JPH03187549A - Two-phase psk demodulation circuit - Google Patents

Abstract

PURPOSE:To always obtain a stable demodulation output by selecting the output signal of a larger amplitude out of the two output signal, which phases are made different about at 90 deg., and generating the demodulation output so that the polarity can not be inverted before and after the output signal to be selected is switched. CONSTITUTION:The phase different about at 90 deg. is generated between an output signal A1 (t) of a first mixer 2a not to use a delay circuit 3, which shifts the phase of one of a received wave and a reference phase carrier by about 90 deg., and an output signal A2(t) of a second mixer 2b to use this delay circuit 3. Therefore, since the amplitude of one output signal is enlarged even when the amplitude of the other output signal is reduced, the demodulation output of the large amplitude can be always obtained by selecting the signal of the large amplitude by an amplitude comparator 6. A polarity comparator 8 compares the polarities of the two output signals so that the demodulation output can not be inverted before and after the output signal to be selected is switched. Thus, the stable demodulation output can be always obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a two-phase PSK demodulation circuit for demodulating received waves subjected to two-phase PSK modulation. It is used by the system.

[Prior Art] Conventionally, two-phase PSK (2-phase PSK) transmits data of O or 1 by applying phase modulation of 0 or
A phase 5-shift keying) modulation method is known. In addition, in order to demodulate this two-phase PSK modulated received wave, a synchronous detection method (homodyne method) is used that mixes the reference phase carrier wave used as the transmitted wave with the received wave and detects the phase difference component. (Tokugan Sho 6)
(See application No. 2-101334). Such two-phase PSK
The modulation method and its synchronous detection method are suitable as a modulation/demodulation method for a mobile object identification system using radio waves.

FIG. 4 is a schematic diagram of a conventional general mobile object identification system 11. As shown in FIG. The interrogator 20 installed in the fixed station detects the presence in the communication area A using signal waves such as microwaves while the transponder 30 installed in the mobile body passes through the communication area A of the interrogator 20. The transponder 30 reads the data (for example, the identification number of the transponder 30, etc.) sent.

In such a mobile object identification system, since the transponder is used while being housed in the mobile object, it is essential to reduce power consumption, size and weight of the transponder. For this reason, it is not desirable to provide a carrier wave oscillation circuit inside the transponder, and in conventional mobile object identification systems, a reflection type PSK is used as the data transmission method from the transponder to the interrogator.
A modulation method is used (see Japanese Patent Publication No. 60-27077).

FIG. 5 is a diagram showing the principle of a conventional reflective PSK modulation system.

The unmodulated carrier wave S sent out from the antenna 21 of the interrogator 20 is received by the antenna 31 of the transponder 30, reaches the termination circuit 32, is reflected, and is sent out again from the antenna 31 toward the interrogator 20. Ru. At this time, the termination circuit 32 can switch the termination impedance between a short circuit state and an open state using a switch 33, and by switching this switch 33, two-phase PSK modulation is applied. The interrogator 20 receives the PSK-modulated reflected wave S2 with the antenna 22, mixes it with the original carrier wave S1 with the mixer 23, and generates a phase difference component between the two waves Sl and S2 as a low frequency component of the mixed output. Take out. 24 is a local oscillator for providing the original carrier wave Sl to the mixer 23, and 25 is an amplifier for amplifying the mixed output. The output signal A of the mixer 23 (
L) is the following formula (%) In the above formula, A is the amplitude that depends on the reception level on the interrogator side, θ(L) is the phase change component due to PSK modulation on the transponder side, and φ is the length of the transmission path. This is a phase difference component that depends on the That is, the interrogator 20 transmits the reference phase carrier wave S1 toward the transponder 30, but when the transponder 30 receives this signal, the phase difference φ/2 according to the distance between the interrogator 20 and the transponder 30 is occurring. Then, the transponder 30 applies phase modulation θ(1) of O or π to the received carrier wave and sends it back to the interrogator 20, but when the interrogator 20 receives this signal, the interrogator 20 and response 2ii30
A phase difference φ/2 is generated depending on the distance between the two. Interrogator 2
0, this received wave S2 is the transmitted reference phase carrier wave S
, and output signal A (
t), the extracted output signal A
(L) includes, in addition to the phase change component θ(r) of O or π phase-modulated in the transponder 30, a phase difference component φ corresponding to the distance between the interrogator 20 and the transponder 30. become. Therefore, by moving the transponder 30, the interrogator 2
When the distance between 0 and the transponder 30 changes, the phase difference component φ
There is a problem in that the magnitude of the output signal A(t) of the mixer 23 fluctuates. For example, if the phase difference component φ is mπ
(m=o, ±1.±2....), then θ(
Depending on whether 1) is O or π, the output signal A (
t) becomes +A or -A, and the detection output becomes maximum.

