JPH06188762A - Fsk receiving device - Google Patents

Abstract

PURPOSE:To adjust filter characteristics which enable accurate signal restoration of an input signal without any influence of temperature, etc. CONSTITUTION:A control circuit 6 measures the pulse signal width of the output signal of a waveform shaping circuit 5 by sampling detection and compares it with predetermined reference signal values as pulse widths when filters 1 and 2 are normal, thereby obtaining the differences in signal width from the normal states of pulse widths of signals 1 and 2. Delay becomes long judging from the filter characteristics when the band is narrow, so a tuning frequency shifts to a side corresponding to a frequency having a large difference. For the purpose, the control circuit 6 varies the control voltage of a voltage- dependency capacity varying element 7 consisting of a varicap to vary the capacity that the tuning frequency shifts to a frequency side corresponding to pulses having the large difference. Consequently, the tuning frequency shifts to the desired frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an FSK receiving device that receives an SK signal.

[0002]

2. Description of the Related Art In a high frequency filter circuit, in order to secure a signal band including fluctuations in frequency due to temperature, etc.,
The filter band needs a sufficient margin, cannot necessarily be narrowed, and sensitivity and selectivity cannot be further improved. Further, adjustment of the filter is indispensable for stabilizing the band at the time of manufacture, and the influence of temperature and the like is unavoidable at the time of use.

As a means for solving this, a superheterodyne receiver shown in FIG. 7 will be described. The circuit configuration shown in FIG. 7 includes a frequency conversion circuit 11 that converts an input frequency into an IF frequency, a local frequency oscillation circuit 12 that outputs a reference signal for conversion to the frequency conversion circuit 11, and an output signal of the frequency conversion circuit 11. Filter 13 for band limiting
An IF amplifier 14 that amplifies the output signal of the IF filter 13, a detection circuit 15 that detects the output signal of the IF amplifier 14 and demodulates it into a baseband signal, and a smoothing circuit 16 that smoothes the output signal of the detection circuit 15. Is equipped with.

Further, a reference voltage generating circuit 17 for generating a reference voltage corresponding to the case where the center frequency of the filter and the input signal is normal, and the output signal of the smoothing circuit 16 and the reference of the reference voltage generating circuit 17. Sensitivity calculator 18 that compares the voltage and calculates the sensitivity from the voltage difference from the reference voltage
And a control circuit 19 for varying the frequency of the local frequency oscillating circuit 12 so that the sensitivity becomes stable on the basis of the data of the sensitivity calculating section 18.

The control circuit 19 is in the best state in accordance with the frequency of the input signal in order to fix the frequency when the sensitivity becomes stable.

[0006]

However, the above method has the following problems. That is, since the incoming radio wave intensity fluctuates depending on the communication state (fading or the like), the detection circuit 15 as shown in FIG.
Of the output voltage fluctuates, and it takes time to determine the sensitivity level. In other words, in order to search for the best sensitivity level, it is necessary to shift the frequency up and down, and the deviation between the initial reception state and the incoming wave frequency is unknown. Becomes longer.

Even if the filter characteristic is adjusted to match the best frequency due to fluctuations in temperature or the like, a waveform as shown in FIG. There is a time difference. On the other hand, since the control circuit 19 makes the determination using the smoothed signal, when the output signal of the detection circuit 15 is waveform-shaped, a difference occurs in the pulse width of the output signal (see FIG. 8C. )
₂ -T ₃ ).

Therefore, the filter characteristics are not completely compensated. From these problems, it is impossible to compensate the filter characteristic only by changing the IF frequency, and it is necessary to improve the filter characteristic. The present invention has been provided in view of the above-mentioned points, and has an object to adjust a filter characteristic that enables accurate signal restoration for an input signal without being affected by temperature or the like. A device is provided.

[0009]

According to the present invention, there is provided a first filter which allows a received signal to pass therethrough, a second filter which is cascade-connected to the first filter, the first filter and the second filter. A tuning circuit having variable elements such as inductance and capacitance added to the connection point of, a detection circuit for detecting the output signal of the second filter, and a waveform shaping circuit for shaping the output signal of the detection circuit, A control circuit is provided which measures the signal width of the pulse signal output from the waveform shaping circuit, compares it with a predetermined time width, and uses the comparison result to adjust the synchronization frequency of the tuning circuit. is there.

[0010]

According to the present invention, by measuring the pulse width of the received signal and controlling the variable elements such as the inductance and capacitance of the tuning circuit from the control circuit so that there is no band ripple of the filter characteristic from the difference. It is possible to flatten the in-band frequency characteristics of the filter, reduce the difference due to frequency, and perform stable signal restoration, and further improve stability because temperature and other corrections are performed at any time. Therefore, the filter characteristics are always properly adjusted, and the influence of temperature or the like can be reduced. further,
Since it is detected by the pulse width, it can be appropriately adjusted regardless of the receiving state regardless of the input signal level, and is an effective means for accurately restoring the signal. Further, when this means is used, it is not necessary to inspect and adjust the filter characteristics in manufacturing, and the improvement can be achieved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows an overall block diagram of the present invention, which includes a first filter 1 for passing a received signal, a second filter 2 cascade-connected to the first filter 1, a first filter 1 and a second filter 2. The tuning circuit 3 added to the connection point of the second filter 2, the detection circuit 4 for detecting the output signal of the second filter 2, the waveform shaping circuit 5 for shaping the output signal of the detection circuit 4, and the above waveform. The control circuit 6 measures the signal width of the pulse signal output from the shaping circuit 5, compares it with a predetermined time width, and uses the comparison result to adjust the synchronization frequency of the tuning circuit 3. ing.

