JPS6149851B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a limiter circuit constituted by a microstrip line formed on a dielectric substrate and a plurality of limiter diodes.

FIG. 1 shows an equivalent circuit of an example of a conventional limiter circuit having the above-described configuration. In Fig. 1, 1, 2, and 3 are microstrip lines formed on a dielectric substrate, 4, 5 are limiter diodes, and 6 to 9 are connection electrodes of these diodes to the microstrip lines. Bonding wires 10 and 11 indicate an input terminal and an output terminal, respectively.

The limiter diode used in the limiter circuit is usually of PIN structure, and in order to increase the allowable input power and reduce leakage power, the input terminal 10
A diode with a large I-layer width is used as the diode 4 close to , and a diode with a small I-layer width is used as the other diode 5.

By the way, a limiter circuit can be thought of as a capacitor that puts a diode in an Ov bias state in a small signal state, and is determined by its junction capacitance at high frequencies. FIG. 2 shows an equivalent circuit in this case, where capacitors 12 and 13 correspond to the junction capacitance Cj of the diode.

On the other hand, in a large signal state, the limiter diode has a sufficiently small resistance, which can be represented by the equivalent circuit shown in FIG. In FIG. 3, the resistances indicated by 14 and 15 correspond to the resistance Rs of the limiter diode.

The high-frequency characteristics required for limiter circuits include low insertion loss and low standing wave ratio in small signal conditions, and large insertion loss and high standing wave ratio in large signal conditions.
The goal is to reduce leakage power. The parameters that determine these characteristics are the junction capacitance _Cj of the diode, the characteristic impedance Za of the microstrip line between the diodes, and The electrical length is θa. Especially junction capacitance
Once the value of Cj has been determined, the electrical length θ between the diodes shown in Figure 3 must be set to minimize the standing wave ratio when the signal is small and to maximize the isolation when the signal is large. From the condition that the impedance is an odd multiple of 90°, the characteristic impedance Za and the electrical length θ are
a will be uniquely determined.

Therefore, if the junction capacitance Cj of the diode deviates from the specified value, the characteristic impedance Za, θa should be adjusted so that the above-mentioned conditions are satisfied.
need to change. To change the characteristic impedance Za, it is necessary to change the width of the microstrip line, and to change the electrical length θa, it is necessary to change the connection position of the diode, and both methods are time-consuming and extremely troublesome. Furthermore, once the circuit pattern has been determined, it is necessary to strictly control and adapt the junction capacitance Cj of the diode in order to satisfy the above-mentioned conditions, and non-standard diodes cannot be used, resulting in poor yield. Ta.

This invention eliminates the above-mentioned drawbacks and provides a limiter circuit that easily satisfies the conditions required for a limiter circuit and can obtain optimal characteristics by adding an adjustment function for fluctuations in diode junction capacitance. This is what I am trying to do.

An embodiment of the present invention will be described below with reference to the drawings. In the embodiment of FIG. 4, 1, 2, 3
10, 11 are microstrip lines formed on a dielectric substrate; 4 and 5 are limiter diodes; 6 to 9 are bonding wires connecting the electrodes of these diodes and the microstrip lines;
denote an input terminal and an output terminal, respectively, and these structures are the same as in the conventional example shown in FIG. In this embodiment, an open stub 16 for adjustment is added to the microstrip line 2 located particularly near the limiter diodes 4 and 5.

5 and 6 are equivalent circuit diagrams of the embodiment shown in FIG. 4 in a small signal state and a large signal state, respectively, and correspond to FIGS. 2 and 3 for the conventional example, respectively. . 5 and 6, the open stub 16 of FIG. 4 is shown as a capacitor 17 for simplicity.

In such a limiter circuit, the characteristic impedance Za of the microstrip line between the diodes, the electrical length θa, and the junction capacitance of the diodes are
If Cj satisfies the conditions of minimum standing wave ratio for small signals and maximum isolation for large signals, the open stub 16 should not be necessary, but there is usually variation in the junction capacitance Cj of diodes. Therefore, the existence of this open stub 16 is effective.

Now, hypothetically, the junction capacitance of diode 5 on the output side is
Let Cj _D be smaller than the value Cj _N that satisfies the above-mentioned specified conditions. For simplicity, ignoring the influence of the inductance of the bonding wires 6 to 9, it is sufficient to determine the dimensions of the open stub 16 so that the equivalent capacitance value of the capacitor 17 is Cj _N to Cj _D. , This makes it possible to satisfy the condition that the standing wave at the time of a small signal is minimized.

On the other hand, when the signal is large, the diode has a pure resistance of 15 as shown in Figure 6, and its value Rs is usually 1Ω.
Since the capacitance value of capacitor 17 is small, Cs
The condition of Rs≪1/ωCs is satisfied for
The open stub 16 can satisfy the maximum isolation condition without affecting the characteristics at the time of large signals. In addition, bonding wire 6~
Even when considering the inductance value of 9, there is no essential change as long as the adjustment is made by partially changing the dimensions of the open stub 16.

Further, as shown in FIG. 7, the open stub may be provided as an open stub 18 in order to adjust the variation in the junction capacitance of the limiter diode 5, and the open stub 19 may be provided for the diode 4. Alternatively, it may be provided at the position shown as 20. In any case, if it is provided near the diode 4 or 5, the same effect can be achieved.

In the above embodiment, the case where the capacitance of the diode is smaller than the standard value has been described, but if it varies beyond the standard value, the characteristic impedance Za and electrical length θa of the microstrip lines 1 to 3 can be changed to the junction capacitance. Similar adjustments can be made by optimally designing with the minimum value of the distribution.

The embodiment of FIG. 8 has an island pattern 21 in advance.
Adjustment is facilitated by preparing a plurality of patterns 21 and changing the number of island patterns 21 connected to the microstrip line 2. The number of patterns 21 can be changed depending on whether a plurality of patterns 21 are formed by connecting them in advance and then separated, or conversely, patterns 21 formed independently are connected.

In this invention, since the open stub is provided in the microstrip line near the limiter diode, it does not affect the isolation characteristics at the time of large signals, and the This suppresses the deterioration of the characteristics at the time of a signal and allows adjustment to achieve the optimum characteristics.

Note that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without changing the gist.

In the above embodiment, a two-stage limiter circuit using two limiter diodes has been described, but the present invention can also be implemented by increasing the number of diodes as appropriate and providing open stubs near required diodes. A similar effect can be achieved.

As described above, according to the present invention, by adding an adjustment function for fluctuations in the junction capacitance of the diode, a limiter circuit that can easily satisfy the conditions required for a limiter circuit and obtain optimal characteristics can be created. can be provided.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of an example of a conventional limiter circuit, FIGS. 2 and 3 are equivalent circuit diagrams of the same example at a small signal time and a large signal time, respectively, and FIG. 4 is an equivalent circuit diagram of an example of a limiter circuit according to the present invention. FIG. 5 and FIG. 6 are equivalent circuit diagrams of one embodiment at small signal and large signal times, respectively. FIG. 7 and FIG. 8 show different embodiments of the present invention. It is an equivalent circuit diagram. 1-3...Microstrip line, 4,5...Limiter diode, 6-9...Bonding wire, 10...Input terminal, 11...Output terminal, 12,1
3...Capacitor, 14,15...Low resistance.

Claims (1)

[Claims] 1 A plurality of limiter diodes connected by bonding wires or the like are provided in parallel to a microstrip line formed on a dielectric substrate, separated by a finite electrical length, and the microstrip line near the limiter diodes is A limiter circuit characterized in that an open stub is provided to compensate for variations in the junction capacitance value of a limiter diode.