JP2989863B2 - Variable tilt circuit of high frequency amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention fixes a change in a loss amount in one of a low band and a high band at both ends of a transmission band for a communication signal between stages of a high-frequency amplifier. The present invention relates to a variable tilt circuit of a high-frequency amplifier that continuously changes a slope of a frequency characteristic of a pass loss in an entire transmission band in a state in which the frequency is changed.

[Prior Art] Conventionally, a communication signal between stages of a high-frequency amplifier has a slope of a frequency characteristic of a pass loss of the entire transmission band in a state where a change in a loss amount in one of a low band and a high band is fixed. For example, a circuit as shown in FIG. 4 is used as a variable tilt circuit for continuously changing the value. This circuit is a bridge type T-type circuit, and has a four-terminal network variable attenuation circuit 3 provided between an input terminal 1 and an output terminal 2, a series resonance circuit 4 connected in parallel to the variable attenuation circuit 3, and A parallel resonance circuit 5 is provided between the variable attenuation circuit 3 and the ground.

The variable attenuating circuit 3 includes a parallel circuit including a variable resistor 6 and resistors 7 and 8 connected in series between the terminals 1 and 2, and a circuit between the middle point of the resistors 7 and 8 and the series resonance circuit 4. Is provided with a variable resistor 9. In this case, the variable resistor 6 and the variable resistor 9 are configured using, for example, a PIN diode or the like, and are linked to change the slope of the frequency characteristic of the passage loss.

The series resonance circuit 4 has a coil 11 and a capacitor 12 connected in series, and the parallel resonance circuit 5 has a coil 13 and a capacitor 14 connected in parallel.

In the above configuration, the values of the resistors 7 and 8 of the variable attenuation circuit 3 are determined by the characteristic impedance of the circuit. On the other hand, the resonance points of the series resonance circuit 4 and the parallel resonance circuit 5 are determined by the frequency at which the change in the amount of loss is fixed.

In the variable tilt circuit, when the tilt amount is minimum, the resistance value of the variable resistor 6 is very small compared to the values of the resistors 7 and 8. At this time, the variable resistor 6 also acts as a resistor and also as an inductance under the influence of the lead and the like. Note that the values of the resistors 7 and 8 are assumed to be unaffected because they are larger than the resistance value and inductance of the variable resistor 6, and that the value of the variable resistor interposed between the connection point of the resistors 7 and 8 and the ground. The resistor 9, the coil 13 of the parallel resonance circuit 5, and the capacitor 14 are assumed to have no influence.

In consideration of the above points, the circuit of FIG. 4 is rewritten as shown in FIG. 5 (a), and further rewritten as shown in FIG. 5 (b).
Becomes This means that in the parallel resonance circuit including the coil 11 and the inductance of the variable resistor 6 and the capacitor 12, the signal passes through the tap portion of the inductance of the variable resistor 6, and the signal passes through as shown in FIG. In the frequency characteristics of the loss, a dip appears at the resonance point A of the parallel resonance circuit. FIG. 6 shows the transmission loss characteristics when the change in the loss amount is fixed for the high band of the transmission band.

[Problems to be Solved by the Invention] As described above, in the conventional variable tilt circuit, a dip occurs near the resonance point of the series resonance circuit 4 including the coil 11 and the capacitor 12 in the frequency characteristic of the passage loss when the tilt amount is minimum. There is a disadvantage that it will.

As a method to prevent this,. Setting the resonance point of the series resonance circuit 4 outside the transmission band so that the influence of the dip in the frequency characteristic of the pass loss does not occur in the transmission band; A method of incorporating a resistor in series with the series resonance circuit 4 is conceivable.

However, in the above method, the resonance point of the series resonance circuit 4, that is, the frequency for fixing the change in the loss amount is set outside the transmission band. The amount will increase.

Therefore, when changing the amount of tilt in either method,
There is a problem in that either the low band or the high band in the transmission band increases the fluctuation range in which the change in the loss amount should be fixed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and does not cause a dip near the resonance point of the resonance circuit in the frequency characteristic of the passage loss when the tilt amount of the variable tilt circuit is minimized, and changes the tilt amount. It is an object of the present invention to provide a variable tilt circuit of a high-frequency amplifier capable of adjusting a tilt amount without increasing a fluctuation range of the loss amount at a frequency at which a change in the loss amount is fixed when the change is performed.

Means and Action for Solving the Problems According to the present invention, a variable resistor for adjusting the Q dump of the resonance circuit and a variable resistor for adjusting the slope of the frequency characteristic of the passing loss are linked to each other, and the resonance circuit is operated when the tilt amount is minimum. By reducing Q, a dip occurring near the resonance point of the resonance circuit in the frequency characteristic of the passage loss is prevented.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(First Embodiment) A variable tilt circuit of a high-frequency amplifier according to the present invention has a first
As shown in the figure, a four-terminal network variable attenuation circuit 3 provided between an input terminal 1 and an output terminal 2, a series resonance circuit 4A connected in parallel to the variable attenuation circuit 3, and a variable attenuation circuit 3
And a parallel resonance circuit 5A provided between the ground and the ground.

The variable attenuation circuit 3 has a parallel circuit including a variable resistor 6 and resistors 7 and 8 connected in series between terminals 1 and 2,
The variable resistor 9 is provided between the middle point of the resistors 7 and 8 and the series resonance circuit 4A. In this case, the variable resistor 6 and the variable resistor 9 are configured using, for example, a PIN diode or the like.
In order to change the slope of the frequency characteristic of the passage loss, they are linked.

