CN113315539A

CN113315539A - Trap circuit for suppressing local oscillator leakage of frequency mixer

Info

Publication number: CN113315539A
Application number: CN202110723148.8A
Authority: CN
Inventors: 秦旭; 王鹏举; 李永涛; 莫坤山; 李海兵; 盖晓娜
Original assignee: Guilin University of Aerospace Technology
Current assignee: Guilin University of Aerospace Technology
Priority date: 2021-06-29
Filing date: 2021-06-29
Publication date: 2021-08-27

Abstract

The invention belongs to the field of radio frequency signal processing circuits, in particular to a trap circuit for inhibiting the local oscillator leakage of a mixer, which comprises a radio frequency input transformer and a radio frequency output transformer, and is characterized by also comprising a plurality of resonance circuits and LC network circuits, wherein the number of the resonance circuits and the LC network circuits is equal to n, the resonance circuits comprise a plurality of quartz crystals connected in parallel, the frequency of the quartz crystals is consistent with the local oscillator frequency, the LC network circuits are 1/4-wavelength impedance conversion circuits, the LC network circuits are connected with the resonance circuits in series at intervals, the output end of the radio frequency input transformer is electrically connected with the input end of the first resonance circuit, the electrical input end of the radio frequency output transformer is electrically connected with the output end of the last LC network circuit, and the trap circuit achieves a very high trap attenuation value through a structure of the quartz crystals and the LC networks for a plurality of iterations, the effect of inhibiting the local oscillation signals in the radio frequency signals input by the transformer is good.

Description

Trap circuit for suppressing local oscillator leakage of frequency mixer

Technical Field

The invention belongs to the field of radio frequency signal processing circuits, and particularly relates to a trap circuit for inhibiting local oscillator leakage of a frequency mixer.

Background

The mixer is an important component in rf technology, and the local oscillator signal driving level of the conventional passive or active mixer is large, which easily causes the problem of undesired local oscillator leakage, i.e. the coupled local oscillator signal appears at the output of the mixer. When the mixing working frequency of the mixer is far away from the local oscillator frequency, the leaked local oscillator signal can be filtered out easily through the filter network, but when the mixing working frequency of the system is close to the local oscillator signal frequency, the traditional filter network cannot.

Disclosure of Invention

The invention aims to provide a trap circuit for inhibiting local oscillator leakage of a frequency mixer, which has a simple structure and a good effect.

The technical solution to achieve the above object includes the following contents,

the utility model provides a trapper circuit for suppressing mixer local oscillator leaks, includes radio frequency input transformer and radio frequency output transformer, still includes several resonance circuit and LC network circuit, and resonance circuit and LC network circuit's quantity is the same for n, resonance circuit includes a plurality of parallelly connected quartz crystal, and quartz crystal's series resonance frequency is unanimous with local oscillator frequency, LC network circuit is 1/4 wavelength impedance transformation circuit, and LC network circuit and resonance circuit interval are established ties, and radio frequency input transformer's output is connected with first resonance circuit's input electricity, and radio frequency output transformer electric input is connected with last LC network circuit's output electricity.

Further, said n is equal to 3; the larger n is, the better the trap effect is, but the more complex the circuit structure is, and the proper iteration times are beneficial to ensuring the working stability of the circuit and the controllable volume of the device.

Further, the winding ratio of the radio frequency input transformer is 1:4, and the winding ratio of the radio frequency input transformer is 4: 1.

Further, the number of quartz crystals in the resonant circuit is 2-3.

The trap circuit forms an attenuation network through the quartz crystal, the series resonance characteristic of the quartz crystal is utilized, the quartz crystal can reach an extremely high Q value, the attenuation bandwidth can be extremely narrow, and the trap circuit can reach a very high trap attenuation value through repeated iteration of the structure of the quartz crystal and the LC network, and has a good effect of inhibiting local oscillation signals in radio frequency signals input by the transformer.

Drawings

FIG. 1 is a schematic block diagram of an embodiment of the present invention;

FIG. 2 is a schematic circuit diagram according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a frequency response according to an embodiment of the present invention.

