JP2002111758A - Waveform shaping circuit and method of shaping waveform with this circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent data sequence reproduction error in a burst signal which is generated in a waveform shaping circuit especially in a FSK(Frequency Shift Keying) demodulation circuit for reproducing an information signal data sequence from an FSK signal. SOLUTION: The peak signal and the bottom signal in a demodulation output signal are detected by a peak detecting circuit 1 and a bottom detecting circuit 2 respectively. A threshold circuit 3 generates a signal obtained by averaging these detected signal waveforms to output it to the comparator 4. The comparator 4 reproduces a signal information data sequence from the demodulated output signal by using the median of a peak-to-peak value of the signal input from the circuit 3 i.e., demodulated output signal.

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, and more particularly to a waveform shaping circuit for reproducing an information signal data sequence of a FSK (Frequency Shift Keying) demodulated wave and a waveform shaping method therefor.

[0002]

2. Description of the Related Art At present, in a digital radio communication, an FSK system in which a frequency of a carrier is changed according to a digital signal is widely used. On the receiving side receiving the FSK modulated signal, a waveform shaping circuit for reproducing a data sequence of an original digital signal from the received FSK signal, for example, an FSK demodulation circuit as shown in FIG. 7 is used.

In FIG. 1, a conventional FSK demodulation circuit 20
Is composed of an LPF (Low-Pass Filter) 23 and a comparator 24. An information signal component (hereinafter, referred to as a demodulation output signal) on which a DC voltage component is superimposed, which is input to the FSK demodulation circuit 20, is supplied to a comparator 24 and an LPF.
23.

For example, when the demodulated output signal shown in FIG. 8A is input to the FSK demodulation circuit 20, the high frequency component of the demodulated output signal input to the LPF 23 is removed.
Only the DC voltage component as shown in (b) passes through the LPF 23 and is output to the connected comparator 24.

The demodulated output signal (see FIG. 8A) input to the comparator 24 is compared with the signal waveform (see FIG. 8B) input from the LPF 23 as a threshold waveform. "1 (High)" when the demodulated output signal is larger than the threshold waveform, and "0 (Low)" when the demodulated output signal is smaller than the threshold waveform.
Are respectively output.

That is, a data string of “0” and “1” output from the comparator 24 can be obtained as an information signal data string reproduced from a demodulated output signal input to the FSK demodulation circuit 20.

As described above, in the conventional FSK demodulation circuit 20, the high frequency component of the input demodulated output signal is
, And a threshold waveform at the time of data string reproduction is used to prevent an error in data string reproduction between the transmitting side and the receiving side due to a change in the DC voltage component.

[0008]

However, in the conventional FSK demodulation circuit 20, since the LPF 23 integrates the demodulated output signal to form a threshold waveform at the time of data string reproduction, the demodulated output signal becomes a burst. When input, as shown in FIG. 9, an error may occur in the reproduced data string due to the transient response of the LPF.

FIG. 9 is a diagram showing the data sequence reproduction of the demodulated output signal by the FSK demodulation circuit 20. The demodulated output signal (burst signal) input to the FSK demodulation circuit 20 and the demodulated output signal from the LPF 23 are output from the LPF 23. An output waveform (that is, a threshold waveform input to the comparator 24) is displayed as a voltage level with the passage of time.

[0010] In addition, a data sequence (ie, an information signal data sequence of a demodulated output signal reproduced by the FSK demodulation circuit 20) compared and output by the comparator 24 with respect to these signal waveforms, and data before transmission. Columns and are displayed.
Comparing the data sequence after reproduction / before transmission, it can be seen that an error has occurred at the head of the reproduced data sequence.

This reproduction error is caused by high level noise peculiar to the FM system, which occurs when there is no RF signal.
When the noise component is close to the DC drift component due to the shift of the carrier frequency, it is an error caused by the transient response of the LPF 23.

An object of the present invention is to provide a waveform shaping circuit, particularly an FS
An object of the present invention is to prevent a data string reproduction error of a burst signal which occurs in an FSK demodulation circuit for reproducing an information signal data string from a K signal.

[0013]

In order to solve the above-mentioned problems, the invention according to claim 1 provides an input analog signal (for example, a demodulated output signal in FIG. 1) and a reference signal generating means (for example, Peak detection circuit 1 and bottom detection circuit 2 of FIG.
And a reference signal generated by the threshold circuit 3) and outputting a digital signal (for example, FIG. 1)
In the waveform shaping circuit (for example, the FSK demodulation circuit 10 shown in FIG. 1) including the comparator 4), the reference signal generation means generates a peak-to-peak signal of the input analog signal.
A median peak value (PP value) is generated as the reference signal.

