JP5042773B2 - FSK modulation circuit - Google Patents

Description

  The present invention relates to an FSK (Frequency Shift Keying) modulation circuit, and more particularly to adjustment of the frequency shift width thereof.

  For FSK modulation circuits used in wireless communication devices such as simple data for calling or wireless communication devices such as specified low power, the occupied frequency bandwidth, adjacent channel leakage power, etc. are determined by the Radio Law. In order to satisfy this, the modulation degree of FSK is adjusted. FIG. 6 is a block diagram showing an electrical configuration of a typical prior art FSK modulation circuit 1. In the FSK modulation circuit 1, the transmission signal from the output port TX such as the CPU 2 is amplified by the transistor 3, and after the waveform shaping for removing harmonic components and noise is performed in the baseband filter (LPF) 4, the oscillation circuit Is given to 5. Then, modulation is performed by the capacitance change of the variable capacitor 7 in the LC parallel resonance circuit 6 in the oscillation circuit 5, and the signal is output from the output terminal 10 of the output circuit 9 to the antenna via the coupling capacitor 8. The LC parallel resonance circuit 6 includes a capacitor 11 and an inductor 12 in parallel with the variable capacitor 7. The output circuit 9 includes a transistor 13 including resonance capacitors 14 and 15.

As described above, in the method of modulating by the capacitance change of the oscillation circuit 5 as described above, the voltage value given to the transistor 3 is set by the variable resistor 16 so as to satisfy the radio standards such as the occupied frequency bandwidth and the adjacent channel leakage power. By adjusting, the voltage applied to the variable capacitor 7 is changed. That is,
f = 1 / 2π√LC
By changing C, the frequency shift is suppressed within a predetermined width.

  In the prior art as shown in FIG. 6, it is necessary to mechanically adjust the variable resistor 16, and the position of the semi-fixed resistor that becomes the variable resistor 16 is recognized by image recognition. An operation of inserting and rotating an adjustment bit is performed. Therefore, it takes time, and when a certain number of adjustments are made, it is necessary to adjust the adjusting device itself such as the amount of protrusion of the bit, and the work is very complicated.

  An object of the present invention is to provide an FSK modulation circuit capable of performing accurate FSK modulation with a simple configuration.

  In the FSK modulation circuit according to the present invention, a switching element is switched according to a transmission signal and a predetermined power supply voltage is applied to a variable capacitor provided in the oscillation circuit, whereby the frequency is changed by changing the capacitance of the variable capacitor due to the transmission signal. In an FSK modulation circuit configured to perform modulation, a PWM circuit that generates a PWM signal, an LPF that smoothes the PWM signal into a DC voltage and supplies the PWM signal to the switching element as the power supply voltage, and the variable capacitance at the power supply voltage And a DC voltage generating means comprising adjusting means for adjusting the pulse period and width of the PWM circuit so that the frequency shift width by the capacitor becomes a predetermined value.

  According to the above configuration, when changing the power supply voltage of the switching element that determines the frequency shift width in the FSK modulation, the DC voltage generating means is provided, and the PWM signal is generated by the PWM (Pulse Width Modulation) circuit provided therein. The PWM signal is smoothed to a DC voltage by an LPF (Low Pass Filter) to create the power supply voltage. Then, the frequency shift width of the transmission signal is monitored externally or internally (own device), and as a result, the adjusting means is configured to adjust the power supply voltage so as to be within the frequency shift width predetermined in the standard. Adjust the pulse period and width of the PWM signal.

  Therefore, in the adjustment at the time of shipment, the frequency deviation width can be adjusted by electrical adjustment such as the adjustment of the OFF timing of the pulse. As a result, the complexity of work such as mechanical adjustment is eliminated, and reliability against deterioration over time can be improved. Also, accurate FSK modulation can be performed with a simple configuration such as a PWM circuit and an LPF.

