JPH01149512A - Automatic frequency control circuit - Google Patents

Abstract

PURPOSE:To dispense with the manual adjustment of the self-traveling oscillating frequency of a horizontal oscillating circuit by adding a voltage comparing circuit equipped with a reference voltage source instead of a voltage setting circuit. CONSTITUTION:A voltage comparing circuit 14 compares the voltage of a capacitor 10 and an input voltage from a reference voltage source 15, and applies a feedback to a horizontal oscillating circuit 5 so that the voltage of the capacitor 10 can be made equal to a reference voltage from the reference voltage 15. Consequently, even when the self-traveling oscillating frequency of the oscillating circuit 5 is widely deviated from a synchronizing signal frequency, by the work of the comparing circuit 14, the terminal voltage of the capacitor 10 connected to an LPF 8 is controlled at the reference voltage inputted to the comparing circuit 14, and the self-traveling oscillating frequency of the oscillating circuit 5 is made to approach the synchronizing signal frequency. Consequently, the voltage to be directly inputted from the LPF 8 to the oscillating circuit 5 is also controlled at the input voltage of the reference voltage source 15 inputted to the comparing circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic frequency control (hereinafter referred to as AFC) circuit used in televisions, video tape recorders, and the like.

2. Description of the Related Art A conventional AFC circuit will be explained with reference to the block diagram shown in FIG. First, the signal input terminal 1 is connected to the synchronization signal separation circuit 2, and only the synchronization signal is separated from the television signal input from the signal input terminal 1. An output terminal 3 of the synchronization signal separation circuit 2 is connected to a phase comparison circuit 4, and the separated synchronization signal is input to the phase comparison circuit 4. Further, another input terminal of the phase comparator circuit 4 is connected to a horizontal oscillation circuit 3.
The output terminal 6 of the horizontal oscillation circuit 5 is connected, and the oscillation waveform of the horizontal oscillation circuit 5 is input to the phase comparison circuit 4. And phase comparator circuit 4
compares the phase of the synchronization signal and the horizontal oscillation waveform to generate a signal corresponding to the phase shift. An output terminal 7 of the phase comparison circuit 4 is connected to a low-pass filter circuit (hereinafter referred to as LPF) 8, and an output terminal 9 of the LPF 8 is connected to a capacitor 10. The LPF 8 passes the output signal whose phase has been compared by the phase comparator circuit 4 while blocking high frequency components, and temporally integrates the passed signal using the capacitor 10 . In other words, even if the output of the phase comparison circuit 4 is a signal that changes rapidly over time, it is integrated over time and averaged over time at the output terminal 9 of the LPF 8 due to the action of the capacitor 8. Output with gradual changes can be obtained. Next, the output terminal 9 of the LPF 8 is connected to the horizontal oscillation circuit 5. As a result, a voltage corresponding to the phase shift is fed back to the horizontal oscillation circuit, and the horizontal oscillation frequency is brought closer to the synchronization signal frequency. Further, the horizontal oscillation circuit 5 includes a voltage setting circuit 11 that can generate a variable voltage.
is connected. The oscillation frequency of the horizontal oscillation circuit is determined by the voltage of the voltage setting circuit 11 and L input through the output terminals.
It is determined by the control signal inputted via the output terminal 9 from the PF8. Note that 13 is a signal output terminal for taking out an oscillation signal from the horizontal oscillation circuit 5.

Problems to be Solved by the Invention In FIG. 4, the voltage setting circuit 11 is generally used to set the free-running oscillation frequency of the horizontal oscillation circuit 5. In FIG. That is,
When the output signal from LPF 8 is zero, horizontal oscillation circuit 5
The oscillation frequency of is determined by the voltage of the voltage setting circuit 11. If the free-running oscillation frequency of the horizontal oscillation circuit 11 is different from the synchronization signal frequency of the television signal input to the synchronization separation circuit 2, in order for the horizontal oscillation circuit 5 to synchronize with the synchronization signal, it is necessary to synchronize from the LPF 8. I have to get the output of

Therefore, a signal corresponding to the difference between the synchronizing signal frequency of the input television signal and the free-running oscillation frequency of the horizontal oscillation circuit 5 is generated in the phase comparator circuit 4, and is fed back to the horizontal oscillation circuit 5 via the LPF 8. The free-running oscillation frequency of the horizontal oscillation circuit 5 is
Even if the signal is significantly different from the synchronizing signal, the phase comparator circuit 4 and L
If the output dynamic range of the PF 8 is sufficient, the oscillation frequency of the horizontal oscillation circuit 5 can be locked to the synchronization signal. However, since the output dynamic range cannot exceed the power supply voltage, the free-running oscillation frequency of the horizontal oscillation circuit 5 cannot be brought into a phase-locked state unless it falls within a certain range. Therefore, in order to obtain a stable horizontal oscillation frequency that is phase-synchronized with the synchronization signal, the free-running oscillation frequency of the horizontal oscillation circuit 5 must be adjusted so that the output voltage of the voltage setting circuit 11 is within a certain range around the synchronization signal. must be adjusted manually. Furthermore, when this AFC circuit is mass-produced, variations in the free-running oscillation frequency occur due to the output current value of the phase comparison circuit 4, the frequency characteristics of the LPF 8, the voltage input to the horizontal oscillation circuit 5, etc.

The cause of this variation is that there are variations in the resistance value of the resistor, the capacitance value of the capacitor, and the inductance value of the coil used in each circuit.

Therefore, in order to correct such variations, it is necessary to manually adjust the free-running oscillation frequency of the horizontal oscillation circuit 5 to be almost equal to the synchronization signal using the voltage setting circuit 11.

As explained above, in the conventional AFC circuit,
Manual adjustment of the free-running oscillation frequency of the horizontal oscillation circuit is essential, and the inclusion of this adjustment step has been a major problem during mass production of circuits.

Means for Solving the Problems In the AFC circuit of the present invention, a signal input terminal is connected to a synchronous signal separation circuit, and an output terminal of the synchronous signal separation circuit and an output terminal of the horizontal oscillation circuit are connected to separate inputs of a phase comparison circuit. terminal, the output terminal of the in-phase comparison circuit is connected to a low-pass filter circuit, and the output terminal of the low-pass filter circuit is connected to one input terminal of the voltage comparison circuit, the first capacitor, and the horizontal oscillation circuit. A reference voltage source is connected to the other input terminal of the voltage comparison circuit, an output terminal of the voltage comparison circuit is connected to a second capacitor and the horizontal oscillation circuit, and the output terminal of the horizontal oscillation circuit is connected to the signal output terminal.

According to the AFC circuit of the present invention, the voltage comparison circuit
By comparing the output voltage of F and the reference voltage and applying feedback to the horizontal oscillation circuit so that the output voltage of the LPF becomes equal to the reference voltage, the oscillation frequency of the horizontal oscillation circuit is automatically brought closer to the synchronization signal frequency. You can leave it there.

Embodiment An embodiment of the AFC circuit of the present invention will be described with reference to the block diagram shown in FIG. First, the signal input terminal 1 is connected to the synchronization signal separation circuit 2, and only the synchronization signal is separated from the television signal input from the signal input terminal 1. An output terminal 3 of the synchronization signal separation circuit 2 is connected to a phase comparison circuit 4, and the separated synchronization signal is input to the phase comparison circuit 4.

Further, the output terminal 6 of the horizontal oscillation circuit 5 is connected to another input terminal of the phase comparison circuit 4, and the oscillation waveform of the horizontal oscillation circuit 5 is input to the phase comparison circuit 4, and the phase comparison circuit 4 receives the synchronization signal. and the phase of the horizontal oscillation waveform. The output terminal 7 of the phase comparison circuit 4 is connected to the LPF 8, and the output terminal 9 of the LPF 8 is connected to the capacitor 10. The LPF 8 passes the output signal whose phase has been compared by the phase comparator circuit 4 while blocking high frequency components, and passes the passed signal to the capacitor 1.
Integrate over time using 0. Output terminal 9 of LPF8
is connected to the horizontal oscillation circuit 5, and the output signal of the LPF 8 is fed back to the horizontal oscillation circuit 5. Further, the output terminal 9 of the LPF 8 is connected to one input terminal of the voltage comparison circuit 14, the reference voltage source 15 is connected to the other input terminal of the voltage comparison circuit 14, and the output terminal 16 of the voltage comparison circuit 14 is connected to the horizontal It is connected to the oscillation circuit 5, compares the voltage of the capacitor 10 with a reference voltage, and outputs the comparison result to the horizontal oscillation circuit 5.

Note that a capacitor 17 is connected to the output terminal 16 of the voltage comparison circuit 14, and integrates the comparison result of the voltage comparison circuit 14 over time. In other words, even if the comparison result of the voltage comparison circuit 14 is a comparison result that changes rapidly over time,
By the action of the capacitor 17, the comparison result is converted into a signal that changes gradually over time. The AFC circuit of the present invention shown in FIG. 1 differs from the conventional example shown in FIG. What I did was different.

Next, the operating waveforms of the AFC circuit of the present invention are shown in FIG.
The circuit operation will be explained with reference to this. In Figure 2, a
is the output terminal 30 waveform of the synchronization signal separation circuit 2, b is the oscillation waveform of the output terminal 60 of the horizontal oscillation circuit 5, and C is the phase comparator circuit 4.
, d is the waveform at the output terminal 9 of the LPF 8 , and e is the waveform at the output terminal 16 of the voltage comparison circuit 14 .

In addition, in this operation waveform diagram, the AFC circuit is the horizontal oscillation circuit 5.
This figure shows the waveform in a phase synchronized state (locked state) where the waveform of the synchronizing signal and the synchronizing signal are in phase. That is, the output waveform of the horizontal oscillation circuit 5 oscillates around the voltage v0, and the timing t3° at which the oscillation waveform intersects the voltage v0 while changing from a low potential to a high potential is caused by the synchronization separation circuit. Low potential of a which is the output waveform of 2 (synchronization signal)
coincides with the center of the period. The phase comparator circuit 4 operates only during the synchronization signal period and stops operating during other periods.

Furthermore, the phase comparator circuit 4 determines that the voltage of the oscillation waveform is equal to the voltage v0.
When the voltage of the oscillation waveform is lower than the voltage v0, a positive polarity current is output, and when the voltage of the oscillation waveform is higher than the voltage v0, a negative polarity current is output. In addition,
to and td shown on the time axis are for showing the function of the phase comparison circuit 4, jO is the period during which the phase comparison circuit 4 outputs a positive polarity current (+), and td is the period when the phase comparison circuit 4 outputs a positive polarity current (+). 4 is a period during which a negative polarity current (-) is output.

Next, since the output of the phase comparison circuit 4 is integrated through the LPF 8, the output waveform of the LPF 8 becomes a waveform as shown in d. When the AFC circuit is in a locked state, jc=td, and the positive and negative output currents of the phase comparator circuit 4 are equal, and the output current is applied to the LPF 8 in one horizontal period (IH) between one synchronization signal and the next synchronization signal. The sum of flowing charges is zero.

Therefore, the output waveform d of LPF 8 performs charging (1o period) and discharging (td period) during the synchronous signal period, but since the amount of charge and the amount of discharged charge are equal, the output waveform d after the synchronous signal period ends before the synchronous signal period. Therefore, since a constant voltage (Vpo) is applied to the horizontal oscillation circuit 5, the waveform output from the horizontal oscillation circuit 5 is fixed. becomes.

In addition, in this locked state, the waveform e output from the voltage comparison circuit 14 is equal to the reference voltage V output from the reference voltage source.
It becomes s.

