JP2000224059A - Method for removing interference waves - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which the interference wave superimposed upon a desired signal wave can be removed with a relatively simple circuit configuration, without using any additional circuit exclusively used for fetching offsetting error signals nor requiring complicated control circuits for uniting two independent error signals with each other. SOLUTION: Carrier frequency power inputted to a receiving input terminal 5 is divided into two parts by means of a distributor 7 and the parts are respectively supplied to first and second phase detectors. The low-frequency components outputted from the first phase detector are inputted to a weighting circuit 3, and compensate power 10 is obtained by controlling the carrier frequency power component which is in phase with first local oscillating power 12. The low-frequency component outputted from the second phase detector is inputted to another weighting circuit 4, and compensating power 11 is obtained by controlling the carrier frequency power component, which is in phase with second local oscillating power 13. An interference wave component is removed by combining the two compensating powers 10 and 11 and the carrier frequency power inputted to the input terminal 5 by means of a combining unit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an interference wave removing method for removing an interference wave superimposed on a desired signal wave.

[0002]

2. Description of the Related Art In wireless communication using signals, particularly radio waves, undesirable interference waves are superimposed on desired signal waves, resulting in noise and the like, and the quality of communication often deteriorates. For example, in a receiving unit or the like that applies a phase modulation to a non-modulated wireless signal of an interrogator by a transponder and receives the signal, as in a mobile object identification device, it is essential to remove an interference wave. is there.

A conventional moving object identification device is disclosed in, for example,
No. -20238. An interference wave canceling method or an interference compensating circuit is disclosed in, for example,
No. 6 and JP-A-1-188145.

[0004]

The conventional mobile object identification device has a problem that a signal from a transponder cannot be efficiently amplified in a radio frequency band (hereinafter referred to as RF). The reason is that the transmitted wave leaking into the receiving unit via the circulator is larger than the signal from the transponder, and when trying to amplify the signal wave, the leaked power saturates the RF amplifier and distorts the signal wave. On the other hand, if the signal wave is amplified at a low gain so as not to cause distortion, the signal wave cannot be sufficiently amplified. This problem also occurs when a transmitted wave is reflected by a part other than the transponder and enters the receiver.

[0005] In order to solve this problem, unnecessary waves may be removed by the RF section of the receiving section. For this purpose, the conventional techniques disclosed in JP-A-60-77556 and JP-A-1-188145 described above can be employed, but each has the following problems.

First, in the former case, the control circuit is relatively simple, but if the phase of the interference wave at the input of the adder and the phase of the output of the weighting circuit slightly deviate, the phase of the output of the weighting circuit will be reduced. There is a problem that a component orthogonal to the above remains without being removed.

In the latter case, the signal for canceling the interference does not have the above-mentioned problem because the real part and the imaginary part are controlled on the vector plane, but the circuit for providing the control signal is complicated. . That is, a complicated cancellation error detection circuit other than the main transmission signal path is required. Further, a control circuit in which two error signals eg and ei as independent variables are combined is required.

Accordingly, it is an object of the present invention to control independent parameters without adding a dedicated circuit for extracting a cancellation error signal and without having to couple two independent difference signals to each other. It is an object of the present invention to provide an interference wave removing method capable of removing an interference wave.

[0009]

In order to solve the above-mentioned problems, an interference wave removing method according to the present invention employs the following characteristic configuration.

(1) A mixed wave of a phase-modulated wave and a non-modulated interference wave having the same carrier frequency as the phase-modulated wave is received.
Branching, and using a local oscillation power orthogonal to each of the first and second phase detectors, canceling power having substantially the same amplitude and opposite phase as the unmodulated interference wave is applied to a receiver that performs synchronous detection and demodulates a signal. In the interference wave elimination method, the interference wave elimination method includes controlling a vector amount of the canceling power using a frequency equal to or lower than a transmission signal component included in each of the phase detectors.

(2) The carrier frequency power is decomposed into components having substantially the same phase as the local oscillation power of each phase detector, and the output low-frequency component of the first phase detector is substantially in phase with the first local oscillation power. The interference wave elimination method according to (1), wherein the carrier frequency power component of the second phase detector is controlled, and the carrier frequency power component having substantially the same phase as the second local oscillation power is controlled by the output low frequency component of the second phase detector.

(3) The interference wave elimination method according to (1), further comprising a combiner between a reception input terminal and the distributor, and combining the canceling power from the weighting circuit and the mixed wave.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for removing interference waves according to the present invention will be described below in detail with reference to the accompanying drawings.

First, a block diagram of a control loop including an interference wave removing method according to the present invention will be described with reference to FIG. This control loop includes a radio frequency (RF) oscillator 1, distributors 2 and 7, weighting circuits 3 and 4, a receiving input terminal 5, a combiner 6, and phase detectors 8 and 9. Here, the canceling powers 10 and 11 are supplied to the combiner 6 from the weighting circuits 3 and 4, respectively. In addition, local oscillation powers 12 and 13 are supplied from the distributor 2 to the phase detectors 8 and 9, respectively.

Next, the operation of the control loop of FIG. 1 will be described. The reception wave input from the reception input terminal 5 is generally a mixed wave in which an interference wave is superimposed on a desired signal wave. As described above, the received wave, which is a mixed wave, is passed through the combiner 6 to the distributor 7.
Is divided into two signals. Among the outputs of the divider 7, the signal input to the phase detector 8 is compared with the reference phase of the local oscillation power 12 obtained by dividing the output of the RF oscillator 1 by the divider.

The other output from the distributor 7 is input to a phase detector 9. The phase detector 9 compares this input with the reference phase of the local oscillation power 13 obtained by dividing the output of the RF oscillator 1 by the divider 2. Here, the local oscillation powers 12, 13
Have mutually orthogonal phases, and the outputs of the phase detectors 8 and 9 are demodulated outputs of the in-phase and quadrature components, respectively, and at the same time, the detections representing the in-phase components with the local oscillation powers 12 and 13 in the interference wave, respectively. Output. This detection output becomes a DC component when the amplitude and phase of the interference wave are in a steady state.
Further, when feedback (feedback) of the interference wave is applied, the signal becomes a control error signal after removing the interference wave. Therefore, these error signals are canceled out by the weighting circuits 3 and 4 for the in-phase component and the quadrature component, respectively, to generate canceling powers 10 and 11, and are combined with the reception wave from the reception input terminal 5 by the combiner 6 to generate the interference wave. Eliminate the effects.

Next, orthogonal local oscillation powers 12, 1
3 will be described with reference to the block diagram of FIG. FIG. 2 shows a control loop model of each phase component of the local oscillation powers 12 and 13. It has an adder 21, a detector 22, an amplifier (amplifier) 23, and a weighting circuit 24. In FIG. 2, A represents the transfer function of the interference wave residual error level (dBm) versus the direct current (low frequency) output (V) of the phase detector. G
(S) represents a loop amplifier gain, and S represents a Laplace transform operator. B represents a transfer function between the control voltage (V) and the canceling power (dBm).

Here, assuming that LG (s) is a loop gain, the closed loop characteristic is expressed by the following equation. Here, since X and Y hold for the same phase component in the local oscillation powers 12 and 13 (FIG. 1), the relationship between the arbitrary vector X￣ of the interference wave and the output vector Y￣ is Y￣ / X￣ = 1 / LG (s), and the interference wave can be removed.

Next, FIG. 3 will be described. FIG. 3 is a control loop for explaining the operation when the phase of the cancellation power 10 and the phase of the local oscillation power 12 (in other words, the phase of the cancellation power 11 and the phase of the local oscillation power 13) slightly shift at the input of the synchronous detector. It is a block diagram showing a model. Here, the outputs Y1 and Y2 are respectively expressed as follows. X1 = E · cos θ (1) X2 = E · sin θ (2) X1−Y2 · LG (s) · sin θ−Y1 · LG (s) · cos θ = Y1 (3) X2−Y1 · LG (s) · sin θ −Y2 · LG (s) · cosθ = Y2 (4) where | θ | <π / 6 LG (s) ≫1 / {cosθ−sinθ} (5) LG (s) ≫1 / ｛cosθ + sinθ Since (6) LG (s) ≫1 / cos θ (7), an approximate solution is obtained. Y1 = {1 / LG (s)}｝ {X1 · cos θ−X2 · sin θ} / cos 2θ (8) Become. Similarly, when Y2 is obtained, Y2 = {1 / LG (s)}｝ {X2 ・ cosθ-X1 ・ sinθ} / cos2θ (9) From this, the vector Y￣ is given by: Y￣ = {1 / LG (s) · cos2θ} · {X1 (1-jθ) + jX2 (1 + jθ)} = {1 / LG (s) · cos2θ} · (X1 + jX2) + jθ ) (JX2-X1) = {1 / LG (s) · cos2θ} · (X￣−jθX}) {X} / {LG (s) · cos2θ} (10) Even if there is a phase shift, It can be compressed almost by the loop gain.

As can be understood from the above description, components which cannot be completely removed by the conventional interference wave removing method disclosed in Japanese Patent Application Laid-Open No. Sho 60-77556 are left. It is possible to compress by the minute. Note that the low-frequency outputs of the phase detectors 8 and 9 may change between positive and negative, and the weighting circuits 3 and 4 also correspond to positive and negative phases according to this sign. However, since this technique is known, its description is omitted.

Next, another embodiment of the present invention will be described with reference to FIG. However, since it includes many components similar to the embodiment of FIG. 1, the same reference numerals are used for the same components for convenience. The embodiment of FIG. 4 differs from the embodiment of FIG. 1 in that the weighting circuit 4 and the canceling power 11 are excluded. When the phase of the interference wave is within a limited range (for example, within about ± 30 ° with respect to the local oscillation power 12), the weighting circuit 3 cancels the power 10 by the low frequency output component of the phase detector 8.
Is controlled by controlling the phase of the cancellation power 10 by the phase shifter 14 using the low-frequency output component of the phase detector 9.

[0022]

As described above, according to the present invention,
Since independent parameters are controlled on the vector plane by the weighting circuit based on the cancellation error signal, the circuit configuration for controlling the signal for canceling the interference is simplified.

Further, since a low frequency component of the output of the phase detector for extracting the demodulated signal is used, it is not necessary to add a dedicated circuit for extracting the cancellation error signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a control loop including an interference wave removing method according to the present invention.

FIG. 2 is a diagram showing a control loop model of each phase component of local transmission powers 12 and 13 in FIG.

FIG. 3 is an operation explanatory diagram of a control loop shown in FIG. 1;

FIG. 4 is a block diagram showing another embodiment of an interference wave removing method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radio frequency oscillator 2, 7 Divider 3, 4 Weighting circuit 5 Reception input terminal 6 Combiner 8, 9 Phase detector 10, 11 Cancellation power 12, 13 Local oscillation power 14 Phase shifter 21 Adder 22 Detector 23 Amplifier 24 Weighting circuit

Claims (3)

[Claims] 1. A mixed wave of a phase-modulated wave and an unmodulated interference wave having the same carrier frequency as the phase-modulated wave is received, branched into two by a divider, and orthogonalized by a first and a second phase detector, respectively. A local oscillation power, a receiver that performs synchronous detection and demodulates a signal, and an interference wave removal method that adds canceling power having substantially the same amplitude and opposite phase as the unmodulated interference wave, wherein the transmission signal included in each of the phase detectors An interference wave elimination method, wherein a vector amount of the cancellation power is controlled using a frequency equal to or lower than a component. 2. The method according to claim 1, wherein the carrier frequency power is decomposed into components having substantially the same phase as the local oscillation power of the respective phase detectors, and the low frequency component output from the first phase detector has a component having substantially the same phase as the first local oscillation power. The interference according to claim 1, wherein the carrier frequency power component is controlled, and the carrier frequency power component having substantially the same phase as the second local oscillation power is controlled by the output low frequency component of the second phase detector. Wave removal method. 3. The method according to claim 1, further comprising a combiner between a reception input terminal and the distributor, and combining the canceling power from a weighting circuit and the mixed wave.