  In the FSK modulation circuit of the present invention, a table that stores in advance the relationship between the DC voltage value obtained by LPF processing of the PWM signal and the period and pulse width of the PWM signal that realizes the voltage value is provided. And the adjustment means reads a period and a pulse width corresponding to a DC voltage value at which the frequency shift width is a predetermined value from the table, and sets it in the PWM circuit.

  According to the above configuration, the adjusting means writes a table of periods and pulse widths corresponding to each DC voltage value in advance in, for example, the ROM of the CPU, and the adjusting means sets a period corresponding to the desired DC voltage value. In addition, the frequency deviation width can be set to fall within a predetermined width in the standard simply by reading the pulse width from the table and setting it in the PWM circuit.

  Accordingly, it is possible to eliminate the need for complicated calculations in determining the period and pulse width.

  Furthermore, the FSK modulation circuit according to the present invention includes the table corresponding to each channel when corresponding to a plurality of channels.

  According to the above configuration, when supporting a plurality of channels, for example, a table corresponding to each channel is held in an external storage device such as an EEPROM in advance, and when the CPU detects a channel change instruction, the CPU ROM The corresponding channel table is read out from the table, and the channel is changed by changing the table.

  Therefore, it is possible to easily cope with the channel change.

  In the FSK modulation circuit according to the present invention, the adjusting means adjusts a pulse period and a width of the PWM circuit from a reception result of a pair of receivers.

  According to the above configuration, instead of using a measuring device at the time of adjustment in the process, a paired receiver is used to detect the adjustment direction and amount from the deviation of the received signal, and the frequency deviation width is determined in advance. The pulse period and width of the PWM circuit are adjusted so as to be a value.

  Therefore, it is possible to simultaneously calibrate the variation of the frequency discriminator of the paired receiver.

  Furthermore, in the FSK modulation circuit of the present invention, a 1, 0 alternating test signal is used as the transmission signal, and the adjustment means sets an adjustment absolute value based on a deviation from a predetermined reception signal value in a pair of receivers. Detecting and adjusting the pulse period and width of the PWM circuit.

  According to the above configuration, the frequency deviation width can be adjusted by measuring the absolute value of the voltage output of the frequency discriminator of the paired receiver using a 1, 0 alternating test signal as the transmission signal. If necessary, you can know its approximate value.

  Therefore, the adjustment can be completed with a small number of times from 1 degree.

  In the FSK modulation circuit of the present invention, the adjustment means adjusts the pulse period and width of the PWM circuit in response to feedback of the adjustment value from the paired receiver.

  According to the above configuration, when communication from the paired receiver is possible, the pulse period and width of the PWM circuit are adjusted by feeding back the adjustment direction and adjustment value from the receiver side through the communication. To do. Note that communication may be performed particularly for adjustment, and the adjustment direction and adjustment value data may be added to a normal communication format.

  Therefore, a simple configuration does not require a measuring instrument, and real-time calibration is possible in the field.

  As described above, the FSK modulation circuit of the present invention is configured such that the switching element is switched according to the transmission signal and the predetermined power supply voltage is applied to the variable capacitor provided in the oscillation circuit. In the FSK modulation circuit that performs frequency modulation by changing the capacitance of the DC, a DC voltage generating means is provided to change the power supply voltage of the switching element that determines the frequency shift width, and the PWM signal is provided by the PWM circuit provided therein. The PWM signal is generated and smoothed to a DC voltage by an LPF so as to create the power supply voltage, and the frequency deviation width of the transmission signal is monitored externally or internally (own device). The adjustment means controls the pulse period of the PWM signal so that the power supply voltage falls within a predetermined frequency deviation width. And adjusting the width.

  Therefore, in the adjustment at the time of shipment or the like, the frequency deviation width can be adjusted by electrical adjustment such as adjustment of the OFF timing of the pulse. As a result, the complexity of work such as mechanical adjustment is eliminated, and reliability against deterioration over time can be improved. Also, accurate FSK modulation can be performed with a simple configuration such as a PWM circuit and an LPF.

