JP3442208B2 - High frequency electronic circuit - 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 electronic circuit used in a microwave band or a millimeter wave band, and more particularly to a technique for suppressing an image frequency in a high frequency electronic circuit including a field effect transistor (FET). Regarding

[0002]

2. Description of the Related Art A high-frequency receiving circuit is an example of a high-frequency electronic circuit including an FET. A general function desired for this high-frequency receiving circuit is to amplify a weak high-frequency input signal (RF signal) containing a required signal component with as low noise as possible and to demodulate this signal component at a predetermined intermediate frequency. It is a reliable frequency conversion into a signal (IF signal). In this case, when an external wave having the same frequency as the image frequency generated in the frequency conversion unit (mixer), that is, a noise component is injected into the mixer, this noise component is added to the IF signal and the quality of the demodulated signal component is increased. Deteriorates. For this reason, conventionally, an image blocking filter is usually placed in front of the mixer to suppress the image frequency.

FIG. 6 is a general configuration diagram of a conventional high frequency receiving circuit. An RF signal input to an RF input terminal 1 is amplified by a low noise amplifier 10 and an image frequency is sufficiently high by an image blocking filter 20. After being damped, Mixer 3
Input to 0. The mixer 30 mixes the output of the image blocking filter 20 with a predetermined local wave (local oscillation wave whose IF frequency is different from the RF signal) input from the local wave input terminal 3, and converts the output into an IF signal. , Which is output from the output terminal 2 to the outside.

FIG. 7 shows a configuration example in which an FET is used as the low noise amplifier 10. In the configuration shown,
The RF signal sent from the RF input terminal 11 is matched by the input matching circuit 13 and the source 1 is grounded.
After being injected into the gate G of No. 5 and output from the drain D with a predetermined gain, the output is matched by the output matching circuit 14 and output from the output terminal 12 to the mixer side. In addition, FET
In the case of an amplifier, a bias circuit is necessary, but since it is included in the input matching circuit 13 and the output matching circuit 14, its description is omitted here.

In the image blocking filter 20, the frequency response characteristic is determined by the selection of the IF signal, and a plane circuit filter, a waveguide filter, a SAW (surface acoustic wave) filter or the like is selected. The SAW filter is more preferable as a bandpass filter because of its steep frequency characteristics, but has a drawback that it has a larger loss than other types of filters.

FIG. 8 is a diagram showing a general structure of an FET mixer which is a gate injection type mixer using an FET as the mixer 30. Referring to FIG. 8, the RF signal input from the RF input terminal 31 through the image suppression filter 20 is combined with the local wave input from the local wave input terminal 3 in the combining circuit 33, and is input in the input matching circuit 34. It is matched and injected into the gate G of the FET 36. F
The source S of the ET 36 is grounded, the IF signal is generated by the non-linearity of the transconductance gm, and the IF signal is output from the drain D. This IF signal is
It is output to the output terminal 32 via the output matching circuit 35.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The design of the amplifier and FET mixer is R
Emphasis is placed on the matching with respect to the F signal, and the image frequency suppression performance is limited to the image rejection filter 20.
Is dominated by the damping characteristics of. For this reason, when the IF signal is selected to be a low value, it is necessary to connect narrow band filters in multiple stages in order to sufficiently secure the amount of suppression by the image blocking filter 20, or to employ a SAW filter in some cases. . However, this causes a decrease in gain due to an increase in insertion loss of the filter, is disadvantageous in terms of mountability, cost, adjustment of characteristic variations, and the like, and further increases the size of the entire high-frequency receiving circuit.

In view of the above-mentioned conventional problems, an object of the present invention is to maintain a function similar to the conventional one with respect to a frequency band of signal components (hereinafter referred to as a signal frequency), but with a sufficient image suppression amount with respect to an image frequency band. It is to provide a high-frequency electronic circuit having a configuration capable of ensuring the above.

[0009]

The present invention provides a first high frequency electronic circuit suitable for use as a FET amplifier. This high-frequency electronic circuit has R injected from the input end.
A high frequency electronic circuit used in a frequency band in which a high frequency signal component is amplified from an output end of the FET to an input end by amplifying the F signal with a predetermined gain and output to the output end. A feedback adjustment circuit is connected between the input and output ends of the. Then, the combined impedance between the input and output terminals including the feedback adjustment circuit is fed back with a high frequency signal component that neutralizes the high frequency signal component in a required signal frequency band and suppresses the RF signal in an image frequency band. It is a value to make.