On the other hand, when the phase difference component φ is (mπ+π/2>), the output signal A(L) is always zero and detection is impossible. There is a problem in that a dead zone (dead zone) occurs.

The present invention has been made in view of these points, and its purpose is to mix a two-phase PSK modulated received wave with a reference phase carrier wave and detect the phase difference component thereof. The purpose of the present invention is to enable a phase PSK demodulation circuit to always obtain a stable demodulated output regardless of the length of the transmission path.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the first
As shown in the figure, in a demodulation circuit that mixes a two-phase PSK modulated received wave S2 with a reference phase carrier wave S and detects a signal according to the phase difference between the two waves, the received wave and the reference phase carrier wave are mixed. a first mixer 2a that outputs a signal according to the phase difference between the two waves; a delay circuit 3 that shifts the phase of one of the received wave and the reference phase carrier wave by about 90 degrees; A second mixer 2b mixes the received wave whose phase has been shifted by about 90 degrees and the reference phase carrier wave and outputs a signal according to the phase difference between the two waves, and the output signal of the first mixer 2a and the second an amplitude comparator 6 that compares the amplitude of the output signal of the first mixer 2b, a polarity comparator 8 that compares the polarity of the output signal of the first mixer 2a and the output signal of the second mixer 2b, and Based on the comparison result by the comparator 6 and the polarity comparator 8, the output signal having a larger amplitude among the output signals of the first and second mixers 2a and 2b is selected as a signal for generating a demodulated output, Moreover, it is characterized by having an output circuit 12 that generates a demodulated output so that the polarity is not reversed before and after the selection of the output signals of the first and second mixers 2a and 2b is switched.

In the circuit configuration shown in FIG. 1, the delay circuit 3 is inserted before the high frequency input of the second mixer 2b, but the delay circuit 3 may be inserted before the local oscillation input.

Further, it is most desirable that the phase difference provided by the delay circuit 3 is 90 degrees, but it does not need to be strictly 90 degrees, and may be sufficiently far from 0 degrees or 180 degrees.

[Function] In the present invention, since the delay circuit 3 that shifts the phase of one of the received wave and the reference phase carrier wave by approximately 90 degrees is provided, the output of the first mixer 2a that does not use this delay circuit 3 Between the signal A+(t) and the output signal A2(t) of the second mixer 2b using this delay port R13, there is a
), a phase difference of about 90 degrees occurs. Therefore, even if the amplitude of one output signal becomes small, the amplitude of the other output signal becomes large, so if the signal with the larger amplitude is selected by the amplitude comparator 6, a demodulated output with a larger amplitude can always be obtained. . Furthermore, the polarity comparator 8 compares the polarities of the two output signals, and by configuring the system so that the demodulated output does not invert before and after the selected output signal is switched, a stable demodulated output can always be obtained. .

[Embodiment] FIG. 1 is a block diagram of a two-phase PSK demodulation circuit according to an embodiment of the present invention. This demodulation circuit is provided on the interrogator side of the mobile object identification system as described above. The reflected wave from the transponder is received by the antenna 1 and becomes the high frequency input of the first mixer 2a, and is also the high frequency input of the second mixer 2b via the delay circuit 3 which provides a phase delay of π/2. It is said that

The local oscillator 4 generates an original reference phase carrier wave to be used as a transmission wave, and transmits this to the first and second mixers 2a, 2b.
local oscillation input. First and second mixer 2m, 2
The output signals A + (t) and A z (t) of b are given by the following equations, respectively.

A + (L) -A +cos(θ(1)+φ)A
z (t) = A 2eas (θ (1) + φ - π/2) Figure 2 (a) shows that the output signals A, (t), A2 (t) of the first and second mixers 2a, 2b are , shows how it changes depending on the length of the transmission path, that is, the phase difference component φ).

In the figure, only the phase difference component φ is changed without changing the phase change component θ(1) caused by the modulation signal. FIG. 2(b) is a vector diagram showing the relative phase relationship of the output signals A+(t) and A2(t). As shown in the figure, the output signal A2(t) has a waveform in which the change in amplitude is delayed by π/2 with respect to the output signal A10>. Therefore, the length of the transmission path changes and the two output signals A+(t) and Ai(t)
Even if one of them becomes zero, the other will always be output. Therefore, if the configuration is such that the one with the larger amplitude is automatically selected and outputted among these two output signals A + (t) and A 2 (t), it will be possible to avoid communication failure areas (dead zones) as in the past. ) will not occur, however, for example, φ in Fig. 2(a)
-φX communication position, when trying to switch from output signal A+(t> to output signal A2(t),
), since the polarities of the output signals A+(t) and 8x(t) are opposite, the polarity of the output signal is reversed, making normal demodulation impossible. In FIG. 2(c), the phase change component θ(1) due to the modulation signal is changed to 0. The phase difference component φ is φ=φ.
It is set as constant with ×. As shown in FIG. 2(e),
If the output signal before switching and the output signal after switching have opposite polarities, it is necessary to invert the polarity of one of the output signals so that the polarity does not reverse before and after switching the output signal. Furthermore, if the polarities of the output signal before switching and the output signal after switching are the same, the output signal may be switched as is.

Hereinafter, a circuit configuration for realizing the above operation will be explained. The output signal of the first mixer 2a is amplified by the first amplifier 5a and becomes one input of the amplitude comparator 6. The output signal of the second mixer 2b is amplified by the second amplifier 5b and becomes the other input of the amplitude comparator 6. The amplitude comparator 6 compares the output amplitude of the first amplifier 5a with the output amplitude of the second amplifier 5.
The output amplitudes of b are compared as absolute values, and when the former is larger than the latter, an output at the "Los" level is generated, and when the former is less than the latter, an output at the "Higl+" level is generated. The outputs of the first and second amplifiers 5a, 5b are input to level converters 7a, 7b, respectively.

Each of the level converters 7m and 7b outputs a "High" level when the input is negative, and outputs a "Log" level when the input is positive. This level converter 7
The outputs of m and 7b are input to a polarity comparator 8. The polarity comparator 8 generates a "Los" level output if the outputs of the level converters 7a and 7b are in phase, and generates a "High" level output if the outputs are in opposite phases. Level converter 7
The outputs of the amplitude comparators m and 7b are level-inverted by the level inverters 9m and 9b.Next, the change point detection circuit 10 generates a one-shot pulse when the output of the amplitude comparator 6 is inverted. When this one-shot pulse is generated, the polarity holding circuit 11 operates, and the switching operation by the output circuit 12 is set to M so that the polarity before and after switching is not reversed.
m is done. The output circuit 12 is a level converter 7a.

7b and the outputs of the level inverters 9a and 9b, one is selected and used as a demodulated output. If the output of the polarity comparator 8 is "Low" level when the one-shot pulse is generated, the polarity holding circuit 11
Level converter 7a before and after switching.

Assuming that the outputs of the level converters 7b are in phase, the polarity of the output signals before and after switching is not inverted. Specifically, when the output of the level converter 7a is selected as the demodulated output by the output circuit 12, the level Switch to the output of converter 7b,
When the output of the level converter 7b is selected, it is switched to the output of the level converter 7a, and when the output of the level inverter 9a is selected, it is switched to the output of the level inverter 9b. When the output of the level inverter 9a is selected, the output is switched to the output of the level inverter 9a.

