JP2002344550A - Waveform shaping circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveform shaping circuit capable of accurately reproducing information signal data rows from an information signal component on which a DC voltage component is superimposed. SOLUTION: A waveform shaping circuit compares transmission signals composed of a DC voltage component and information signals superimposed thereon with a voltage obtained by filtering the transmission signals through a low-pass filter 1 by a comparator 2 so as to extract information signals. The comparison level of the comparator 2 is changed by signals corresponding to whether the information signals are present or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform shaping circuit for reproducing an information signal data sequence from an information signal component on which a DC voltage component is superimposed.

[0002]

2. Description of the Related Art Conventionally, in a waveform shaping circuit for reproducing an information signal data sequence from an information signal component on which a DC voltage component is superimposed, an input signal to a comparator is a demodulation output and an information signal using a fixed reference voltage. A reproducing device for reproducing a data string has been used. However, FSK (Freque
In the demodulation output by the ncy-Shift-Keying method, a drift due to the carrier frequency shift occurs in the DC component, but if the drift level is larger than the information signal level, a fixed reference voltage may be supplied to the comparator. However, a correct information signal data sequence could not be reproduced therefrom.

Therefore, in this conventional waveform shaping circuit, an LPF (Low Pass Filter) for cutting the information signal out of the demodulated output and passing only the DC drift component is provided, and the demodulated output passed through the LPF is fixed. The information signal data string is reproduced by supplying it to the comparator instead of the reference voltage.

Here, the internal circuit of the above-mentioned conventional waveform shaping circuit and the shaping processing of an input signal by the waveform shaping circuit will be described with reference to FIG. FIG. 2 is a schematic block diagram illustrating a conventional waveform shaping circuit and signal waveforms carried in the circuit. The waveform shaping circuit includes an LPF 21 and a comparator 22. The comparator 22 is connected to the input terminal T21 via the signal line L21,
1 is connected to the input terminal T21 and the comparator 22 via signal lines L22 and L23, respectively.

The LPF 21 outputs an information signal (RF signal) among the demodulated output signals supplied via a signal line L22.
Is cut to pass only the DC drift component, and is output to the comparator 22 via the signal line L23. The comparator 22 has an input terminal T via a signal line L21.
21 and the demodulated output signal supplied directly from
A comparison operation process is performed on the DC drift component supplied from 21 to extract an information signal data sequence (c) from the demodulated output signal supplied via the signal line L22.

FIG. 2 shows the configuration of the waveform shaping circuit.
The demodulated output signal having the waveform shown in FIG.
21 and the comparator 2 via the signal line L22.
2 and the LPF 21 respectively.

FIG. 2 (a) supplied to the LPF 21
The information signal component of the demodulated output signal shown in (2) is cut by the LPF 21 and shaped into the output waveform shown in FIG. Then, the signal is output to one input terminal of the comparator 22 via the signal line L23.

The other input terminal of the comparator 22 is supplied with the demodulated output signal shown in FIG.
The output signal from the PF 21 shown in FIG. That is, the comparator 22 extracts the information signal data sequence shown in FIG. 2C from the demodulated output signal shown in FIG. 2A using the output signal from the LPF 21 as a reference level.

[0009]

However, the above-described conventional waveform shaping circuit has the following problems. When the FSK system is used for a wireless system, the demodulated output signal is
When there is no RF (Radio Frequency) signal as shown in FIG. 3, a high-level noise component unique to the FM system is obtained. In particular, as shown in FIG. 3, when the RF signal is input in a burst form, the demodulated output has a large noise component in a portion where there is no RF signal, and the DC component output from the LPF 21 is also shown in FIG. As shown, it has a waveform. That is, FIG.
As shown in the NG part shown by the two-dot chain line, the LPF
Is larger than the demodulated output component.

