JPS5916450B2 - High frequency automatic frequency control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency automatic frequency control circuit, in which automatic frequency control (hereinafter referred to as AFC)
A circuit that lowers the FC operating voltage to below the minimum operating voltage, and an AF
By providing a circuit that raises the AFC operating voltage above the maximum operating voltage before the C-loop operation stabilizes, the AFC operating voltage is always pulled to the normal stable point without being pulled to the estimated stable point.
It is an object of the present invention to provide a high frequency A10 circuit that can prevent erroneous operation and ensure reliable tuning.

Before explaining the high frequency A10 circuit of the present invention in detail, first, it will be explained in which part of the configuration of the television receiver the AFC circuit, which is closely related to the circuit of the present invention, is located.

FIG. 8 shows a block diagram of a television receiver including the circuit of the present invention.

The television receiver includes an antenna 5 and a high frequency amplification circuit 6.
, mixing circuit 7, video intermediate frequency amplification circuit 8, AFC circuit 9
, high frequency AFC circuit 10 and local oscillation circuit 1 according to the present invention
1, audio processing circuit 12, speaker 13, video processing circuit 1
4, a picture tube (CRT) 15.

All of the illustrated configurations, except for the high frequency AFC circuit 10 according to the present invention, are those of a well-known television receiver.

The AFC circuit 9 detects fluctuations in intermediate frequencies (due to fluctuations in local oscillation frequency) contained in video and audio intermediate frequency signals that arrive via the high frequency amplification circuit 6, mixing circuit 7, and video intermediate frequency amplification circuit 8. This circuit detects the local oscillation frequency and supplies a control voltage to the local oscillation circuit 11 via the high frequency AFC circuit 10 to control the local oscillation circuit 11 so that the local oscillation frequency maintains a predetermined oscillation frequency.

The high frequency AFC circuit 10 according to the present invention has an AFC loop (
This circuit is inserted between the local oscillation circuit 11 and the AFC circuit 9 in the local oscillation circuit 11, mixing circuit 7, video intermediate frequency amplification circuit 8, and AFC circuit 9. This is a circuit that prevents the AFC loop from malfunctioning.

Conventionally, there is an AFC circuit that temporarily lowers the AFC operating voltage below the loop operating voltage in order to avoid being drawn into the stable malfunction point due to the presence or absence of a synchronization signal, but when receiving adjacent channels, the normal stable point is lower than the stable malfunction point. The voltage may also be high, so this operation alone is effective only against malfunctions caused by the audio carrier wave of the receiving channel.
There are drawbacks such as the fact that AFC operation cannot always be performed reliably in all cases.

On the other hand, in a circuit without measures to prevent malfunction, there are drawbacks such as a heavy burden of managing various drifts including the tuner and variations in AFC sensitivity, and there is a limit to the management of these.

The invention eliminates the above-mentioned drawbacks, and each embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of a first embodiment of a high frequency AFC circuit according to the present invention.

Terminals 1, 2.4 are connected to the following circuits, respectively.

Terminal 1 is connected to a pulse generating circuit (not shown) that outputs a power-on signal pulse or channel switching signal pulse when the receiver is powered on or channels are switched.

Terminal 2 is connected to local oscillation circuit 11, and terminal 4 is connected to AFC circuit 9.

In the figure, the switch SW1 is closed and the AF
Power supply 1B1 with a voltage higher than the upper limit of the C loop operating voltage range
is applied and the power supply B2 is not applied, the channel switching signal pulse or power-on signal pulse coming from the input terminal 1 is supplied to the capacitor C1 and charges it, and the base voltage of the transistor X1 becomes Rise.

The emitter of the transistor X1 is at ground potential and the transistor X1 is on during the period when the capacitor is discharged, and the potential at the point (2) decreases from 10B1 to zero V and becomes below the loop minimum operating voltage.

As a result, the polarity of the diode between the collector and base of transistor X2 turns on the collector and base, and as shown in FIG. becomes below the loop minimum operating voltage corresponding to the discharge time constant setting.

When the discharge of the capacitor C1 is completed and the 1 transistor x1 is turned off, the potential at point 2 returns to 10B1.

As a result, the collector and base of the transistor rises at
It is stable at the first stable point, that is, the stable point of low voltage, and even if there is a stable point of high voltage, it will not reach that point.

At this time, since the collector-base and emitter-collector regions of the transistor X2 are off, the voltage at the terminal 2 does not rise to 10B1.

In this case, it is necessary to make the ON period of one transistor X1 longer than the pull-in time constant of the AFC, but it is possible within a practical range.

