JPH0697844A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To eliminate the leaked local oscillation signal for a frequency conversion circuit which sends the intermediate frequency modulated wave obtained by a base band signal after converting the intermediate frequency into the radio frequency by synthesizing the branched local oscillation signal and the leaked local oscillation signal with the same amplitude and the reverse phase. CONSTITUTION:A local oscillation signal is branched and the phase of this signal is controlled by a phase shifter 7 so that the leaked local oscillation signal is eliminated. Then the amplitude of the local oscillation signal is controlled by an attenuator 8. The phase and the amplitude of the local oscillation signal are set equal and reverse to those of the leaked local oscillation signal. Then the synthesization of electric power is carried out by a power synthesizer 9. At the same time, the phase shift extent of the shifter 7 and the attenuated variable of the attenuator 8 are always controlled by the external control signal. Thus the fluctuation of the leaked local oscillation signal can be satisfactorily suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion circuit,
In particular, the present invention relates to a frequency conversion circuit that converts an intermediate frequency modulation signal used on the transmission side of a wireless communication device into a radio frequency.

[0002]

2. Description of the Related Art In a conventional frequency conversion circuit, as shown in FIG. 4, in order to suppress leakage of a local oscillation signal at the output of a frequency mixer 2, a band pass filter 3 having a large out-of-band attenuation is provided. In addition, the band stop filter 4 for removing the local oscillation signal was added and used.

A conventional example will be described with reference to FIG. The modulated wave modulated to the intermediate frequency by the baseband signal is amplified by the intermediate frequency amplifier 1 to the frequency mixer 2 to an appropriate input power level. The modulated signal is frequency-mixed by the frequency mixer 2 with the sine wave signal of a specific frequency output from the local oscillator 6 and output. The spectrum of the output signal of the frequency mixer 2 has the same frequency component as the input intermediate frequency signal, the same frequency component as the local oscillation signal, the DC component, twice the frequency component of the input intermediate frequency signal, and twice the local oscillation signal. The frequency component, the difference frequency component between the input intermediate frequency signal and the local oscillation signal, and the sum frequency component between the input intermediate frequency signal and the local oscillation signal are included. Only the difference frequency component or the sum frequency component is extracted, and only the desired radio frequency signal is extracted through the band pass filter 3. The leaked local oscillation signal, which has the same frequency component as the local oscillation signal at the output of the frequency mixer 2 here, is separated from the radio frequency to be transmitted by only the intermediate frequency, and therefore the band pass filter 3 Is difficult to remove,
In addition, there is a possibility that it may become an interfering wave of a radio system of an adjacent radio frequency. A band stop filter 4 for removing the leaked local oscillation signal is inserted, and then a radio frequency amplifier 5 amplifies the power to a required output power.

[0004]

In the above-mentioned conventional frequency conversion circuit, in order to prevent the local oscillation signal from leaking to the output side of the frequency mixer, a band pass filter and a band stop filter are used. In addition, there is a drawback that a filter with strict characteristics is required as compared with the case where there is no leakage of a local oscillation signal.

[0005]

The frequency conversion circuit of the present invention frequency-mixes a local oscillator for generating a sine wave signal having a local oscillation frequency for transmission and an input signal having a frequency different from that of the local oscillation signal. And a frequency mixer that converts the spectrum of the input signal into an output signal of a component that is shifted by a certain frequency as it is, and only a signal component that is obtained by frequency-converting the input signal from the output signal of the frequency mixer to a desired different frequency. In a frequency conversion circuit having a band pass filter for extracting the phase shifter for branching the output of the local oscillator and controlling the phase of the branched local oscillation signal, and the amplitude of the branched local oscillation signal. And an electric power combiner that combines a local oscillation signal whose phase and amplitude are controlled at the output of the band pass filter.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention.
1, the same symbols as those in FIG. 4 have the same configurations. That is, in FIG. 1, one of the local oscillation signals, which is a sine wave signal of a specific frequency output from the local oscillator 6, is input to the frequency mixer 2, but the other branched local oscillation signal controls the phase. After passing through the phase shifter 7 and the attenuator 8 that controls the amplitude, the band pass filter 3 combines the desired radio frequency signal with the power combiner 9. The power combiner 9 operates to cancel the leakage local oscillation signal appearing at the output of the frequency mixer 2. That is, a signal whose phase and amplitude are adjusted is generated from the original local oscillation signal, and power is combined so that the signals have the same amplitude but different phases of 180 °. In this case, since it is considered that the amplitude and phase of the leaked local oscillation signal appearing at the output of the frequency mixer 2 do not change when the amplitude and phase fluctuations of the original local oscillation signal are excluded, If the amplitude and phase fluctuations of the leakage local oscillation signal are large due to the characteristics of the mixer 2, the phase shifter 7 and the attenuator 8 are used.
It is necessary to control the amount of phase shift and the amount of attenuation at.