Detailed Description

The present invention will be described in detail with reference to examples.

Referring to fig. 1 and 2, a trap circuit for suppressing the local oscillator leakage of a mixer includes a radio frequency input transformer T1 and a radio frequency output transformer T2, and further includes 3 resonance circuits and 3 LC network circuits, where the resonance circuit includes 2 parallel quartz crystals Y, the series resonance frequency of the quartz crystals is consistent with the local oscillator frequency, the LC network circuit is a 1/4 wavelength impedance transformation circuit, the LC network circuit is connected in series with the resonance circuits at intervals, the output terminal of the radio frequency input transformer T1 is electrically connected to the input terminal of the first resonance circuit, and the input terminal of the radio frequency output transformer T2 is electrically connected to the output terminal of the last LC network circuit;

in this embodiment, the winding ratio of the radio frequency input transformer T1 is 1:4, and the winding ratio of the radio frequency input transformer T2 is 4: 1;

in the embodiment, the input impedance and the output impedance are all unified to be 50 ohms, the impedance of the radio frequency input impedance of 50 ohms is converted to be 200 ohms through a 4:1 transformer T1, so that the resistance of 200 ohms is connected with the quartz crystal Y1 in series, and the series resonance frequency of the quartz crystal is equivalent to pure resistance (the typical value of the series resonance of the quartz crystal is 20 ohms); according to the principle of resistance voltage division, a local oscillation signal generates 10-time attenuation on 200 ohms and a first quartz crystal Y1, the more quartz crystals Y are connected in parallel, the smaller the series resonance resistance formed by the quartz crystals Y is, the final result is that the attenuation value obtained by resistance voltage division is larger, but the attenuation quantity obtained by connecting a plurality of quartz crystals in parallel is limited, in order to improve the attenuation intensity of the trap filter, the impedance after resistance voltage division can be improved to more than 200 ohms again by using an equivalent 1/4 wavelength line circuit formed by an LC network, the series resonance resistance effect of the quartz crystals is repeatedly used for resistance voltage division, the structure of the quartz crystals and the LC network can be repeatedly iterated for many times to achieve a very high trap attenuation value, and finally, the radio frequency signal impedance is restored to 50 ohms by a 4:1 transformer at the output end of the trap filter;

the quartz crystal Y in the trap circuit of this embodiment is selected and designated as 50MHz (actually measured, the series resonance frequency thereof is 49.49224 MHz), referring to fig. 3, when the trap circuit is used, the 3dB bandwidth of the circuit is 7.2KHz, the attenuation at the center frequency of 49.49224MHz is-60 dB, taking a passive mixer SLB-1 of typical Mini-circuit company as an example, the local oscillator leakage is-38 dBm, after-60 dB attenuation by the trap circuit of this embodiment, the local oscillator signal leakage of only-98 dBm is finally output, which can completely neglect the influence on the system after the whole mixing. Therefore, the wave trap of the invention can obtain very good effect of inhibiting local oscillator leakage.

Claims

1. The utility model provides a trapper circuit for suppressing mixer local oscillator leaks, includes radio frequency input transformer and radio frequency output transformer, characterized by, still includes several resonance circuit and LC network circuit, and resonance circuit and LC network circuit's quantity is the same for n, resonance circuit includes a plurality of parallelly connected quartz crystal, and quartz crystal's frequency is unanimous with local oscillator frequency, LC network circuit is 1/4 wavelength impedance transformation circuit, and LC network circuit and resonance circuit interval are established ties, and radio frequency input transformer's output is connected with first resonance circuit's input electricity, and radio frequency output transformer electrical input is connected with last LC network circuit's output electricity.

2. The trap circuit for suppressing local oscillator leakage of a mixer of claim 1, wherein n is equal to 3.

3. A trap circuit for suppressing local oscillator leakage in a mixer as claimed in claim 1 or 2, wherein the number of quartz crystals in said resonant circuit is 2-3.

4. The trap circuit according to claim 1 or 2, wherein the winding ratio of the rf input transformer is 1:4, and the winding ratio of the rf input transformer is 4: 1.