First, the operation of the high-frequency electronic circuit configured as described above will be described focusing on the interaction between the FET and the feedback adjusting circuit. FIG. 4 is a diagram showing a connection example of an equivalent circuit of a general FET and a feedback adjustment circuit, and for the sake of convenience, only the minimum necessary elements are shown for explaining the operation of the present invention. In the figure, a capacitor Cgd between the gate G and the drain D
Returns a part of the high frequency signal component from the output end (drain side) to the input end (gate side) during the operation of the FET. In this case, the relationship between the capacitor Cgd and the gain (when the amplifier is unconditionally stable: the stability coefficient ≧ 1) is defined as the power gain when the impedance matching of the input and output is simultaneously achieved, as shown in FIG. The maximum available power gain increases as the capacitor Cgd decreases.

Therefore, in the present invention, this capacitor Cgd
In parallel with this, that is, between the input and output ends of the FET, a feedback adjusting circuit including an inductor L and capacitors C1 and C2 is added to neutralize the high frequency signal component to be fed back in a required signal frequency band. Here, the neutralization of the high frequency signal component means that the combined impedance of the capacitor Cgd and the feedback adjustment circuit is made infinite as viewed from the input end of the FET to stop the feedback of the high frequency signal component. The combined impedance Z in this case is shown in equation (1), and the combined impedance Z
Is the frequency f _RF (=
ω / 2π) is shown in equation (2).

[0012]

[Equation 1]

When the condition shown in the equation (2) is satisfied,
The capacitor Cgd becomes equivalent to the FET as if it does not exist, and the maximum available power gain becomes maximum as shown in FIG. Therefore, if the input and output terminals are sufficiently matched, the power gain of the FET amplifier can be as close as possible to the maximum available power gain.

Next, the principle of suppressing the input signal (RF signal) to the FET in the image frequency band by the feedback adjusting circuit will be described with reference to FIG. In FIG. 5, Z is the impedance of the feedback adjustment circuit. Now, when the input signal Vexp-jωt is input to the gate G of the FET, this input signal is amplified by the FET and output to the drain D. The determined high frequency signal component βexp-jφ is fed back to the gate G. The total input signal Vg (t) at this time is as shown in Expression (3).

[0015]

[Equation 2]

Suppressing the image frequency means
The input signal Vg (t) is set to a zero value infinitely in the image frequency band, and the condition is that the first input signal and the high-frequency signal component to be fed back are combined with the same amplitude and opposite phase. This is the case. That is, the following equation (4) and (5)
This is the case when the expression holds.

[0017]

[Formula 3] V = β (4) φ = ωt + (2n + 1) π ... (5) However, n is an integer, and the condition of formula (5) (reverse phase)
The element value that satisfies the above is obtained by the equation (6).

[0018]

[Equation 4] Here, ANG [S ₂₁ ] is the phase angle of the transmission coefficient from the gate G to the drain D among the S parameters of the source-grounded FET, and ANG [2 / (2 + Zn)] is the transmission phase of the feedback circuit. Yes, Zn is the normalized impedance of the feedback adjustment circuit.

By implementing a feedback adjustment circuit with element values that simultaneously satisfy the above conditions (1), (2), (4), (5), and (6), the required signal frequency band is input to the FET without attenuation. The image frequency band is suppressed and input to the FET.

The output end of the series resonance circuit receiving the RF signal and the other end of the parallel resonance circuit, one end of which is connected to the ground line, are connected to the input end of the FET, and the series resonance circuit and the series resonance circuit are connected. By configuring the parallel resonant circuit including the circuit elements that resonate in the required signal frequency band, oscillation due to the negative resistance of the FET in the signal frequency band can be prevented, and the amplifying action becomes stable.

The present invention also provides a second high frequency electronic circuit suitable for use as a FET mixer. This electronic circuit has an FET that converts a mixed wave of a high frequency signal (amplified RF signal) injected from an input end and a local wave into a predetermined IF signal and outputs the IF signal to an output end. A high-frequency electronic circuit used in a frequency band in which a high-frequency signal component is fed back from an end to an input end, said FET
A feedback adjustment circuit is connected between the input and output ends of the. Then, the combined impedance between the input and output ends including the feedback adjusting circuit is a high frequency for neutralizing the high frequency signal component for a required signal frequency band and suppressing the mixed wave for an image frequency band of the signal frequency. It is a value for returning the signal component.

When this high-frequency electronic circuit is used as an FET mixer, it operates as a FET amplifier for high-frequency signals. Therefore, the operation of the feedback adjusting circuit is basically the same as that of the first high-frequency electronic circuit described above. In the same manner as in the above case, the image frequency is suppressed.

