A method and apparatus for obtaining an intermediate frequency signal

Abstract

The application relates to a kind of intermediate frequency signal acquisition methods, belong to radio frequency processing technical field, solve the problem of signal-to-noise ratio deterioration caused by over-saturation amplification of radio frequency receiving front stage circuit, mixing intermodulation spur deterioration in prior art.The application provides a kind of intermediate frequency signal acquisition method, including the power distribution of radio frequency receiving input signal, one way into coupling branch, recorded as radio frequency signal 1, another way into coupling main road, recorded as radio frequency signal 2;Radio frequency signal 1 is detected and handled, and tuning voltage Vt is obtained;Radio frequency signal 2 is attenuated using electrically adjustable attenuator, and radio frequency signal 3 is obtained;Wherein, the sum of attenuation amount Gt and radio frequency receiving input signal power is a fixed value;Radio frequency signal 3 is power amplified, mixed and filtered, and stable intermediate frequency signal is obtained.Adaptive adjustment of radio frequency receiving front stage circuit is realized, signal-to-noise ratio deterioration and intermodulation spur deterioration are suppressed, and system spur index is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of radio frequency processing technology, and in particular to a method for acquiring intermediate frequency signals. Background Technology

[0002] Countermeasure electronic devices are used to detect microwave signals emitted by enemy early warning radar and jamming radar. After analysis and processing, they obtain information such as the frequency, pulse width, and debugging method of the enemy radar signals, and then guide radio equipment to perform frequency evasion or release deceptive false echoes in the opposite direction.

[0003] Countermeasures electronic devices can detect a very wide range of radio frequency input frequencies, covering the S / C / X bands, with a bandwidth of no less than 4 GHz for a single radio frequency receiving channel. These devices operate on a superheterodyne receiving principle, requiring a mixer to down-convert the radio frequency signal to an intermediate frequency signal with a frequency not exceeding 4.5 GHz.

[0004] Countermeasures electronic devices achieve analog-to-digital conversion of intermediate frequency (IF) signals using high-speed analog-to-digital converters (ADCs). According to the sampling theorem, the ADC sampling rate must be no less than twice the IF signal frequency, i.e., at least 9 Gs / s. However, due to limitations in ADC device characteristics, a higher sampling rate results in a lower effective bit depth and lower power dynamic range (PDR). Currently, an ADC with a 9 Gs / s sampling rate can guarantee a PDR of 24 dB, far less than the 50 dB PDR for RF input signals.

[0005] Existing anti-jamming electronic devices employ saturation amplification in the pre-stage receiver circuit to compress the dynamic power of the RF input signal from 50dB to less than 10dB before it enters the mixer, outputting an intermediate frequency (IF) signal with a smaller power fluctuation range to meet the ADC power dynamic requirements. However, the saturation amplification method has disadvantages: when a large RF input signal is encountered, the amplifier suffers from over-saturation, resulting in a severe deterioration of the signal-to-noise ratio. Simultaneously, the intermodulation spurious signals at the mixer output are also severely aggravated. Therefore, there is an urgent need to design a method for acquiring the IF signal. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide an intermediate frequency signal acquisition method to solve the problems of signal-to-noise ratio degradation and mixing intermodulation spurious degradation caused by oversaturation amplification in the pre-amplifier circuit of the radio frequency receiver in the prior art.

[0007] On one hand, embodiments of the present invention provide a method for acquiring intermediate frequency signals, including:

[0008] The power of the RF received input signal is divided, one path goes into the coupling branch, denoted as RF signal 1, and the other path goes into the coupling main path, denoted as RF signal 2;

[0009] The radio frequency signal 1 is detected and processed to obtain the tuning voltage Vt;

[0010] The radio frequency signal 2 is attenuated by an electrically adjustable attenuator to obtain the radio frequency signal 3; wherein, the electrically adjustable attenuator linearly attenuates the radio frequency signal 2 under the control of the tuning voltage Vt, and makes the sum of the attenuation amount Gt and the power of the radio frequency received input signal a fixed value.

[0011] The radio frequency signal 3 is amplified, mixed, and filtered to obtain a stable intermediate frequency signal.

[0012] Furthermore, the step of detecting and processing the radio frequency signal 1 to obtain the tuning voltage Vt includes: using a logarithmic detector in the coupling branch to quickly detect the radio frequency signal 1 to obtain the output voltage Vd, and then performing operational amplification on the output voltage Vd to obtain the tuning voltage Vt.

[0013] Furthermore, before power distribution of the RF received input signal, the following steps are also included: the RF received input signal is sequentially subjected to amplitude limiting and low-noise amplification.

