Ultra-wideband down-conversion method without preselection filtering

Abstract

The invention provides an ultra-wideband down-conversion method without preselection filtering, which adopts a secondary frequency conversion scheme, does not need preselection filtering of an input radio frequency signal, after the radio frequency signal is filtered by a low-pass filter, the radio frequency signal is up-converted to an intermediate frequency, and then the radio frequency signal is filtered by an intermediate frequency filter and then down-converted to obtain an intermediate frequency signal. When up-conversion is carried out for the first time, a passive mixer with the third-order cross modulation (LO-2IF) suppression larger than 60 dBc is used, meanwhile, through passive frequency multiplication and segmented filtering of a local oscillator fundamental wave signal, strict control over the harmonic component of a local oscillator signal entering the first mixer is achieved, and therefore the harmonic component of the local oscillator signal entering the second mixer is strictly controlled. An intermediate-frequency signal is filtered through a different intermediate-frequency filter on an intermediate-frequency link, and the frequency conversion assembly achieved through the method still has the false suppression level larger than 45 dBc under the condition that pre-selection filtering is not needed. According to the invention, the complexity, cost, volume and weight of the system can be reduced, and the system has excellent telecommunication performance.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave circuits. Background Art

[0002] This situation will be encountered when designing an ultra-wideband down-conversion component with a relatively wide operating frequency. In order to improve the false suppression level of the component, a switch filter group module is generally cascaded before the first mixer of the frequency conversion component. The switch filter group module performs segmented pre-selection filtering on the radio frequency signal RF entering the frequency conversion component through filters of multiple different operating frequency bands. This can avoid false signals such as image frequency signals and half-radio frequency signals RF / 2. This can improve the false suppression level of the frequency conversion component, but increases the hardware cost, increases the complexity of the link, and also increases the volume and weight of the system. However, if the switch filter group module is not cascaded, the telecommunications performance of the frequency conversion component cannot be guaranteed. Therefore, at this stage, people often make a fuss about the miniaturization of the switch filter group module and use chips made of GaAs, MEMS and other processes. However, the out-of-band suppression effect of such chips is poor, the insertion loss is large, and the price of the switch filter group chip is high, the segmentation is not flexible enough, and customization is often required. The chip supply cycle is long. At the same time, multiple TTL signals are required to switch and control the chip, so serial-to-parallel chips have to be introduced.

[0003] With the continuous development of domestic microwave devices, passive mixers manufactured using 0.7μmInPHBT technology have emerged. This mixer not only has the characteristics of broadband, low frequency conversion loss, high isolation, and wide intermediate frequency operation, but also has a third-order intermodulation (LO-2IF) suppression characteristic of more than 60dBc. Some manufacturers use GaAs process to design mixers that can also achieve the above technical indicators. By rationally utilizing these mixers and designing appropriate microwave circuits, ultra-wideband frequency conversion components can be freed from the constraints of switch filter group modules while still having a false suppression level greater than 45dBc. Summary of the invention

[0004] Aiming at the problem that the ultra-wideband frequency conversion component in the prior art needs to cascade switch filter group modules in order to improve the false suppression level, which leads to increased system complexity, cost, volume and weight, the present invention proposes an ultra-wideband down-conversion method without pre-selection filtering.

[0005] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0006] The first step is to perform low-pass filtering on the input radio frequency signal RF with a frequency of f1 to f5, without the need for pre-selection filtering by the switch filter group, and to add a DC blocking capacitor before the first mixer. The DC blocking capacitor can protect the first mixer and prevent the PIN transistor in the mixer from being damaged;

[0007] The second step is to up-convert the radio frequency signal through the first mixer to obtain an intermediate frequency signal IF1, and at the same time, provide a high local oscillator signal to the first mixer through a local oscillator link;

