JPH01166604A - Detection circuit - Google Patents

Abstract

PURPOSE:To prevent the disturbance due to reflection by constituting a circuit receiving a high frequency signal by a hybrid circuit a hybrid circuit and a reflected wave from a detection diode connecting to a two-branch terminal at a terminal receiving the high frequency signal. CONSTITUTION:A radio wave of a frequency being GHz or over received by an antenna 1 is amplified by a high frequency circuit 2 and given to a coupling circuit 3 via a transmission line 8. The coupling circuit 3 consists of a hybrid circuit 3 having a branch line type four-terminal, the inputted signal is branched into amplitude modulation signals with a different phase by 90 deg., which are fed individually to diodes 4a, 4b and detected, and carriers with a different phase by 90 deg. are eliminated by bypass capacitors 5a, 5b. The detected signal is summed by a transmission line 9 and a modulation signal is outputted at a terminal 10. The reflected waves from the diodes 4a, 4b are opposite in the phase and cancelled at a terminal 7 and terminated by a termination resistor 6. Thus, the effect of the reflected wave is suppressed over a wide range of the level of the high frequency signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a detection circuit for amplitude-modulated high-frequency signals, and particularly to improvement of the reflection characteristics of the detection circuit.

[Prior Art] As a detection circuit for extracting a modulated signal from an amplitude-modulated high-frequency signal, there is a conventional circuit shown in FIG. In FIG. 3, 1 is an antenna, 2 is a high frequency circuit that performs processing such as amplification of the high frequency signal received by the antenna 1, and 4 is a detection diode.

As the detection diode 4, a Schottky barrier diode with high detection sensitivity and excellent high frequency characteristics is often used.

6 is a DC return circuit for the detection diode 4, 7 is an input terminal for a high frequency signal, 10 is an output terminal, and 15 is a matching circuit provided between the high frequency circuit 2 and the detection diode 4. This matching circuit 15 uses a λ impedance conversion circuit. 1B is a bias circuit, 17 is a filter, and 18 is a load.

In the circuit configured as described above, an amplitude modulated signal of a high frequency of gigahertz or higher, such as a microwave or millimeter wave, received by the high frequency circuit 2 through the antenna 1 is applied to the detection diode 4 via the matching circuit 15. The detection diode 4 has non-linear characteristics such as a linear characteristic when the input signal level is high and a square-law characteristic when the input signal level is low. Therefore, bias circuit 1
Reference numeral 6 is provided to improve the detection sensitivity by approaching linear detection even when the input signal level of the detection diode 4 is small.

The amplitude-modulated high-frequency signal is detected by the detection diode 4 and then sent to the filter 17, where the carrier signal is removed and output as a modulated signal from the output terminal 1o.

[Problems to be Solved by the Invention] In the conventional detection circuit that directly detects the above-mentioned high-frequency signal, when the reflected wave from the detection diode 4 interferes with the gain characteristics of the high-frequency circuit 2, the characteristics change and the accuracy becomes inaccurate. Received signal level cannot be obtained. This causes an error when making measurements using the received signal level. Therefore, it is required to sufficiently suppress reflected waves from the detection diode 4.

However, even if a λ bimbedance conversion circuit is used as the matching circuit 15 provided between the high frequency circuit 2 and the detection diode 4, the detection diode 4 has sufficient power to exhibit nonlinear characteristics with respect to the input signal level. Impedance matching could not be obtained, and it was difficult to suppress reflected waves from the detection diode 4.

In addition, from the stage when the input signal level is small, the detection diode 4 is biased in order to approximate the characteristics of the detection diode 4 to linear detection characteristics, improve detection sensitivity, and improve the voltage standing wave ratio (VSVR). Even if the bias voltage -VB was applied from the circuit 16, it was difficult to reliably suppress the reflection of the detection diode 4.

Therefore, it is difficult to suppress the interference of the reflected wave from the detection diode 4 with the high frequency circuit 2, and there is a problem that a modulated signal corresponding to an accurate received signal level cannot be obtained.

This invention has been made to solve these problems, and aims to provide a detection circuit that can reliably suppress the interference of reflected waves from a detection diode with high-frequency circuits. .

[Means for Solving the Problems] The detection circuit according to the present invention is a coupling circuit consisting of a hybrid circuit having four terminals to which a high frequency signal sent from a high frequency circuit and a two-branch output output to a detection diode are connected. and a terminating resistor connected to the other end of the coupling circuit to form a DC return circuit for the detection diode.

[Operation] In this invention, the coupling circuit that inputs the high frequency signal is
By constructing a hybrid circuit that divides and combines high-frequency signals, the reflected waves from the detection diodes connected to the two-branch output of the coupling circuit are made to have opposite phases to each other at the terminals to which the high-frequency signals are applied, and cancel each other out. Therefore, the above-mentioned problems can be solved.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
In the figure, 1', 2, 7.10 are the same as the conventional example shown in FIG. 3 is a coupling circuit provided between the high frequency circuit 2 and the detection diodes 4a, 4b.

