JPH01286505A - Frequency converter - Google Patents

Abstract

PURPOSE:To improve the D/U without using an expensive band-pass filter with high performance by excluding a leakage signal of a conversion signal being an undesired wave from a input signal converted by a frequency converter and extracting a transmission signal by a band-pass filter. CONSTITUTION:In order to suppress a leakage wave being a leaked signal of a conversion signal LO caused in case of mixing an input signal IF and a conversion signal LO by a frequency converter 2, suppressed wave generating circuits 8, 9 generate a suppressed wave and the result is mixed with a hybrid circuit 6. Since a leakage wave being a leaked signal of the conversion signal LO is canceled, a band-pass filter 4 can filter the wave even without any steep characteristic and a transmission signal is extracted from an output signal of the hybrid circuit 6. Then the D/U is kept high without using any expensive band-pass filter with high performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a frequency conversion device used in communication equipment.

(Prior Art) Generally, transmitters used for satellite communications etc. use a frequency converter (up converter) that converts a transmission wave into a high frequency signal with good linearity in order to transmit a transmission wave to a long distance.

Here, a conventional frequency conversion device is shown in FIG.

In the figure, the input signal F input from input terminal 1 is
It has an intermediate frequency of about 140 MHz.

This input signal IF is mixed in a frequency converter 2 with a converted signal LO generated by a local oscillator 3. Here, the conversion signal LO generated from the local oscillator i has a high frequency of about 14 GHz. Mixed wave R of this converted signal LO and input signal IF
F is caused by the leakage K in the frequency converter 2 of the multi-channel wave A1 having a frequency of IF+LO. Leak wave B, IF-
It has each frequency component of the image wave C having the frequency of LD. Here, carrier wave A with frequency of IP+LO
is a signal wave that is the target output of this device, and leak wave B and image wave C are unnecessary waves. Such a mixed wave RF having three frequency components is an unnecessary wave in the bandpass filter 4. The leak wave B and the image wave C are filtered, and only the carrier wave device is outputted from the output terminal 5.

Here, the mixed wave RF generated from the frequency converter 2 is
As shown in the figure. In the figure, the waveform is composed of a carrier wave A, a leak wave B, and an image wave C in order of frequency. Therefore, in order to filter both the leak wave B and the image wave C, which are unnecessary waves, the carrier waves A and L as shown in FIG.
The fast wave characteristics must change rapidly at frequencies between O leak waves B. However, it is difficult to create a wave with such rapid changes in wave characteristics, and since the wave characteristics change depending on the ambient temperature, the D/U ratio, which is the ratio of the carrier signal to the spurious signal, deteriorates. There was a problem with this.

(Problems to be Solved by the Invention) As described above, conventional frequency conversion devices require the use of high-performance bandpass filters with sharp filtering characteristics. Become. However, there are problems in that such a bandpass filter is difficult to manufacture and expensive. Furthermore, since the bandpass characteristic of the bandpass filter changes with temperature, there is a problem that the DZU ratio deteriorates.

Therefore, an object of the present invention is to eliminate this problem and provide a frequency conversion device in which the D/U ratio does not deteriorate even without using an expensive and high-performance bandpass filter.

[Structure of the invention]

(Problems to be Solved by the Invention) The present invention includes a local oscillator that generates a conversion signal that converts the frequency of an input signal, and a local oscillator that converts the frequency of the input signal by mixing the conversion signal with the input signal. The present invention includes a frequency converter, a hybrid circuit that mixes the frequency of the suppression wave generated by the suppression wave generator with the output of the frequency converter to suppress leakage signals of the converted signal, and this hybrid circuit. In order to suppress the leakage wave, which is a leakage signal of the converted signal that occurs when the input signal and the converted signal are mixed in the frequency converter, a suppression wave is generated in the first suppression wave generation circuit and mixed in the no-brit circuit. There is. This makes it possible to cancel leakage waves, which are leakage signals of the converted signal, so that the bandpass filter can perform filtering even if the characteristics are not abrupt. Therefore, it is possible to maintain a high DZU ratio without using an expensive and high-performance bandpass filter.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, an input signal IF introduced from an input terminal 1 is supplied to a frequency converter 2, mixed with a converted signal LO from a local oscillator 3, and frequency-converted. This frequency converter 2
The mixed wave RFK from is carrier wave (IP+LO) and leak wave (1,0).

It is derived with each frequency component of the image wave (IF-LO) and is supplied to the hybrid circuit 6.

Further, a directional coupler 7 is provided between the frequency converter 2 and the local oscillator 3, and the converted signal LO is branched.

This branched converted signal LO is introduced into the phase converter 8, and its phase is inverted. The phase-inverted output signal of the phase converter 8 is level-adjusted by a variable attenuator 9, and is supplied to the hybrid circuit 6 as a leakage wave suppression signal. Mixed wave RF whose leakage waves are suppressed by this hybrid circuit 9
is introduced into a band pass filter band (BPF) 4, the image wave is removed, and only the carrier wave is led out to the output terminal 5.

In such a circuit configuration, the input signal IP is 140M
The frequency is about Hz, and the converted signal LO generated from the local oscillator 3 that is mixed to increase this frequency is 14G.
It has a frequency of about Hz.

The cram school mixed wave RF%, which is the output of the frequency converter 2 that mixes these signals, is derived as having three different frequency components as shown in Figure 2. In Figure 2, A is a carrier wave. IP+LO frequency, B is leak wave and conversion signal L
C has the same frequency as O, and C is an image wave having the frequency of IF-LO. The mixed wave RF including three frequency components shown in FIG. 2 is a converted signal LO branched from the local oscillator 3.
The leak wave suppression signal is mixed with a leak wave suppression signal whose phase is inverted and the level is adjusted to be the same level as the leak wave B in the no-bit circuit 6. In the hybrid circuit 6, the leak wave B is suppressed by the leak wave suppression signal, and a mixed wave having frequency components of the carrier wave A and the image wave C is derived. Since the carrier wave A and the image wave C have different frequencies, the mixed wave supplied from the no-brid circuit 6 is
Even if a passband filter 4 whose wave characteristics gradually change as shown in the figure is used, the image wave C can be removed and only the carrier wave filter can be output.

What has been described above is only one embodiment of the present invention, and the present invention is not limited thereto. For example, input signal IF or conversion signal L
The frequency of O may be any value.

Further, in this embodiment, in order to generate a suppression wave for suppressing a leakage wave, a conversion signal of a trapped local oscillator is taken in and generated, but an oscillator whose phase and level can be specified may be used instead. In this case as well, the D/U ratio can be kept high.

〔Effect of the invention〕

As described above, in the present invention, after removing the leakage signal of the converted signal, which is an unnecessary wave, from the input signal converted by the frequency converter, the signal to be transmitted is extracted by the bandpass filter. There is no need to use an abrupt filter, and the D/U ratio can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing frequency characteristics of a bandpass filter used in an embodiment of the present invention, and FIG. 3 is a block diagram showing a conventional example. , 4th
The figure is a diagram showing the frequency characteristics of a bandpass filter used in a conventional example. 1... Input terminal, 2... Frequency converter, 3.
...Local oscillator, 4...Band pass filter (BPF)
), 5... Output terminal, 6... Hybrid circuit, 7... Directional coupler, 8... Phase converter,
9...Variable attenuator. Representative Patent Attorney Noriyuki Chika Yamashita - Figure 2

Claims (1)

[Claims] a local oscillator that generates a conversion signal that converts the frequency of an input signal; a frequency converter that converts the frequency of the input signal by mixing the conversion signal with the input signal; a suppression wave generator that generates a suppression wave that suppresses the leakage signal of the converted signal of the local oscillator; and a suppression wave generator that mixes the suppression wave generated by the suppression wave generator with the output of the frequency converter to suppress the leakage signal of the converted signal. 1. A frequency conversion device comprising: a hybrid circuit that suppresses a signal; and a bandpass filter that extracts a signal to be transmitted from the output signal of the hybrid circuit.