Next, when power supply 1B1 and power supply 1B2 with a voltage higher than the upper limit of the AFC loop operating voltage range (however, B2<B1 because F run raster X2 is not always on) are applied at the same time, input from terminal 1 is applied. The channel switching signal pulse that has arrived turns on the transistor X1, and the potential at point (2) falls toward zero (3).

When the potential at point ■ is lower than the emitter potential of transistor X2 by the voltage between the base and emitter, transistor X2 is turned on, and the collector potential of transistor The voltage drops below the minimum operating voltage.

When the discharge of the capacitor C1 ends and the transistor
It is in the on state during the period when the base-emitter voltage is lower than the emitter of the transistor.

As a result, the collector of the F-run raster X2, that is, the terminal voltage of the AFC terminal 2, increases in link with the emitter potential of the transistor X2 and moves toward B2, as shown in FIG. 2B, exceeding the upper limit of the loop operating voltage range. .

Due to the rise in the potential at point ■, the potential at point ■ and transistor
When the difference between the emitter potential of transistor X2 and the emitter potential of transistor X2 becomes smaller than the Mars-emitter voltage of transistor
is turned off.

With transistor X2 turned off, the terminal voltage of AFC terminal 2, which was once raised below the loop maximum operating voltage, is
As shown in FIG. 2B, the voltage starts to fall and becomes stable at the first stable point, that is, the stable point of high voltage, and even if there is a stable point of low voltage, it will not reach that point.

As described above, according to the AFC circuit of the present invention, the channel switching operation is not affected by the level of the operating voltage before turning on the power, and when only the power supply element B1 is applied, When power supplies B1 and B2 are applied at the same time, each loop pull-in operation starts from above, so that the loop can always be reliably pulled into the normal stable point, and malfunctions can be prevented.

Considering VHF broadcasting and UHF broadcasting, considering the nature of radio waves and the large number of channels allocated, normally when receiving UHF broadcasting, the probability of receiving adjacent channels is small, and when receiving VHF broadcasting, the probability of receiving adjacent channels is lower than that of UHF broadcasting. Since it handles many frequencies, it is easy to manage various drifts and AFC sensitivity, but in recent years CATV (Community Antenna Television) has become popular, and adjacent channels in the VHF band have become popular. There are more and more opportunities to receive it.

Figure 3 shows the AFC output voltage taken out from the AFC output terminal 4 in the desired channel and the adjacent (non-desired) channel, and the curves ■ and ■ are the S curve and audio carrier wave of the desired channel to be received, respectively. The curve (■) is the S-curve due to the audio carrier wave of the channel adjacent to the desired reception channel, the straight line (2) is the varicap characteristic, O is the normal stable point, and (2) is the malfunction stable point.

Therefore, considering adjacent channel reception only for VHF, the first
In the figure, if the power supply for the RF amplification stage and oscillation stage of the VHF tuner is used for the power supply element B2, it can be drawn in from above as shown in Figure 2B only when receiving VHF broadcasting. It can be reliably pulled into the stable point O, and it can be operated stably without being pulled into the malfunction stable point @ of the adjacent channel.

In this case, in the electronic tuner, the VHF tuner's R
Since the power supply for the F amplification stage and oscillation stage and the power supply for the mixing stage of the VHF tuner are provided separately, this R
Power supplies for the F amplification stage and oscillation stage are used.

Further, even in a mechanical tuner, it is easy to provide a switch that applies power to the power source B2 only when receiving VHF broadcasting.

On the other hand, when receiving UHF, since 10B2 is not applied, it can always be drawn in from below as shown in FIG. 2A.

Also, regardless of whether it is VHF broadcasting or UHF broadcasting, when there is no reception of the adjacent channel, the pulling range will be wider if you pull in from below, and there are many opportunities to do this, so regardless of the band, the lower frequency adjacent channel It is effective to provide a switch that is set to apply power to the power source B2 only to the receiving channel.

Such a switch may be moved according to the rotation of the tuner or linked to the output of an electronic tuning system. For example,
As shown in Figure 4, the purpose can be achieved by connecting a channel memory switch SW corresponding to each channel to the emitter of one transistor X2 in Figure 1 to control the application of 10B2 to each channel. obtain.

In this case, if a pre-certification F switch is used as the switch SW, it is possible to perform a reliable retracting operation by only performing the pre-certification operation once and then only by changing the channel.

In addition, when adjusting the local oscillation frequency of the tuner, open switch SW1 and connect the power supply voltage +Bo to resistors R2 and R.
3 and adjust this to the AFC reference voltage.