The coupling circuit 3 has, for example, four terminals of a branch line type,
It is composed of a 90° hybrid circuit that divides and combines high frequency signals, and detection diodes 4a and 4b are individually connected to two branch outputs. 5a,
5b is a bypass capacitor for removing the carrier wave signal, 6 is a terminating resistor connected to the remaining terminals of the coupling circuit 3,
It forms a DC return circuit for the detection diode 4.

8 is a high frequency signal transmission line, and 9 is a video transmission line.

In the circuit configured as described above, a high frequency of gigahertz or higher (
The amplitude modulated signal (microwave, millimeter wave) is sent from the input terminal 7 to the coupling circuit 3 via the transmission line 8 . The high-frequency amplitude modulation signal sent to the coupling circuit 3 is branched into amplitude modulation signals with a 90° phase difference by the 90° hybrid circuit that constitutes the coupling circuit 3, and the two branched outputs are individually connected to detection diodes 4a and 4b. sent to. These amplitude modulated signals with different phases of 90° are detected by the detection diode 4a.
, 4b, and then sent to bypass capacitors 5a, 5b to remove carrier waves with a 90° phase difference.

These signals are added at the video transmission line 9 and the output terminal l
Obtain a modulated signal at O. On the other hand, detection diodes 4a and 4b
The reflected wave from the terminating resistor 6 is applied to the terminal resistor 6.

In the detection circuit configured as described above, the coupling circuit 3 consists of a 90゛ hybrid circuit having four terminals,
Since the high frequency amplitude modulated signal is branched into amplitude modulated signals with a 90° phase difference and sent to the detection diodes 4a and 4b, the high frequency circuit 2 and the detection diodes 4a and 4
The reflected waves from the respective detection diodes 4a and 4b due to impedance mismatch with the input terminal 7 have opposite phases to each other at the input terminal 7. Further, in the terminating resistor 6, the signals are terminated in the same phase.

Therefore, the reflected waves from the detection diodes 4a and 4b are combined and canceled at the input terminal 7, so that the level of the reflected waves applied to the high frequency circuit 2 is significantly suppressed. As a result, the high frequency circuit 2 and the detection diode 4a can be connected from the low level to the high level of the high frequency signal without providing a matching circuit or applying a bias voltage to the detection diode.
, 4b can almost avoid interference with the characteristics of the high frequency circuit 2 due to mismatching of the reflected waves with the input impedances. Therefore, a modulated signal having a level that accurately corresponds to the received signal level can be obtained at the output terminal IO.

FIG. 2 is a front view showing an example of the configuration of the detection circuit configured as described above, and in the figure, 11 is a dielectric substrate on which the detection circuit is mounted. As shown in the figure, the coupling circuit 3, the transmission circuit 8 and the video transmission line 9 form a strip line,
It is formed as a planar circuit on a dielectric substrate 11. Beam lead type Schottky barrier diodes are used as the detection diodes 4a and 4b, chip capacitors are used as the bypass capacitors 5a and 5b, and a 50Ω chip resistor that terminates the terminals of the hybrid circuit is used as the termination resistor 6. , each component is mounted on the above-mentioned planar circuit.

Therefore, the transmission loss is small, and the structure is simple, compact, and lightweight, and the reflected waves from the detection diodes 4a and 4b interfere with the characteristics of the high-frequency circuit 2 over a wide range of signal levels of the high-frequency signal applied to the input terminal 7. can be suppressed.

In the above embodiment, a branch line type hybrid circuit is used as the hybrid circuit constituting the coupling circuit 3. However, even if a rat race type hybrid circuit is used as the hybrid circuit, the same effect as in the above embodiment can be achieved. be able to.

[Effects of the Invention] As explained above, the present invention has four terminals between the high frequency circuit and the detection diode, to which the high frequency input, the two-branch output connected to the detection diode, and the terminating resistor are connected. By providing a coupling circuit using a hybrid circuit, reflected waves from the detection diode due to impedance mismatch between the high frequency circuit and the detection diode are canceled out by mutually opposing phases at the high frequency signal input terminal.

Therefore, over a wide range of high-frequency signal levels, the influence of reflected waves on the high-frequency circuit can be significantly suppressed, and interference with the characteristics of the high-frequency circuit can be largely avoided, and the output of the detector circuit can accurately match the received signal level. This has the effect that a corresponding modulation signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a front view showing the configuration of the above embodiment, and FIG. 3 is a block diagram showing a conventional example. DESCRIPTION OF SYMBOLS 1... Antenna, 2... High frequency circuit, 3... Coupling circuit, 4, 4a, 4b... Detection diode, 5a,
5b... Bypass capacitor, 7... Input terminal, 8
...Transmission line, 9...Video transmission line, 10...
Output terminal, 11... dielectric substrate.

Claims (1)

[Claims] In a detection circuit that uses a diode and a bypass capacitor to obtain a modulated signal from an amplitude-modulated high-frequency signal of gigahertz or higher, a high-frequency signal sent from the high-frequency circuit and a two-branch output output to the diode are connected. A coupling circuit comprising a hybrid circuit having four terminals and dividing and combining high frequency signals, and a terminating resistor connected to the other end of the coupling circuit and forming a DC return circuit for the diode. Characteristic detection circuit.