[0008] The third step is to control the single-pole three-throw switch according to the different frequencies of the input signal, select one of the three intermediate frequency branches, and use intermediate frequency filters with different center frequencies and bandwidths to filter the intermediate frequency signal. The three intermediate frequency branches are designed to obtain better telecommunication performance, not to solve new problems caused by removing the pre-selection filter circuit;

[0009] The fourth step is to cascade an attenuator between the first mixer and the single-pole three-throw switch to attenuate the signal reflected from the switch and entering the first mixer. The signal reflected and entering the first mixer may be superimposed with the signal entering from the IF port of the first mixer in an anti-phase manner, resulting in a decrease in the gain flatness of the frequency conversion component. Therefore, it is necessary to add the attenuator or improve the isolation between the ports of the first mixer.

[0010] Step 5: Amplify an intermediate frequency signal IF1 using an intermediate frequency amplifier, filter the intermediate frequency signal IF1 through a high-pass filter, suppress the signal with a lower frequency entering the second mixer, prevent the second harmonic and the third harmonic generated by the second mixer from falling within the intermediate frequency IF band, and improve the false suppression level of the frequency conversion component;

[0011] Step 6: Down-convert an intermediate frequency signal IF1 through the second mixer to obtain an intermediate frequency signal IF, and provide two local oscillator frequency signals, high and low, to the second mixer through the two local oscillator links. The two high and low frequency signals are also for obtaining better telecommunication performance, not for solving new problems caused by removing the pre-selection filter circuit;

[0012] Furthermore, the power of the radio frequency signal entering the first mixer is controlled to be less than -10 dBm.

[0013] Furthermore, the first mixer has a LO-2IF third-order intermodulation suppression characteristic greater than 60 dBc, except when the frequency of the input RF signal is half of the frequency of the intermediate frequency signal IF1.

[0014] Furthermore, an intermediate frequency link includes three branches, and the center frequency and working bandwidth of the filter on each branch are different. The center frequency of the first intermediate frequency filter is F1, and the working bandwidth is BW1. The center frequency of the second intermediate frequency filter is F1, and the working bandwidth is BW2, BW2>BW1. The center frequency of the third intermediate frequency filter is F2, and the working bandwidth is BW2, F2>F1>f5. When the frequency of the radio frequency signal is between f1 and f2, the single-pole three-throw switch switches to the branch where the first intermediate frequency filter is located. When the frequency of the radio frequency signal is between f2 and f3 or f4 and f5, the single-pole three-throw switch switches to the branch where the second intermediate frequency filter is located. When the frequency of the radio frequency signal is between f3 and f4, the single-pole three-throw switch switches to the branch where the third intermediate frequency filter is located; wherein, f3+f4=F1, 2×(f4-f3)=BW2, f1<f2<f3<f4<f5.

[0015] Furthermore, the high-pass filter cascaded before the second mixer is used to filter out radio frequency signals below the IF band of the intermediate frequency signal, ie, DC to IF+BW2 / 2.

[0016] Furthermore, the local oscillator signal of the first mixer in the second step is provided by a local oscillator link, including: in a local oscillator link, firstly, an input local oscillator fundamental wave signal LO1 / 2 is amplified, and then the local oscillator fundamental wave signal LO1 / 2 is doubled by a passive frequency multiplier to obtain a local oscillator signal LO1; since the third harmonic LO1×3 / 2 of the local oscillator fundamental wave signal and leakage of the local oscillator fundamental wave signal LO1 / 2 are generated during the frequency multiplication process, it is necessary to perform segmented filtering on the frequency multiplied signal, and then amplify it again, and finally provide it to the first mixer for use.