FIG. 3 shows waveforms when the AFC circuit is in an asynchronous state, where 0 is the output waveform of the synchronization signal separation circuit 2, p is the oscillation waveform of the horizontal oscillation circuit 5, and the output waveform of the synchronization signal separation circuit 2 is 0.
This shows a state in which the phase is more advanced than that of . Further, r is an oscillation ferry of the horizontal oscillation circuit 5, which indicates a state in which the phase is delayed from the output waveform 0 of the synchronization signal separation circuit 2. q indicates the waveform output from the phase comparison circuit 4 for the oscillation waveform p whose phase is advanced from the horizontal oscillation circuit 5, and S indicates the waveform output from the phase comparison circuit 4 for the oscillation waveform r whose phase is delayed from the horizontal oscillation circuit 5. This shows the waveform. When the phase of the horizontal oscillation waveform p is ahead of the synchronization signal waveform 0, the output current of the phase comparison circuit 4 has a large amount of negative polarity current (
As a result, the output voltage of the LPF 8 decreases. LPF
When the output voltage of horizontal oscillation circuit 8 decreases, the oscillation waveform of horizontal oscillation circuit 5 is controlled so that the phase thereof is delayed. On the other hand, if the phase of horizontal oscillation source form r lags behind synchronization signal waveform 0,
The output current of the phase comparison circuit 4 has a large positive polarity current, and the L
The output voltage of PF8 increases. When the output voltage of the LPF 8 increases, the oscillation waveform of the horizontal oscillation circuit 5 is controlled to advance in phase. In this way, by comparing the phases of the waveform of the horizontal oscillation circuit 5 and the synchronization signal waveform, a horizontal oscillation waveform whose phase is synchronized with the synchronization signal can be obtained.

Next, the operation of the voltage comparison circuit 14 will be explained. The voltage comparator circuit 14 compares the voltage of the capacitor 10 with the reference voltage source 1.
5, and feedback is applied to the horizontal oscillation circuit 5 so that the voltage of the capacitor 10 becomes equal to the reference voltage 12 from the reference voltage source. Therefore, even if the free-running oscillation frequency of the horizontal oscillation circuit 5 deviates significantly from the synchronizing signal frequency, the terminal voltage of the capacitor 10 connected to the LPF 8 will be
The free-running oscillation frequency of the horizontal oscillation circuit is controlled by the reference voltage input to 4 and is brought close to the synchronizing signal frequency.

Therefore, the voltage directly inputted from the LPF 8 to the horizontal oscillation circuit 5 is also controlled to the input voltage of the reference voltage source 15 inputted to the voltage comparison circuit 14.

As explained above, in the AFC circuit of the present invention, the free-running oscillation frequency of the horizontal oscillation circuit is automatically made thicker (closer to the synchronization signal frequency) by the voltage comparison circuit, and delicate phase control is performed using the LPF 8. The output voltage is determined by a signal directly input to the horizontal oscillation circuit 5.

Effects of the Invention According to the AFC circuit of the present invention, there is no need to adjust the free-running oscillation frequency of the horizontal oscillation circuit, and even if there is initial variation in the free-running oscillation frequency, stable phase-synchronized oscillation is automatically achieved. Waveforms can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the AFC circuit of the present invention, FIG. 2 is an operating waveform diagram of the AFC circuit in a phase-locked state, and FIG. 3 is an operating waveform diagram of the AFC circuit in a non-phase-locked state.
FIG. 4 is a block diagram of a conventional AFC circuit. DESCRIPTION OF SYMBOLS 1... Signal input terminal, 2... Synchronous signal separation circuit, 3... Output terminal of the synchronous signal separation circuit, 4... Phase comparison circuit, 5 ...Horizontal oscillation circuit, 6...Horizontal oscillation circuit output terminal, 7.
...Output terminal of phase comparison circuit, 8...Low pass filter circuit (LPF), -9...
...LPF output terminal, 10.17... Capacitor, 13... Signal output terminal, 14...
・Voltage comparison circuit, 15... Reference voltage source, 16.
...Output terminal of the voltage comparison circuit. Name of agent: Patent attorney Toshio Nakao Idiot I21-
Riko ) To Rita Ward (Mi % L Gin-\I \I
'Figure 4

Claims (1)

[Claims] The signal input terminal is connected to the synchronous signal separation circuit, the output terminal of the synchronous signal separation circuit and the output terminal of the horizontal oscillation circuit are connected to separate input terminals of the phase comparison circuit, and the output terminal of the same phase comparison circuit is connected to the low frequency The output terminal of the low-pass filter circuit is connected to one input terminal of a voltage comparison circuit, the first capacitor, and the horizontal oscillation circuit, and the other input terminal of the voltage comparison circuit is connected to a pass filter circuit. A reference voltage source is connected, and the output terminal of the voltage comparison circuit is connected to a second
an automatic frequency control circuit, characterized in that the automatic frequency control circuit is connected to a capacitor and the horizontal oscillation circuit.