JPH05175736A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To provide the frequency conversion circuit in which number of filters is reduced and which employs also a band pass filter with a characteristic easily realized. CONSTITUTION:Part of a local signal inputted to a mixer is extracted from a coupler and a phase shifter controls the phase of the signal so as to be opposite to that of a leaked local signal and the signal whose phase is controlled is injected to an output signal of the mixer at the coupler. Then two input signals having a phase difference of 180 deg. and two local signals having a phase difference of 90 deg. are mixed by two mixers and signals outputted from the mixers are synthesized by a 90 deg. hybrid circuit. Thus, the local signal leaked to the input of the band pass filter is completely erased and the band pass filter having a characteristic easily realized is used and number of filters is reduced.

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 for mixing a local signal and an input signal in a mixer and generating a signal having a sum or a difference between them.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional frequency conversion circuit. In the figure, 1 is a frequency conversion local signal and an intermediate frequency (hereinafter referred to as an IF signal) as an input signal whose frequency is converted by the local signal.
This is a mixer that mixes with. Further, 2a and 2b are bandpass filters having different pass bands of center frequencies f ₁ and f ₂ and removing unnecessary frequency components in the signal output from the mixer 1, and 3a and 3b are This is a switch for switching between the band pass filters 2a and 2b.

Next, the operation will be described. L of mixer 1
When a local signal is input to the port and an IF signal is input to the I port, a signal having a frequency component represented by the following formula (1) is output from the R port.

± mf _LO ± nf _IF (1) where m and n are integers, f _LO is the frequency of the local signal, and f
_IF is the frequency of the IF signal.

Usually, the necessary frequency to be taken out by the frequency conversion is (f _LO −f _IF ) or (f _LO + f _IF ), and the signals of other frequency components need to be removed as unnecessary waves. The removal of the unnecessary frequency component is performed by the bandpass filters 2a and 2b whose passband is matched to the required frequency. FIG. 4 shows how unnecessary waves are removed by a bandpass filter when the required frequency is (f _LO −f _IF ). (F _LO −f _IF ) is f
_When the frequency is in the band centered at ₁ , only the necessary frequency component is passed by the bandpass filter 2a having the center frequency f ₁ . Also, (f _LO −f _IF ) is f ₂
In the case of the band centered at, the bandpass filter 2b has a center frequency of f ₂ . The required frequency (f _LO −f _IF ) is the band pass filter 2a,
Which of the passbands 2b is in is determined by changing the frequency f _{LO of the} local signal.

Here, in the mixer 1, the local signal and the IF signal are mixed by switching the diode in the mixer 1 by the high level local signal, and the signal of the frequency component shown in the equation 1 is generated. However, in the normal mixer 1, the isolation between the L port and the R port is about 20 to 30 dB, and it is impossible to completely prevent the leakage from the L port to the R port. The frequency component of the local signal leaked together with the component is also output from the R port at the same time. The frequency of this signal is close to the frequency of the required signal, and its level is relatively high, which cannot be ignored especially when the level of the IF signal is low.

Note that, as a document in which a technique related to such a conventional frequency conversion circuit is described, there is, for example, JP-A-2-79505.

[0008]

Since the conventional frequency conversion circuit is constructed as described above, in order to remove unnecessary frequency components such as a local signal leaked to the R port by the L port of the mixer 1. Has a problem that it is necessary to use, as the bandpass filters 2a and 2b, a high-performance filter having a sharp attenuation characteristic and a large amount of attenuation, or a narrowband bandpass filter connected in parallel in multiple stages. It was

The present invention has been made in order to solve the above-mentioned problems, and it is possible to use an easily available bandpass filter, and further to obtain a frequency conversion circuit in which the number of filters is minimized. The purpose is to

[0010]

A frequency conversion circuit according to a first aspect of the present invention is a coupler for extracting a part of a local signal input to a mixer, and a phase shift for controlling the phase of the signal extracted by the coupler. And the signal output from this phase shifter is injected into the signal output from the mixer,
A coupler is provided to cancel the leaked local signal.

The frequency conversion circuit according to a second aspect of the present invention uses two mixers, divides the local signal into two signals having a phase difference of 90 °, and supplies the two signals to each mixer. Hybrid circuit, input signal to each other 1
A 180 ° hybrid circuit that distributes two signals with a phase difference of 80 ° and supplies them to each mixer, and these two
A 90 ° hybrid circuit for synthesizing signals output from two mixers is provided.