For this reason, in the NG partial region indicated by the two-dot chain line, the output signal from the LPF 21 becomes a value obtained by integrating high-level noise, and is optimal at the start of the RF signal (burst head). This does not result in a threshold value, and loses its role as a reference level when extracting information signal data. Therefore, the output signal data string of the comparator 22 becomes as shown in FIG. 3C, and a problem occurs that the transmitted data string does not match with FIG. 3D and the information signal data is not correctly extracted. I was

An object (object) of the present invention is to provide a waveform shaping circuit capable of accurately reproducing an information signal data string from an information signal component on which a DC voltage component is superimposed.

[0012]

In order to solve the above problems, a transmission signal in which an information signal is superimposed on a DC voltage component,
A comparator 22 compares the transmission signal with a voltage obtained via a low-pass filter 21 and extracts an information signal. In a waveform shaping circuit, a comparison level of the comparator is changed by a signal corresponding to the presence or absence of the information signal. By doing so, when the RF signal is input in a burst,
The problem of the conventional waveform shaping circuit that the demodulation output has a large noise component in a portion where there is no RF signal and the information signal data is not correctly extracted can be solved.
(Claim 1)

The signal according to the presence or absence of the information signal may be an RSSI signal indicating a signal level of an RF signal. (Claim 2) In addition, by using the comparison voltage of the comparator as the output voltage of the low-pass filter only during the period when the RSSI signal is present, demodulation can be performed when the RF signal is input in a burst form with a simpler configuration. In the portion where the output does not include the RF signal, the noise component becomes large, and the problem of the conventional waveform shaping circuit that the information signal data is not correctly extracted can be solved. (Claim 3) Further, it is possible to include switches 1-1 and 4 for separating an output capacitor of the low-pass filter from the transmission signal and charging to a fixed DC voltage during a period when the RSSI signal is absent. . (Claim 4)

Further, when the transmission signal in which the information signal is superimposed on the DC voltage component is a signal demodulated by the FSK method, the waveform shaping circuit of the present invention is more effective.
(Claim 5) The value of the fixed DC voltage is about the DC component of the demodulated output of the transmission signal. (Claim 6)

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a waveform shaping circuit according to the present invention will be described with reference to FIG. In FIG. 1, 1 is an LPF, as in the conventional waveform shaping circuit of FIG.
2 is a comparator. Reference numeral 3 denotes an inverter, and a switch in the LPF 1 is turned on / off by an output of the inverter. 4 is a fixed DC signal according to the presence or absence of the RSSI signal corresponding to the received RF signal level.
This is a switch for turning on and off the voltage.

A demodulated output signal (FIG. 1 (a)) is supplied to one input terminal of the comparator 2, and an LPF 1 is supplied to the other input terminal according to the presence or absence of the RSSI signal.
Or a fixed DC voltage is supplied. Therefore, the voltage of the other input terminal of the comparator 2 is
As shown in (d), depending on the presence or absence of the RSSI signal, FIG.
And the output waveform of the comparator 1 is as shown in FIG.
An information signal data sequence as shown in (c) is obtained.

Next, the operation of the waveform shaping circuit of the present invention shown in FIG. 1 will be described with reference to FIG. In the waveform shaping circuit of FIG. 1, the switch 4 is turned ON during a period without a burst signal (no RF signal period) by using an RSSI signal,
Switch 1-2 on the input side of output capacitor 1-1 of LPF to O
Set to FF. Therefore, the comparison input of the comparator 2 becomes a fixed DC voltage and the output capacitor of the LPF 1
1-1 is charged with a fixed DC voltage and is fixed to this voltage. It is desirable that the fixed DC voltage has a value on the order of the DC component of the demodulated output.

As a result, the period (R
During the period of the F signal, the switch 1-2 in the LPF is turned on and the switch 4 connected to the fixed DC is turned off, so that the comparison voltage of the comparator 2 is set to the fixed DC voltage at the start of the RF signal. be able to.