Further, according to the present invention, an analog signal to be inputted (for example, a demodulated output signal in FIG. 1) and a reference signal generating means (for example, a peak detection circuit 1, a bottom detection circuit 2 in FIG. The waveform shaping circuit (for example, the waveform shaping circuit 10 in FIG. 1) including a comparing unit (for example, the comparator 4 in FIG. 1) for comparing the reference signal generated by the threshold circuit 3) and outputting a digital signal. In the waveform shaping method, a reference signal generating step of generating a median of peak-to-peak values (PP values) of the input analog signal as the reference signal (for example, steps S2 to S4 in FIG. 6). It is characterized by including.

According to the first or fourth aspect of the present invention, the peak-to-peak (Peak-to-Pe
ak) By reproducing the data string of the demodulated output signal using the median value of the voltage as a threshold value, it is possible to prevent the reproduction error due to the transient response of the LPF, which is generated in the conventional FSK demodulation circuit, and the burst signal Even if input, the data string can be reproduced accurately.

According to a second aspect of the present invention, in the waveform shaping circuit according to the first aspect, the reference signal generating means includes a first peak detecting means for holding a peak signal of the input analog signal. 1 peak detection circuit 1),
A second peak detection unit (for example, a bottom detection circuit 2 in FIG. 1) for holding a bottom signal of the input analog signal, wherein the detection is held by the first and second peak detection units, respectively. A median after adding the signals is generated as the reference signal.

According to a fifth aspect of the present invention, in the waveform shaping method according to the fourth aspect, the reference signal generating step includes:
First peak detection step of holding the peak signal of the input analog signal (for example, step S2 in FIG. 6)
And a second peak detection step of holding the bottom signal of the input analog signal (for example, step S in FIG. 6).
2) and a step of generating, as the reference signal, a median value after adding the detection signals held in the first and second peak detection steps (for example, step S3 in FIG. 6). It is characterized by.

According to the second or fifth aspect of the present invention, the peak value and the bottom value of the demodulated output signal are detected, and the median value of these detected signals (that is, the peak-to-peak voltage of the demodulated output signal) is detected. The data string can be reproduced using the median value as a threshold value.

According to a third aspect of the present invention, in the waveform shaping circuit according to the second aspect, the second peak detecting means subtracts a predetermined signal value from the input analog signal (for example, FIG. 2), third peak detecting means for holding a negative peak signal of the subtraction signal output from the subtracting means (for example, the negative peak detecting circuit 21 in FIG. 2), and the third An adding unit (for example, an adder in FIG. 2) for adding the detection signal held by the peak detecting unit and the predetermined signal value, and a signal output from the adding unit is used as the bottom signal. It is characterized by holding.

According to a sixth aspect of the present invention, in the waveform shaping method according to the fifth aspect, the second peak detection step includes a subtraction step of subtracting a predetermined signal value from the input analog signal, A third peak detection step of holding a negative peak signal of the subtraction signal output in the subtraction step, and a detection signal held in the third peak detection step and the predetermined signal value are added. Including an addition step, the signal output in the addition step,
The signal is held as the bottom signal.

According to the third or sixth aspect of the invention, the predetermined value is subtracted from the demodulated output signal, a negative peak value is detected, and the predetermined voltage is added again. Can be detected.

[0022]

Embodiments of the present invention will be described below in detail with reference to FIGS. First, the configuration will be described.

FIG. 1 is a block diagram showing a configuration of an FSK demodulation circuit to which the present invention is applied. In FIG.
The demodulation circuit 10 includes a peak detection circuit 1, a bottom detection circuit 2, a threshold circuit 3, and a comparator 4. The demodulated output signal input to the FSK demodulation circuit 10 is
The signals are input to the peak detection circuit 1, the bottom detection circuit 2, and the comparator 4, respectively.

For example, when the demodulated output signal shown in FIG. 3A is input to the FSK demodulation circuit 10, the peak detection circuit 1
Is a peak hold circuit that holds the positive maximum value of the input signal, detects the peak value of the input demodulated output signal, and inputs the detected waveform shown in FIG. The bottom detection circuit 2 detects the bottom value of the input demodulation output signal and inputs the detected waveform shown in FIG. 3C to the threshold circuit 3, and the inside of the circuit is shown in FIG. It is configured as shown.