[0012]

In the phase shifter according to the first aspect of the present invention, the coupler leaks the phase of a signal obtained by extracting a part of the local signal input to the mixer into the signal output from the mixer. Achieved by suppressing the signal so that it has the opposite phase to that of the signal, supplying it to the coupler that injects it into the signal output from the mixer, and canceling the local signal leaking into the signal output from the mixer. A frequency conversion circuit that can use a bandpass filter with easy characteristics and can reduce the number of filters is realized.

Further, in the frequency conversion circuit according to the second aspect of the invention, the input signals having a phase difference of 180 ° and the local signals having a phase difference of 90 ° are mixed by two mixers, respectively. By combining the signals output from each mixer with a 90 ° hybrid circuit and disassembling the required signal and the leaked local signal, a bandpass filter having characteristics that are easy to realize can be used, and the number of filters can be reduced. Realize a frequency conversion circuit that can be reduced.

[0014]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the invention described in claim 1. In the figure, 1 is a mixer,
Reference numeral 2 is a bandpass filter, which is the same as or equivalent to those of the conventional ones shown in FIG.

Reference numeral 4 denotes a coupler which is coupled to the line connected to the L port of the mixer 1 with a predetermined coupling amount and extracts a part of the local signal input to the mixer 1. Reference numeral 5 denotes the coupler 1. Is a phase shifter for controlling the phase of the signal taken out by the control unit so that the phase is opposite to the phase of the local signal leaked into the signal output from the R port of the mixer 1. 6 is coupled with a line connected to the R port of the mixer 1 with a predetermined coupling amount, and is phase-controlled by the phase shifter 5 in order to cancel the local signal leaked into the signal sent to the line. It is a coupler that injects the generated signal into the signal output from the R port of the mixer 1.

Next, the operation will be described. The local signal is input to the L port of the mixer 1, and a part of the local signal is taken out by the coupler 4 and sent to the phase shifter 5. The phase shifter 5 phase-controls the received signal and sends it to the coupler 6 to inject it into the signal output from the R port of the mixer 1. If the signal injected by the coupler 6 has the same amplitude and opposite phase as the local signal leaked from the L port of the mixer 1 to the R port, the local signal leaked to the R port is totally reflected. Since it is cancelled, the bandpass filter 2 is not input to it either. The amplitude and phase of the signal injected by the coupler 6 are set by the coupling amount of the couplers 4 and 6, and further by the phase shifter 5.

As described above, since the frequency component of the local signal does not have f _LO in the signal input to the bandpass filter 2, it is not necessary to remove it, and the frequency component f _LO -2
When the level of f _IF is sufficiently small, unnecessary frequency components can be removed by using only one bandpass filter 2 having a band in which the conventional bandpass filters 2a and 2b are combined.

Example 2. Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the invention described in claim 2. In the figure, 1a, 1b
2 is a prepared mixer, and 2 is the same bandpass filter as that of the first embodiment. Reference numeral 7 divides the local signal into two signals having a phase difference of 90 °, and supplies one of them to the mixer 1a and the other to the mixer 1b.
A 0 ° hybrid circuit, 8 is a 180 ° hybrid circuit which distributes an IF signal as an input signal into two signals having a phase difference of 180 ° from each other and supplies one of them to the mixer 1a and the other to the mixer 1b. , 9 are 90 ° hybrid circuits for synthesizing the signals output by these two mixers 1a, 1b and outputting them to the bandpass filter 2. Further, 10 to 12 are terminators for signal absorption, which are respectively connected to the hybrid circuits 7 to 9.

Next, the operation will be described. The local signal input to the 90 ° hybrid circuit 7 is divided into two,
Signals having a phase difference of 90 ° from each other are input to the reports of the mixers 1a and 1b, respectively. FIG. 2 shows a case where the signal input to the mixer 1b is delayed by 90 ° with respect to the signal input to the mixer 1a. As described above, since the signals input to the L ports of the mixers 1a and 1b have a phase difference of 90 ° as described above, the local signals leaking into the R ports of the mixers 1a and 1b are also mutually different.
It has a phase difference of 0 °. That is, the phase of the local signal leaking into the R port of the mixer 1b is delayed by 90 ° from the phase of the local signal leaking into the R port of the mixer 1a. When there is such a phase relationship, the signals output from the mixers 1a and 1b are set to 90 ° hybrid circuit 9
When combined in, the local signals leaked in the respective mixers 1a and 1b appear only on the terminator 12 side and are all absorbed.

Further, of the signals output to the R ports of the mixers 1a and 1b, the required frequency component (f _LO-
When the signal of (f _IF ) has a phase relationship opposite to that of the leaked local signal, that is, (f _LO − from the mixer 1b).
When the signal of (f _IF ) leads the signal of the mixer 1a by 90 °, the signal synthesized by the 90 ° hybrid circuit 9 is output from the 0 ° port side and input to the bandpass filter 2. It As a result, the leaked local signal and the required frequency component (f _LO -f _IF ) signal can be separated.

The phase difference between the signals of (f _LO -f _IF ) is as follows.
It is obtained by dividing into two signals whose phases are shifted from each other by 180 °. That is, the 180 ° hybrid circuit 8
The signals output from the mixers 1a and 1 have equal amplitudes.
The signal input to the I port of the mixer 1b and input to the I port of the mixer 1b is delayed by 180 ° with respect to the local signal input to the I port of the mixer 1a. Then, the local signal input to the L port of the mixer 1b is 9 times the local signal input to the L port of the mixer 1a.
Since it is delayed by 0 °, the component of the signal (f _LO −f _IF ) output from the R port of the mixer 1b is delayed by 270 °, that is, 90 ° ahead of that output from the R port of the mixer 1a. As a result, the leaked local signal can be separated as described above.

[0022]

As described above, according to the first aspect of the invention, the coupler leaks the phase of the signal obtained by extracting a part of the local signal input to the mixer to the signal output from the mixer. Control the phase shifter so that the phase is opposite to the phase of the local signal injected, inject it into the signal output from the mixer by the coupler, and cancel the local signal leaked to the signal output from the mixer. With this configuration, it is possible to completely eliminate the leaking local signal at the input port of the bandpass filter, reduce the number of filters, and use a bandpass filter with characteristics that are easy to realize. There is an effect that the frequency conversion circuit can be obtained.

According to the invention of claim 2, 1
Two input signals with a phase difference of 80 ° and two local signals with a phase difference of 90 ° are mixed by two mixers respectively, and the signals output from each mixer are combined by a 90 ° hybrid circuit. Since it is configured to separate the required signal from the leaked local signal, it is possible to completely eliminate the leaked local signal at the input port of the bandpass filter, reducing the number of filters and realizing it. It is possible to obtain a frequency conversion circuit that enables the use of a bandpass filter having a characteristic that is easy to obtain.

[Brief description of drawings]

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

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

FIG. 3 is a block diagram showing a conventional frequency conversion circuit.

FIG. 4 is an explanatory diagram showing removal of unnecessary frequency components by a bandpass filter.

[Explanation of symbols]

 1 mixer 1a, 1b mixer 2 bandpass filter 4 coupler 5 phase shifter 6 coupler 7 90 ° hybrid circuit 8 180 ° hybrid circuit 9 90 ° hybrid circuit

Claims (2)

[Claims] 1. A mixer for mixing a local signal for frequency conversion with an input signal whose frequency is converted by the local signal, and a part of the local signal input to the mixer to a predetermined coupling amount. A coupler for taking out the signal, a phase shifter for controlling so that the phase of the signal taken out by the coupler is opposite to the phase of the local signal leaked into the signal output from the mixer, and the phase shifter. A signal injected with a coupling amount that cancels the local signal leaked to the signal, to the signal output from the mixer, the signal whose phase is suppressed by the phaser,
A frequency conversion circuit, comprising: a bandpass filter for removing unnecessary frequency components from a signal in which the leaked local signal is canceled by the coupler. 2. A 90 ° hybrid circuit that distributes a local signal for frequency conversion into two signals having a phase difference of 90 ° from each other, and an input signal whose frequency is converted by the local signal. A 180 ° hybrid circuit that distributes to two signals having a phase difference of 180 °, and a mixer that mixes one of the signals output by the 90 ° hybrid circuit and one of the signals output by the 180 ° hybrid circuit, A mixer that mixes the other of the signals output by the 90 ° hybrid circuit and the other of the signals output by the 180 ° hybrid circuit; a 90 ° hybrid circuit based on a signal that combines the signals output by the mixers; ° A frequency conversion circuit equipped with a bandpass filter that removes unnecessary frequency components from the signal output from the hybrid circuit. .