At this time, the transistor X is only turned on when switching channels, and is already turned off during adjustment, so that adjustment can be made without any problem.

In addition, the retraction range when retracted from below can be secured in a wider range than ever before in UHF, as shown in Figure 5.
The degree of freedom in consideration of deviations in local oscillation frequency and AFC sensitivity is greatly improved.

In the figure, curves ■ and ■ are the S curves of the desired channel video carrier wave and audio carrier wave, respectively, curve V is the S curve of the adjacent adjacent channel audio carrier wave, the point θ is the normal stable point, and the point ■ is the malfunction stable point. be.

Furthermore, since the circuit shown in FIG. 1 does not require a critical judgment mechanism, reliable operation can be achieved.

FIG. 6 shows a circuit diagram of a second embodiment of the high frequency AFC circuit according to the present invention.

In the figure, the same components as in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted.

In the figure, 3 is a synchronization signal input terminal, and for example, as shown in FIG. On the other hand, as shown in FIG. 7, when the desired channel's audio carrier wave (curve I/) causes the malfunction stability point @ to be reached, the video signal component of the desired channel becomes extremely small and no synchronizing signal is received.

In the case of America and Japan, the distance between the video carrier wave of the desired channel and the audio carrier wave of the lower adjacent channel is 1.
5 MHz, and the distance between the video carrier wave and the audio carrier wave of the desired channel is 4.5 MHz.

In FIG. 7, the curve I shows the S curve based on the desired channel carrier wave, the straight line 2 shows the varicap characteristic, and the point 2 shows the normal stable point.

In Fig. 6, for example, if we consider the malfunction stable point of the audio carrier wave of the desired channel as shown in Fig. 7, the synchronizing signal does not enter terminal 3, so transistor X3 is turned off, and transistor X4 is turned on by power supply B3. Therefore, the state is substantially the same as when the power supply B2 is not applied to the transistor X2.

Here, in exactly the same way as explained in FIG. 1, when a channel switching signal pulse or a power-on signal pulse is input from terminal 1, the terminal voltage of AFC terminal 2 changes to the lower voltage side as shown in FIG. 2 A. drawn into a stable point.

On the other hand, if the audio carrier of the adjacent channel is pulled into the malfunction stable point O as shown in Figure 3, for example, a synchronizing signal is input to terminal 3, so transistor X3 is turned on, transistor X is turned off, and transistor X2Q is turned on. A power source 1B2 is applied to the emitter.

Here, when a channel switching signal pulse or a power-on signal pulse enters from terminal 1, the terminal voltage of AFC terminal 2 becomes stable on the high voltage side as shown in Fig. 2B, as explained in Fig. 1. drawn to the point.

Furthermore, as shown in FIG. 5, the varicap sensitivity of the tuner can be set within a range that does not intersect with the S curve of the audio carrier wave of the lower adjacent channel at the lower frequency pull-in limit point P. The AFC can be operated accurately between the pull-in limit point Q of the higher frequency, and an unprecedentedly wide pull-in range can be secured, and consideration for deviations in local oscillation frequency and degree of freedom regarding AFC sensitivity have been greatly improved. obtain.

That is, in the second embodiment, only VHF outputs B2, and a channel memory switch shown in FIG. 4 is provided to output B2.
Therefore, the AFC sensitivity can be increased within the range shown in FIG. 5 regardless of the UHF-VHF band.

Note that in the receiving state, since a synchronization signal exists, 10B2 is always applied to the emitter of F-run raster Therefore, there is no problem when adjusting the local oscillation frequency of the tuner by opening the switch SW1.

