JPS5912050B2 - automatic phase control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic phase control circuit suitable for use, for example, in obtaining a local oscillation frequency signal of a tuner of an FM radio receiver, and more particularly, the present invention relates to an automatic phase control circuit suitable for use in obtaining a local oscillation frequency signal of a tuner of an FM radio receiver. The system is designed to continuously obtain oscillation frequency signals and at the same time remove noise when switching local oscillation frequency signals.

A conventional automatic phase control circuit was constructed as shown in FIG.

That is, in FIG. 1, 1 indicates a voltage-controlled variable frequency oscillation circuit, and this variable frequency oscillation circuit 1 has a parallel circuit of a variable capacitor 1a and a coil Ib, and
This parallel circuit has a circuit including a capacitor Ic, a variable capacitance diode Id, and a capacitor Ie connected in parallel. Then, the anode of the variable capacitance diode Id is connected to the control signal input terminal lf. In this way, the capacitance of the variable capacitor 1a is C4, the inductance of the coil Ib is L, and the capacitor Ic and the variable capacitance diode Id are
Let the combined capacitance of the series circuit of capacitor Ie and capacitor Ie be C2,
If the oscillation frequency of variable frequency oscillation circuit 1 is fs, then fs
=・・・・・・(1f2π L(C1+C2)).

Then, the oscillation frequency signal from the output terminal Ig of the variable frequency oscillation circuit 1 is transferred to one input terminal 2a of the phase comparator circuit 2.
A reference signal from the reference signal generation circuit 3 is supplied to the other input terminal 2b.

The output of the phase comparator circuit 2 is then supplied to the control signal input terminal If of the variable frequency oscillation circuit 1 described above via the low-pass filter circuit 4. In such an automatic phase control circuit, assuming that the oscillation frequency fs of the variable frequency oscillation circuit 1 and the oscillation frequency fR of the reference oscillation circuit 3 are fs=NfR (N=1, 2, 3.・・・・・・
... ) is established.

This state will be explained with reference to FIGS. 2 and 3.

In FIGS. 2 and 3, f is the oscillation frequency when no control voltage is supplied to the control voltage supply terminal 1f of the variable frequency oscillation circuit, 2fL is the lock range, and 2fc is the capture range. In the lock state, when the oscillation frequency f of the variable frequency oscillation circuit 1 completely matches Fs, the output voltage of the phase comparator circuit 2 is O, and the variable capacitor 1a is varied manually, for example. , When this capacitance is made smaller and the oscillation frequency f of the variable frequency oscillation circuit 1 is increased from Fs, the output voltage of the phase comparator circuit 2 is the difference between Fs and f in the range of f Fs + FL. A positive voltage corresponding to the voltage is applied to the town capacitive diode 1d via the low-pass filter circuit 4 and the control signal input terminal 1f so as to apply a reverse bias.

Therefore, the combined capacitance C2 including the town capacitive diode 1d is increased to keep the capacitance (C1+C2) constant, and the oscillation frequency of the variable frequency oscillation circuit 1 is kept constant as shown in FIG. Conversely, when the oscillation frequency f of the variable frequency oscillation circuit 1 is decreased from Fs by increasing the capacitance of the town capacitor 1a, the output of the phase comparator circuit 2 decreases in the range of f>Fs-FL. The voltage becomes a negative voltage according to the difference between this f and Fs, and this is the low-pass filter circuit 4,
Town variable capacitance diode 1d via control signal input terminal 1f
is added to increase the reverse bias. Therefore, the combined capacitance C2 including the variable capacitance diode 1d decreases and the capacitance (C
1+C2) is kept constant, and the oscillation frequency of the variable frequency oscillation circuit 1 is kept constant as shown in FIG. Here, when this lock state changes from the state of 01114 to 11 or to the state of
When Fc<FR, a non-lock state occurs between the lock states as shown in FIGS. 2 and 3, and in this non-lock state, the oscillation frequency of the automatic phase control circuit decreases. is the free running frequency of the variable frequency oscillation circuit 1.

When attempting to obtain a local oscillation frequency signal of the tuner of an FM radio receiver using this automatic phase control circuit, unnecessary noise is generated in this unlocked state. By the way, if the total gain of this automatic phase control circuit is G, then 2f
There is a relationship of L+1G.

Therefore, although it is possible to change the lock range and eliminate the non-lock state by changing the total gain, changing the total gain G changes all the constants of the automatic phase control circuit, such as the capture range and noise characteristics, which is not preferable. In view of these points, the present invention is designed to change the lock range in appearance without changing the overall gain G, eliminate the non-lock state, and prevent noise from occurring when the lock frequency changes.

An embodiment of the automatic phase control circuit of the present invention will be described below with reference to FIG.

Components in FIG. 4 having the same functions as those in FIG. 1 are given the same numbers, and detailed explanation thereof will be omitted. 4, the output signal of the low-pass filter circuit 4 is supplied to the input terminal 5a of the controller circuit 5, and the output voltage of the controller circuit 5 is supplied to the control signal input terminal 1f of the variable frequency oscillator 1. supply to.

The input terminal 5a and output terminal 5b of this controller circuit 5 are connected via a resistor 6. However, here, the terminal 5c is a muting signal output terminal. When the potential of the muting signal output terminal 5c is a predetermined positive voltage indicated by the broken line in FIG. 6H, the primary side of the coil L that drives the speaker SP is short-circuited by the switch S. Therefore, the audio output is short-circuited together with noise when switching the local oscillation frequency signal. However, here, the terminal t is an audio signal input terminal. The configuration of this controller circuit 5 is shown in FIG. That is, the output voltage of the low-pass filter circuit 4 is supplied to the Schmitt trigger circuits 7 and 8, respectively, via the input terminal 5a. Here, the output voltage of the Schmitt trigger circuit 7 is normally at ground potential, and when its input voltage exceeds a predetermined threshold voltage, it becomes a predetermined positive potential, and the output of the Schmitt trigger circuit 8 is normally at the ground potential. When the input voltage falls below a predetermined threshold voltage, which will be described later, a predetermined negative level is achieved. When the input voltage of the controller circuit 5 is within a predetermined value, the Schmitt trigger circuits 7 and 8 do not operate, so the controller circuit 5 also does not operate, and the output voltage of the reduced pass filter circuit 4 is The signal is supplied to the control signal input terminal 1f of the variable frequency oscillation circuit 1 through the device 6. Further, the output voltage of the above-mentioned Schmitt trigger circuit 7 is supplied to the base of an NPN transistor 10 forming an inverting amplifier via a capacitor 9 forming a differentiating circuit.
The base of 0 is grounded through a resistor 11 forming a differential circuit. The collector of this transistor 10 is connected via a resistor 12 to a positive power supply terminal 5d to which a positive DC voltage of, for example, +15V is supplied. This transistor 1
Capacitor 13 forming a circuit for differentiating the collector voltage of 0
is supplied to the base of the NPN transistor 14 via
The base of this transistor 14 is connected through a resistor 15 to -
It is connected to the negative power supply terminal 5e to which a negative DC voltage of 15V is supplied. The collector of this transistor 14 is connected to the output terminal 5b via a resistor 24, and the emitter is connected to the negative power supply terminal 5e via a resistor 16. On the other hand, the cathode of a diode 17 is connected to the collector of the transistor 10 described above, and the anode is connected to the positive power supply terminal 5d through a resistor 18, and the PN
Connected to the base of P-type transistor 20. The emitter of this transistor 20 is connected to the power supply terminal 5d, and the collector is grounded via a resistor 21. Further, the collector of this transistor 20 is connected to a muting signal output terminal 5c, and this muting signal output terminal 5c is grounded via a capacitor 22. When the potential of the muting signal output terminal 5c is a predetermined positive voltage, the primary side of the coil L that drives the speaker SP in FIG. 4 is short-circuited by the switch S. Further, the output voltage of the Schmitt trigger circuit 8 mentioned above is supplied to the base of a PNP transistor 24 constituting an inverting amplifier via a capacitor 23 constituting a differentiating circuit, and the base of this transistor 24 is connected to a resistor 29 constituting the differentiating circuit. Ground through. The collector of this transistor 10 is connected to a resistor 2.
5 to the negative power supply terminal 5e. The collector voltage of this transistor 24 is supplied to the base of an NPN transistor 27 via a capacitor 26 constituting a differentiating circuit, and the base of this transistor 27 is connected via a resistor 28 to the positive power supply terminal 5d. Further, the collector of this transistor 27 is connected to the output terminal 5b through the resistor 24, and the emitter is connected to the positive power supply terminal 5d through the resistor 29. On the other hand, the collector of the aforementioned transistor 24 is connected to the base of an NPN transistor 32 via a resistor 31, and the base of this transistor 32 is connected via a resistor 33 to the negative power supply terminal 5e.
The emitter of this transistor 32 is grounded, and the collector is connected to the anode of the diode 17 mentioned above via a resistor 34. When the controller circuit 5 is configured as shown in FIG. 5, the controller circuit 5 performs the following operations.

That is, when the capacitance of the variable capacitor 1a is reduced to change the lock state from the frequency FS1 state to the frequency FS2 state, the output voltage of the low-pass filter circuit 4 increases. , when this output voltage exceeds the threshold value of the Schmitt trigger circuit 7 at the timing indicated by the broken line 1 as shown in FIG. 6A, the output voltage of the Schmitt trigger circuit 7 drops to the ground potential as shown in FIG. 6B. It becomes a predetermined positive potential. This is differentiated by a capacitor 9 and a resistor 11 and supplied to the base of a transistor 10. Therefore, the voltage at the base of this transistor 10 becomes as shown in FIG. 6C. Then this transistor 1
The collector voltage of 0 becomes as shown in FIG. 6D, and this is differentiated by a differentiating circuit composed of a capacitor 13 and a resistor 15, and the base voltage waveform of the transistor 14 becomes as shown in FIG. 6E. Become. This transistor 14 is the sixth
As shown in FIG. return. On the other hand, when the collector voltage of the transistor 10 reaches the ground potential as shown in FIG. The potential of the terminal 5d becomes positive.
After the transistor 20 is turned off at the time indicated by the broken line J, the voltage at the muting signal output terminal 5c is changed to the circuit connected to the capacitor 22 of the resistor 21 and the muting signal output terminal 5c as shown in FIG. 6H. discharges with a time constant determined by the input impedance of When the potential of this muting signal output terminal 5c is a predetermined positive voltage shown by the broken line in FIG. 6H, the speaker SP in FIG.
The primary side of the coil L driving the is short-circuited by a switch S. For this reason, the audio output is short-circuited together with noise when switching the local oscillation frequency signal. This controller circuit 5
The output voltage of the variable frequency oscillator 1 is the control signal of the human power terminal 1
added to f.

The output voltage of the low-pass filter circuit 4 is applied to the control signal input terminal 1f of the variable frequency oscillation circuit 1 via the resistor 6. Since the output voltage of circuit 5 is applied in a superimposed manner, the reverse voltage of variable capacitance diode 1d is as shown in Fig. 6A.
As shown in , the capacitance of the variable capacitance diode 1d decreases. Therefore, since the oscillation frequency Fs of the variable frequency oscillation circuit 1 is expressed by equation (1), this oscillation frequency Fs becomes large. If the increased oscillation frequency Fs of the variable frequency oscillator 1 is within the capture range in the lock state of the frequency FS2, the automatic phase control circuit will increase the frequency Fs as shown in FIG. 6G. enters the lock state. On the other hand, when the capacitance of the town capacitor 1a is increased to change the lock state from the frequency FS1 state to the frequency FS3 state, the output voltage of the low-pass filter circuit 4 decreases. , when this output voltage falls below the threshold value of the Schmitt trigger circuit 8 at the timing indicated by the broken line K as shown in FIG. 7A, the output voltage of the Schmitt trigger circuit 8 becomes negative from the ground potential as shown in FIG. 7B. The potential is . This is differentiated by a capacitor 23 and a resistor 29 and supplied to the base of a transistor 24. Therefore, the voltage at the base of this transistor 24 becomes as shown in FIG. 7C. The collector voltage of this transistor 24 is differentiated by a differentiating circuit composed of a capacitor 26 and a resistor 28, and the voltage of the transistor 24 is
The voltage waveform of the base of 7 is as shown in FIG. 7E. As shown in FIG. 7F, this transistor 27 is turned on only in the period where the base potential is negative, and the potential at the output terminal rises to the positive voltage supplied to the positive power supply terminal 5d for a time indicated by the broken line L. Then go back. On the other hand, when the collector voltage of the transistor 24 reaches the ground potential as shown in FIG. The potential at the base of the transistor 20 decreases and the transistor 20 turns on.
The potential of the collector becomes the positive potential of the positive power supply terminal 5d. After the transistor 20 is turned off at the time indicated by the broken line J, the voltage of the muting signal output terminal 5c is changed to the circuit connected to the capacitor 22 of the resistor 21 and the mutating signal output terminal 5c as shown in FIG. 7H. Discharge occurs with a time constant determined by the input impedance. When the potential of the muting signal output terminal 5e is a predetermined positive voltage indicated by the broken line in FIG. 7H, the primary side of the coil L that drives the speaker SP is short-circuited by the switch S. Therefore, the audio output is short-circuited together with noise when switching the local oscillation frequency signal. The output voltage of this controller circuit 5 is applied to the control signal input terminal 1f of the variable frequency oscillation circuit 1.

