JPH04172002A - Frequency modulation circuit by pll control - Google Patents

Abstract

PURPOSE:To keep a modulation degree to be constant towards the carrier of an arbitrary frequency by independently providing a variable capacitor C which changes the frequency of the carrier, and a variable capacitor C for modulation. CONSTITUTION:A VCO is equipped with a variable capacitor C2 for controlling a carrier oscillation frequency, a variable capacitor C3 for modulation to which a modulation signal is inputted, and a modulation degree correcting voltage generating circuit 24. Then, a voltage for controlling the VCO outputted from a PLL control part 112 is inputted to the variable capacitor C2 for the carrier oscillation. On the other hand, a modulation degree correcting voltage outputted from the modulation degree correcting voltage generating circuit 24 is inputted to the variable capacitor C3 for modulation, and the modulation degree of the modulation signal is kept to be constant at the time of changing the frequency of the carrier. Thus, a frequency modulation circuit by a PLL control in which the modulation degree is constant even at the time of changing the frequency of the carrier, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a circuit for arbitrarily setting a frequency and keeping the degree of modulation constant when performing RF multiplied signal wireless or wired communication.

(Prior Art) FIG. 3 shows the circuit configuration of a conventional FM modulation circuit using PLL control.

The voltage controlled oscillator circuit (hereinafter referred to as VCO) has fixed coil 1.
01 (hereinafter referred to as fixed), variable capacitor 102 (hereinafter referred to as variable C), capacitors 103 to 105 (hereinafter referred to as C
) and a transistor 106 (hereinafter referred to as TR), and the collector of TR 106 is grounded to the power supply (hereinafter referred to as Vcc) through a choke coil 107 and bypass capacitors 108 and 109, making it a collector-grounded type circuit. .

The output of the VCO is taken out from the emitter of TR106, and one is connected to the F through a coupling capacitor 110.
This becomes the output of the M modulation circuit, and the other is input to the phase-locked loop control section (hereinafter referred to as PLL control section) 112 through the coupling capacitor Ill.

Here, resistors (hereinafter referred to as R) 113 and R114 are load resistances of the emitter of TR106. The signal input to the PLL control unit 112 is frequency-divided by a frequency divider 115, and the output whose phase is compared by a phase comparator 116 passes through a low-pass filter (hereinafter referred to as LPF) 117 and becomes the control voltage of the VC○. variable C through current control resistor 118
It is input to lO2 and is called a phase-locked loop (hereinafter referred to as PLL).
) is completed.

To change the oscillation frequency, the microcomputer 119 sets the division ratio of the frequency divider 115, and thereby the
This is done by changing the control voltage of C102 and changing the capacitance of variable C102.

The modulation signal is input to the fixed L 101 via Cl2O, which changes the reverse voltage of the variable C102 and outputs the variable Cl
FM modulation is applied by changing the O2 capacity. Here, R12 for fixed LIOI and variable ClO2
1 is for DC grounding, and C122 is for high frequency grounding.

(Problem to be Solved by the Invention) In the above circuit, since the variable C for changing the frequency of the carrier wave and the variable C for modulation are used, even if the input level of the modulation signal is constant, the frequency of the carrier wave If this is changed, the degree of modulation changes as shown in FIG. 5 due to the reverse voltage-capacitance characteristic of the variable C shown in FIG.

An object of the present invention is to solve the above problems, and to provide an FM modulation circuit using PLL control in which the degree of modulation remains constant even when the frequency of a carrier wave is changed.

(Means for solving problems) Books! @ Akira's FM modulation circuit with PLL control has a fixed L,
It is composed of a VCO consisting of a variable C and a TR, and a PLL control section, and this VCO is equipped with a variable C for carrier wave oscillation frequency control, a variable C for modulation into which a modulation signal is input, and a voltage generation circuit for correcting the degree of modulation. , the VCO control voltage output from the PLL control section is input to the variable C for carrier wave oscillation, while the modulation degree correction voltage output from the modulation degree correction voltage generating circuit is input to the variable C for modulation. is entered in
The modulation degree of the modulation signal is kept constant when the frequency of the carrier wave is changed.

Further, the modulation degree correction voltage is configured to be determined from a voltage difference between the VCO control voltage and the power supply voltage, which are output from the PLL control section.

(Function) In the present invention, since the degree of modulation is kept constant for a carrier wave of an arbitrary frequency, when the output of a transmitter equipped with this FM modulation circuit is demodulated by a receiver, the demodulated signal output is A demodulated output of a constant level can be obtained without the level changing depending on the reception frequency.

(Example) An example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. In the same figure, the VCO is fixed L1, variable C2°3, C4 to C
7 and TR8, and the collector of TR8 is grounded to Vcc by a choke coil 9 and bypass capacitors 10 and 11, making it a collector-grounded type circuit.

The output of the VCO is taken out from the emitter of TR8, one of which is passed through a coupling capacitor 12 to become the output of the FM modulation circuit, and the other is input to the PLL control section through the same coupling capacitor 13. Here R1
4 and R15 are the emitter load resistances of TR8.

The signal input to the PLL control section is frequency-divided by a frequency divider 16, and the phase is compared by a phase comparator 17, and the output is output from the LPF1.
8, it becomes the control voltage of the VCO, and is input to the variable C2 through the current control resistor 19, completing the PLL circuit.

The oscillation frequency is changed by setting the frequency division ratio of the frequency divider 16 by the microcomputer 20, thereby changing the control voltage of the VCO and changing the capacitance of the variable C2.

The modulation signal is adjusted to an appropriate level by R22 via C21 and inputted to the variable C3, thereby changing the reverse voltage of the variable C3 and changing the capacitance of the variable C3.
FM modulation is applied. Here, C23 is for high frequency grounding with respect to variable C3.

Next, the operation of the present invention will be explained.

The modulation degree of the modulated signal on a carrier wave of an arbitrary frequency is variable C
2 and the capacitances C4 to C7 of the variable C3, and the ratio of the minute change ΔC of the capacitance of the variable C3 with respect to a modulation signal input of a constant level. However, if the frequency of the carrier wave is changed, the combined capacitance Ct of the capacitances of variable C2 and variable C3 and the capacitances of C4 to C7 will change, so even if the modulation signal input is at a constant level, the amount of slight change ΔC in the capacitance of variable C3 will change. Even if is constant, the degree of modulation will change.

Therefore, a correction voltage is applied to the variable C3 by the correction voltage circuit 24, and as the combined capacitance Ct changes when the frequency of the carrier wave changes, the capacitance of the variable C3 changes slightly in response to a modulation signal input of a constant level. The degree of modulation is kept constant by changing the amount ΔC and keeping the ratio of the variable C2 and composite capacitance Ct and the minute change amount ΔC constant.

Next, FIG. 2 shows a second embodiment of the FM modulation circuit.

In the same figure, VC○ has a fixed L51, variable C52, 53,
The LC oscillation circuit consists of C54 to C57 and TR58, and T
R58 collector with choke coil 59 and bypass capacitor 60
It is a collector grounded type circuit that is grounded to Vcc at 61°C.

The output of the VCO is taken out from the emitter of TR58,
One becomes the output of the FM modulation circuit through the coupling capacitor 62, and the other is input to the PLL control section through the coupling capacitor 63 as well. Here R
64 and R65 are emitter load resistances. Said P
The signal input to the LL control section is frequency-divided by a frequency divider 16,
The output whose phase has been compared by the phase comparator 17 passes through the LPF 18 and becomes the control voltage of the VC○, and the current control resistor 66
The signal is input to the variable C52 through the PLL circuit to complete the PLL circuit.

The oscillation frequency is varied by setting the frequency division ratio of the frequency divider 16 by the microcomputer 20, thereby changing the control voltage of the CO and changing the capacitance of the variable C52.

The modulation signal is adjusted to an appropriate level by R68 via C67 and input to the variable C53, thereby changing the reverse voltage of the variable C53 and changing the capacitance of the variable C53, thereby increasing the FM modulation. Here, C69 is variable C53
This is for high frequency grounding.

In this embodiment, the VCO is used as the correction voltage of the variable C53.
The control voltage of R70 and variable resistor (hereinafter referred to as VR) 7
By dividing it by 1 and inputting it to the anode of the variable C53, and inputting Vcc to the cathode of the variable C53 through R72 and R68, the voltage at which the difference between the control voltage of the vc○ and the power supply voltage Vcc is found is variable. The voltage is applied to C53 and the voltage is adjusted by VR71 so that the degree of modulation is constant regardless of the frequency of the carrier wave.

(Effects of the Invention) According to the present invention, the modulation degree on the transmitting side can be kept constant, and the output level can be obtained at a constant level without changing the output level when the receiving frequency changes on the receiving side. , its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the FM modulator of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the FM modulator of the present invention, and FIG. 3 is a conventional FM modulator. FIG. 4 is a diagram showing the reverse voltage-capacitance characteristic of variable C, and FIG. 5 is a diagram showing the carrier frequency-modulation degree characteristic of a conventional FM modulator. 1.51...Fixed coil for oscillation, 2,52...Variable capacitor for oscillation, 3,53...Variable capacitor for modulation, 4,5,6,7゜54, 55.56.57.
...Oscillation capacitor, 8.58...Oscillation transistor, 9,59...Choke coil, 10.11.
60.61-・pass capacitor, 14.15.64.65・
...Load resistor, 12. +3.62.63...Coupling capacitor, 16...Frequency divider, 17...Phase comparator, 18...Low pass filter, 19°66.
...Current control resistor, 20...Microcomputer, 22, 68
...Modulation signal level adjustment resistor, 21, 67...
Modulation signal input coupling capacitor, 23.69・
... Capacitor for high frequency grounding, 24 ... Correction voltage circuit, 70° 72 ... Resistor, 71 ... Variable resistor for adjusting correction voltage. Patent applicant Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] (1) Fixed coil (hereinafter referred to as fixed L), variable capacitor (hereinafter referred to as variable C), and transistor (hereinafter referred to as TR
In a variable frequency FM modulation circuit composed of a voltage controlled oscillator circuit (hereinafter referred to as VCO) and a phase-locked loop control section (hereinafter referred to as PLL control section),
The VCO includes a variable C for carrier wave oscillation frequency control, a variable C for modulation into which a modulation signal is input, and a voltage generation circuit for modulation degree correction, and a VC output from the PLL control section.
O control voltage is input to the variable C for carrier wave oscillation, while the modulation degree correction voltage output from the modulation degree correction voltage generation circuit is input to the modulation variable C, and the frequency of the carrier wave is adjusted. An FM modulation circuit using PLL control, characterized in that the degree of modulation of a modulation signal is kept constant when the degree of modulation is changed. (2) FM modulation by PLL control according to claim (1), characterized in that the modulation degree correction voltage is obtained from the voltage difference between the VCO control voltage output from the PLL control section and the power supply voltage. circuit.