[0014] On the other hand, embodiments of the present invention provide an intermediate frequency signal acquisition device, which includes a coupler, a coupling branch, a coupling main path, and an amplification, mixing, and filtering circuit; the coupler is used to distribute the power of the radio frequency received input signal, with one path entering the coupling branch, denoted as radio frequency signal 1, and the other path entering the coupling main path, denoted as radio frequency signal 2;

[0015] The coupling branch is used to detect and process the radio frequency signal 1, and output the tuning voltage Vt to the coupling main branch;

[0016] The coupling main circuit is used to linearly attenuate the RF signal 2 under the control of the tuning voltage Vt, and to make the sum of the attenuation amount Gt and the RF received input signal power a fixed value, and output the attenuated RF signal 3 to the amplification, mixing and filtering circuit.

[0017] The amplification, mixing, and filtering circuit amplifies, mixes, and filters the radio frequency signal 3 to obtain a stable intermediate frequency signal.

[0018] Based on further improvements to the above system, the coupling branch includes a logarithmic detector and a voltage linearization circuit;

[0019] The logarithmic detector is used to quickly detect the radio frequency signal 1 and output voltage Vd;

[0020] The voltage linear operation circuit is used to perform operational amplification on the output voltage Vd to obtain the tuned voltage Vt.

[0021] Furthermore, the coupling main circuit includes two electrically adjustable attenuators connected in series, which linearly attenuate the input signal under the control of the tuning voltage Vt.

[0022] Furthermore, the amplified mixing and filtering circuit includes a power amplifier, a mixer, and a filtering circuit;

[0023] The power amplifier is used to adjust the power of the radio frequency signal 3;

[0024] A mixer is used to convert the radio frequency signal output from a subsequent amplifier into an intermediate frequency signal;

[0025] The filter circuit is used to remove stray signals from the intermediate frequency signal output by the mixer and output a stable intermediate frequency signal.

[0026] Furthermore, the device also includes a limiter and a low-noise amplifier. The limiter is used to limit the radio frequency received input signal, and the low-noise amplifier is used to amplify the limited signal with low noise before outputting it to the coupler.

[0027] Furthermore, the power dynamics of the logarithmic detector are not lower than the power dynamics of the RF received input signal.

[0028] Furthermore, the power of the electrically adjustable attenuators is preferably 30dB.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] 1. A negative feedback loop is formed by the coupling branch and the coupling main path, which realizes the adaptive adjustment of the RF receiving input signal and has the characteristics of large dynamic range and fast response.

[0031] 2. The tuning voltage Vt controls the electrically tunable attenuator to linearly attenuate the RF signal 2, so that the sum of the RF received input signal and the attenuation is a fixed value. This achieves adaptive adjustment of the RF received input signal, keeps the output power of the low-noise amplifier basically constant across the full power dynamic range, keeps the amplifier saturation level basically constant, and ensures that the mixer input power is kept at a low level, thereby improving the signal-to-noise ratio and reducing the problem of intermodulation spurious degradation.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 This is a flowchart illustrating the intermediate frequency signal acquisition method.

[0035] Figure 2 This is a schematic diagram of the intermediate frequency signal acquisition device; Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0037] A specific embodiment of the present invention discloses a method for acquiring intermediate frequency signals, such as... Figure 1 As shown:

[0038] Step 1: Distribute the power of the RF receiver input signal, one path goes into the coupling branch, denoted as RF signal 1, and the other path goes into the coupling main path, denoted as RF signal 2;

[0039] Step 2: Detect and process the radio frequency signal 1 to obtain the tuning voltage Vt;

[0040] Step 3: Use an electrically adjustable attenuator to attenuate the radio frequency signal 2 to obtain the radio frequency signal 3; wherein, the electrically adjustable attenuator linearly attenuates the radio frequency signal 2 under the control of the tuning voltage Vt, and makes the sum of the attenuation amount Gt and the power of the radio frequency received input signal a fixed value.

[0041] Step 4: Amplify, mix, and filter the RF signal 3 to obtain a stable intermediate frequency signal.

[0042] Specifically, the coupling branch is used to detect the amplitude of the RF received input signal and control the attenuation of the RF signal 2 in the coupling main branch. The coupling branch and the coupling main branch form a negative feedback loop, realizing the adaptive adjustment of the RF received input signal, which has the characteristics of large dynamic range and fast response.

[0043] Specifically, the dynamic range of the RF received input signal power is -55dBm to -5dBm.

[0044] Preferably, before performing step one, i.e., before power allocation of the radio frequency received input signal, the radio frequency received input signal is subjected to amplitude limiting and low-noise amplification processing in sequence;

[0045] In practice, a coupler can be used to distribute the power of the RF received input signal;

[0046] Before the coupler distributes power to the RF received input signal, it first performs clipping and low-noise amplification. Clipping can prevent large signals (external interference, noise, etc.) from burning out the low-noise amplifier. The low-noise amplifier is used to amplify small signals that are useful under normal conditions and improve the noise figure.

[0047] Furthermore, the detection and processing of the radio frequency signal 1 in step two to obtain the tuning voltage Vt includes: using a logarithmic detector in the coupling branch to quickly detect the radio frequency signal 1 to obtain the output voltage Vd, and then performing operational amplification on the output voltage Vd to obtain the tuning voltage Vt.

[0048] Specifically, there is a linear mapping relationship between the RF receiver input signal power and the output voltage Vd, which can be expressed as Equation 1 within the dynamic range of the logarithmic detector:

[0049] Vd = a*Pin + b,

[0050] Where Pin is the RF receiver input signal power, a is the logarithmic detector proportional coefficient, and b is a constant. The values ​​of a and b are different for different logarithmic detectors and can be obtained through measurement.

[0051] Specifically, in step three, the sum of the attenuation Gt and the RF received input signal power is a fixed value, which can be expressed as formula two:

[0052] Pin + Gt = Pfix

[0053] Wherein, Pfix is ​​a fixed power value. Since the power of the RF signal 1 distributed to the coupling branch by the coupler is very small, the power of the RF signal 2 entering the coupling main circuit is approximately equal to the power of the RF received input signal, and the ratio difference between the RF received input signal and the RF signal 2 entering the coupling main circuit is fixed, this application uses the sum of the power value of the RF input signal and the attenuation amount Gt of the RF signal 2 in the coupling main circuit as a fixed value, which can make the output intermediate frequency signal stable.

[0054] In practice, two electrically adjustable attenuators connected in series can be used to attenuate the signal;

[0055] Specifically, the attenuation Gt and the tuning voltage Vt have a linear functional relationship, which is derived from Formula 3:

[0056] Gt = c * Vt + d

[0057] Where c and d are constants, and the attenuation Gt is the sum of the attenuations of the two series-connected electrically adjustable attenuators.

[0058] Specifically, the mapping relationship between the RF received input signal power and the tuning voltage Vt is derived from Formulas 2 and 3, as shown in Formula 4:

[0059] Pin + c * Vt + d = Pfix;

[0060] Specifically, the linear mapping relationship between the tuning voltage Vt and the output voltage Vd is determined by formulas one and four, thus obtaining the tuning voltage Vt, which is given by formula five:

[0061] Vt = [Pfix - d - (Vd - b) / a] / c;

[0062] After obtaining the linear relationship between the tuning voltage Vt and the output voltage Vd, the output voltage Vd can be amplified using a linear amplifier in step two to obtain the tuning voltage Vt.

[0063] Example 2

[0064] On the other hand, embodiments of the present invention provide an intermediate frequency signal acquisition device, such as... Figure 2 As shown, the device includes a coupler, a coupling branch, a coupling main circuit, and an amplification, mixing, and filtering circuit; the coupler is used to distribute the power of the RF received input signal, with one path entering the coupling branch, denoted as RF signal 1, and the other path entering the coupling main circuit, denoted as RF signal 2;

[0065] The coupling branch is used to detect and process the radio frequency signal 1, and output the tuning voltage Vt to the coupling main branch;

[0066] The coupling main circuit is used to linearly attenuate the RF signal 2 under the control of the tuning voltage Vt, and to make the sum of the attenuation amount Gt and the RF received input signal power a fixed value, and output the attenuated RF signal 3 to the amplification, mixing and filtering circuit.

[0067] The amplification, mixing, and filtering circuit amplifies, mixes, and filters the radio frequency signal 3 to obtain a stable intermediate frequency signal.

[0068] Specifically, in order to ensure normal output of the RF received input signal power and to ensure that the power at the input of the logarithmic detector is within the power linear region of the device under dynamic full input power of the RF received input signal, the pass-through loss of the main coupling path is -1dB and the coupling amount of the coupling branch is -10dB.

[0069] Furthermore, the coupling branch includes a logarithmic detector and a voltage linearization circuit;

[0070] The logarithmic detector is used to quickly detect the radio frequency signal 1 and output voltage Vd;

[0071] The voltage linear operation circuit is used to perform operational amplification on the output voltage Vd to obtain the tuned voltage Vt.

[0072] Specifically, the voltage linear operation circuit is implemented using a high-speed linear operation circuit;

[0073] Furthermore, a high-speed linear operation circuit is used to realize the linear mapping relationship between the tuning voltage Vt and the output voltage Vd, so that the tuning voltage Vt changes in real time with the output voltage Vd. The high-speed linear operation circuit is connected to the logarithmic detector and two series-connected electrically adjustable attenuators.

[0074] Furthermore, the coupling main path includes two electrically adjustable attenuators connected in series.

[0075] Under the control of the tuning voltage Vt, the coupled main RF signal 2 is linearly attenuated by two series-connected electrically adjustable attenuators, and the power of the two series-connected electrically adjustable attenuators is preferably 30dB.

[0076] Furthermore, the amplified mixing and filtering circuit includes a power amplifier, a mixer, and a filtering circuit;

[0077] The power amplifier is used to adjust the power of the radio frequency signal 3;

[0078] A mixer is used to convert the radio frequency signal output from a subsequent amplifier into an intermediate frequency signal;

[0079] The filter circuit is used to remove stray signals from the intermediate frequency signal output by the mixer and output a stable intermediate frequency signal.

[0080] Furthermore, the device also includes a limiter and a low-noise amplifier. The limiter is used to limit the power of the radio frequency received input signal, and the low-noise amplifier is used to amplify the limited signal with low noise before outputting it to the coupler.

[0081] Specifically, limiters are used to protect devices in the receiving link from damage caused by abnormally high-power microwave radiation or leaked signals. Low-noise amplifiers are used to amplify signals and improve the noise figure.

[0082] Specifically, to prevent a decrease in signal-to-noise ratio, the low-noise amplifier should ensure that its output power is lower than its own output P-1 specification across the full power dynamic range. In terms of circuit design, the low-noise amplifier should be selected with a high P-1 specification to ensure that the low-noise amplifier operates in the linear region under full RF input power dynamics. At this time, the output power of the low-noise amplifier increases linearly with the RF receiver input power.

[0083] Specifically, the low-noise amplifier has a gain of +20dB and an output P-1 ≥ 15dBm.

[0084] Specifically, the limiter insertion loss is -0.5dB.

[0085] Furthermore, the power dynamics of the logarithmic detector are not lower than the power dynamics of the RF received input signal.

[0086] Specifically, the dynamic range of the logarithmic detector power is set to 50dB, and the power detection time of the logarithmic detector is no more than 30ns.

[0087] Furthermore, in this embodiment of the invention, the logarithmic detector has fast transient response characteristics, and the rise and fall times of the detected radio frequency pulse signal can be better than 25ns.

[0088] Furthermore, the power of the electrically adjustable attenuators is preferably 30dB.

[0089] Specifically, in this embodiment, the electrically tunable attenuator linearly attenuates the RF signal 2 via the coupled main path under the control of the tuning voltage Vt. Since the attenuation amount remains constant relative to the input RF signal power during the control process, a larger attenuation is achieved for large signals. This results in a larger gain for small signals and a smaller gain for large signals (the gain in this paper is negative gain). Furthermore, in a logarithmic coordinate system, the gain adjustment maintains a good linear relationship with the RF input signal power, ensuring constant output power of the receiving link. The receiving link includes the entire circuitry of the intermediate frequency signal acquisition device.

[0090] Specifically, the coupling branch and coupling main branch of this invention form a negative feedback loop. The self-detection of the logarithmic detector can automatically adjust the output voltage Vd according to the RF received input signal, which has the characteristics of large dynamic range and fast response. This makes the output power of the low noise amplifier basically constant and the saturation level of the amplifier basically constant throughout the full power dynamic range, and ensures that the input power of the mixer is maintained at a low level, thereby improving intermodulation spurious.

[0091] Compared with existing technologies, this embodiment provides an intermediate frequency (IF) signal acquisition method. It allocates power to the RF received input signal and designs a tuning voltage based on the RF signal 1 of the branch. This tuning voltage controls the linear attenuation of the coupled main RF signal 2, achieving automatic adjustment of the pre-amplifier link gain according to the power of the RF input signal. The pre-amplifier link includes a limiter, a low-noise amplifier, and an electrically adjustable attenuator, ensuring that the output power of the RF low-noise amplifier circuit remains essentially constant across the entire power dynamic range. Based on this, the saturation level of the subsequent amplifier remains essentially constant, and the mixer input power is maintained at a low level, thereby improving intermodulation spurious signals. This invention requires no external control and achieves adaptive adjustment of the receiver pre-amplifier gain through a negative feedback loop composed of its own detector, voltage linear operation circuit, and electrically adjustable attenuator module. It possesses characteristics of large dynamic range and fast response, solving the technical problems of signal-to-noise ratio degradation and mixing intermodulation spurious signal degradation caused by excessive saturation amplification of the RF receiver pre-amplifier circuit in current anti-jamming electronic devices.

[0092] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for acquiring intermediate frequency signals, characterized in that: include: The power of the RF received input signal is divided, one path goes into the coupling branch, denoted as RF signal 1, and the other path goes into the coupling main path, denoted as RF signal 2; The radio frequency signal 1 is detected and processed to obtain the tuning voltage Vt, including: using a logarithmic detector in the coupling branch to quickly detect the radio frequency signal 1 to obtain the output voltage Vd, and then performing operational amplification on the output voltage Vd to obtain the tuning voltage Vt, Vt=[Pfix-d-(Vd-b) / a] / c, where Pfix is ​​a fixed power value, Vd is the output voltage, a is the proportional coefficient of the logarithmic detector, and b, c and d are constants; Radio frequency signal 2 is attenuated using an electrically adjustable attenuator to obtain radio frequency signal 3. The electrically adjustable attenuator linearly attenuates radio frequency signal 2 under the control of tuning voltage Vt, and makes the sum of attenuation amount Gt and radio frequency received input signal power a fixed value, which is Pfix. The attenuation amount Gt and radio frequency received input signal power Pin satisfy Pin + Gt = Pfix. The attenuation amount Gt and tuning voltage Vt have a linear functional relationship. The radio frequency signal 3 is amplified, mixed, and filtered to obtain a stable intermediate frequency signal.

2. The intermediate frequency signal acquisition method according to claim 1, characterized in that: Before power distribution of the RF received input signal, the following steps are also included: the RF received input signal is sequentially subjected to amplitude limiting and low-noise amplification.

3. A medium frequency signal acquisition device, characterized in that: The device includes a coupler, a coupling branch, a coupling main circuit, and an amplification, mixing, and filtering circuit. The coupler is used to distribute the power of the RF received input signal. One signal goes into the coupling branch, denoted as RF signal 1, and the other goes into the coupling main path, denoted as RF signal 2. The coupling branch is used to detect and process the radio frequency signal 1, and output the tuning voltage Vt to the coupling main branch; The coupling branch includes a logarithmic detector and a voltage linear operation circuit; The logarithmic detector is used to quickly detect the radio frequency signal 1 and output voltage Vd; The voltage linear operation circuit is used to perform operational amplification on the output voltage Vd to obtain the tuned voltage Vt, Vt=[Pfix-d-(Vd-b) / a] / c, where Pfix is ​​a fixed power value, Vd is the output voltage, a is the logarithmic detector scaling factor, and b, c and d are constants; The coupling main circuit is used to linearly attenuate the radio frequency signal 2 under the control of the tuning voltage Vt, and to make the sum of the attenuation amount Gt and the power of the radio frequency received input signal a fixed value, the fixed value being Pfix. The attenuation amount Gt and the power of the radio frequency received input signal Pin satisfy Pin + Gt = Pfix. The attenuated radio frequency signal 3 is output to the amplification, mixing and filtering circuit. The amplification, mixing, and filtering circuit amplifies, mixes, and filters the radio frequency signal 3 to obtain a stable intermediate frequency signal.

4. The intermediate frequency signal acquisition device according to claim 3, characterized in that: The main coupling path includes two electrically adjustable attenuators connected in series, which linearly attenuate the input signal under the control of the tuning voltage Vt.

5. The intermediate frequency signal acquisition device according to claim 3, characterized in that: The amplification, mixing, and filtering circuit includes a power amplifier, a mixer, and a filtering circuit. The power amplifier is used to adjust the power of the radio frequency signal 3; A mixer is used to convert the radio frequency signal output from a subsequent amplifier into an intermediate frequency signal; The filter circuit is used to remove stray signals from the intermediate frequency signal output by the mixer and output a stable intermediate frequency signal.

6. An intermediate frequency signal acquisition device according to any one of claims 3-5, characterized in that: The device also includes a limiter and a low-noise amplifier. The limiter is used to limit the radio frequency received input signal, and the low-noise amplifier is used to amplify the limited signal with low noise before outputting it to the coupler.

7. The intermediate frequency signal acquisition device according to claim 3, characterized in that: The power dynamics of the logarithmic detector are not lower than the power dynamics of the RF received input signal.

8. The intermediate frequency signal acquisition device according to claim 4, characterized in that: The power of each electrically adjustable attenuator is 30dB.

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