Further, the present invention provides a third high frequency electronic circuit which can be used as a high frequency receiving circuit having a simple structure. The electronic circuit amplifies the RF signal injected to the input end and outputs the amplified RF signal to the output end, and a predetermined mixed wave of a high frequency signal (amplified RF signal) injected from the input end and a local wave. The second FET for converting into an IF signal and outputting it to the output end, and an image frequency component from the RF signal amplified by the first FET positioned between the output end of the first FET and the input end of the second FET. In a conventional high-frequency electronic circuit that has an image suppression filter for suppressing, and is used in a frequency band in which a high-frequency signal component is fed back from an output terminal to an input terminal of each FET, in place of the image suppression filter, First FET and second FE
A feedback adjustment circuit is connected between at least one input / output terminal of T, and the combined impedance between the input / output terminals including the feedback adjustment circuit is used to neutralize the high frequency signal component for a required signal frequency band. The image frequency band of the signal frequency is characterized in that it is a value for feeding back a high frequency signal component that suppresses the signal injected to the input end.

In the case of this structure, it is general that the first FET operates as a FET amplifier and the second FET operates as a FET mixer. However, the feedback is provided between at least one of these FETs, preferably between both input and output terminals. Since the image frequency is effectively suppressed by connecting the adjusting circuit, it is not necessary to provide an image blocking filter as in the conventional case, and the circuit scale can be reduced and the loss can be reduced at the same time.

The input end of the first FET is connected to the output end of a series resonance circuit that receives an RF signal and the other end of a parallel resonance circuit, one end of which is connected to a ground line, and the series resonance circuit is connected. And a parallel resonance circuit including circuit elements that resonate in a required signal frequency band of the RF signal, respectively.
Oscillation due to the negative resistance of the FET can be prevented, and the operation as a high frequency receiving circuit becomes stable.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment in which the high frequency electronic circuit of the first invention is applied to an FET amplifier will be specifically described. FIG. 1 is a diagram showing a configuration example of the FET amplifier according to this embodiment, and the same components as those of the conventional product shown in FIG. 7 are designated by the same reference numerals.

Referring to FIG. 1, the RF input terminal 1 is connected to the gate G of the source-grounded FET 15 via the input matching circuit 13, the series stabilizing circuit 17, and the parallel stabilizing circuit 18, and the drain of the FET 15 is connected. D is connected to the output terminal 2 via the output matching circuit 14. FET
A feedback adjustment circuit 16 is connected between the gate and drain of 15. The feedback adjustment circuit 16 is composed of, for example, a parallel circuit of an inductor L and a capacitor C1 and a series circuit of a capacitor C2. The gate bias circuit and the drain bias circuit necessary for the operation of the FET 15 are included in the input matching circuit 13 and the output matching circuit 14.

In the FET amplifier having such a configuration, when the feedback adjusting circuit 16 is not connected, the capacitor Cgd is parasitic between the gate and the drain as described above, and a part of the high frequency signal component is fed back. Therefore, a feedback adjusting circuit 16 is added to adjust the combined impedance between the gate and the drain so that the image frequency is effectively suppressed while maintaining the conventional amplification gain in the signal frequency band. Is. At this time, the values of the inductor L and the capacitors C1 and C2 forming the feedback adjustment circuit 16 are, for example, S ₁₂ of the S-parameter of the source-grounded FET is the minimum in the signal frequency component, and S ₂₁ is the minimum in the image frequency. To decide. When the FET amplifier is operated in a conditionally stable condition, the input / output matching circuits 13 and 14 may be determined thereafter under the conditions that satisfy the required performances of gain and noise figure.
In this embodiment, as is clear from FIG. 1, a configuration example of an unconditionally stable FET amplifier is shown. Therefore, a stabilizing circuit will be described.

The stabilizing circuit, as shown in FIG.
The series stabilizing circuit 17 is inserted and connected between the gate G of 15 and the input matching circuit 13, and the parallel stabilizing circuit 18 is connected between the gate G of the FET 15 and the ground line. The series stabilization circuit 17 includes a series resonance circuit of a capacitor C3 and an inductor L3 that resonate in series at a signal frequency, and a series stabilization resistor R3 in parallel with the series resonance circuit. It is effective for frequency components other than the signal frequency. On the other hand, the parallel stabilizing circuit is composed of a parallel resonant circuit of a capacitor C4 and an inductor L4 which resonate at a signal frequency, and a parallel stabilizing resistor R4 inserted and connected between the parallel resonant circuit and the gate G. The parallel stabilizing resistor R4 is effective for frequencies other than the signal frequency. By providing the stabilizing circuit having such a configuration at the input stage of the FET 15, it is possible to prevent oscillation due to the negative resistance in the signal frequency band, and to stabilize the amplifying action. The input matching circuit 13 needs to determine an optimum element value including the effects of the series stabilizing circuit 17, the parallel stabilizing circuit 18, and the feedback adjusting circuit 16.