The case where the phase shifter and the attenuator are always automatically controlled in this way will be described below. 2 is a block diagram of a second embodiment of the present invention. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. In the second embodiment, there are an infinite phase shifter 7A whose amount of phase shift can be controlled by an external control voltage and a voltage control type attenuator 8A whose amount of attenuation can be controlled by an external control voltage. Further, an amplitude / phase control circuit 13 for generating each control signal, and a band pass filter 1 for extracting a leakage local oscillation signal included in the output signal of the power combiner 9 are provided.
0, the power amplifier 11 that amplifies the extracted residual leakage local oscillation signal to a level at which the power level can be detected, and the amplitude / phase control circuit 13 by detecting the level of the output signal thereof to the power level of the leakage local oscillation signal. And a power level detector 12 for sending information. Since this control loop controls the infinite phase shifter 7A and the voltage control type attenuator 8A so that the power level of the residual leaked local oscillation signal appearing at the output of the power combiner 9 is minimized, Even if the characteristics of the mixer 2 change, a sufficient suppression effect of the local oscillation signal can be obtained. Here, the amplitude / phase control circuit 13 is realized by software control using a microprocessor or the like.

FIG. 3 shows a block diagram of a third embodiment of the present invention. In FIG. 3, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals. The third embodiment has an infinite phase shifter 7A and a voltage control type attenuator 8A, and is largely different from the second embodiment in that the leak local oscillation signal is extracted before the power combiner 9. That is what you are doing. That is, the leaked local oscillation signal before suppression by anti-phase synthesis is extracted by the bandpass filter 10 and the power amplifier 11 and then branched, and one is a local oscillation signal whose phase is controlled by the infinite phase shifter 7A. Phase difference is detected by the phase comparator 14, and based on the phase difference information, the phase control circuit 13A controls the phase shift amount of the infinite phase shifter 7A so that the phase shift amount becomes an opposite phase at the time of combination by the power combiner 9. is doing. The other is that the power level detection circuit 12 detects the power level of the leakage local oscillation signal, and the amplitude control circuit 13B combines the attenuation amount of the voltage control type attenuator 8A in the power combiner 9 according to this power level. Sometimes it is controlled to have equal amplitude.

[0009]

As described above, the present invention forms the control loop for suppressing the leaked local oscillation signal at the output of the frequency conversion circuit, and thereby the filter and the band stop filter as in the conventional example are formed. There is an effect that an extra large amount of suppression of the local oscillation signal can be obtained because it is not necessary to add a wave filter.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is a block diagram of a third embodiment of the present invention.

FIG. 4 is a block diagram of a conventional frequency conversion circuit.

[Explanation of symbols]

 1 intermediate frequency amplifier 2 frequency mixer 3, 10 band pass filter 4 band stop filter 5 radio frequency amplifier 6 local oscillator 7 phase shifter 7A infinite phase shifter 8 attenuator 8A voltage controlled attenuator 9 power combiner 11 power amplifier 12 power level detection circuit 13 amplitude / phase control circuit 13A phase control circuit 13B amplitude control circuit 14 phase comparator

Claims (3)

[Claims] 1. A local oscillator for generating a sine wave signal having a local oscillation frequency for transmission and an input signal having a frequency different from the frequency of the local oscillation signal are frequency-mixed, and the spectrum of the input signal is polarized as it is at a constant frequency. A frequency converter having a frequency mixer for converting the output signal of the shifted component, and a band-pass filter for taking out only a signal component of the output signal of the frequency mixer, which is obtained by frequency-converting the input signal into a desired different frequency. In the circuit, the output of the local oscillator is branched, a phase shifter for controlling the phase of the branched local oscillation signal, an attenuator for controlling the amplitude of the branched local oscillation signal, and its phase and amplitude. And a power combiner for combining the controlled local oscillation signal at the output of the bandpass filter. 2. The phase shifter is an infinite phase shifter that controls the amount of phase shift by an external control signal, and the attenuator is a voltage control type attenuator that controls the amount of attenuation by an external control signal. A combiner branches its output and extracts the local oscillation signal component contained in the output signal. A local oscillation signal bandpass filter and a leakage of the local oscillation signal bandpass filter. And a detector that outputs as power level information, and inputs the residual power level information and outputs a control signal for controlling the amount of phase shift in the infinite phase shifter and the amount of attenuation in the voltage controlled attenuator The frequency conversion circuit according to claim 1, further comprising: 3. In order to control the amount of phase shift in the infinite phase shifter and the amount of attenuation in the voltage controlled attenuator, the input to the power combiner is branched and included in the input signal thereof. A second bandpass filter for extracting the local oscillation signal component, a phase for comparing the extracted local oscillation signal component and the output signal of the infinite phase shifter, and a phase for outputting phase difference information. A comparator, a detector that detects the power level of the extracted local oscillation signal component and outputs the leakage of the local oscillation signal to the frequency mixer output as leakage power level information, and the phase difference information input A phase control circuit that outputs a control signal that controls the amount of phase shift in the infinite phase shifter, and an amplitude control that outputs the control signal that inputs the leakage power level information and controls the amount of attenuation in the voltage controlled attenuator And a circuit. And the frequency conversion circuit according to claim 2.