Zero intermediate frequency circuit based on orthogonal down-conversion

Abstract

For equipment with simultaneous transmitting and receiving requirements, echo signals in a receiving channel and transmitting leakage signals are often difficult to distinguish, and the leakage signals can bring great influence on detection of normal signals. The zero intermediate frequency circuit based on orthogonal down-conversion overcomes the defects in the prior art, the zero intermediate frequency circuit based on orthogonal down-conversion is provided and achieved, and leakage signals are suppressed by filtering the zero frequency component of IQ signals. According to the method, the influence of the amplitude-phase instability characteristic of the leakage signal is avoided, and the very high suppression capability on the leakage signal can be obtained. Meanwhile, the method is simple in circuit structure, easy to implement and high in engineering applicability.

Description

Technical Field

[0001] The invention belongs to the field of microwave technology, and in particular relates to a zero intermediate frequency circuit based on orthogonal down-conversion. Background Art

[0002] For devices that need to transmit and receive simultaneously, it is often difficult to distinguish the echo signal in the receiving channel from the transmission leakage signal. The leakage signal will have a significant impact on the detection of normal signals. The specific situation is as follows:

[0003] 1. Echo signal and leakage signal exist at the same time

[0004] When transmitting and receiving at the same time, when the echo signal reflected by the target reaches the receiving channel, the device may still be radiating signals to the outside, and its leaked signal will enter the receiving channel together with the echo signal.

[0005] 2. Similar frequency

[0006] The echo signal and the transmitted leakage signal may have similar frequencies, and the RF filter cannot effectively suppress the leakage signal.

[0007] 3. The leakage signal is highly random

[0008] The path of the transmitted leakage signal entering the receiving channel is usually unstable, and the characteristics such as amplitude and phase are always changing, making it impossible to cancel the leakage signal during operation through testing and compensation methods.

[0009] In order to solve the above problems, it is necessary to design a zero intermediate frequency circuit based on orthogonal down-conversion. Based on the FMCW (frequency modulated continuous wave) transmitting signal and receiving local oscillator, there is a frequency difference between the echo signal and the leakage signal, and the SFC high-pass filter is used to filter the zero-frequency component in the receiving channel to suppress the leakage signal. Summary of the invention

[0010] The present invention overcomes the shortcomings of the prior art, proposes and implements a zero intermediate frequency circuit based on orthogonal down-conversion, and filters the zero-frequency component of the IQ signal through an SFC filter to suppress the leakage signal. The present invention avoids the influence of the amplitude and phase instability characteristics of the leakage signal, and can obtain a strong ability to suppress the leakage signal. At the same time, the circuit architecture of the method is simple, easy to implement, and has strong engineering applicability.

[0011] The zero intermediate frequency circuit based on orthogonal down-conversion of the present invention comprises: a passive orthogonal mixer, a power divider, and an operational amplifier. The radio frequency signal is down-converted by the passive orthogonal mixer to generate an orthogonal IQ signal, and the I-path signal and the Q-path signal are each split into four paths by the power divider, and each power branch is then filtered by the operational amplifier to suppress the zero-frequency component in the IQ signal, thereby suppressing the leakage signal.

[0012] Part of the operational amplifier is used for amplifying IQ signals, and part of it is used for active high-pass filtering, and different cut-off frequencies can be achieved by adjusting parameters. The operational amplifier includes capacitor C1, capacitor C2, adjustable resistor R1, adjustable resistor R2 and OpAmp operational amplifier; one end of capacitor C1 is connected to Vin, and the other end is connected to one end of capacitor C2 and one end of adjustable resistor R1; the other end of capacitor C2 is connected to one end of adjustable resistor R1 and the same-direction input end of OpAmp operational amplifier; the other end of adjustable resistor R1 is grounded; the other end of adjustable resistor R2 is connected to the output end of OpAmp operational amplifier; the reverse input end of OpAmp operational amplifier is connected to the output end.

[0013] The present invention is based on the fact that both the transmitting signal and the receiving local oscillator are FMCW (frequency modulated continuous wave), and utilizes the characteristic of the path difference of the echo signal. By adjusting the frequency of the receiving local oscillator, the echo signal is made to have a non-zero frequency after down-conversion, thereby ensuring that it passes through the SFC high-pass filter normally. The transmission leakage signal has a short path, and when it leaks into the receiving channel, its frequency is consistent with the receiving local oscillator, so it has a zero frequency after down-conversion, ultimately achieving the suppression of the leakage signal.

[0014] The beneficial effects of the present invention are

[0015] 1. The present invention solves the problem that the transmission leakage signal cannot be effectively suppressed in the simultaneous transmission and reception device.

[0016] 2. The present invention solves the possible impact caused by the unstable state of the leakage signal.

[0017] 3. The present invention can effectively adjust the cutoff frequency of the SFC high-pass filter by adjusting the operational amplifier parameters.

[0018] 4. The circuit architecture of the present invention is simple and easy to design and implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a principle block diagram of the present invention.

[0020] Figure 2 This is a circuit design diagram of the present invention.

[0021] Figure 3 This is the design diagram of the 10kHz second-order active filter circuit.

[0022] Figure 4 This is the design diagram of the 20kHz second-order active filter circuit.

[0023] Figure 5 This is the design diagram of the 50kHz second-order active filter circuit.

[0024] Figure 6 This is the design diagram of the 100kHz second-order active filter circuit.

[0025] Figure 7 It is the structural appearance diagram of the present invention. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] 1. Design principles

[0028] The RF signal is down-converted through a passive orthogonal mixer to generate two orthogonal IQ signals. The IQ signals are then split into four branches through a power divider. Each branch then passes through an SFC filter (based on an operational amplifier) ​​to filter the zero-frequency component in the IQ signal, thereby suppressing the leakage signal. The SFC filter in each branch adjusts the operational amplifier parameters to achieve high-pass filtering functions with different cutoff frequencies.

[0029] The present invention is based on the fact that both the transmitting signal and the receiving local oscillator are FMCW (frequency modulated continuous wave). The transmitting leakage signal has a short path. When it leaks into the receiving channel, its frequency is consistent with the receiving local oscillator, so it is zero frequency after down-conversion. By taking advantage of the path difference of the echo signal, the frequency of the receiving local oscillator is adjusted to make the echo signal non-zero frequency after down-conversion, so as to ensure that it can pass through the SFC high-pass filter normally. The principle block diagram of the present invention is shown in FIG. Figure 1 shown.

[0030] 2. Circuit design

[0031] The zero intermediate frequency circuit based on orthogonal down-conversion of the present invention comprises: a passive orthogonal mixer, a power divider, and an operational amplifier. Part of the operational amplifier is used for amplifying IQ signals, and part of the operational amplifier is used for active high-pass filtering, and different cut-off frequencies can be achieved by adjusting parameters. The circuit design diagram of the present invention is shown in FIG. Figure 2 As shown, the operational amplifier structure is as follows Figure 3-6 shown.

[0032] 3. Structural appearance

[0033] In order to ensure the RF performance, the present invention adopts a metal shell shielding design on the outside, and a cavity is designed inside to ensure the close contact between the cavity and the shell through screws to ensure the isolation between channels; at the same time, an SMP RF connector is used for external interconnection. Figure 7 shown.

[0034] The present invention is not limited to the above specific implementations, and the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the above implementations based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A zero intermediate frequency circuit based on orthogonal down-conversion, characterized in that: include: a passive quadrature mixer, two power dividers, and an operational amplifier; The RF signal is down-converted by a passive orthogonal mixer to generate an orthogonal IQ signal. The I-channel signal and the Q-channel signal are each divided into four channels by a power divider. Each power branch is then passed through an operational amplifier to filter the zero-frequency component in the IQ signal, thereby suppressing the leakage signal.

2. The zero intermediate frequency circuit based on orthogonal down conversion according to claim 1, characterized in that: The operational amplifier is used partly for amplifying the IQ signal and partly for active high-pass filtering, and different cut-off frequencies can be achieved by adjusting parameters.

3. A zero intermediate frequency circuit based on orthogonal down conversion according to claim 2, characterized in that: The operational amplifier includes a capacitor C1, a capacitor C2, an adjustable resistor R1, an adjustable resistor R2 and an OpAmp operational amplifier; one end of the capacitor C1 is connected to Vin, and the other end is connected to one end of the capacitor C2 and one end of the adjustable resistor R1; the other end of the capacitor C2 is connected to one end of the adjustable resistor R1 and the same-direction input end of the OpAmp operational amplifier; the other end of the adjustable resistor R1 is grounded; the other end of the adjustable resistor R2 is connected to the output end of the OpAmp operational amplifier; the reverse input end of the OpAmp operational amplifier is connected to the output end.

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