  Further, as described above, the FSK modulation circuit of the present invention stores in advance the relationship between the DC voltage value obtained by LPF processing of the PWM signal and the period and pulse width of the PWM signal that realizes the voltage value. The adjustment means reads from the table a period and a pulse width corresponding to a DC voltage value at which the frequency shift width becomes a predetermined value, and sets the PWM circuit by simply setting the PWM circuit. The frequency deviation width is set to be within a width predetermined by the standard.

  Therefore, it is possible to eliminate the need for complicated calculations in determining the period and the pulse width.

  Furthermore, as described above, the FSK modulation circuit according to the present invention includes the table corresponding to each channel when corresponding to a plurality of channels, and changes the table to be used when there is a channel change instruction.

  Therefore, it is possible to easily cope with the channel change.

  Further, as described above, the FSK modulation circuit of the present invention does not use a measuring device at the time of adjustment in the process, but uses a paired receiver and detects the adjustment direction and amount from the deviation of the received signal, The pulse period and width of the PWM circuit are adjusted so that the frequency shift width becomes a predetermined value.

  Therefore, the variation of the frequency discriminator of the paired receiver can be calibrated at the same time.

  Furthermore, as described above, the FSK modulation circuit according to the present invention uses the 1, 0 alternating test signal as the transmission signal, and sets the absolute adjustment value based on the deviation from the predetermined reception signal value in the paired receiver. Detect and adjust the pulse period and width of the PWM circuit.

  Therefore, by measuring the absolute value of the voltage output of the frequency discriminator of the paired receiver, if the adjustment of the frequency deviation width is necessary, the approximate value can be known, and the adjustment can be performed by 1 It can be completed in less than a few degrees.

  Further, as described above, the FSK modulation circuit of the present invention feeds back the adjustment direction and adjustment value from the receiver side through the communication when the communication from the paired receiver is possible. Adjust the pulse period and width of the circuit.

  Therefore, with a simple configuration, no measuring instrument is required, and real-time calibration is possible in the field.

[Embodiment 1]
FIG. 1 is a block diagram showing an electrical configuration of the FSK modulation circuit 21 according to the first embodiment of the present invention. The FSK modulation circuit 21 is similar to the FSK modulation circuit 1 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In this FSK modulation circuit 21, an amplifying transistor 3, which is a switching element that switches a predetermined power supply voltage according to a transmission signal, an LPF 4 for waveform shaping, and a variable capacitor 7 that performs frequency modulation by changing capacitance are LC-parallel. The oscillation circuit 5 provided in the resonance circuit 6 is the same as the FSK modulation circuit 1.

  It should be noted that the FSK modulation circuit 21 uses the PWM port PWM of the CPU 22 to output a PWM signal, and the DC smoothed output by the LPF 23 is used as the power supply voltage of the transistor 3. Accordingly, the power supply side of the transistor 3 is a fixed resistor 24. The CPU 22 outputs a transmission signal from the output port TX to the transistor 3. When the power supply voltage is lowered, the pulse width of the PWM signal is short, i.e., low duty, and when it is high, the pulse width is long, i.e., high duty.

  FIG. 2 is a diagram for explaining an adjustment method at the time of shipment adjustment of the FSK modulation circuit 21. An antenna 25 is connected to the output terminal 10. The FSK modulation circuit 21 outputs a PWM signal from the PWM port PWM at a pulse period and a pulse width stored in a ROM 26 built in the CPU 22. The transistor 3 is switched in response to the transmission signal from the output port TX of the CPU 22 by using the output smoothed to DC by the LPF 23 as a power supply voltage, and the frequency modulation is performed by changing the capacitance of the variable capacitor 7. Thus, an FSK signal is created and transmitted from the antenna 25.