As described above, by changing the voltage input to the other input terminal of the comparator 2 in accordance with the presence or absence of the RF signal (the presence or absence of the RSSI signal), the voltage is superimposed on the DC voltage during the absence of the RF signal. The effect of high level noise can be eliminated. Therefore, comparator 2
As shown in FIG. 4 (c), the output waveform coincides with the transmitted data sequence (FIG. 4 (d)), and the signal is accurately extracted.

[0020]

According to the first aspect of the present invention, the transmission signal in which the information signal is superimposed on the DC voltage component is compared with the voltage obtained by passing the transmission signal through the low-pass filter by the comparator. In the waveform shaping circuit that extracts
By changing the comparison level of the comparator by a signal in accordance with the presence or absence of the information signal, when the RF signal is input in a burst, the demodulated output has a large noise component in the portion without the RF signal, The disadvantage of the conventional waveform shaping circuit that information signal data is not correctly extracted can be solved.

According to the second aspect of the present invention, the signal according to the presence or absence of the information signal can be an RSSI signal indicating a signal level of an RF signal, and an RSSI signal accompanying the RF signal is effectively used. Can be used for According to the third aspect of the invention, the RF signal is input in a burst configuration with a simpler configuration by setting the comparison voltage of the comparator as the output voltage of the low-pass filter only during the period when the RSSI signal is present. At this time, the problem of the conventional waveform shaping circuit that the noise component becomes large in the demodulated output where there is no RF signal and the information signal data is not correctly extracted can be solved. In the invention according to claim 4, a switch for disconnecting an output capacitor of the low-pass filter from the transmission signal and charging the output capacitor of the low-pass filter to a fixed DC voltage during a period in which the RSSI signal is absent.
With the configuration including 1-1 and 4, the output capacitor of the LPF can be maintained at a predetermined voltage during the period when there is no RF signal, so that the influence of noise superimposed on the DC voltage at the start of the RF signal is eliminated. Can be.

According to the fifth aspect of the present invention, the transmission signal in which an information signal is superimposed on the DC voltage component is FSK.
When the signal is a signal demodulated by the method, the waveform shaping circuit of the present invention is more effective. Further, by setting the value of the fixed DC voltage to about the DC component of the demodulated output of the transmission signal, the threshold value of the comparator is stabilized, and the data is correctly extracted from the burst head.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a waveform shaping circuit of the present invention.

FIG. 2 is a diagram illustrating a configuration of a conventional waveform shaping circuit.

FIG. 3 is a diagram for explaining an operation of a conventional waveform shaping circuit.

FIG. 4 is a diagram for explaining the operation of the waveform shaping circuit of the present invention.

[Explanation of symbols]

 1 LPF (Low Pass Filter) 2 Comparator 3 Inverter 1-1, 4 Switch

Claims (6)

[Claims] 1. A waveform shaping circuit for extracting an information signal by comparing a transmission signal in which an information signal is superimposed on a DC voltage component with a voltage obtained by passing the transmission signal through a low-pass filter by a comparator, A waveform shaping circuit, wherein a comparison level of the comparator is changed by a signal according to the presence or absence of an information signal. 2. A signal according to the presence or absence of the information signal is R
The waveform shaping circuit according to claim 1, wherein the waveform shaping circuit is an RSSI signal indicating a signal level of the F signal. 3. Only when the RSSI signal is present,
3. The waveform shaping circuit according to claim 2, wherein a comparison voltage of a comparator is an output voltage of the low-pass filter. 4. The waveform shaping method according to claim 3, further comprising a switch for disconnecting an output capacitor of the low-pass filter from the transmission signal and charging the output capacitor of the low-pass filter to a fixed DC voltage during a period in which the RSSI signal is absent. circuit. 5. The waveform shaping circuit according to claim 1, wherein the transmission signal in which the information signal is superimposed on the DC voltage component is a signal demodulated by an FSK method. . 6. The fixed DC voltage value is about a DC component of a demodulated output of a transmission signal.
The waveform shaping circuit according to 1.