On the other hand, if the output of the polarity comparator 8 is at "High" level when the one-shot pulse is generated, it is assumed that the outputs of the level converters 7a, 71+ before and after switching are in opposite phase, and the outputs before and after switching Inverts the polarity of the signal.
Specifically, the output circuit 12 switches to the output of the level inverter 9b when the output of the level converter 7 & is selected as the demodulated output, and switches to the output of the level inverter 9b when the output of the level converter 7b is selected. switches to the output of the level inverter 9a, if the output of the level inverter 9a is selected, switches to the output of the level converter 7b, and if the output of the level inverter 9b is selected, the output of the level converter 9a is selected. This is to switch to the output of 7a.

FIG. 3 is an operation waveform diagram for explaining the output signal switching operation in this embodiment. In this example, amplifier 5
Since the outputs of a and 5b have opposite polarities, the outputs of the level converters 7a and 7b have opposite phases, and the output of the polarity comparator 8 is at a "High" level.

At time ts, the output of the amplitude comparator 6 is “Los”
When the level changes from high to high, the change point detection circuit 10 outputs a one-shot pulse. At this time, since the output of the polarity comparator 8 is at the "High" level, the polarity holding circuit 11 generates an output at the "High" level to notify the output circuit 12 of the necessity of polarity inversion. The output circuit 12 is configured so that the output of the amplitude comparator 6 is “High”.
Since it is at the "h" level, it is determined that the output of the amplifier 5b needs to be selected, and since the output of the polarity holding circuit 11 is "High" and is a bell, it is determined that the polarity needs to be inverted. However, if the level converter 7a is selected based on this information, the level inverter 9b is selected.
If the level inverter 9a is selected, the level converter 7b is selected.

In addition, in the two-phase PSK modulation/demodulation method, when the modulation signal θ(1) is O1π, it is not known whether the detected signal A(t) will be positive, negative, negative, or positive, respectively. 1,0 of the signal and 1.0 of the received signal. If it is necessary to correspond to O, it is common to use the FSX modulation method together. In other words, if the modulation signal is 1,
If θ0) is switched to O1π in the first cycle and the modulation signal is O, θ(1) is switched to O1π in the second cycle. Therefore, the output signals A+(t) and Az(t) output from the mixer become square wave signals that alternate between positive and negative at a predetermined period, as shown in FIG. 2(c). be.

[Effect of the Invention 1] In the present invention, as described above, the first and second mixers generate two output signals having a phase difference of about 90 degrees, and of these two output signals, the amplitude is Since the larger output signal is selected and the demodulated output is generated so that the polarity is not reversed before and after the selected output signal is switched, a stable demodulated output is always obtained regardless of the transmission path length. There is an effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a two-phase PSK demodulation circuit according to an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of the same operation, and FIG. 4 is a schematic configuration diagram of a conventional mobile object identification system. FIG. 5 is a diagram explaining the principle of the conventional reflective PSK modulation method. 2m and 2b are mixers, 3 is a delay circuit, 4 is a local oscillator,
6 is an amplitude comparator, 8 is a polarity comparator, and 12 is an output circuit.

Claims (1)

[Claims] (1) In a demodulation circuit that mixes a two-phase PSK modulated received wave with a reference phase carrier wave and detects a signal according to the phase difference between the two waves, (a) Mixes the received wave and the reference phase carrier wave and (b) a delay circuit that shifts the phase of one of the received wave and the reference phase carrier wave by approximately 90 degrees; (d) a second mixer that mixes the received wave whose phase is shifted by about 90 degrees and the reference phase carrier wave and outputs a signal according to the phase difference between the two waves; (e) a polarity comparator that compares the polarities of the output signals of the first mixer and the output signal of the second mixer; (f) Based on the comparison results by the amplitude comparator and the polarity comparator, the output signal having a larger amplitude among the output signals of the first and second mixers is selected as a signal for generating a demodulated output; and an output circuit that generates a demodulated output so that the polarity is not reversed before and after the selection of the output signal of the second mixer is switched.