JPS6027450B2 - High frequency limiter circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency limiter circuit, and more particularly to a high frequency limiter circuit using two diodes connected in parallel with opposite polarities.

The secondary IJ transmitter circuit for high frequency is 2 as shown in Figure 1.
A circuit unit in which two diodes 1 and 2 are connected in parallel with opposite polarities and inserted in parallel into a transmission line is used.

This means that when the input power is small, the diode turns off, and the capacitances 1' and 2' of the diode decrease as shown in Figure 2a.
In addition to this, an inductance 3 due to the wiring leads remains as shown in FIG. Therefore, the circuit of the transmission path is disturbed by this element, and a portion of the signal is reflected, causing transmission loss. Also, when excessive input power is applied and the diode turns on, the inductance 7 of the lead wire remains as shown in Figure 2b, preventing a complete short circuit.
The limiter's isolation characteristics are not sufficient.

In particular, this effect increases as the frequency increases, and it is difficult to obtain a limiter with good characteristics in a high frequency band. Of course, it is possible to improve the overall limit effect by inserting a circuit to compensate for these parasitic elements such as capacitance and inductance on the transmission line side, but system design and device design cannot be separated, making it impractical for practical use. Moreover, this poses a major obstacle in terms of reducing design costs and maintenance. Furthermore, if the parasitic elements are corrected using an external circuit, the circuit size becomes large, and no effective improvement in the limiter characteristics at high frequencies can be expected. The purpose of the present invention is to improve such a slave limiter circuit.
Even at particularly high frequencies, transmission loss is small for small signals, and sufficient blocking effect is achieved against excessive signals.Furthermore, the entire limiter circuit can be made independent as a small circuit unit, allowing it to be placed anywhere on the high frequency transmission path. The purpose is to make it possible to install it in

The present invention will be explained below according to Examples.

FIG. 3 is an equivalent circuit showing an embodiment of the present invention, in which diodes 1 and 2 are striped in parallel with opposite polarities, i.e., they are made into a single line. It is configured as a small circuit unit 7.

The actual dimensions of this circuit 7 are 1 of the wavelength of the signal to be handled.
Raise it close enough to below the order of magnitude. A capacitor 4 is connected in series to this circuit unit 7, and this circuit block 8 is connected in parallel to one point of the transmission line. At this time, the leads required for connection and the internal inductance 3 of the diode are connected in series to these. On the other hand, an inductance 5 is connected in parallel with these circuit blocks 8 at the same point on this transmission line. The operation of this circuit is as follows.

When the input signal is small, the diode is turned off, as shown in FIG. At this time, the diode has a small capacitance 10, and the circuit block 8 is capacitive as a whole, which causes parallel resonance with the inductance 5 in the frequency band used, and the connection point 1 of the limiter of the transmission line.
1, 12, and 12 are open, so transmission loss is minimized. Further, when an excessive input signal is input, the diode is turned on and the resonant circuit becomes as shown in FIG. At this time, inductances 3 and 4 caused by the diodes and the cables used to configure the circuit cause series resonance, and the connection point 1 of the transmission line
Between 1 and 12, a short circuit occurs.

Therefore, when an excessive input is applied, the transmission line is disconnected and a good limiting effect can be obtained. The limiter circuit of the present invention can be designed in the following steps.

First, determine the conditions for series resonance. That is, the range in which the inductance 3 shown in FIG. 5 can be set is determined from the structural conditions, including the diode, and the capacitance 4 that resonates in series in the frequency band used is determined. Next, determine the conditions for parallel resonance. First, in FIG. 3, as a condition for the series circuit block 8 to become capacitive, the capacitance 1 of the diode is
Select a diode whose reactance is greater than the reactance due to 0 or the reactance due to inductance 3.
Thereafter, an inductance 5 is determined so as to resonate in parallel with the capacitive reactance of the entire circuit block 8.

An example of realizing such a circuit in a waveguide transmission line is shown in FIG. FIG. 6 shows a waveguide type glue module (circuit unit) viewed from the flange surface direction. In the figure, 13 is an inductive window, which corresponds to the inductance 5 in Figure 3, and 16 is a third diode circuit unit with a tortoise-shaped wire.
7 in the figure, 14 is an inductance for configuring a series resonant circuit and corresponds to 3 in FIG. Corresponds to 4 in the figure. As is clear from this example, in the present invention, the resonant circuit is concentrated at one point on a transmission line such as a waveguide, and a part of the resonant circuit is connected in the form of a tome, which is an element with a limit effect. Since there is a circuit unit of diodes, the high frequency current path is the shortest distance, and since the diodes are connected in a tome shape, there is no need for a DC return, making it easy to create a series circuit with capacitance 4. This configuration has the effect of reducing the size, reducing the loss of the resonant circuit, and improving the limiter action.

Further, the advantage of using a circuit unit connected in a tombular configuration is that the impedance of the diode becomes low when an excessive input is applied, so there is no risk of voltage breakdown of the diode because no high voltage is applied. In general, limiter diodes can be designed with sufficient margin for forward current, but the withstand voltage is inconsistent with the responsiveness of the limiter action and the series resistance, which is an element of loss, so a high withstand voltage element is used. is not a good idea. For this reason,
In order to handle excess power, it is desirable to use only the directional characteristics. Therefore, this is achieved by a so-called cross-connected element in which elements arranged very closely and with opposite directions are connected in parallel. The features of the present invention are that this circuit block of diodes connected in a tombular shape is incorporated into the resonant circuit to improve the limiter effect circuit-wise, and that the conditions for selecting the limiter element are advantageous. By eliminating the need for the diode element, we have made it possible to connect the capacitance in series with the diode element. As a result, series resonance can be caused when the diode is turned on due to overpower, and a transmission-type low-loss, high-isolation passive limiter (a type that breaks the circuit due to overpower) has been realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional Mituta circuit using two diodes, and FIG. 2a is an equivalent circuit of the limiter of FIG. 1 when a small signal is used. FIG. 2b is an equivalent circuit when the excessive signal of FIG. 1 is input. FIG. 3 is an equivalent circuit diagram of an embodiment of the present invention, and FIG. 4 is an equivalent circuit diagram of the circuit of FIG. 3 when a small signal is used. FIG. 5 is an equivalent circuit of the circuit shown in FIG. 3 when an excessive signal is input. 6th
The figure shows an example in which the present invention is applied to an IJ transmitter circuit for a waveguide transmission line. 1 and 2 are limiter diodes, 3 is the lead-in wire and inductance of the diode, 4 is a capacitor for series resonance, 5 is an inductance for parallel resonance, 7 is a circuit unit in which diodes are connected in a tome shape, and 8 is a limiter diode. 9 is a resonant circuit including a circuit unit in which a diode is formed into a tortoise-shaped wire, and 10 is the equivalent capacitance of the circuit unit 7 when a small signal is generated. Tsutomu' figure bell 2 figure younger brother 3 figure 4 younger brother s figure 6

Claims (1)

[Claims] 1 includes a diode circuit having two diodes connected in parallel with opposite polarities, a capacitor, and first and second inductances, the diode circuit, the capacitor, and the first inductance.
A high-frequency limiter circuit, characterized in that the second inductance and the series-connected circuit are connected in parallel to a high-frequency transmission line.