In the series resonance circuit 4A, a coil 11 and a capacitor 12 are connected in series, and a variable resistor 21 is connected to the capacitor 12 in parallel. In the parallel resonance circuit 5A, a coil 13 and a capacitor 14 are connected in parallel, and a variable resistor 22 is connected to the coil 13 in series.

In the above configuration, the values of the resistors 7 and 8 of the variable attenuation circuit 3 are set to values equal to the characteristic impedance of the circuit. On the other hand, the resonance points of the series resonance circuit 4A and the parallel resonance circuit 5A are set to a frequency that fixes the change in the amount of loss in the low band or the high band. In addition, series resonance circuit 4A, parallel resonance circuit 5A
The variable resistances 21 and 22 provided for adjusting the Q dump are each made of a PIN diode or the like, and are linked with the variable resistances 6 and 9 of the variable attenuation circuit 3. In this case, the variable resistors 21 and 22 are linked with the variable resistors 6 and 9 so that the Q of the series resonance circuit 4A and the parallel resonance circuit 5A is reduced when the tilt amount is minimum. That is, the variable resistors 21 and 22 and the variable resistors 6 and 9
By adjusting the slope of the frequency characteristic of the passage loss, the series resonance circuit 4A and the parallel resonance circuit
The adjustment of the Q dump of 5A is enabled.

As described above, by providing variable resistors 21 and 22 in the series resonance circuit 4A and the parallel resonance circuit 5A to enable adjustment of the Q dump, the generation of a dip near the resonance point of the resonance circuit as shown in FIG. Can be prevented. FIG. 2 shows an example of characteristics in a case where a change in the amount of loss in the high band of the transmission band is fixed. As described above, in the frequency characteristic of the pass loss, the cause of the dip occurring when the tilt amount is the minimum is due to the series resonance circuit of the coil 11 and the capacitor 12 and the variable resistor 6. This can be prevented by adjusting the Q dump.

On the other hand, a variable resistor that adjusts the Q dump of the parallel resonance circuit 5A
Numeral 22 operates to keep the impedance characteristic of the entire circuit closer to a constant resistance in response to a change in the variable resistor 21.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention. In the second embodiment, the variable resistor 21 for Q dump is provided only in the series resonance circuit 4A, and the variable resistor for Q dump in the parallel resonance circuit 5A is omitted.

As described above, in the first embodiment, the parallel resonance circuit 5A
The variable resistor 22 for adjusting the Q dump provided in the circuit is operated to keep the impedance characteristic of the whole circuit closer to a constant resistance with respect to the change of the variable resistor 21. This can be omitted as long as the change in the characteristics is within the allowable range. Therefore, even when the variable resistor for Q dump adjustment of the parallel resonance circuit 5A is omitted as shown in the second embodiment, it is possible to prevent a dip occurring near the resonance point of the resonance circuit.

[Effects of the Invention] As described above in detail, according to the present invention, a variable resistor for adjusting a Q dump is provided in a resonance circuit for fixing a change in the loss amount, and the variable resistor for the Q dump and the slope of the passage loss are adjusted. Since the variable resistance of the variable attenuation circuit to be adjusted is linked, the tilt amount can be adjusted without causing a dip near the resonance point of the resonance circuit when the tilt amount is minimum in the frequency characteristic of the passage loss.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a variable tilt circuit of a high-frequency amplifier according to a first embodiment of the present invention, FIG. 2 is a diagram showing pass loss characteristics in the same embodiment, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a circuit configuration diagram showing a variable tilt circuit according to an example, FIG. 4 is a circuit configuration diagram showing a variable tilt circuit of a conventional high-frequency amplifier, and FIGS. 5 (a) and 5 (b) show the amounts of tilt in the circuit of FIG. FIG. 6 is a diagram showing an effective circuit when it is minimized, and FIG. 6 is a diagram showing a transmission loss characteristic in the variable tilt circuit of FIG. 1 ... input terminal, 2 ... output terminal, 3 ... variable attenuation circuit, 4,4A ... series resonance circuit, 5,5A ... parallel resonance circuit, 6,
9,21,22 …… Variable resistance.

Continuation of the front page (56) References JP-A-60-64515 (JP, A) JP-A-49-106752 (JP, A) JP-A-57-182914 (JP, U) JP-A-49-95836 (JP, A) , U) Japanese Utility Model Showa 60-61831 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H03H 7/01

Claims (2)

(57) [Claims] 1. A communication signal between stages of a high-frequency amplifier is obtained by converting the frequency characteristic of the pass loss of the entire transmission band in a state where the change in the loss amount of either the low band or the high band is fixed at both ends of the transmission band. In a variable tilt circuit for continuously changing the slope, a series resonance circuit connected in parallel in a signal passing direction of a four-terminal network variable attenuator in order to fix a change in a loss amount at either end of a transmission band. And a parallel resonance circuit connected in series in the ground direction, a Q dump means for performing a Q dump with a variable resistor on the series resonance circuit and the parallel resonance circuit, and changing the variable resistor to change the loss amount of the variable attenuator. A variable tilt circuit for a high-frequency amplifier, comprising: a variable resistor that operates in conjunction with a variable resistor. 2. A communication signal between stages of a high-frequency amplifier is used to determine the frequency characteristic of the pass loss of the entire transmission band in a state in which the change in the loss of either the low band or the high band is fixed at both ends of the transmission band. In a variable tilt circuit for continuously changing the slope, a series resonance circuit connected in parallel in a signal passing direction of a four-terminal network variable attenuator in order to fix a change in a loss amount at either end of a transmission band. A parallel resonance circuit connected in series in the ground direction, a Q dump unit for performing a Q dump with a variable resistor on the series resonance circuit, and a unit for interlocking with a variable resistor for changing a loss amount of the variable attenuator. A variable tilt circuit for a high frequency amplifier, comprising: