Radio reception circuit and control method

Abstract

Provided are a radio reception circuit and a control method capable of operating a response signal in correspondence to an input of a desired signal without requiring a pre-selector. The radio reception circuit comprises a circuit means including: first and second mixers for mixing an input reception signal with a first LO signal and a second LO signal obtained by shifting the first LO signal by 90°; an addition circuit of which first and second inputs are connected to a first signal line through which a first signal of an intermediate frequency down-converted by the first mixer is transmitted and a second signal line through which a signal obtained by shifting, by 90°, a second signal of an intermediate frequency, which has been frequency-converted by the second mixer, is transmitted; a detection circuit connected to an output of the addition circuit; and a control circuit connected to the detection circuit. At any one signal line among the first signal line and the second signal line, the circuit means varies the phase and / or amplitude of the signal of the intermediate frequency on the one signal line on the basis of a control signal from the control circuit. The control circuit determines whether the reception signal is a desired signal or an image signal on the basis of the detected signal from the detection circuit when the setting of the phase and / or amplitude of the signal of the intermediate frequency on the one signal line is varied.

Description

Wireless receiving circuit and control method

[0001] (Disclosure of related applications) This invention is based on a priority claim to Japanese Patent Application No. 2025-011708 (filed on January 27, 2025), and the entire contents of said application are incorporated herein by reference. This disclosure relates to a wireless receiving circuit and a control method.

[0002] In wireless communication systems, interference waves other than the desired signal can enter the wireless receiving circuit, causing a degradation in the signal's distortion characteristics and resulting in a decrease in communication quality. For example, in aircraft navigation aids such as DME (Distance Measuring Equipment) and TACAN (Tactical Air Navigation), it is not possible to distinguish between an image signal of the desired signal and the desired signal itself based on the power of the received signal. As a result, they are processed as the same IF (Intermediate Frequency) signal, and there is a risk that the transmitting circuit will malfunction in order to return a response signal. In DME, distance information is obtained by the onboard DME transmitting an interrogation signal to the ground DME, which then transmits a response signal. In TACAN, similar to DME, the onboard TACAN transmits an interrogation signal to the ground TACAN, which then transmits a response signal to obtain aircraft bearing and distance information.

[0003] As a countermeasure against image signal suppression in general wireless receiving circuits, the image signal is either directly suppressed using a frequency-selective type BPF (Band Pass Filter) such as a preselector, or the image signal is attenuated by an image suppression filter after generating an I (In-phase) signal and a Q (Quadrature) signal by performing frequency conversion by multiplying the received signal by two mutually orthogonal signals within the receiving circuit. For example, Patent Document 1 discloses a circuit that uses a phase shifter to improve characteristics because the image suppression ratio decreases when there is amplitude error and phase error from the ideal phase difference between the I signal and the Q signal (called IQ mismatch).

[0004] Japanese Utility Model Publication No. 5-15521

[0005] The configuration disclosed in Patent Document 1, etc., does not take amplitude differences into consideration. Therefore, correction is not performed sufficiently, and the desired image characteristics cannot be met.

[0006] Furthermore, a configuration that uses a preselector to directly suppress the image signal has disadvantages such as degradation of reception characteristics and increased product costs.

[0007] The object of this disclosure is to provide a wireless receiving circuit and control method that can operate a response signal in response to a desired signal input without requiring a preselector.

[0008] According to one embodiment of the present disclosure, the wireless receiving circuit includes a first mixer and a second mixer that mix an input received signal with a first local oscillator signal and a second local oscillator signal obtained by shifting the first local oscillator signal by 90°, respectively; an adder circuit whose first input and second input are connected to a first signal line that transmits a first signal of an intermediate frequency converted by the first mixer and a second signal line that transmits a signal obtained by shifting the second signal of an intermediate frequency converted by the second mixer by 90°, respectively; and a detection circuit connected to the output of the adder circuit. The system comprises at least a control circuit connected to the detection circuit, and one of the signal lines of the first signal line and the second signal line is provided with circuit means for varying the phase and / or amplitude of the intermediate frequency signal on the one signal line based on a control signal from the control circuit, and the control circuit determines whether the received signal is a desired signal or an image signal based on the detection signal from the detection circuit when the setting of the phase and / or amplitude of the intermediate frequency signal on the one signal line is varied, and

[0009] According to one aspect of the present disclosure, a method for controlling a wireless reception circuit includes: for an input received signal, performing mixing processes on the first mixer and the second mixer respectively with a first local oscillation signal and a second local oscillation signal obtained by shifting the first local oscillation signal by 90°; transmitting a first signal of an intermediate frequency frequency-converted by the first mixer through a first signal line, and transmitting a signal obtained by shifting a second signal of an intermediate frequency frequency-converted by the second mixer by 90° through a second signal line; detecting, by a detection circuit, a sum of signals on the first signal line and the second signal line; and determining whether the received signal is a desired signal or an image signal based on a detection signal from the detection circuit when the phase and / or amplitude of the signal of the intermediate frequency on one of the first signal line and the second signal line is / are variably set.

[0010] According to the present disclosure, it is possible to provide a wireless reception circuit that can operate a response signal corresponding to an input of a desired signal without requiring a preselector.

[0011] It is a diagram for explaining an embodiment of the present disclosure. It is a diagram for explaining related art. It is a diagram for explaining an embodiment of the present disclosure. It is a diagram for explaining an embodiment of the present disclosure. It is a diagram for explaining an embodiment of the present disclosure. It is a diagram for explaining an embodiment of the present disclosure. It is a diagram for explaining a comparative example.

[0012] Embodiments of the present disclosure will be described. FIG. 1 is a diagram for explaining a wireless reception circuit according to an embodiment of the present disclosure. In FIG. 1, the circuit configuration surrounded by the broken line corresponds to the subject matter of the present disclosure. The wireless reception circuit employs a superheterodyne (SH) system. The low noise amplifier (LNA) 32 outputs an RF (Radio Frequency) signal obtained by amplifying the signal input from the antenna 31 to the mixer 2. The mixer 2 mixes (performs mixing) the received signal (RF signal) 1 and the local oscillation signal 6 generated by the local signal generator 3 to perform frequency conversion (down-conversion) and outputs an intermediate frequency (IF) signal 7. Note that a configuration including, for example, an attenuator (not shown) may be provided between the antenna 31 and the low noise amplifier 32 (however, it is omitted for simplicity).

[0013] The decoder circuit 4 is a circuit for performing signal processing such as decoding on the IF signal 7 frequency-converted (down-converted) by the mixer 2. Note that a configuration including, for example, an intermediate frequency filter (IF Filter), an intermediate frequency amplifier (IF Amplifier), a detection circuit, etc. (not shown) may be provided between the mixer 2 and the decoder circuit 4 (however, it is omitted in FIG. 1 for simplicity). The decoder circuit 4 may convert the IF signal 7 into a digital signal using an ADC (Analog-to-Digital Converter: not shown) and perform signal processing such as decoding.

[0014] When the received signal 1 is a desired signal, the decoder circuit 4 outputs a transmission (Tx) trigger signal 5, which serves as a trigger for sending, for example, a response signal, toward the transmitter side (not shown) (if the Tx trigger signal 5 is a digital signal, it is activated (for example, set to a high level in the case of high active)).

[0015] The coupler 11 may be configured as a directional coupler installed, for example, on the signal line (transmission line) between the input terminal 30 of the received signal 1 and the mixer 2. In this case, the coupler 11 may be configured as a 3-port directional coupler having an internal termination port p4, for example. The coupler 11 outputs a monitor waveform (monitor power) of the received signal 1 (forward wave) incident from the input port p1 from the coupling port p3. The insertion loss of the coupler 11 is given by the attenuation amount when the power input from the input port p1 is output from the transmission port p2 (the ratio of input power (P1) to power output to the transmission port (p2) (P2) = 10log(P1 / P2)). The directional coupler may be configured as a hybrid coupler.

[0016] The monitor waveform 8 from the coupling port p3 of the coupler 11 (3-port directional coupler) is split into two by the distributor (power distributor) 10. As the distributor (power distributor) 10, for example, one of the following may be used: a resistor distributor using a resistance value of one-third of the characteristic impedance during use, a Wilkinson power distributor using parallel quarter-wavelength transmission line transformers, or a hybrid power distributor using a center-tapped transformer.

[0017] The mixer 12 mixes the signal 8A, which has been split into two by the power distributor 10, with the local oscillator signal (LO signal) 9, which is obtained by shifting the phase of the local oscillator signal (LO signal) 6 from the local signal generator 3 by 90° using the first 90° phase shifter 22. By doing so, the frequency of signal 8A is down-converted to obtain the IF signal 25. The LO signal 9 is also referred to as the LO (Q) signal 9. The IF signal 25 is also referred to as the IF (Q) signal 25.

[0018] The mixer 14 mixes the signal 8B, which has been split into two by the power distributor 10, with the local oscillator signal (LO signal) 6 from the local signal generator 3, thereby downconverting the frequency of signal 8B to obtain the IF signal 26. The LO signal 6 is also referred to as the LO(I) signal 6. The IF signal 26 is also referred to as the IF(I) signal 26.

[0019] Although not particularly limited, mixers 12 and 14 may be composed of analog multipliers such as Gilbert cell multipliers. The first 90° phase shifter 22 for high frequencies may use a 90° hybrid circuit with a characteristic impedance Z0 (e.g., 50Ω) and a transmission line combination of Z0 / √2, with an electrical length of one-quarter wavelength, to receive the local oscillator signal from the local signal generator 3 at the input port and output local oscillator signals LO(I) signal 6 and LO(Q) signal 9 with a 90-degree phase difference at the two output ports.

[0020] To address amplitude errors (relative errors) between the IF(I) signal 26 and the IF(Q) signal 25, or phase shifts from 90° in the first 90° phase shifter 22, the phase adjuster 15 adjusts the phase of the IF(I) signal 26 to be orthogonal to the IF(Q) signal 25 based on the control signal 20 from the control circuit 19. The phase adjuster 15 may be configured as a variable phase shifter that controls the phase variably by applying a control voltage to a variable capacitance diode (varicap, varactor diode) via a resistor and varying its impedance.

[0021] The variable attenuator 16 adjusts the amplitude of the IF(I) signal 26 to match the amplitude of the IF(Q) signal 25 based on the control signal 21 from the control circuit 19 (variable attenuation rate). The variable attenuator 16 may be configured as a voltage-variable PIN diode (P Intrinsic N diode) attenuator or the like, where the control signal 21 is used as the control voltage and the attenuation rate is continuously varied based on the control voltage.

[0022] The summing circuit 24 combines (adds) the IF(Q) signal 27 output from the second 90° phase shifter 13 and the IF(I) signal 28 output from the variable attenuator 16 and outputs the result.

[0023] The second 90° phase shifter 13, which shifts the IF signal 25 by 90°, is not particularly limited, but may be configured as an operational amplifier or the like, for example, having a positive terminal (+) connected to the input terminal via a resistor R1 and connected to ground via a capacitor C1, and an inverting terminal (-) connected to the input terminal via a resistor R and connected to the output terminal via a feedback resistor R (the output amplitude is 1 times the input amplitude regardless of frequency, the phase is delayed according to frequency, and the phase is shifted by 90° at frequency f = 1 / (2πC1R1)).

[0024] The detection circuit 17 measures the level (power) of the signal 29 output from the summing circuit 24 and outputs a detected signal (voltage) 18.

[0025] The control circuit 19 receives the detection signal 18 (detection voltage) and sets the phase adjustment voltage V as the first control signal 20. θ The output is sent to the phase adjuster 15, and the attenuation adjustment voltage V is used as the second control signal 21. att This is output to the variable attenuator 16.

[0026] The control circuit 19 controls the phase adjuster 15 and the variable attenuator 16 to adjust the phase and amplitude of the IF(I) signal 26, and determines whether the received signal 1 is a desired signal or an image signal from the fluctuation level of the voltage (detection voltage) of the detected signal 18, and outputs the determination result as a determination signal 23 to the decoder circuit 4.

[0027] The received signal 1 is input to the mixer 2, mixed with the LO signal 6 generated by the local signal generator 3, down-converted to an IF signal 7, and then input to the decoder circuit 4, where it is determined that the received signal 1 has been input to the receiving circuit. At that time, based on the determination signal 23, if the received signal 1 is the desired signal, the decoder circuit 4 transmits a transmit trigger signal (Tx trigger signal) 5 to send a response signal to a transmitter (not shown).

[0028] Figure 2 is a diagram illustrating an embodiment, schematically showing the frequency relationships of each signal. Generally, in a mixer, the RF signal (frequency = f RF ) and LO signal (frequency = f LO The signal is multiplied to form the IF signal (frequency = f IF ) is obtained. The frequency f of the LO signal is on the frequency axis. LOSignals in the symmetric positions on the high-frequency side and the low-frequency side centered around RF = f LO + f IF are down-converted to the same frequency band. If the desired signal has a frequency f IM = f LO - f IF and the image signal has a frequency f RF - f LO = f LO - f IM = f IF , that is, they are converted to the same IF frequency (frequency band) (f ＩＦ ), and the desired signal and the image signal cannot be distinguished. The reverse case is the same. That is, if the frequency of the image signal is f IM = f LO + f IF and the frequency of the desired signal is f RF = f LO - f IF ), then through frequency conversion (down-conversion) by the mixer, IM - f LO = f LO - f RF = f IF . In FIG. 3, the frequency of the desired signal is schematically illustrated as a line spectrum on the frequency axis. However, if the desired signal is a pulse signal, a frequency band is generated (the shorter the pulse width, the wider the bandwidth of the frequency spectrum), and it may also be regarded as the frequency band of the desired signal and the frequency band of the image signal.

[0029] The image rejection mixer removes the received signal 1 when it is an image signal.

[0030] The case where the received signal 1 is a desired signal will be described. If the amplitude of the desired signal is A RF and the frequency (angular frequency) is ω RF , it can be expressed by the following equation (1).

[0031] …(1) However, j 2 = -1.

[0032] The angular frequency ω is given by ω = 2πf for a given frequency f. In the following, unless there is a specific need to distinguish between f and ω, the angular frequency will also be referred to as frequency.

[0033] The local oscillator signal (LO signal) 6 from the local signal generator 3 has an amplitude of A LO , angular frequency ω LO Therefore, it can be expressed by the following equation (2).

[0034] …(2) Here, the angular frequency ω of the desired signal RF ω is the angular frequency of the LO signal 6. LO It should be greater than or equal to

[0035] Mixer 14 multiplies the received signal 1 and the LO signal 6. The IF signal 26 output from mixer 14 is given by the following:

[0036] …(3)

[0037] Although the second term of equation (3) is blocked by a low-pass filter (not shown) connected to the output of mixer 14, it is left in for explanatory purposes.

[0038] The first 90° phase shifter 22 supplies the mixer 12 with an LO signal 9 obtained by shifting the phase of the LO signal 6 by 90°. The LO signal 9 (LO (Q) signal) can be expressed by the following equation (4).

[0039] …(4)

[0040] Mixer 12 multiplies the received signal 1 and the LO signal 9. The IF signal 25 output from mixer 12 is given by the following:

[0041] …(5)

[0042] For example, a low-pass filter (not shown) is placed between the mixer 12 and the second 90° phase shifter 13, blocking the second term of equation (5), and allowing only the first term to be input to the second 90° phase shifter 13. However, for explanatory purposes, the first term is left in place here.

[0043] The IF signal 27 obtained by shifting the phase of the IF signal 25 by 90° using the second 90° phase shifter 13 can be expressed by the following equation (6).

[0044] …(6)

[0045] If there is no amplitude error (relative error) between IF signal 26 and IF signal 25, and no phase shift from 90° in the 90° phase shifters 22 and 13, then the sum of IF signal 26 and IF signal 27 by the summing circuit 24 will be, from the sum of equations (3) and (6), the angular frequency component (ω) will be as shown in equation (7). RF +ω LO ) cancel each other out, and the received signal 1 (angular frequency ω RF ) and angular frequency (ω RF -ω LO = ω IF The IF signal is obtained by down-converting it to ).

[0046] …(7)

[0047] Next, we will explain how to remove the image signal. The amplitude of the image signal input as received signal 1 is A IN , the frequency (angular frequency) is ω IM (Angular frequency ω IM <Local signal frequency ω LO If so, this image signal can be expressed by the following equation (8).

[0048] …(8)

[0049] Mixer 14 multiplies the received image signal (received signal 1) by the LO signal 6. The IF signal 26 output from mixer 14 is given by the following: ​​

[0050] …(9)

[0051] Although the second term of equation (9) is blocked by a low-pass filter (not shown) connected to the output of mixer 14, it is left in for explanatory purposes.

[0052] Mixer 12 receives the image signal as received signal 1 and the LO(Q) signal 9 of equation (4) shown below. Multiply by (5).

[0053] The IF signal 25, which is the output from mixer 12, is given as follows.

[0054] …(10)

[0055] For example, a low-pass filter (not shown) between the output of mixer 12 and phase shifter 13 blocks the second term of equation (10), and only the first term is input to the second 90° phase shifter 13. However, for explanatory purposes, it is left in place here.

[0056] The IF signal 27 obtained by shifting the phase of the IF signal 25 by 90° using the second 90° phase shifter 13 is given by the following equation (11).

[0057] …(11)

[0058] If there is no amplitude error (relative error) or phase shift from 90° in the 90° phase shifters 22 and 13 between the IF signal 26 output from mixer 14 and the IF signal 27 from mixer 12, then when the received signal 1 is an image signal, the sum of the IF signals 26 and 27 by the summing circuit 24 corresponds to the sum of equations (9) and (11), and is 0, as shown in equation (12).

[0059] …(12)

[0060] However, if there is an amplitude error (relative error) or a phase shift from 90° in the 90° phase shifters 22 and 13 between IF signal 26 and IF signal 27, it is difficult for the image rejection mixer to completely remove the image, as shown in equation (12).

[0061] The received signal 1 contains a mixture of the desired signal and the image signal, and the LO signal 6 from the local signal generator 3 (equation (2) shown below) …(2) There is a phase difference of 90° between this and the LO(Q) signal 9 output from the first 90° phase shifter 22, and the amplitude is (A LO LO (Q) signal 9 (+ε) ...(13) will be examined.

[0062] Furthermore, the outputs of mixer 12 and mixer 14 have frequency components (ω) added, similar to a Hartley-type image rejection mixer. RF +ω LO ) and (ω LO +ω IM ) are assumed to be removed by low-pass filters, etc. (not shown) connected to the outputs of mixers 12 and 14.

[0063] The IF signal 26 output from the mixer 14 can be expressed by the following equation (14), using the first term of equation (3) relating to the IF signal 26 when the received signal 1 is a desired signal, and the first term of equation (9) relating to the IF signal 26 when the received signal 1 is an image signal.

[0064] …(14)

[0065] The IF signal 27 output from the second 90° phase shifter 13 can be expressed by the following equation (15), using the first term of equation (6) relating to the IF signal 27 when the received signal 1 is a desired signal, and the first term of equation (11) relating to the IF signal 26 when the received signal 1 is an image signal.

[0066] …(15)

[0067] The sum of signals 26 and 27 in the adder circuit 24 produces the following frequency (ω RF -ω LO The desired signal x, down-converted to ) sig and frequency (ω LO -ω IM Image signal x down-converted to ) im You can obtain this.

[0068] …(16) …(17)

[0069] x expressed by equations (16) and (17) im (t) and x sig The average power of (t) is P im , P sig In that case, …(18)

[0070] …(19)

[0071] In equation (18), cos 2 Since the time average of [ωt] is 1 / 2 and the time average of cos[2ωt] is 0, the time average of equation (18) can be expressed as follows, for example. …(20)

[0072] Image rejection ratio (IRR) is P im / P sig to A IM 2 / A RF 2 You can also use the value obtained by dividing by (Reference 3).

[0073] Here, …(21) Thus, the IRR is given by the following equation (22).

[0074] …(twenty two)

[0075] Regarding equation (21), year, in the case of, …From (23), the following approximation can be derived as the IRR of equation (22).

[0076] …(twenty four)

[0077] however, …(25) is the gain mismatch.

[0078] The above is a simplified model, but from equation (24), it can be seen that the IRR depends on the sum of the squares of the gain error and the squares of the phase error. In reality, errors such as the phase error in the second 90° phase shifter 13 in Figure 1 will be added. The image rejection ratio (IRR) is typically said to be, for example, 30 to 40 dB, corresponding to a gain error of 0.2 to 0.6 dB and an I / Q phase imbalance of 1 to 5° (Reference 3).

[0079] The decoder circuit 4 receives the IF signal 7, which is obtained by down-converting the received signal 1 by the mixer 2, and outputs the transmit (Tx) trigger signal 5 after receiving the determination signal 23 from the control circuit 19. The decoder circuit 4 does not generate the transmit trigger signal 5 unless the determination signal 23 is output from the control circuit 19. Note that if the IF signal 7 (analog baseband signal) is not input to the decoder circuit 4, the transmit trigger signal 5 will not be activated (no response signal will be transmitted). The decoder circuit 4 performs predetermined signal processing (demodulation, decoding) on ​​the IF signal 7.

[0080] The aircraft is equipped with an interrogator as onboard equipment. This interrogator transmits interrogation pulses (paired pulses) in the UHF band (Ultra High Frequency: radio waves with frequencies from 300 MHz (Mega-Hertz) to 3 GHz (Giga-Hertz)) to a transponder on the ground, and measures the distance based on the time it takes to receive a response pulse (paired pulse) from the transponder. The aircraft's interrogator and the ground station's transponder are designed to respond with a 63 MHz difference, with the interrogator operating at 1,025–1,150 MHz and the transponder at 962–1,213 MHz. The ground station's transponder transmits a random pulse signal of approximately 1000 pps (Pulse pairs Per / Second) even when there is no interrogation pulse signal from the onboard equipment (interrogator). Only when it receives an interrogation pulse signal (desired signal) does it transmit a response pulse signal instead of the random pulse signal. Normally, ground equipment (interrogation equipment) constantly transmits pulse signals of 1000 to 2700 pps, including random pulse signals and response pulse signals. Onboard equipment (interrogation equipment) sequentially transmits interrogation pulses to ground equipment at random time intervals (for example, 30 times per second). Ground equipment receives and demodulates the interrogation pulse signal of a predetermined frequency emitted from the onboard equipment (interrogation equipment), decodes (decodes) this interrogation pulse signal (desired signal: IF signal 7) with the decoder circuit 4, adds a predetermined system delay time (for example, 50 μs (micro-seconds)), activates the transmit (Tx) trigger signal 5, re-encodes it, and transmits it as a response pulse signal to the onboard equipment mounted on the aircraft via the transmission system. The onboard equipment installed on the aircraft that receives the transmitted response pulse receives and demodulates the response pulse signal, measures the elapsed time between the interrogation pulse signal and the response pulse signal, and obtains distance information from the ground equipment to the aircraft from the time difference between the transmission of the interrogation pulse signal and the reception of the response pulse signal (References 1, 2, etc.).

[0081] The procedure for generating a determination signal in the control circuit 19 will be explained below.

[0082] The received signal 1 is taken out by the coupler 11, distributed, and input to the mixer 12 and mixer 14.

[0083] The signal 26 output from mixer (I) 14 is denoted as IF(I).

[0084] The mixer (Q) 12 receives an LO signal 9, which is obtained by shifting the phase of the local oscillator signal 6 from the local signal generator 3 by 90° using the first 90° phase shifter 22.

[0085] The phase of the signal 25 (IF (Q) signal) output from the mixer (Q) 12 is shifted by 90° using the second 90° phase shifter 13.

[0086] The signal 26 output from the mixer (I) 14 has its phase and amplitude variably controlled by the phase adjuster 15 and the variable attenuator 16, and is output as signal 18, which is input to the adder circuit 24.

[0087] The control circuit 19 reduces the deviation in quadrature balance by using a phase adjustment voltage Vθ given as a control signal (control voltage) 20 and an attenuation adjustment voltage Vatt obtained as a control signal (control voltage) 21 to correct errors (mismatches) in the transmission loss of the first 90° phase shifter 22 and signal lines, thereby controlling the IF(I) signal 26 and IF(Q) signal 25 to be orthogonal. As a result, the real part of the desired signal (complex signal) is obtained from the output of the adder circuit 24 as shown in equation (7) above. Only the part can be extracted, and from equation (12) above, the image signal is canceled. The IF signal 29 output by the summing circuit 24 is input to the detection circuit 17. If the orthogonal balance deviation is corrected, and the received signal 1 is the desired signal, the detection circuit 17 outputs a signal 18 (detection voltage) corresponding to the level of the desired signal. On the other hand, if the received signal 1 is an image signal, the IF signal 29 output by the summing circuit 24 is 0, and the output from the detection circuit 17 is a value corresponding to the level of the IF signal 29 (for example, 0V).

[0088] The control circuit 19 receives a detection signal 18 (for example, an analog voltage signal) from the detection circuit 17. For example, it compares the level of the signal with a threshold voltage using a comparator or the like to determine whether the received signal 1 is a desired signal or an image signal, and supplies the determination result as a determination signal 23 to the decoder circuit 4. The determination signal 23 may also be a digital signal.

[0089] When the determination signal 23 from the control circuit 19 indicates the reception of the desired signal, the decoder circuit 4 determines that the IF signal 7 from the mixer 2 is the desired signal and outputs a transmit (Tx) trigger signal 5 based on the decoding result, so that a response signal is output from the transmit circuit (not shown).

[0090] While there are no particular restrictions, in applications to DME / TACAN, the circuit must function correctly even when an image signal of -15dBm (80dB higher than the minimum received electric field of -95dBm) enters the receiving circuit (dBm is a unit of decibels (dB) where 1 milliwatt (mW) is the reference value (1mW = 0dBm)). For this reason, the image component needs to be reduced by, for example, 80dB or more. As mentioned above, the typical image rejection ratio (IRR) is said to be around 30-40dB. Theoretically, the orthogonal components are completely canceled, but the subtle amplitude and phase difference between the IF (I) signal and the IF (Q) signal leaves some image components behind.

[0091] Figure 3 shows the IRR (Image Rejection Ratio) characteristics for the amplitude and phase difference of the IF(I) and IF(Q) signals. In Figure 3, the vertical axis represents the IRR in decibels [dB], and the horizontal axis represents the gain error (amplitude difference) = ΔA / A and the phase difference θ = ΔΦ. The IRR characteristics with respect to the gain error (amplitude difference) = ΔA / A are shown in the graph connecting the squares (■), and the IRR characteristics with respect to the phase difference θ = ΔΦ are shown in the graph connecting the circles (●). The IRR characteristics show a characteristic of around 40 dB for each difference up to about 0.01%, but it can be seen that in order to satisfy characteristics of 80 dB or more, the difference needs to be almost eliminated.

[0092] Figure 4 shows the IRR characteristics for the phase adjustment voltage Vθ and the attenuation adjustment voltage Vatt. In Figure 4, the vertical axis represents the IRR in decibels [dB], and the horizontal axis represents the attenuation adjustment voltage Vatt [V] and the phase adjustment voltage Vθ [V]. The IRR characteristics with respect to Vθ are shown by the graph connecting the squares (■), and the IRR characteristics with respect to Vatt are shown by the graph connecting the circles (●). The attenuation adjustment voltage Vatt and the phase adjustment voltage Vθ are adjusted so that the IRR becomes 80 dB or higher. These values ​​are defined as Vatt_min and Vθ_min, respectively.

[0093] Figure 5 shows an example of the characteristics of the power level (Pdet_In(dBm)) of the signal 29 input to the detection circuit 17 and the detected signal 18 (detection voltage: V_det) output from the detection circuit 17, with respect to the phase adjustment voltage Vθ and the attenuation adjustment voltage Vatt. The horizontal axis in Figure 5 corresponds to the phase adjustment voltage Vθ [V] and the attenuation adjustment voltage Vatt [V]. The left vertical axis in Figure 5 is the input level (Pdet_In(dBm)) to the detection circuit 17 (logarithmic scale), and the right vertical axis is the detection voltage V_det [V] of the detection circuit 17. The graph connected by triangles (▲) represents the case where the received signal 1 is only the desired signal. The signal 29 input to the detection circuit 17 corresponds to equation (16), and the graph connected by circles (●) represents the case where the received signal 1 is only the image signal. The signal 29 input to the detection circuit 17 corresponds to equation (17). The graph connecting the squares (■) represents the case where the received signal 1 is the desired signal + image signal (a mixture of the desired signal and image signal). The signal 29 input to the detection circuit 17 corresponds to equation (16) + equation (17). Note that this is the power level (Pdet_In[dBm]) of signal 29 and corresponds to the square of signal 29.

[0094] When the power level Pdet_In[dBm] of the signal 29 input to the detection circuit 17 is, for example, -95dBm or less, the phase adjustment voltage Vθ, attenuation adjustment voltage Vatt, and detection voltage V_det are Vθ_min, Vatt_min, and Vdet_min, respectively.

[0095] Let Vθ_tmp, Vatt_tmp, and Vdet_tmp be the phase adjustment voltage Vθ, attenuation adjustment voltage Vatt, and detection voltage V_det, respectively, when the power level of the signal 29 input to the detection circuit 17 is constant between, for example, -95 dBm and -15 dBm.

[0096] Let Vθ_0, Vatt_0, and Vdet_0 be the phase adjustment voltage Vθ, attenuation adjustment voltage Vatt, and detection voltage V_det, respectively, when the power level of the signal 29 input to the detection circuit 17 is, for example, -15 dBm.

[0097] If the received signal 1 is only the desired signal, the power level Pdet_In[dBm] of the signal 29 input to the detection circuit 17 and the detection voltage V_det output from the detection circuit 17 will be constant, regardless of the phase adjustment voltage Vθ and the attenuation adjustment voltage Vatt.

[0098] When the received signal 1 is a mixture of the desired signal and the image signal (desired signal < image signal), adjusting the phase adjustment voltage Vθ and the attenuation adjustment voltage Vatt will cause the power level Pdet_In[dBm] of the signal 29 input to the detection circuit 17 of the desired signal and the detection voltage output from the detection circuit 17 to decrease to -60dBm and Vdet_tmp, but thereafter remain constant at -60dBm and Vdet_tmp.

[0099] If the received signal 1 consists only of an image signal, adjusting the phase adjustment voltage Vθ and the attenuation adjustment voltage Vatt will allow the power level Pdet_In[dBm] of the signal 29 input to the detection circuit 17 of the desired signal, and the detection voltage V_det output from the detection circuit 17, to be adjusted down to -100dBm or less / 0V.

[0100] Figure 6 shows a flowchart illustrating the operation of the control circuit 19. Assume that the phase adjuster 15 and variable attenuator 16 in Figure 1 are subjected to a phase adjustment voltage Vθ and an attenuation adjustment voltage Vatt of a given voltage value, and that in this state, an interrogation pulse signal from the onboard equipment is received by the antenna 31, and the received signal 1 is input via the low-noise amplifier 32 (step S101). The control signals 20 (control voltage: phase adjustment voltage) Vθ and 21 (control voltage: attenuation adjustment voltage) Vatt applied to the phase adjuster 15 and variable attenuator 16 are initially set to their respective values ​​and are subsequently varied by the control circuit 19. When the control circuit 19 determines whether the received signal 1 is a desired signal based on the detection signal (detection voltage) 18 from the detection circuit 17, the control voltage (phase adjustment voltage) Vθ and control voltage (attenuation adjustment voltage) Vatt applied to the phase adjuster 15 and variable attenuator 16 may be reset to their initial values, or they may remain at the control voltage (phase adjustment voltage) Vθ and control voltage (attenuation adjustment voltage) Vatt at the time the determination of whether it is a desired signal was made. These are referred to as the given voltage values ​​Vθ and Vatt.

[0101] The received signal 1 is taken from the coupling port of the coupler 11, the signal is distributed, and input to mixers 12 and 14 (step S102). The signal 26 output from mixer 14 is also called the IF (I) signal. The LO signal 9, which is obtained by shifting the phase of the local oscillator signal 6 from the local signal generator 3 by 90° using the first 90° phase shifter 22, is input to mixer 12.

[0102] The phase of the IF(Q) signal 25, which has been frequency-converted (down-converted) by the mixer 12, is shifted by 90° by the second 90° phase shifter 13. The IF(I) signal 26, which has been frequency-converted (down-converted) by the mixer 14, has its phase and amplitude controlled by the phase adjuster 15 and the variable attenuator 16, and is output as signal 18, which is input to the adder circuit 24. The output signal 29 of the adder circuit 24 is detected by the detection circuit 17, and the detected signal (detected voltage) 18 is output to the control circuit 19 (step S103).

[0103] The control circuit 19 may hold the detected signal (detected voltage) 18 in correspondence with the voltage value of the control voltage (phase adjustment voltage Vθ, attenuation adjustment voltage Vatt) (step S104).

[0104] The control circuit 19 varies the control voltage (both or either of the phase adjustment voltage Vθ and / or the attenuation adjustment voltage Vatt) to set a new value for the phase adjuster 15 and the variable attenuator 16 (both or either of them). The IF(I) signal 26, which has been frequency-converted (down-converted) by the mixer 14, is then input to the adder circuit 24 as a signal 28 whose phase and / or amplitude are controlled by the phase adjuster 15 and / or variable attenuator 16, whose control voltages (phase adjustment voltage Vθ and / or attenuation adjustment voltage Vatt) are varied. The output signal 29 of the adder circuit 24 is detected by the detection circuit 17, and the detected signal (detection voltage) 18 is output to the control circuit 19 (step S105).

[0105] The control circuit 19 checks (determines) whether the detection voltage V_det from the detection circuit 17 is variable by setting the control voltage (phase adjustment voltage Vθ and / or attenuation adjustment voltage Vatt) to the phase adjuster 15 and / or variable attenuator 16 to be variable (step S106). If the detection voltage V_det is not variable (No branch in step S106), the control circuit 19 determines that the received signal 1 is the desired signal (see the graph of "Desired signal only" (-▲-) in Figure 5), and activates and outputs the determination signal 23 (step S107). The decoder circuit 4 outputs the transmit trigger signal 5 to the transmit circuit (not shown) that emits the response signal (step S108). In step S106, Vθ and Vatt may be varied within the ranges of Vθ_0 and Vθ_tmp, and Vatt_0 and Vatt_tmp in Figure 5.

[0106] If the detected voltage V_det is variable (Yes branch in step S106), the control circuit 19 determines whether the detected voltage V_det is less than or equal to the minimum voltage (lowest level) Vdet_min (see Figure 5) (step S109). In this case, the control circuit 19 sets the control voltages (phase adjustment voltage Vθ and attenuation adjustment voltage Vatt) to less than or equal to Vθ_min and Vatt_min in Figure 5, and the IF(I) signal 26, which has been frequency-converted (down-converted) by the mixer 14, checks whether the detected voltage V_det obtained by detecting the output signal 29 of the adder 24, which receives a signal 28 whose phase and / or amplitude are controlled by a phase adjuster 15 and / or variable attenuator 16 with variable Vθ and / or Vatt, is less than or equal to the minimum voltage (lowest level) Vdet_min.

[0107] If, as a result of the determination in step S109, the detected voltage V_det is not less than or equal to the minimum voltage (lowest level) Vdet_min (No determination in step S109), the control circuit 19 determines that the received signal 1 is the desired signal + image signal (see the graph of "desired signal + image signal" (-■-) in Figure 5), and activates and outputs the determination signal 23 (step S110). The decoder circuit 4 outputs the transmit trigger signal 5 to the transmit circuit (not shown) that emits the response signal (step S108).

[0108] If, as a result of the determination in step S109, the detected voltage V_det is less than or equal to the minimum voltage (lowest level) Vdet_min (Yes determination in step S109), the control circuit 19 determines that the received signal 1 is an image signal (see the graph of "image signal only" (-●-) in Figure 5) (step S111). In this case, the control circuit 19 does not activate the determination signal 23, and the decoder circuit 4 does not output the transmit trigger signal 5 even if an IF signal is input from the mixer 2 (step S112).

[0109] The phase adjuster 15 and the variable attenuator 16 may be configured to be located on the signal transmission line 25.

[0110] The control circuit 19 may detect the change in the detected voltage V_det by fixing one of the control voltages Vθ and Vatt supplied to the phase adjuster 15 and the variable attenuator 16, and varying (sweeping) the other. Alternatively, the control circuit 19 may detect the change in the detected voltage V_det by varying (sweeping) both the control voltages Vθ and Vatt supplied to the phase adjuster 15 and the variable attenuator 16.

[0111] Figure 7 illustrates a configuration with a preselector (variable bandpass filter) 33 as a comparative example. The preselector 33 is placed between the low-noise amplification circuit 32 and the mixer 2 to remove the image signal.

[0112] According to this embodiment, as shown in Figure 7 as a comparative example, it is possible to realize a wireless receiving circuit that can determine whether the received signal 1 is a desired signal or an image signal when it is input, and operate a response signal in response to the input of the desired signal, without requiring correction by a preselector (variable bandpass filter) 33 or the like.

[0113] In this disclosure, if the coupler 11, distributor 10, quadrature mixers (12, 14), 90° phase shifters (13, 22), phase adjuster 15, variable attenuator 16, adder 24, detection circuit 17, and control circuit 19 in Figure 1 are referred to as a discrimination circuit that determines whether the received signal is a desired signal or an image signal, it goes without saying that this discrimination circuit is not limited to application to the wireless receiving circuit of a DME device.

[0114] [Reference 1] Japanese Patent No. 2629612 [Reference 2] Japanese Patent Application Publication No. 2008-298595 [Reference 3] Behzad Razavi, "RF MICROELECTRONICS", 5.2.3 Image-Reject Receivers, pp. 138-146, Prentice Hall PTR, 1998

[0115] Furthermore, the disclosures in the above-mentioned patent documents and references are incorporated herein by reference. Within the framework of the disclosure of this application (including the claims), further modifications, adjustments, and combinations of embodiments or examples are possible based on the fundamental technical concept. Also, within the framework of the claims of this disclosure, various combinations or selections of various disclosed elements (including each element in each appendix, each element in each example, each element in each drawing, etc.) are possible. In other words, this disclosure, including the entire disclosure including the claims, naturally includes various modifications and alterations that a person skilled in the art could make in accordance with the technical concept.

[0116] 1. Received signal 2. Mixer 3. Local Oscillator 4. Decoder circuit 5. Transmit trigger signal 6. Local Oscillator signal (LO signal) 7. IF signal 8. 8A. 8B. Monitor signal 9. Local Oscillator signal (LO signal) 10. Distributor 11. Coupler 12. Mixer 13. Second 90° phase shifter 14. Mixer 15. Phase adjuster 16. Variable attenuator 17. Detection circuit 18. Detection signal (detection voltage) 19. Control circuit 20. Control signal 21. Control signal 22. First 90° phase shifter 23. Decision signal 24. Adder circuit 25. 27. IF signal 26. 28. IF signal 29. IF signal (addition result signal) 30. Input terminal 31. Antenna 32. Low-noise amplifier circuit 33. Preselector

Claims

1. A first mixer and a second mixer that mix an input received signal with a first local oscillator signal and a second local oscillator signal obtained by shifting the first local oscillator signal by 90°, respectively; an adder circuit whose first input and second input are connected to a first signal line that transmits a first signal of an intermediate frequency converted by the first mixer and a second signal line that transmits a signal obtained by shifting the second signal of an intermediate frequency converted by the second mixer by 90°, respectively; a detection circuit connected to the output of the adder circuit; and a control circuit connected to the output of the detection circuit, wherein one of the signal lines of the first signal line and the second signal line is provided with circuit means for varying the phase and / or amplitude of the intermediate frequency signal on the one signal line based on a control signal from the control circuit. The control circuit is configured to determine whether the received signal is a desired signal or an image signal based on the detection signal from the detection circuit when the phase and / or amplitude settings of the intermediate frequency signal on one of the signal lines are varied.

2. The wireless receiving circuit according to claim 1, wherein the circuit means comprises a phase adjuster that varies the phase in accordance with a first control signal from the control circuit and / or a variable attenuator that varies the amplitude in accordance with a second control signal from the control circuit.

3. The wireless receiving circuit according to claim 2, wherein the control circuit is configured such that when the first control signal and / or the second control signal are varied within a predetermined range, the level of the detection signal from the detection circuit does not change, and the received signal is determined to be the desired signal.

4. The wireless receiving circuit according to claim 2, wherein the control circuit is configured such that, as a result of varying the first control signal and / or the second control signal, the level of the detection signal from the detection circuit changes, and if the level of the detection signal from the detection circuit changes to a predetermined level or less, the received signal is determined to be the image signal, and if it does not change to a predetermined level or less, the received signal is determined to be a signal in which the desired signal and the image signal are mixed.

5. The wireless receiving circuit according to claim 1, further comprising a coupler for monitoring the received signal, and a distributor for splitting the signal from the coupling port of the coupler into two and distributing it to the first mixer and the second mixer.

6. The wireless receiving circuit according to claim 1, comprising: a third mixer that mixes the received signal with the first local oscillator signal on a signal line from a terminal that inputs the received signal; and a decoder circuit that inputs and decodes a third signal of an intermediate frequency output from the third mixer, wherein the decoder circuit, upon receiving a determination result from the control circuit that the received signal is the desired signal, transmits a signal to the transmitting circuit instructing the transmission of a response signal to the received signal.

7. A ground station comprising a wireless receiving circuit according to any one of claims 1 to 6, wherein the wireless receiving circuit receives an interrogation signal from an onboard device.

8. A control method for a wireless receiver circuit, comprising: mixing the input received signal with a first local oscillator signal and a second local oscillator signal obtained by shifting the first local oscillator signal by 90° using a first mixer and a second mixer, respectively; transmitting a first signal of the intermediate frequency converted by the first mixer on a first signal line; transmitting a signal obtained by shifting the second signal of the intermediate frequency converted by the second mixer by 90° on a second signal line; detecting the sum of the signals from the first signal line and the second signal line using a detection circuit; and determining whether the received signal is a desired signal or an image signal based on the detected signal from the detection circuit when the phase and / or amplitude settings of the intermediate frequency signal on one of the signal lines of the first signal line and the second signal line are varied.

9. A control method for a wireless receiving circuit according to claim 8, wherein if the phase and / or amplitude settings of the intermediate frequency signal on one of the signal lines are varied within a predetermined range, and the level of the detected signal from the detection circuit does not change, the received signal is determined to be the desired signal.

10. A control method for a wireless receiving circuit according to claim 9, wherein, as a result of varying the setting of the phase and / or amplitude of the intermediate frequency signal on one of the signal lines, the level of the detection signal from the detection circuit changes, and if the level of the detection signal from the detection circuit changes to a predetermined level or lower, the received signal is determined to be the image signal, and if it does not change to a predetermined level or lower, the received signal is determined to be a signal in which the desired signal and the image signal are mixed.

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