  When a measuring instrument (not shown) composed of a spectrum analyzer or the like receives the FSK signal and the frequency shift width is out of the standard, the operator can adjust the PWM signal so that the value is within the standard. The adjustment values of the pulse period and width are obtained, and the values stored in the ROM 26 in the CPU 22 are rewritten from the personal computer 27. The same operation is repeated, and when the frequency deviation width is within the standard, the value of the ROM 26 is stored in the nonvolatile EEPROM 28 provided outside, and the adjustment operation is completed. When the power is turned on, the CPU 22 copies the contents of the EEPROM 28 to the ROM 26 and adjusts the power supply voltage of the transistor 3. Therefore, the CPU 22 as the PWM circuit and the LPF 23 constitute DC voltage generating means, and the CPU 22 and the personal computer 27 constitute adjusting means.

  With this configuration, the power supply voltage of the transistor 3 that determines the frequency shift width in FSK modulation can be adjusted by electrical adjustment such as adjustment of the pulse OFF timing in the PWM signal. As a result, the complexity of work such as mechanical adjustment is eliminated, and reliability against deterioration over time can be improved. Further, accurate FSK modulation can be performed with a simple configuration such as the PWM port PWM and the LPF 23 mounted on the CPU 22.

[Embodiment 2]
FIG. 3 shows the contents stored in the ROM in the FSK modulation circuit according to the second embodiment of the present invention. In the present embodiment, the configuration of the FSK modulation circuit 21 shown in FIG. 1 described above can be used. It should be noted that in this embodiment, the stored contents of the EEPROM 28 are as shown in FIG. It is that. That is, the EEPROM 28 stores in advance a table showing the relationship between the DC voltage value obtained by LPF processing of the PWM signal and the period and pulse width of the PWM signal that realizes the voltage value. From 27 to the CPU 26, a DC voltage value applied to the transistor 3 as a power supply voltage is input according to the measured frequency shift width. The CPU 26 reads the period and pulse width corresponding to the voltage value from the table of the EEPROM 28 and sets them in the ROM 26.

  Therefore, in determining the period and the pulse width, the frequency shift width can be set to fall within a predetermined width in the standard without performing complicated calculations.

  Further, the table is stored in advance for each of a plurality of channels to be used. When the CPU 32 detects a channel change instruction by a dip switch or the like in actual use, the table corresponding to the channel to be used is selected from the EEPROM 38. The contents may be copied to the ROM 36. With this configuration, it is possible to easily cope with the channel change in addition to making a complicated calculation unnecessary.

[Embodiment 3]
FIG. 4 is a block diagram of an FSK receiver for explaining a method of adjusting the FSK modulation circuit according to the third embodiment of the present invention. Also in this embodiment, the FSK modulation circuit 21 shown in FIG. 1 can be used. It should be noted that in this embodiment, a measuring device such as the above-described spectrum analyzer is not used at the time of adjustment in the process, but a paired receiver is used, and the adjustment direction and amount are determined from the deviation of the received signal. And the personal computer 27 adjusts the pulse period and width of the PWM signal from the PWM port PWM of the CPU 31.

  Specifically, the FSK receiver simply mixes the received signal from the antenna 41 and the signal from the local oscillation circuit 42 with a mixer 43, as shown in FIG. By discriminating the signal with the frequency discriminator 44, the difference in frequency of the 1 and 0 signals is output as the difference in voltage. Therefore, the voltage output of the frequency discriminator 44 is measured, and when the voltage is biased to the high side as a result of applying the 1,0 alternating signal having a uniform 1,0 to the transmission side, the power supply voltage is high. Therefore, if the duty is lowered to lower the power supply voltage and biased to the lower side, the power supply voltage is biased to the lower side. Increase the duty.

  With this configuration, it is possible to simultaneously calibrate the variation of the frequency discriminator 44 of the paired receiver.

  Further, when the 1, 0 alternating test signal is used as a transmission signal, the paired receivers can detect an adjustment absolute value from a deviation from a predetermined reception signal value. The pulse period and width of the PWM signal are adjusted from the adjusted absolute value. Specifically, when the absolute value of the voltage output of the frequency discriminator 44 is measured using the 1, 0 alternating test signal, if adjustment is necessary, the adjustment direction and the approximate value of the adjustment value are known. Can do. This is because the absolute value of the measured voltage can be read as a frequency by comparing it with the characteristic curve of the frequency discriminator 44 shown in FIG. 5, and it is possible to know how much the frequency is deviated from the reference value. It is possible. This is because the frequency shift width can be converted to the voltage value again corresponding to the voltage sensitivity (MHz / V or kHz / V) of the oscillation circuit 5 on the transmission side.

  In this way, it is possible to know how much the displacement is in which direction, and for example, the adjustment value can be known by applying to a table as shown in FIG. As a result, the adjustment can be completed in a small number of times from 1 degree.

  Furthermore, when communication from the paired receiver is possible, an adjustment value is fed back through the communication, and the adjustment period is adjusted by the CPU 22 so that the pulse period of the PWM signal from the PWM port PWM is adjusted. By adjusting the width and width, it is possible to calibrate in real time in the field with a simple configuration, without requiring a measuring instrument. In that case, communication may be performed particularly for adjustment, and the adjustment direction and adjustment value data may be added to a normal communication format.

1 is a block diagram showing an electrical configuration of an FSK modulation circuit according to a first embodiment of the present invention. It is a figure for demonstrating the adjustment method at the time of shipment adjustment of the said FSK modulation circuit. It is a figure which shows the storage content of ROM in the FSK modulation circuit which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the example of a simplified structure of a FSK receiver. It is a graph which shows the characteristic curve of the frequency discriminator of a FSK receiver. It is a block diagram which shows the electric constitution of a typical prior art FSK modulation circuit.

Explanation of symbols

3 Transistor 4 Baseband filter (LPF)
5 Oscillation Circuit 6 LC Parallel Resonance Circuit 7 Variable Capacitor 9 Output Circuit 21 FSK Modulation Circuit 22 CPU
23 LPF
24 Fixed resistance 25, 41 Antenna 26 ROM
27 Personal computer 28 EEPROM
42 Local oscillator circuit 43 Mixer 44 Frequency discriminator

Claims (6)

FSK modulation in which a predetermined power supply voltage is switched by a switching element according to a transmission signal and applied to a variable capacitor provided in an oscillation circuit, thereby performing frequency modulation by changing the capacitance of the variable capacitor according to the transmission signal. In the circuit
A PWM circuit that generates a PWM signal, an LPF that smoothes the PWM signal into a DC voltage and applies the power supply voltage to the switching element, and a frequency shift width by the variable capacitor at the power supply voltage is a predetermined value. An FSK modulation circuit comprising DC voltage generation means configured to include adjustment means for adjusting the pulse period and width of the PWM circuit. A table that stores in advance the relationship between the DC voltage value obtained by LPF processing of the PWM signal and the period and pulse width of the PWM signal that realizes the voltage value;
2. The FSK modulation according to claim 1, wherein the adjustment unit reads a period and a pulse width corresponding to a DC voltage value at which the frequency shift width is a predetermined value from the table, and sets the period in the PWM circuit. circuit.   3. The FSK modulation circuit according to claim 2, further comprising the table corresponding to each channel when supporting a plurality of channels.   3. The FSK modulation circuit according to claim 1, wherein the adjustment unit adjusts a pulse period and a width of the PWM circuit based on a reception result of a pair of receivers. A 1, 0 alternating test signal is used as the transmission signal, and the adjustment means detects an adjustment absolute value based on a deviation from a reception signal value predetermined for a pair of receivers, and detects the pulse period and width of the PWM circuit. The FSK modulation circuit according to claim 1, wherein the FSK modulation circuit is adjusted. In response to the feedback of the adjustment value from the receiver forming the pair, the adjusting means, FSK modulation circuit according to claim 4 or 5, wherein the adjusting the pulse period and width of the PWM circuit.

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