FIGS. 3A, 3B and 3C show the S ₂₁ parameter of the FET amplifier whose signal frequency band is 2 GHz band,
FIG. 2 is a relational diagram of S ₁₂ parameter, stability coefficient and frequency. In the configuration of FIG. 1, the capacitor C3 of the series stabilizing circuit 17 is 7.12 pF, the inductor L3 is 1 nH, the resistance of the inductor L3 is 2Ω, and the series stability is stable. The resistance R3 to 20
Ω, the capacitor C4 of the parallel stabilizing circuit is 1.78 pF,
Inductor L4 is 4 nH, its resistance is 3 Ω, series stabilizing resistor R4 is 100 Ω, capacitor C1 of the feedback adjusting circuit is 0.58 pF, C2 is 0.9 pF, and inductor L is 10 Ω.
9 shows an example of calculation in the case of nH and the resistance component thereof is 9Ω.

By setting each circuit element to the above value, S
₁₂ is the minimum in the 2 GHz band which is the signal frequency (RF), and S ₂₁ is the minimum in the image frequency band, and the intended purpose can be achieved. In addition, the stability coefficient also becomes "1" or more in all bands, and oscillation due to negative resistance is prevented.

FIG. 2 shows a high-frequency electronic circuit of the second invention as F
It is a figure which shows the structural example at the time of applying to an ET mixer, The same code | symbol is attached | subjected about the same component as the conventional product shown in FIG. Although an example of the gate injection type mixer is shown here, the high frequency electronic circuit of the present invention can be applied to the drain injection type mixer in substantially the same manner.

In FIG. 2, the RF signal input from the RF input terminal 31 is combined with the local wave input from the local wave input terminal 3 by the combining circuit 33 and matched by the input matching circuit 34. It is injected into the gate G of the FET 36. The FET 36 generates an IF signal by the non-linearity of the transconductance gm and outputs it from the drain D. At that time, a capacitor C is provided between the gate and the drain.
Although gd is parasitic and feedback of the high frequency signal component becomes a problem, by adding the feedback adjustment circuit 16 to adjust the combined impedance between the gate and the drain, while maintaining the conventional gain in the signal frequency band. , Effectively suppress the image frequency. At this time, the method of determining the inductor L and the capacitors C1 and C2 forming the feedback adjustment circuit 16 is the same as that of the FET amplifier described above. FET3
The IF signal obtained from the drain D of 6 is output to the output terminal 32 via the output matching circuit 35.

As described above, even when the high-frequency electronic circuit of the present invention is used as an FET amplifier or an FET mixer, the image frequency input to the FET is reliably suppressed. Therefore, in addition to the original function as the amplifier or the mixer, the function as the image blocking filter can be provided at the same time, which is suitable for constructing a simple high-frequency receiving circuit.

For example, in an application requiring a steep frequency characteristic such as a high-frequency receiving circuit of an L-band mobile phone, a SAW filter which is expensive and has a large insertion loss is conventionally used as an image suppression filter, and the SAW filter is used in the image frequency band. Although it is usual to secure an amount of suppression of about 40 dB, if the FET amplifier and the FET mixer of this embodiment are cascaded so that an image suppression amount of 20 dB can be obtained in each image frequency band, that is enough. 40d in total
Since the image suppression amount of B is obtained, the image blocking filter itself is not necessary, and it is expected that the circuit scale is reduced, the cost is reduced, and the electrical performance is improved with the reduction of the circuit components. Even in the case of high frequency receiving circuits for other applications,
Since the image frequency is suppressed without exception, it is possible to replace the conventional image blocking filter with a simpler filter, for example, a microstrip line filter, which greatly improves the conventional technology in terms of cost, mountability, and electrical performance. Can be improved.

[0036]

As is apparent from the above description, according to the high frequency electronic circuit of the first aspect of the present invention, the amplification function similar to the conventional one is maintained for the required signal frequency band, and the image frequency band is maintained. As a result, there is an effect that a sufficient amount of image suppression is secured. Further, according to the high frequency electronic circuit of the second aspect of the invention, the same mixer function as the conventional one is maintained for the required signal frequency band, and a sufficient image suppression amount is secured for the image frequency band. There is. Therefore, by applying the high-frequency electronic circuit of the third invention including these circuits to the same purpose as the conventional high-frequency receiving circuit, the circuit scale is reduced, the cost is reduced, and the number of parts is reduced. It is possible to improve electrical performance.

[Brief description of drawings]

FIG. 1 is a configuration diagram when a high frequency electronic circuit of the present invention is applied to a FET amplifier.

FIG. 2 is a configuration diagram when the high frequency electronic circuit of the present invention is applied to an FET mixer.

FIG. 3 is a calculation diagram of an S parameter and a stability coefficient in a 2 GHz band according to the present embodiment.

FIG. 4 is a diagram showing a connection state between an FET equivalent circuit and a feedback adjustment circuit according to the present invention.

FIG. 5 is an explanatory diagram showing a principle for suppressing an image frequency according to the present invention.

FIG. 6 is a configuration diagram of a conventional general high-frequency receiving circuit.

FIG. 7 is a configuration diagram when an FET amplifier is used as a conventional low noise amplifier.

FIG. 8 is a configuration diagram when an FET is used as a conventional mixer.

FIG. 9 is a diagram showing a relationship between a maximum available power gain of a general FET and a capacitor Cgd which is a feedback element.

[Explanation of symbols]

1 RF input terminal 2 output terminals 3 Local wave input terminal 11 RF input terminal of FET amplifier 12 FET amplifier output terminal RF input terminal of 31 FET mixer 32 FET mixer output terminal 33 Multiplexing circuit 13,34 Input matching circuit 14,35 output matching circuit 15,36 FET 16 Feedback adjustment circuit 17 Series stabilization circuit 18 Parallel stabilization circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03F 3/72 H03F 1/00-3/72 H03G 3/10 H03H 11/12 H04B 1/10 H04B 15 / 06

Claims (5)

(57) [Claims] 1. A field effect transistor for amplifying a high frequency input signal injected from an input end with a predetermined gain and outputting the amplified high frequency signal to an output end. A high frequency signal component is fed back from the output end of the field effect transistor to the input end. In a high frequency electronic circuit used in a frequency band, a feedback adjustment circuit is connected between the input and output ends of the field effect transistor, and a combined impedance between the input and output ends including the feedback adjustment circuit is set to a required signal frequency band. Is a value for neutralizing the high-frequency signal component, and for the image frequency band, a value for feeding back a high-frequency signal component for suppressing the high-frequency input signal. 2. The input terminal of the field effect transistor,
The output terminal of the series resonance circuit that receives the high frequency input signal is connected to the other end of the parallel resonance circuit whose one end is connected to the ground line, and the series resonance circuit and the parallel resonance circuit are respectively connected to the high frequency input. 2. The high frequency electronic circuit according to claim 1, comprising a circuit element which resonates in a required signal frequency band of a signal. 3. A field effect transistor for converting a mixed wave of a high frequency signal injected from an input terminal and a local wave into a predetermined intermediate frequency signal and outputting the signal to an output terminal. From the output terminal of the field effect transistor. In a high frequency electronic circuit used in a frequency band in which a high frequency signal component is fed back to an input terminal, a feedback adjustment circuit is connected between the input and output terminals of the field effect transistor, and the feedback adjustment circuit is connected between the input and output terminals. A high-frequency electronic circuit, wherein the combined impedance is set to a value that neutralizes the high-frequency signal component for a required signal frequency band and returns a high-frequency signal component that suppresses the mixed wave for an image frequency band. 4. A first field effect transistor for amplifying a high frequency input signal injected to an input end and outputting the amplified high frequency signal to an output end, and a mixed wave of the high frequency signal injected from the input end and a local wave at a predetermined intermediate level. A second field effect transistor for converting into a frequency signal and outputting the same to an output end; and the first field effect transistor located between the output end of the first field effect transistor and the input end of the second field effect transistor. And an image suppression filter that suppresses image frequency components from the high frequency input signal amplified by the field effect transistor of, and is used in the frequency band in which high frequency signal components are fed back from the output end to the input end of each field effect transistor. In the high-frequency electronic circuit according to claim 1, in place of the image suppression filter, at least one of the first field effect transistor and the second field transistor is provided. A feedback adjustment circuit is connected between the input and output terminals, and the combined impedance between the input and output terminals including the feedback adjustment circuit is used to neutralize the high frequency signal component for a required signal frequency band and to be used for the image frequency band. A high frequency electronic circuit having a value for feeding back a high frequency signal component for suppressing a signal injected to an input end. 5. The input end of the first field effect transistor is connected to the output end of a series resonance circuit which receives the high frequency input signal and the other end of a parallel resonance circuit whose one end is connected to a ground line. 5. The high-frequency electronic circuit according to claim 4, wherein the series resonance circuit and the parallel resonance circuit each include a circuit element that resonates in a required signal frequency band of the high-frequency input signal.