As described above, the high frequency AFC circuit according to the present invention includes an intervening device between the local oscillation circuit and the AFC circuit in the AFC loop composed of the local oscillation circuit, the mixing circuit, the video intermediate frequency amplification circuit, and the AFC circuit. a first switch circuit that is inserted between a voltage higher than the upper limit of the operating voltage range of the AFC loop and ground and turns on when a channel switching signal pulse or a power-on signal pulse is supplied; Provided at the next stage of this first switch circuit,
When a predetermined voltage different from the output voltage supplied from the first switch circuit is not supplied, the operating voltage of the AFC loop is temporarily changed to the operating voltage by switching according to the output of the first switch circuit. The operating voltage of the AFC loop is once lowered to the upper limit of the operating voltage range when it is switched in accordance with the output of the first switch circuit when a predetermined voltage is supplied. For example, if there is a stable malfunction point due to an audio carrier wave with a frequency above the video carrier wave of the desired channel, the above switch circuit activates the AFC when switching channels or turning on the power. If the voltage is lowered once below the minimum operating voltage and then guided to the normal stable point, even if there is a high malfunction stable point, the AFC operation can be performed reliably without reaching the malfunction stable point. If there is a stable malfunction point due to the adjacent channel audio carrier wave of the lower frequency of the desired channel video carrier wave, the AF will be activated by the above switch circuit when switching channels or turning on the power.
If the C operating voltage is once raised above the maximum operating voltage and then brought to the normal stable point, even if there is a low malfunction stable point, the AFC operation can be ensured without reaching that point.Furthermore, the circuit of the present invention It has features such as being applicable to any channel selection method, easily achieving the U-V quality required by the FCC, improving reliability, and being able to be constructed at low cost.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the first embodiment of the high frequency AFC circuit according to the present invention, and Figures 2A and B are respectively when the power supply 1B1 is applied and the power supply 1B, +82 is applied. AF of
C At the beginning of retracting operation, A from the pushing operation voltage to the retracting stable point
Figure 3 is a diagram showing temporal changes in the FC terminal voltage, and is a diagram for explaining the audio carrier wave of the desired channel when an adjacent channel exists, the audio carrier wave, and the varicap sensitivity that crosses the S curve due to the audio carrier wave of the adjacent channel. figure,
Figure 4 is a circuit diagram when a channel memory switch is connected to transistor A diagram for explaining the permissible range, FIG. 6 is a circuit diagram of a second embodiment of the high frequency AFC circuit according to the present invention, and FIG. 7 is a varicap that intersects the S curve by the video carrier wave and audio carrier wave of the desired reception channel. FIG. 8, which is a diagram for explaining sensitivity, is a block system diagram of a television receiver including the circuit of the present invention. 1... Channel switching signal or power-on signal input terminal, 2... Tuner AFC terminal, 3...
... Synchronization signal input terminal, 4 ... AFC output terminal, 5 ... Antenna, 6 ... High frequency amplification circuit, 7 ... Mixing circuit, 8 ......Video intermediate frequency amplification circuit, 9...AFC circuit, 10.
...High frequency AFC circuit, 11.1...Local oscillation circuit, 12...Audio processing circuit, 13...
...Speaker, 14...Video processing circuit, 1
5...Picture tube, C1゜C2...Capacitor, R1~R10...Resistor, X1~X4...
...Transistor, SWl, SW...Switch.

Claims (1)

[Claims] 1. Local oscillation circuit, mixing circuit, video intermediate frequency amplification circuit,
A circuit interposed between the local oscillation circuit and the AFC circuit in an AFC loop composed of an AFC (automatic frequency control) circuit, the circuit being connected to a voltage higher than the upper limit of the operating voltage range of the AFC loop and grounding. a first switch circuit that is provided between the switch circuit and turns on when a channel switching signal pulse or a power-on signal pulse is supplied; and a switch circuit that is provided at the next stage of the first switch circuit and is supplied from the first switch circuit. When a predetermined voltage different from the output voltage to be supplied is not supplied, the operating voltage of the AFC loop is once lowered below the lower end of the operating voltage range. When the predetermined voltage is supplied, the operating voltage of the AFC loop is once switched from the upper limit of the operating voltage range. A high frequency automatic frequency control circuit comprising: a second switch circuit that lowers the frequency after lowering the frequency. 2 Local oscillation circuit, mixing circuit, video intermediate frequency amplification circuit,
A circuit interposed between the local oscillation circuit and the AFC circuit in an AFC loop composed of an AFC (automatic frequency control) circuit, the circuit being connected to a voltage higher than the upper limit of the operating voltage range of the AFC loop and grounding. a first switch circuit that is provided between the switch circuit and turns on when a channel switching signal pulse or a power-on signal pulse is supplied; and a switch circuit that is provided at the next stage of the first switch circuit and is supplied from the first switch circuit. When a predetermined voltage different from the output voltage to be supplied is not supplied, when switching is performed according to the output of the first switch circuit, the operating voltage of the AFC loop is once lowered than the lower limit of the operating voltage range and then increased. and when the predetermined voltage is supplied, the operating voltage of the AFC loop is once made higher than the upper limit of the operating voltage range and then lowered when switched according to the output of the first switch circuit. and a circuit that is connected to the second switch circuit, determines the presence or absence of a synchronization signal, and sends the predetermined voltage to the second switch circuit when the synchronization signal is determined to be absent. A high frequency automatic frequency control circuit characterized by: