CN202978822U - Down-conversion device based on electric tuning filter - Google Patents

Abstract

The utility model discloses a down-conversion device based on an electric tuning filter. The down-conversion device comprises a radio-frequency signal input port, a local oscillator, a mixer and a low pass filter and is characterized by further comprising the electric tuning filter. The radio-frequency signal input port is connected to an input end of the electric tuning filter. An output end of the electric tuning filter is connected to a radio-frequency port of the mixer. Output of the local oscillator is connected to a local oscillator port of the mixer. A medium frequency port of the mixer is connected to an input end of the low pass filter. An output end of the low pass filter outputs a medium frequency signal. The stepping local oscillator is used, microwave signals are converted to a fixed medium frequency, image interference is restrained effectively, one-to-one correspondence of the fixed medium frequency and the determined local oscillator to microwave input signals is established, performance of a receiver is improved, and the down-conversion device is suitable for miniature application.

Description

A kind of down-conversion device based on electrically tunable filter

Technical field

The utility model relates to microwave technical field, particularly relates to a kind of down-conversion device based on electrically tunable filter.

Background technology

Microwave band is an important frequency range in electromagnetic spectrum, and frequency is generally more than 1GHz, and the electromagnetic wave that is positioned at this frequency range has good radio transmission characteristics, can be widely used in the fields such as communication, radar.Because current digital circuit technique can't be processed microwave signal well, generally by receiver system, microwave signal is passed through to frequency translation, it is transformed to intermediate frequency and processed (usually adopting band-limited fixed intermediate frequency).In application aspect electronic countermeasures, usually use the broadband microwave signal, its useful signal limited bandwidth, but the reference carrier wave variation is greatly, can realize the rapid variation of frequency spectrum by the carrier wave of selecting different frequency.

For receiving terminal, need a stepping, corresponding with microwave signal carrier frequency local oscillation signal, carry out mixing with microwave signal, thereby obtain the fixing useful signal of intermediate frequency.Receiver should possess following characteristic: for this fixed intermediate frequency, in the situation that local frequency is known, radiofrequency signal should be calculated out according to the frequency calculation relation, fixed intermediate frequency and definite local oscillator should corresponding microwave signals, yet, if do not take special measure, this one-to-one relationship is difficult to realize, reason is: at receiving terminal, mixing (being often referred to down-conversion) adopts frequency mixer to realize, frequency mixer can be equivalent to a three-port network, be prevention at radio-frequency port (RF Port), local oscillator port (LO Port), intermediate frequency port (IF Port), corresponding input (output) frequency is respectively f _rf, f _lo, f _if.For downconversion process, have:

$f_{\mathrm{if}}=\left\{\begin{array}{cc}{f}_{\mathrm{rf}}-f_{\mathrm{lo}},& f_{\mathrm{rf}}>f_{\mathrm{lo}}\\ f_{\mathrm{lo}}-f_{\mathrm{rf}},& f_{\mathrm{lo}}>f_{\mathrm{rf}}\end{array}\right.---\left(1\right)$

With f _rff _lofor example, if f _lofixing, when the frequency of input port is (f _rf-2*f _if) time, according to formula (1), in intermediate frequency port, also will obtain a lower sideband signal with the intermediate-freuqncy signal same frequency, (f _rf+ 2*f _if) being commonly referred to image frequency, it is called the mirror image interference when input port occurs, and in actual applications, this mirror image has been hindered and damaged the one-to-one relationship of fixed intermediate frequency and the corresponding microwave signal of definite local oscillator, causes receiver correctly to receive.

Summary of the invention

In order to solve mirror image interference problem of the prior art, the utility model provides a kind of down-conversion device based on electrically tunable filter.

Down-conversion device based on electrically tunable filter of the present utility model comprises: the radio-frequency (RF) signal input end mouth, local oscillator, frequency mixer and low pass filter, it is characterized in that, this down-conversion device also comprises electrically tunable filter, wherein, the radio-frequency (RF) signal input end mouth is connected to the input of described electrically tunable filter, the output of this electrically tunable filter is connected to the prevention at radio-frequency port of frequency mixer, local oscillator output is connected to the local oscillator port of frequency mixer, the intermediate frequency port of frequency mixer is connected to the input of low pass filter, the output output intermediate-freuqncy signal of low pass filter.

Further, the number of described electrically tunable filter is two, and connected mode is two tuned filter cascades.

Further, between described two tuned filters, be provided with a low noise amplifier, its input is connected with first order tuned filter output, and its output is connected with second level tuned filter input.

Wherein, the frequency of the radio-frequency input signals of employing is greater than the frequency of local oscillation signal.

The utility model beneficial effect is as follows:

Down-conversion device based on electrically tunable filter of the present utility model is used the stepping local oscillator, microwave signal is transformed to a fixed intermediate frequency, realized that mirror image disturbs inhibition, set up the one-to-one relationship that a fixed intermediate frequency and is determined the corresponding microwave signal of local oscillator, improved receiver performance; And the electrically tunable filter adopted have power little, be easy to the advantages such as integrated, be desirable YTF(YIG Tuned Filter, YIG tuned filter) substitute, this device is suitable for miniaturized application.

The accompanying drawing explanation

Fig. 1 is the down-conversion device structural representation based on electrically tunable filter of the utility model embodiment.

Fig. 2 is the electrically tunable filter frequency response and controls the variation relation figure between voltage.

Fig. 3 is the down-conversion device structural representation based on electrically tunable filter of another embodiment of the utility model.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the utility model is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the utility model, does not limit the utility model.

Figure 1 shows that the down-conversion device structural representation based on electrically tunable filter of the present utility model, it comprises: the radio-frequency (RF) signal input end mouth, local oscillator, frequency mixer, low pass filter and electrically tunable filter, wherein, the radio-frequency (RF) signal input end mouth is connected to the input of described electrically tunable filter, the output of this electrically tunable filter is connected to the prevention at radio-frequency port (RF Port) of frequency mixer, local oscillator is connected to the local oscillator port (LO Port) of frequency mixer, the intermediate frequency port of frequency mixer (IF Port) is connected to the input of low pass filter, the output output intermediate-freuqncy signal of low pass filter.

Electrically tunable filter has the electric tuning characteristic, its frequency response changes along with the variation of tuning voltage, its typical curve as shown in Figure 2, it is example that the present embodiment be take the HMC897LP4 of Hittite company, the electrically tunable filter fixed intermediate frequency is selected 1.9GHz, the frequency range of radio-frequency input signals is 9GHz ~ 19GHz, adopts low local oscillator, i.e. f _rff _lo, so f _lofrequency range be 7.1GHz ~ 17.1GHz, frequency mixer adopts the M9-0444 of Marki company, low pass filter is responsible for picking up the lower sideband in mixed product.

When input signal is 15GHz, now local oscillation signal is 13.1GHz, corresponding mirror image disturbs as 11.2GHz, need the tuning voltage of regulating HMC897LP4 to be about 7V, now the passband of filter is positioned at 14GHz, and its typical case (insertion) loss is 5dB, and its loss at the 13.1GHz place is about 30dB, both contrasts, realized being about the inhibition of 25dB.If now at the intermediate frequency receiving terminal, signal occurs, can think that input signal is 15GHz, but not 13.1GHz.Also exist in theory 13.1GHz jam-to-signal 15GHz to input the possibility of large 30dB, but in reality, possibility is less.

Below set up a fixed intermediate frequency and and determined the one-to-one relationship of the corresponding microwave signal of local oscillator, when input signal changes, only needed to regulate the tuning voltage of electrically tunable filter, can again realize above-mentioned one-to-one relationship.

In actual applications, if think that the mirror image of 30dB suppresses not, the utility model also can be used the cascade of two-stage electrically tunable filter, as shown in Figure 3, utilize this device can obtain the Image-rejection ration that approximately doubles single electrically tunable filter, i.e. about 60dB, to meet most Image-rejection ration needs.

Preferably, because the impedance matching situation of electrically tunable filter is poor, should add a low noise amplifier between two electrically tunable filters, low noise amplifier input and the coupling of first order tuned filter, its output and the coupling of second level tuned filter.On the one hand, low noise amplifier can increase the isolation between the two-stage electrically tunable filter, can improve gain on the other hand, reduces the noise factor variation brought owing to increasing second level electrically tunable filter.

The down-conversion device based on electrically tunable filter that the utility model provides is used the stepping local oscillator, microwave signal is transformed to a fixed intermediate frequency, wherein electrically tunable filter is voltage-controlled component, there is power little (power consumption is in ten milliwatt magnitudes), be easy to integrated (Surface Mount encapsulation, exemplary height 1mm) advantage such as, the down-conversion device based on electrically tunable filter that utilizes the utility model to provide, adopt Fig. 2 embodiment can realize that the mirror image of about 30dB disturbs inhibition, adopt Fig. 3 can realize that the mirror image interference of about 60dB suppresses.

In addition, in the art, general fixed intermediate frequency frequency is higher, usually need to carry out the secondary down-conversion to intermediate frequency, is transformed into the intermediate-frequency band that is applicable to Digital Signal Processing and does subsequent treatment again, and the technology that the secondary down-conversion is relevant is comparatively ripe, at this, is not described further.

Although be the example purpose, preferred embodiment of the present utility model is disclosed, it is also possible those skilled in the art will recognize various improvement, increase and replacement, therefore, scope of the present utility model should be not limited to above-described embodiment.

Claims (7)

1. the down-conversion device based on electrically tunable filter, comprise: the radio-frequency (RF) signal input end mouth, local oscillator, frequency mixer and low pass filter, it is characterized in that, this down-conversion device also comprises electrically tunable filter, wherein, the radio-frequency (RF) signal input end mouth is connected to the input of described electrically tunable filter, the output of described electrically tunable filter is connected to the prevention at radio-frequency port of frequency mixer, local oscillator output is connected to the local oscillator port of frequency mixer, the intermediate frequency port of frequency mixer is connected to the input of low pass filter, the output output intermediate-freuqncy signal of low pass filter.

2. the down-conversion device based on electrically tunable filter as claimed in claim 1, is characterized in that, described electrically tunable filter is used fixed intermediate frequency 1.9GHz.

3. the down-conversion device based on electrically tunable filter as claimed in claim 2, is characterized in that, the frequency of the radio-frequency input signals of described radio-frequency (RF) signal input end mouth is 9GHz ~ 19GHz.

4. the down-conversion device based on electrically tunable filter as claimed in claim 3, is characterized in that, the frequency of the local oscillation signal of described local oscillator output is 7.1GHz ~ 17.1GHz.

5. the down-conversion device based on electrically tunable filter as claimed in claim 4, is characterized in that, the frequency of the radio-frequency input signals of employing is greater than the frequency of local oscillation signal.

6. the down-conversion device based on electrically tunable filter as claimed in claim 1, is characterized in that, the number of described electrically tunable filter is two, and connected mode is two tuned filter cascades.

7. the down-conversion device based on electrically tunable filter as claimed in claim 6, it is characterized in that, be provided with a low noise amplifier between described two tuned filters, its input is connected with first order tuned filter output, and its output is connected with second level tuned filter input.

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