JPH07123122A - Tracking detection method - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the envelope detection circuit output is not good,
It is an object of the present invention to provide a follow-up detection method that can be reproduced in real time and faithfully in practical use. When the ASK modulated wave 1 is detected by an envelope detection circuit 10 and the detected output is binarized and reproduced by a comparison circuit 20, it is guided to the detected output and delayed by a delay circuit 30 by a predetermined phase, The comparison circuit 20 is characterized in that the delayed output is compared with the detected output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for tracking and detecting an ASK modulated wave.

[0002]

2. Description of the Related Art In a system using a non-contact IC card, for example, a station service system using a non-contact IC card as a commuter pass, the non-contact IC card communicates wirelessly with a fixed station provided at a ticket gate. Since the contact IC card does not have an internal power source and uses the energy of a received wave to drive an internal circuit, an ASK modulation method that requires less power is often adopted.

FIG. 3 shows an ASK-modulated signal. When the modulation frequency is close to the carrier frequency,
The envelope waveform tends to become curved as shown by the broken line in the figure due to the characteristics of the transmission line and the tuning circuit, and the amplitude itself also varies due to the frequency characteristics of the tuning circuit.

[0004]

When such an ASK modulated wave is detected by a general envelope detection circuit, the average value level of the detection output fluctuates as shown in FIG. Even if an attempt is made to reproduce through the binarization circuit, the waveform will be different from the modulated waveform, and the reproduction cannot be performed faithfully.

Further, there is a method in which a threshold voltage is created by an integrating circuit or the like with respect to a waveform in which the above average value fluctuates, and binarization is performed with this threshold voltage to perform follow-up detection. Since the data of 1 is used, it becomes impossible to follow when the modulated wave fluctuates greatly.

The present invention has been made in order to solve this problem. Even when the envelope detection circuit output is not good in quality,
It is an object of the present invention to provide a follow-up detection method that can be reproduced in real time and faithfully in practical use.

[0007]

In order to achieve the above object, the present invention, when envelope-detecting an ASK modulated wave and binarizing the detected output by a comparison circuit for reproduction, leads to the detected output and delays it. The circuit delays the signal by a predetermined phase, and the comparison circuit compares the delayed output with the detection output.

[0008]

In the present invention, although the output A of the envelope has a slight phase lag, the delay output B having the same waveform as the detection output A is used as the threshold value of the comparison circuit 20. Even if the value level fluctuates, this fluctuation is absorbed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an ASK modulated wave, 10 is an envelope detection circuit, 20 is a comparison circuit, and 30 is a delay circuit.

In this configuration, the detection output A from the envelope detection circuit 10 is input to the comparison circuit 20 and also to the delay circuit 30, and from the delay circuit 30, for example, 30 ° to the center frequency of the modulation. The delayed output B whose phase θ is shifted by 45 ° is taken out. The comparison circuit 20 outputs signals A and B
Are compared and the binarized signal C shown in FIG. 2 is output.

In this embodiment, although the phase is slightly delayed with respect to the detection output A, the delay output B having the same waveform as the detection output A is used.
Is used as the threshold value of the comparison circuit 20, even if the average value level of the detection output fluctuates, this fluctuation is absorbed.

Further, in this embodiment, since the difference between the waveforms A and B is obtained, the rate of change of the waveform is obtained.
There is an advantage that the influence of the fluctuation of the average value is extremely smaller than that of other methods.

At the change point of the binarized signal C,
Since the change rate of the detection output A and the change rate of the delay output B have opposite polarities, the occurrence rate of jitter or the like is reduced.

[0015]

As described above, according to the present invention, the detection output of the envelope detection circuit and the delayed signal obtained by delaying the output are compared in real time. The reproduced waveform can be taken out.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of each part in the above embodiment.

FIG. 3 is a waveform diagram for explaining envelope detection of an ASK modulated wave.

FIG. 4 is a diagram for explaining a problem of conventional envelope detection.

[Explanation of symbols]

 1 ASK modulated wave 10 Envelope detection circuit 20 Comparison circuit 30 Delay circuit

Claims (1)

[Claims] 1. When envelope detection is performed on an ASK modulated wave, and the detected output is binarized and reproduced by a comparator circuit, the detected output is delayed by a predetermined phase by a delay circuit, and the comparator circuit outputs the delayed output. A follow-up detection method characterized by comparing with the above detection output.