In FIG. 2, the bottom detection circuit 2 includes a negative peak detection circuit 21, a subtractor and an adder, and outputs a signal shown in FIG. 4A (ie, a demodulated output signal shown in FIG. 3A). ) Is input. The signal input to the bottom detection circuit 2 is subtracted from the voltage level by a positive fixed voltage by a subtractor, and is input to the negative peak detection circuit 21 as a signal waveform shown in FIG.

The negative peak detector circuit 21 is a peak hold circuit that holds the maximum negative value of the input signal, and detects the negative peak value of the input signal waveform (see FIG. 4B). , And outputs the signal waveform shown in FIG. Then, the adder adds the signal waveform output from the negative peak detection circuit to a voltage level corresponding to the positive fixed voltage subtracted by the subtractor, and outputs the signal waveform shown in FIG. I do.

The positive fixed value voltage added / subtracted by the adder and the subtracter is set to be equal to or higher than the voltage level of the input demodulation output signal.

The output waveform shown in FIG. 4D is the output waveform of the bottom detection circuit 2, and is the detection waveform itself shown in FIG. 3C.

The threshold circuit 3 of the FSK demodulation circuit 10 shown in FIG. 1 generates a threshold waveform serving as a reference level for comparison of the demodulated output signal of the comparator 4, as shown in FIG. , Two resistors R1 and R2 having the same resistance value are connected.

Detection waveforms (see FIGS. 3B and 3C) output from the peak detection circuit 1 and the bottom detection circuit 2 are applied to both ends of the connected resistors R1 and R2, respectively. And a connection point a between the resistors R1 and R2.
3 is taken out as an output signal, and FIG.
It is input to the comparator 4 as a threshold waveform shown in FIG.

That is, the threshold circuit 3 generates a median waveform of a detection waveform (see FIG. 3B) by the peak detection circuit 1 and a detection waveform (see FIG. 3C) by the bottom detection circuit 2. , And a threshold waveform (see FIG. 3D).

The comparator 4 compares the input demodulated output signal (see FIG. 3A) with the threshold waveform input from the threshold circuit 3 (see FIG. 3D), Similarly to the above, "1 (High)" when the voltage level of the demodulation output signal is higher than the voltage level of the threshold waveform, and when the voltage level of the demodulation output signal is lower than the voltage level of the threshold waveform. "0 (Low)" is output.

As described above, the data string of “0” and “1” output from the comparator 4 is output to the FSK demodulation circuit 1
It is an information signal data string obtained by reproducing the demodulated output signal input to 0.

FIG. 5 shows how the FSK demodulation circuit 10 reproduces a signal (burst signal) similar to the demodulated output signal shown in FIG. In this figure, as in FIG.
The demodulated output signal (burst signal) input to the FSK demodulation circuit 10 and the output waveform of the demodulated output signal from the threshold circuit 3 are displayed in voltage levels with respect to time.

An output data string (ie, FSK) which is compared and output by the comparator 4 with respect to these signal waveforms
This is an information signal data string reproduced by the demodulation circuit 10. )
And the data string before transmission. From the data sequence after reproduction / before transmission, it can be seen that the error occurring at the head of the reproduced data sequence in FIG. 7 has been improved and the data has been reproduced accurately.

As described above, the average value of the peak value / bottom value of the demodulated output signal (that is, the PP (Peak-t
By reproducing the data string from the demodulated output signal using the o-Peak) (median value of the voltage) as the reference level, it is possible to prevent a reproduction error due to the transient response of the LPF 23 generated in the conventional FSK demodulation circuit 20, Even when a burst signal is input, a data string can be accurately reproduced.

Next, the operation of the FSK demodulation circuit 10 when reproducing a data string from the demodulated output signal shown in FIG.
This will be described with reference to the flowchart shown in FIG. 3, when the demodulation output signal shown in FIG. 3A is input to the FSK demodulation circuit 10, the demodulation output signal is input to each of the peak detection circuit 1 and the bottom detection circuit 2 (step S1). .

Then, the peak detection circuit 1 calculates the peak waveform of the input demodulation output signal (see FIG. 3B),
The bottom detection circuit 2 detects a bottom waveform (see FIG. 3C) of the input demodulation output signal. And
These detected waveforms are input to the threshold circuit 3 (Step S2).

Then, the threshold circuit 3 calculates the average waveform of the input peak waveform and bottom waveform (see FIG. 3D).
And outputs the generated average waveform to the comparator 4 (step S3).

The comparator 4 has a demodulated output waveform input (see FIG. 3A) and an average waveform input from the threshold circuit 3 (ie, a threshold waveform).
(See step (c)) (step S4), and outputs a data string of "0" and "1", that is, a data string reproduced from the demodulated output signal (step S5).

By configuring the FSK demodulation circuit 10 as described above, it is possible to prevent errors in data stream reproduction due to shifts and variations in DC voltage components caused by shifts and variations in carrier waves between the transmitting side and the receiving side. It is possible to prevent a reproduction error due to a high-level noise component generated at the head of the burst signal.

[0042]

According to the first or fourth aspect of the present invention,
Peak-to-peak of demodulated output signal
By reproducing the data sequence of the demodulated output signal using the voltage as a threshold value, the signal sequence is generated by the conventional FSK demodulation circuit.
Reproduction errors due to the transient response of the LPF can be prevented, and even when a burst signal is input, a data string can be reproduced accurately.

According to the second or fifth aspect of the invention, in addition to the effects of the first or fourth aspect, the peak value and the bottom value of the demodulated output signal are detected, and the average value of these detected signals (ie, the average value of the detected signals) The data string can be reproduced using the peak-to-peak voltage of the demodulated output signal as a threshold.

According to the third or sixth aspect of the invention, in addition to the effect of the second or fifth aspect, a predetermined voltage is subtracted from the demodulated output signal, a negative peak value is detected, and the predetermined voltage is again applied. By adding, the bottom value of the demodulated output signal can be detected. The time constant of the positive or negative peak detection described above is selected so as to be peak-held with respect to the frequency of the data signal and to follow a signal fluctuation having a frequency sufficiently lower than the frequency of the data signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an internal configuration of an FSK demodulation circuit.

FIG. 2 is a block diagram illustrating an internal configuration of a bottom detection circuit.

FIG. 3 is a diagram showing a signal waveform in an FSK demodulation circuit.

FIG. 4 is a diagram illustrating a signal waveform in a bottom detection circuit.

FIG. 5 is a diagram illustrating data string reproduction in the FSK demodulation circuit.

FIG. 6 is a flowchart illustrating an operation of the FSK demodulation circuit.

FIG. 7 is a block diagram showing an internal configuration of a conventional FSK demodulation circuit.

FIG. 8 is a diagram showing a signal waveform in a conventional FSK demodulation circuit.

FIG. 9 is a diagram showing data string reproduction in a conventional FSK demodulation circuit.

[Explanation of symbols]

 Reference Signs List 10 FSK demodulation circuit 1 Peak detection circuit 2 Bottom detection circuit 21 Negative peak detection circuit 3 Threshold circuit 4 Comparator 20 Conventional FSK demodulation circuit 23 LPF 24 Comparator

Claims (6)

[Claims] 1. A waveform shaping circuit comprising a comparison unit for comparing an input analog signal with a reference signal generated by a reference signal generation unit and outputting a digital signal, wherein the reference signal generation unit includes: A waveform shaping circuit for generating a median value of peak-to-peak values (PP values) of analog signals to be generated as the reference signal. 2. The method according to claim 1, wherein the reference signal generation means includes first peak detection means for holding a peak signal of the input analog signal, and second peak detection means for holding a bottom signal of the input analog signal. 2. The waveform shaping circuit according to claim 1, further comprising: generating, as the reference signal, a median value after adding the detection signals held in the first and second peak detection means. 3. The second peak detection means holds subtraction means for subtracting a predetermined signal value from the input analog signal, and a negative peak signal of the subtraction signal output from the subtraction means. A third peak detecting unit; and an adding unit that adds the detection signal held by the third peak detecting unit and the predetermined signal value. The signal output from the adding unit is 3. The waveform shaping circuit according to claim 2, wherein the waveform shaping circuit holds the signal as a bottom signal. 4. A waveform shaping method for a waveform shaping circuit comprising a comparing means for comparing an input analog signal with a reference signal generated by a reference signal generating means and outputting a digital signal. A waveform shaping method, comprising: a reference signal generating step of generating a median of peak-to-peak values (PP values) of signals as the reference signal. 5. The reference signal generating step includes: a first peak detecting step of holding a peak signal of the input analog signal; and a second peak detecting step of holding a bottom signal of the input analog signal. 5. The waveform shaping according to claim 4, further comprising: generating, as the reference signal, a median value after adding the detection signals held in the first and second peak detection steps, respectively. Method. 6. The second peak detection step includes a subtraction step of subtracting a predetermined signal value from the input analog signal, and holding a negative peak signal of the subtraction signal output in the subtraction step. A third peak detection step, and an addition step of adding the detection signal held in the third peak detection step and the predetermined signal value, wherein the signal output in the addition step is 6. The waveform shaping method according to claim 5, wherein the waveform is held as a bottom signal.