the input side of the band pass filter. In the feedback amplifier, the bandpass filter is configured by connecting a plurality of parallel resonant circuits each including an inductor, a capacitor, and a resistor in series, and a plurality of parallel resonant circuits configuring the bandpass filter are provided. Has a resonant frequency.

Further, the series or parallel resonance circuit constituting the band pass filter is formed of a lossy resonator using a distributed constant line or a dielectric instead of the inductor, the capacitor and the resistor, or Instead of the inductor, the capacitor, and the resistor, a resonance circuit including the inductor, the capacitor, and the resistor and a distributed constant line or a resonator having a loss using a dielectric are used.

[0025]

According to the above construction, the bandpass filter is constructed by connecting a plurality of resonance circuits in series or in parallel,
Also, the resonance frequency is set to be plural. Therefore, the bandpass characteristic of the bandpass filter is improved. Further, the band of the distortion improvement amount is wide, or the group delay time of the amplifier is largely distributed, so that a stable negative feedback amplifier can be constructed.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

IN is an input end of the signal, and the signal introduced from the input end IN is added to the bandpass filter 11. The bandpass filter 11 is configured by connecting two series resonance circuits in parallel. Each series resonance circuit is composed of an inductor L, a capacitor C, and a resistor R, and is set so that the resonance frequencies are different from each other. The signal passed through the bandpass filter 11 is amplified by the amplifier 12,
It is output from the output terminal OUT.

A feedback circuit 13 is coupled to the output side of the amplifier 12, and a part of the output taken out by the feedback circuit 13 is returned to the input side of the bandpass filter 11.

Here, the inductor L, the capacitor C and the resistor R which form the series resonance circuit are set so that the fluctuation of the in-band insertion loss of the band pass filter 11 is 3 dB, and the bandwidth in which the loss increases by 15 dB is constant. When the respective constants are defined, the insertion loss characteristics of the bandpass filter are as shown in (b) and (c) of FIG. The transfer function at that time is displayed in polar coordinates as shown in (b) and (c) of FIG. 10.

[0030] In FIGS. 9 and 10, (ii) has a sharpness Q ₀ of the series resonant circuit, in the case of Q ₀ = 350, (c) has a sharpness Q ₀ of the series resonant circuit, when the Q ₀ = 220 Is.

In the case of FIG. 9B, the insertion loss is 6d, as compared with the case of using the conventional one-stage series resonance circuit (A).
The B bandwidth increases, but the 3 dB bandwidth relative to the bandwidth that is increased by 18 dB from the point where the insertion loss is the minimum is:
30% improvement.

In the case of FIG. 9C, the insertion loss is increased by 12 dB as compared with FIG. 9B, but the bandwidth is improved by 40%.

Further, in the high-frequency negative feedback amplifier having the above structure, the center frequency F ₀ = 1 GHz, the loss of the feedback circuit of the formula (2) = 30 dB, τ _a + τ _b = 3 nS, and the transfer function is as shown in FIG. A bandpass filter having characteristics as shown in (C) is used, and the phase margin is 4
When the gain of the amplifier is designed by equation (1) so as to be 5 °, the distortion improvement amount characteristics obtained are (b) and (c) in FIG.
Indicated by.

In FIG. 11, (a) shows the case where the conventional one-stage series resonance circuit is used as described above, and (b) and (c) show the high-frequency negative feedback amplifier of the present invention. This is the case where the bandpass filter having the characteristic, that is, the transfer function having the characteristic shown in (b) and (c) of FIG. 10 is used.

The transfer functions are shown in (b) and (c) of FIG.
When a bandpass filter having a characteristic as shown in FIG. 10 is used, the gain of the amplifier is larger than that when a conventional high frequency negative feedback amplifier using a bandpass filter whose transfer function is shown in FIG. 6dB and 12d respectively
B must be increased.

However, the gain of the amplifier can be easily obtained by attaching a small signal amplifier in the preceding stage. For example, 1G
In the case of the Hz band, a microwave monolithic integrated circuit (MM
IC) and the like, the group delay time is 0.
An amplifier having a sufficiently small group delay time of about 1 nS can be easily realized.

Therefore, in the case of constructing a negative feedback amplifier, the increase in the gain of the amplifier does not cause much problem in terms of power consumption and feasibility.

Regarding the distortion improvement amount shown in FIG. 11, when the high frequency negative feedback amplifiers (b) and (c) of the present invention are compared with the conventional high frequency negative feedback amplifier (a), the distortion improvement amount is 15 dB. In the present invention, the specific bandwidth is 3 in each case.
It is improved by 0% and 40%.

In the above embodiment, the bandpass filter forming the negative feedback amplifier is composed of an inductor, a capacitor,
The case has been described in which two series resonance circuits each including a resistor and having different resonance frequencies are connected in parallel, and the bandpass filter is connected in series to the input side of the amplifier.

However, the band pass filter may be configured by connecting three or more series resonance circuits each including an inductor, a capacitor and a resistor in parallel. In this case, it suffices that the series resonance circuits forming the band pass filter have a plurality of resonance frequencies, and the resonance frequencies of the series resonance circuits may be different.

As the band pass filter, a parallel resonance circuit composed of an inductor L, a capacitor C and a resistor R as shown in FIG. 2 and a plurality of parallel resonance circuits connected in series can be used. When a parallel resonance circuit is used, it is connected to the input side of the amplifier in parallel with the amplifier. .

Further, the band pass filter may be constituted by a microstrip line as shown in FIG. For example, the microstrip line 31 and the capacitor C form one resonance circuit, and two resonance circuits are connected in parallel.

FIG. 4 shows the insertion loss characteristics of the bandpass filter constituted by the microstrip line shown in FIG. 3, and FIG. 5 shows the transfer function in polar coordinates.

FIG. 6 is a circuit diagram in the case where the mutual inductor M is present in the two inductors L constituting the bandpass filter. Also in this case, there is an effect of widening the bandwidth.

Further, the resonance circuit constituting the bandpass filter is not limited to the microstrip line, and a resonator having a loss using a dielectric can be used. It is also possible to combine a resonant circuit including an inductor, a capacitor, and a resistor with a lossy resonator using a microstrip line or a dielectric.

Further, in the above-mentioned embodiment, the explanation is made with one amplifier, but the amplifier is connected to the input side of the bandpass filter and the bandpass filter is connected in series or in parallel between the stages of the amplifier. You may

[0047]

According to the present invention, the bandpass filter constituting the high-frequency negative feedback amplifier has a wider specific bandwidth and a wider bandwidth .
A stable high frequency negative feedback amplifier can be realized.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a bandpass filter used in the present invention.

FIG. 3 is a circuit diagram showing another example of a bandpass filter used in the present invention.

FIG. 4 is a diagram showing characteristics of a bandpass filter used in the present invention.

FIG. 5 is a diagram showing characteristics of a bandpass filter used in the present invention.

FIG. 6 is a circuit diagram showing another example of a bandpass filter used in the present invention.

FIG. 7 is a circuit configuration diagram showing a conventional high-frequency negative feedback amplifier.

FIG. 8 is a circuit diagram showing an example of a bandpass filter used in a conventional high frequency negative feedback amplifier.

FIG. 9 is a diagram showing characteristics of a bandpass filter used in the present invention and the conventional device.

FIG. 10 is a diagram showing characteristics of a bandpass filter used in the present invention and the conventional device.

FIG. 11 is a diagram showing characteristics of the present invention and a conventional device.

[Explanation of symbols]

 11 ... Band pass filter 12 ... Amplifier 13 ... Feedback circuit IN ... Input end OUT ... Output end L ... Inductor C ... Capacitor R ... Resistor

Claims (4)

(57) [Claims] 1. A high-frequency negative amplifier comprising a high-frequency amplifier, a band-pass filter connected in series to the input side of the amplifier, and a feedback circuit for feeding back from the output side of the amplifier to the input side of the band-pass filter. In the feedback amplifier, the bandpass filter includes an inductor and a capacitor,
A high-frequency negative feedback amplifier, characterized in that a plurality of series resonance circuits composed of resistors are connected in parallel, and a plurality of series resonance circuits constituting the bandpass filter have a plurality of resonance frequencies. 2. A high-frequency negative amplifier comprising a high-frequency amplifier, a bandpass filter connected in parallel to the input side of the amplifier, and a feedback circuit for feeding back from the output side of the amplifier to the input side of the bandpass filter. In the feedback amplifier, the bandpass filter includes an inductor and a capacitor,
A high-frequency negative feedback amplifier, characterized in that a plurality of parallel resonant circuits composed of resistors are connected in series, and a plurality of parallel resonant circuits constituting the bandpass filter have a plurality of resonant frequencies. 3. A lossy resonance using a distributed constant line or a dielectric instead of connecting a plurality of series resonance circuits each including an inductor, a capacitor and a resistor in parallel to each other in the band pass filter. Or a plurality of series resonant circuits each including an inductor, a capacitor, and a resistor connected in parallel, instead of the inductor and the inductor. capacitor, the series resonant circuit and distributed constant lines or claim 1, wherein the high frequency negative feedback amplifier, characterized in that it constituted by connecting a resonator with loss using a dielectric in parallel to a resistor. 4. A resonance circuit with a loss using a distributed constant line or a dielectric instead of connecting a plurality of parallel resonance circuits each including an inductor, a capacitor, and a resistor in series in the bandpass filter. Or a plurality of parallel resonant circuits each including an inductor, a capacitor, and a resistor connected in series instead of the inductor and the bandpass filter. capacitor, parallel resonant circuit and distributed constant lines or claim 2 wherein the high frequency negative feedback amplifier, characterized in that configuring the resonator with loss using a dielectric are connected in series to the resistor.