Furthermore, the output voltage of the low-pass filter circuit 4 is applied to the control signal input terminal 1f of the variable frequency oscillation circuit 1 via the resistor 6; Since the output voltage of circuit 5 is applied in a superimposed manner, the reverse voltage of variable capacitance diode 1d is as shown in Fig. 7A.
As shown in the figure, the value of this variable capacitance diode 1d decreases rapidly.
The capacity of will increase. Therefore, since the oscillation frequency Fs of the variable frequency oscillation circuit 1 is expressed by equation (1), this oscillation frequency Fs becomes small. If the reduced oscillation frequency Fs of the variable frequency oscillator 1 is within the capture range in the lock state of frequency FS3, the automatic phase control circuit enters the lock state of frequency FS3 as shown in FIG. 7G. . As described above, according to the present invention, by appropriately selecting the threshold voltages of the Schmitt trigger circuits 7 and 8 in the controller circuit 5, the apparent lock range can be increased without changing the overall gain G. The unlocked state can be lost.

A muting signal is output when changing the lock frequency. Therefore, when the automatic phase control circuit according to the present invention is used to obtain the local oscillation frequency signal of the tuner of an FM radio receiver, it is possible to receive each station continuously, and the local oscillation frequency is changed between each station. This prevents the signal from going out of lock and causing unnecessary noise. Further, according to the present invention, since a muting signal is output when switching the local oscillation frequency signal, no noise is generated when switching the local oscillation frequency signal. still,
It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations can be taken without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional automatic phase control circuit, FIGS. 2 and 3 are diagrams explaining the operation of the conventional automatic phase control circuit, and FIG. 4 is an automatic phase control circuit according to the present invention. FIG. 5 is a block diagram showing an example of the essential parts of the automatic phase control circuit according to the present invention, and FIGS. 6 and 7 are lines for explaining the present invention. It is a diagram. 1 is a variable frequency oscillation circuit, 1a is a variable capacitor,
1d is a variable capacitance diode, 2 is a phase comparison circuit, 3 is a reference signal generation circuit, 4 is a low-pass filter circuit, 5 is a controller circuit, and 5c is a muting signal output terminal.

Claims (1)

[Claims] 1. A variable frequency oscillator having oscillation frequency variable means controlled by a control voltage, a phase comparison circuit that compares the output signal of the variable frequency oscillator and a reference signal, and an error signal obtained at the output side of the phase comparison circuit. In the automatic phase control circuit, the control voltage obtained at the output side of the low-pass filter circuit is supplied to the oscillation frequency variable means. A pair of Schmitt trigger circuits that generate a pair of control pulse signals when positive and negative predetermined values are reached, a pair of differentiating circuits that differentiate the respective control pulse signals of these Schmitt trigger circuits, and these differentiating circuits. and a pair of switching transistors driven by the outputs of the switching transistors, and by adding the respective output pulse signals of these switching transistors to the control voltage, the variable frequency oscillator is unlocked and the pair of Schmitt trigger circuits are activated. An automatic phase control circuit characterized in that a muting signal is generated from the output.