FIG. 5 shows a filter response waveform diagram for demodulation.
(A) shows a filter characteristic when the tuning circuit 3 is displaced, (b) shows a signal waveform of a baseband signal to be transmitted (alternating signal of 1, 0), and (c) shows a normal filter. The output waveform of the waveform shaping circuit 5 at the time is shown, and (d) shows the output waveform of the waveform shaping circuit 5 when the tuning is deviated. In FIG. 5A, the frequency f ₁ is 0
And f ₂ corresponds to data 1.

Here, the difference in demodulation due to the filter characteristics is shown.
5, if the filter characteristic is normal, then FIG.
Only the delay of the waveform shaping circuit 5 of τ shown in
The rise and fall times of the voltage are equal,
The restored signal is only delayed by the above τ. F
If the filter characteristic is not flat as shown in FIG.
If you have a frequency f ₁, F₂Corresponding to its output characteristics
Depends on the rising characteristics as shown in FIG.
Compared to the case where the filter has a flat characteristic within 3 dB,
If there is a numerical rise, τ₁(= T₁-T
₂) Delay occurs.

Therefore, in the waveform shaping circuit 5, the pulse width of τ ₁ appears as a signal pulse deleted from the regular signal pulse width. In the control circuit 6, the waveform shaping circuit 5
The pulse signal of is compared with a predetermined regular pulse signal width, and the tuning frequency is shifted to the side corresponding to the shorter pulse width frequency. Control.

From this difference in pulse width, the control circuit 6 changes the frequency-dependent element such as the varicap of the tuning circuit 3 between the filters 1 and 2 to change and change the tuning frequency.
It is designed to provide appropriate filter characteristics. That is, the pulse width of the received signal is measured, and L and C of the tuning circuit 3 are adjusted from the difference so that there is no band ripple of the filter characteristic.
By controlling the variable element of, the in-band frequency characteristics of the filters 1 and 2 are flattened and the difference due to the frequency is reduced, so that the signal is stably restored, and the temperature is corrected at any time. Therefore, the stability will be further increased.

Next, a specific embodiment will be described with reference to FIGS. FIG. 1 is an overall block diagram showing a concrete example of the tuning circuit 3. The first filter 1 is a crystal filter that allows a received signal to pass through, and a crystal similar to the above that is connected in cascade to the first filter 1. A second filter 2 formed of a filter, and a tuning circuit 3 including an element that is added to a connection point between the first filter 1 and the second filter 2 and that can electrically change the capacitance of the L component or the C component, , The second filter 2
Detection circuit 4 for detecting the output signal of, the waveform shaping circuit 5 for shaping the output signal of the detection circuit 4, the signal width of the pulse signal output from the waveform shaping circuit 5 is measured, and the predetermined time is measured. It is composed of a control circuit 6 which performs comparison with the width and adjusts the synchronization frequency of the tuning circuit 3 using the comparison result.

The data 0 is the modulation frequency f₁, Of the data
1 is the modulation frequency f₂The FSK method
The rise of the signal in each circuit corresponding to 1 and 0 of the data
The rise and fall times depend on the filter characteristics.
The filter has a 3 dB bandwidth in-band characteristic that is flat compared to the case where the characteristics are flat.
If there is a shift or fluctuation in the frequency bands of
As shown in FIGS. 2A and 2D, the circuit 4 and the waveform shaping circuit 5 are used.
Delay τ₁(T₁-T ₂) Appears.

Therefore, as shown in FIG. 2 (d), in the waveform shaping circuit 5, a time difference τ ₁ of the pulse signal occurs in either 1 or 0. Here, FIG. 2A shows the filter characteristics when the tuning circuit 3 is displaced, and FIG. 2B shows the signal waveform of the transmitted baseband signal (alternating signal of 1 and 0).
Further, (c) shows the output waveform of the waveform shaping circuit 5 when the filter is normal, and (d) shows the output waveform of the waveform shaping circuit 5 when the tuning is deviated.

Then, the control circuit 6 measures the pulse signal width by sampling and detecting the output signal of the waveform shaping circuit 5, and compares it with the reference signal value which is the pulse width when the predetermined filter is in the normal state. By doing so, the difference in the signal width from the normal state of the pulse width of each of the 1 and 0 signals is obtained.
From the filter characteristics, when the band is narrow, the delay becomes long, so that the tuning frequency is shifted to the side corresponding to the frequency having the larger difference, and therefore the control circuit 6 changes the tuning frequency to a pulse having a large difference. Voltage-dependent capacitance variable element 7 composed of a varicap so as to shift to the frequency side corresponding to
The control voltage of is changed to change the capacity. This will shift the tuning frequency to the desired frequency.

In the detection by the control circuit 6 which brings the filter characteristic into a flat state as shown in FIG. 3, since the reference of the pulse width is known, the arrival time of the input signal can be known. For example, as shown in FIG. 6, by sampling the code states of the signals before and after the reference pulse width, the sampling time can be shortened and the sampling period for one section can be accelerated, so that the pulse width can be accurately measured. Can be detected.

The control circuit 6 fixes and maintains the control voltage until the next signal input in the state where the signal width difference is at a constant level. Since these are corrected within each communication, the filter characteristics are always in an appropriate state.
That is, FIG. 6 shows an example of the sampling method of the control circuit 6, and the sampling method of the control circuit 6 will be described below in more detail with reference to FIG.

In step S1 of FIG. 6, an H level signal is input to the waveform shaping circuit, and the built-in timer is set to 0 in step S2 to start counting. Then, in step S3, when the timer count Ta-Δt is reached, sampling of the output of the waveform shaping circuit 5 is started. Next, in step S4, when the output of the waveform shaping circuit 5 changes to the L level, the time t ₁ from the start of sampling is measured, and the data of t ₁ -Δt is input to the register a in step S5.

In step S6, the timer is set to 0 at the time t ₁ to start counting. In step S7, when the timer count Ta-Δt is reached, sampling of the output of the waveform shaping circuit 5 is started. Then, in step S8, when the output of the waveform shaping circuit 5 becomes H level, the time t ₂ from the start of sampling is measured. Then, as shown in step S9, the data of t ₂ −Δt is input to the register b. The tuning frequency control voltage is raised or lowered by ΔV above or below Va so that the data frequency is divided by Ta of the registers a and b, and the numerical value with one decimal point is further divided by the real number of division.

Next, as shown in step S10, ΔV
When the shift is performed, the time difference is measured in the same manner as above, and it is determined whether or not the measured value is larger than the previous measured value (division result). Here, if it is larger, the voltage is changed to a direction smaller than ΔV in the opposite direction to which the voltage is changed in step S9. If it is smaller, ΔV is further changed in the voltage changing direction.

Then, as shown in step S11, steps S1 to S10 are repeated, and the voltage is fixed when Δt ₁ or less. Next, step S1
As shown in 2, the time width variation of the data is measured at the value fixed in step S11, and when it is larger than Δt ₁ , the same correction as above is performed. From the above, the filter characteristics can be always stabilized.

[0026]

As described above, according to the present invention, the first filter that passes the received signal, the second filter that is connected in cascade to the first filter, the first filter and the second filter are provided.
A tuning circuit having variable elements such as inductance and capacitance added to the connection point of the filter, a detection circuit for detecting the output signal of the second filter, and a waveform shaping circuit for shaping the output signal of the detection circuit. A control circuit is provided which measures the signal width of the pulse signal output from the waveform shaping circuit, compares the signal width with a predetermined time width, and uses the comparison result to adjust the synchronization frequency of the tuning circuit. Therefore, by measuring the pulse width of the received signal and controlling the variable elements such as the inductance and capacitance of the tuning circuit from the control circuit so that there is no band ripple in the filter characteristics from the difference, The frequency characteristics can be flattened, the difference due to frequency can be reduced, and stable signal restoration can be performed. It is possible to further increase the stability from that. Therefore, the filter characteristics are always properly adjusted, and the influence of temperature or the like can be reduced. further,
Since it is detected by the pulse width, it can be appropriately adjusted regardless of the receiving state regardless of the input signal level, and is an effective means for accurately restoring the signal. Further, by using this means, it becomes unnecessary to inspect and adjust the filter characteristics in manufacturing, and it is possible to achieve improvement.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an FSK receiver according to an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the above.

FIG. 3 is a filter characteristic diagram when the above filter characteristic is flat.

FIG. 4 is a block diagram of the above FSK receiving apparatus.

FIG. 5 is an operation waveform diagram of the above.

FIG. 6 is a flowchart showing a sampling method of the above control circuit.

FIG. 7 is a block diagram of a conventional example.

FIG. 8 is an operation waveform diagram of a conventional example.

[Explanation of symbols]

 1 1st filter 2 2nd filter 3 Tuning circuit 4 Detection circuit 5 Waveform shaping circuit 6 Control circuit

Claims (1)

[Claims] 1. A first filter for passing a received signal, a second filter cascade-connected to the first filter, an inductance added to a connection point between the first filter and the second filter, A tuning circuit having a variable element such as a capacitance, a detection circuit for detecting the output signal of the second filter, and a waveform shaping circuit for shaping the output signal of the detection circuit are provided, and output from the waveform shaping circuit. An FSK receiving apparatus comprising a control circuit for measuring a signal width of a pulse signal, comparing the signal width with a predetermined time width, and adjusting a synchronization frequency of the tuning circuit using the comparison result.