[0017] Furthermore, the local oscillator signal of the second mixer described in the sixth step is provided by a two-local oscillator chain, including: in the two-local oscillator chain, firstly amplifying the input second local oscillator fundamental signal LO2 / 2, and then doubling the frequency of the second local oscillator fundamental signal LO2 / 2 through a passive frequency multiplier to obtain the second local oscillator signal LO2. In this method, the two local oscillator signals are two similar point frequency signals, and an intermediate frequency signal can be down-converted in both high local oscillation and low local oscillation conditions to obtain an intermediate frequency IF signal. Similarly, in the process of frequency multiplication, the third harmonic LO2×3 / 2 of the second local oscillator fundamental signal and the leakage of the second local oscillator fundamental signal LO2 / 2 will be generated. Therefore, the signal after frequency multiplication needs to be filtered and amplified, and finally provided to the second mixer for use.

[0018] Compared with the prior art methods, the present invention has the following beneficial effects: the present invention removes the pre-selection filtering part required in the traditional ultra-wideband frequency conversion scheme, has a first mixer with high intermodulation suppression characteristics, and has an intermediate frequency link with a clean local oscillator signal and three branches, thereby reducing the complexity, cost, volume and weight of the system, while having excellent telecommunications performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a principle block diagram of an embodiment of the present invention;

[0020] Description of the drawings: 1, low-pass filter; 2, first mixer; 3, an intermediate frequency amplifier; 4, a single-pole three-throw switch; 5, a first intermediate frequency filter; 6, a second intermediate frequency filter; 7, a third intermediate frequency filter; 8, a high-pass filter; 9, a second mixer; 10, a local oscillator fundamental amplifier; 11, a passive frequency multiplier; 12, a switch filter group; 13, a band-pass filter; 14, a broadband amplifier; 15, a narrowband amplifier; 16, an attenuator. DETAILED DESCRIPTION

[0021] In order to better understand the technical content of the present invention, specific embodiments are given in conjunction with the attached Figure 1 Instructions are as follows.

[0022] like Figure 1 As shown, the down-conversion link includes a low-pass filter 1, a first mixer 2, an intermediate frequency amplifier 3, a single-pole triple-throw switch 4, a first intermediate frequency filter 5, a second intermediate frequency filter 6, a third intermediate frequency filter 7, a high-pass filter 8, a second mixer 9, a local oscillator fundamental amplifier 10, a passive frequency multiplier 11, a switch filter group 12, a band-pass filter 13, a broadband amplifier 14, a narrowband amplifier 15, and an attenuator 16.

[0023] In this embodiment, the frequency of the radio frequency signal is 1-15 GHz. Preferably, the signal power when entering the first mixer 2 is less than -10 dBm.

[0024] In the first step, filtering is performed by a low-pass filter 1 to suppress the image frequency, and a low-pass filter with a cut-off frequency greater than 15 GHz is preferred.

[0025] In the second step, the filtered RF signal is up-converted to an intermediate frequency IF1 by the first mixer 2. Before the first mixer 2, a DC blocking capacitor is cascaded. A preferred capacitance is 100pF. A preferred intermediate frequency IF1 frequency is 22GHz. When selecting the first mixer 2, it is preferred that its third-order intermodulation suppression is greater than 60dBc. The local oscillator signal required by the first mixer 2 is Figure 1The local oscillator link shown provides that the frequency of the local oscillator fundamental wave signal LO1 / 2 entering the link is 11.5-18.5 GHz, corresponding to the preferred IF1 frequency. The local oscillator fundamental wave signal is amplified before frequency doubling, and the power of the input local oscillator fundamental wave signal is adjusted to 12-18 dBm. The signal frequency after frequency doubling by the passive frequency multiplier 11 is 23-37 GHz. Since the third harmonic of the local oscillator fundamental wave signal 34.5-55.5 GHz and the leakage of the fundamental wave signal 11.5-18.5 GHz will be generated during the frequency doubling process, the local oscillator signal needs to be filtered by the switch filter group 12 after the frequency doubling. The switch filter group 12 can be divided into frequency segments of 23-30 GHz and 30-37 GHz. Because the third harmonic of a local oscillator fundamental wave signal with a frequency of 11.5 to 15 GHz is 34.5 to 45 GHz, a GaAs filter with an operating frequency of 23 to 30 GHz can have a high suppression effect on it. Similarly, a GaAs filter with an operating frequency of 30 to 37 GHz can also have a high suppression effect on the third harmonic of 45 to 55.5 GHz of a local oscillator fundamental wave signal with a frequency of 15 to 18.5 GHz. After segmented filtering, it is amplified by a broadband amplifier 14 and finally output to the local oscillator port of the first mixer 2. In this way, a clean local oscillator signal without harmonic components can be provided to the first mixer 2, so that the intermodulation signal of the local oscillator fundamental wave signal and the radio frequency signal can be avoided to fall within an intermediate frequency band to cause false signals. Specifically, when the input RF signal RF frequency is 1-15 GHz, the frequency of the fundamental signal LO1 / 2 of a local oscillator is 11.5-18.5 GHz. When the sum of the input RF signal RF frequency and the frequency of the local fundamental signal is equal to 22 GHz, the intermodulation signal between the two will fall within an intermediate frequency band and cause false signals. Therefore, the harmonic components of the local oscillator signal entering the first mixer 2 must be strictly controlled.

[0026] The third step, when the frequency of the input RF signal is 1-2 GHz, the single-pole three-throw switch 4 switches to the branch where the first intermediate frequency filter 5 is located, the center frequency of the first intermediate frequency filter 5 is 22 GHz, preferably, the working bandwidth can be selected as 200 MHz, when the frequency of the input RF signal is 2-10.75 GHz or 11.25-15 GHz, the single-pole three-throw switch 4 switches to the branch where the second intermediate frequency filter 6 is located, the center frequency of the second intermediate frequency filter 6 is 22 GHz, preferably, the working bandwidth can be selected as 1 GHz, when the frequency of the input RF signal is between 10.75 and 11.25 GHz, the single-pole three-throw switch 4 switches to the branch where the third intermediate frequency filter 7 is located, the center frequency of the third intermediate frequency filter 7 can be selected as 27 GHz, preferably, the working bandwidth can be selected as 1 GHz.

[0027] In the fourth step, an attenuator is cascaded between the first mixer 2 and the single-pole triple-throw switch 4. Preferably, an attenuator with an attenuation of 3 dB is selected to reduce the signal reflected from the single-pole triple-throw switch 4 and improve matching.

[0028] In the fifth step, an intermediate frequency signal filtered by an intermediate frequency filter is amplified by an intermediate frequency amplifier 3. Preferably, the intermediate frequency amplifier 3 is a narrowband amplifier that only amplifies an intermediate frequency signal. Then, the intermediate frequency signal is filtered by a high-pass filter 8 to suppress the leaked RF signal of 1 to 15 GHz, especially the signal of intermediate frequency IF and below, to avoid the second harmonic or third harmonic generated by the second mixer 9 falling into the intermediate frequency IF band and causing false.

[0029] Step 6: Down-convert an intermediate frequency signal IF1 to an intermediate frequency signal IF through the second mixer 9. The local oscillator signal required by the second mixer 9 is Figure 1 The two local oscillator links shown provide that the two local oscillator fundamental wave signals entering the link are two point frequency signals, and the specific frequencies are related to the frequency of the intermediate frequency signal IF. The two point frequency signals are used so that when the second mixer 9 performs down-conversion on an intermediate frequency signal, either a high local oscillator or a low local oscillator can be selected for down-conversion, so as to avoid the intermodulation signal between the one local oscillator signal and the two local oscillator signals falling within the intermediate frequency signal band and causing false signals. The working principle of the two local oscillator links is basically the same as that of the one local oscillator links, as described in the second step above, and will not be described in detail. It is worth noting that the frequencies of the two point frequency signals are close to each other, and a bandpass filter 13 can be used to suppress the two local oscillator fundamental wave signals and their third harmonics, so that a clean two local oscillator signals can be provided to the second mixer 9.

Claims

1. An ultra-wideband down-conversion method without pre-selection filtering, characterized in that: Step 1: Low-pass filter the input RF signal RF with a frequency of f1 to f5, and add a DC blocking capacitor before the first mixer; Step 2: Up-convert the RF signal through the first mixer to obtain an intermediate frequency signal IF1, and at the same time, provide a high local oscillator signal to the first mixer through a local oscillator link; Step 3: According to the different frequencies of the input signals, the single-pole triple-throw switch is controlled to select one of the three intermediate frequency branches, and an intermediate frequency filter with different center frequencies and bandwidths is used to filter the intermediate frequency signal IF1; Step 4: Cascade an attenuator between the first mixer and the single-pole triple-throw switch to attenuate the signal reflected from the switch and entering the first mixer; Step 5: Amplify an intermediate frequency signal IF1 using an intermediate frequency amplifier, and filter the intermediate frequency signal IF1 using a high pass filter; Step 6: Down-convert an intermediate frequency signal IF1 through the second mixer to obtain an intermediate frequency signal IF. At the same time, provide two point frequency signals of high and low local oscillators to the second mixer through two local oscillator links.

2. The method for ultra-wideband down-conversion without pre-selection filtering according to claim 1, characterized in that: The power of the radio frequency signal entering the first mixer is controlled to be less than -10dBm.

3. The method for ultra-wideband down-conversion without pre-selection filtering according to claim 1, characterized in that: The first mixer has a LO-2IF third-order intermodulation suppression characteristic greater than 60 dBc, except when the frequency of the input RF signal is half the frequency of the intermediate frequency signal IF1.

4. The method for ultra-wideband down-conversion without pre-selection filtering according to claim 1, characterized in that: An intermediate frequency link includes three branches, and the center frequency and working bandwidth of the filter on each branch are different. The center frequency of the first intermediate frequency filter is F1, and the working bandwidth is BW1. The center frequency of the second intermediate frequency filter is F1, and the working bandwidth is BW2, wherein BW2>BW1. The center frequency of the third intermediate frequency filter is F2, and the working bandwidth is BW2. F2>F1>f5. When the frequency of the radio frequency signal is between f1 and f2, the single-pole three-throw switch switches to the branch where the first intermediate frequency filter is located. When the frequency of the radio frequency signal is between f2 and f3 or f4 and f5, the single-pole three-throw switch switches to the branch where the second intermediate frequency filter is located. When the frequency of the radio frequency signal is between f3 and f4, the single-pole three-throw switch switches to the branch where the third intermediate frequency filter is located. Wherein, f3+f4=F1, 2×(f4-f3)=BW2, f1<f2<f3<f4<f5.

5. The method for ultra-wideband down-conversion without pre-selection filtering according to claim 1, characterized in that: The high-pass filter cascaded before the second mixer is used to filter out radio frequency signals below the IF band of the intermediate frequency signal, that is, DC to IF+BW2 / 2.

6. The method for ultra-wideband down-conversion without pre-selection filtering according to claim 1, characterized in that: A local oscillator link amplifies and doubles the frequency of a local oscillator fundamental wave signal LO1 / 2, and then suppresses the local oscillator fundamental wave signal LO1 / 2 and the third harmonic LO1 / 2×3 of the local oscillator fundamental wave signal through segmented filtering by a switch filter group, and then amplifies it and finally provides it to the first mixer as a high local oscillator signal.

7. The method for ultra-wideband down-conversion without pre-selection filtering according to claim 1, characterized in that: The second local oscillator link amplifies and doubles the second local oscillator fundamental signal LO2 / 2, suppresses the second local oscillator fundamental signal LO2 / 2 and the third harmonic LO2 / 2×3 of the second local oscillator fundamental signal through a bandpass filter, and then amplifies it and provides it to the second mixer. The second local oscillator signal is two point frequency signals, namely a high local oscillator signal and a low local oscillator signal.

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