JPS5814089B2 - Automated transportation and maintenance information - Google Patents

Description

Description: The present invention relates to an automatic frequency control device for use in radio equipment and the like, and more particularly to a device useful for automatic frequency control of the local oscillation frequency of a television receiver.

In television receivers and the like, automatic frequency control (AFO) devices are used to maintain stable reception conditions.

FIG. 1 shows the characteristics of the AFO control voltage in a conventional AFC device.

This is a characteristic diagram used in a conventional general AFO circuit, with the horizontal axis representing frequency and the vertical axis representing the detection output voltage VAFO.

This characteristic is well known as the frequency discrimination output characteristic of a Foster-Seeley circuit or a ratio detection circuit, where Vo indicates a reference voltage, and H and VL indicate high and low voltages, respectively.

For the sake of simplicity, the voltages are shown as being clipped at VH and VL, but they do not have to be clipped.

Also shown here is a straight line t, which is the control sensitivity when controlling an oscillator such as a tuner, for example (VH-
Vo)/(f1-f2)(voIt/Hz).

In this way, in the case of this characteristic, the upper and lower limit frequencies of the frequency acquisition range of the AFO circuit become fL-fH.

And when the free oscillation frequency is f2, it is controlled to a frequency of f1, so the deviation from the center frequency fo is Cfo
When it is fH, the deviation is (f2-fo).

However, in an AFC device with such characteristics, when a user selects a station with a continuous variable frequency,
When adjusting the local oscillator from a frequency lower than fL toward the center frequency fo, the AFO pulls in at the frequency fL, so the adjustment may be stopped at this frequency. However, in such a state, the local oscillator may drift and fall below fL due to changes in temperature, voltage, etc. If the power switch is temporarily turned off at such a time, the frequency will not be pulled in when the power is turned on again, and reception will not be possible.

This problem occurs not only at the frequency fH but also when making discontinuous frequency adjustments such as when changing channels on a television receiver.

The present invention aims to eliminate the disadvantages of conventional AFO devices, and to provide a device which can perform more stable and accurate AFO operation by narrowing the pull-in range during continuous frequency adjustment while maintaining a wide holding range during AFO operation, and which can pull in frequencies over a wide frequency range by temporarily widening the pull-in range when making discontinuous frequency adjustments or when the power is turned on, thereby allowing good tuning without the need for fine frequency adjustments each time.

For this reason, the present invention controls the frequency of the tuning circuit using a control voltage, e.g., a frequency discrimination output, which changes within a first voltage region higher (or lower) than a reference voltage at the center frequency on the upper limit frequency side and changes within a second voltage region lower (same higher) than the reference voltage on the lower limit frequency side within a range of an upper limit frequency and a lower limit frequency range, the frequency of the tuning circuit is controlled using a control voltage in a second voltage region lower (same higher) than the reference voltage in a frequency range higher than the upper limit frequency, and a control voltage in a first voltage region higher (same lower) than the reference voltage in a frequency range lower than the lower limit frequency, and is characterized in that the control voltage is temporarily set to the reference voltage at least one of when the power is turned on and when the frequency is discontinuously adjusted.

An embodiment of the present invention will now be described with reference to Figs.

FIG. 2 is a characteristic diagram showing an example of the AFC control voltage used in the present invention, in which the center frequency is fo, and the upper and lower limit frequencies are fo and fH, respectively, which are a fixed frequency away from the center frequency (they do not have to be the same frequency). Within the upper and lower limit frequency range fL-fH, frequency control is performed using a frequency discrimination output which changes in a range higher than the reference voltage vo at the center frequency fo on the upper limit frequency fH side and changes in a range lower than the reference voltage vo on the lower limit frequency fL side. Also, in the frequency range higher than the upper limit frequency fH, a voltage higher than the reference voltage Vo is used, and in the frequency range lower than the lower limit frequency fL, a voltage lower than the reference voltage Vo is used to control the frequency.

Therefore, when such an AFC control voltage is used,
When adjusting the frequency from a low frequency to a high frequency, as shown by t1 in FIG. 2, the stable frequency becomes f3 when the free frequency becomes f, and conversely, when adjusting the frequency from a high frequency to a low frequency, as shown by t2 in FIG. 2, the stable frequency becomes f4 when the free frequency becomes f.

In this way, by using an AFO control voltage having the characteristics as shown in FIG. 2, the pull-in range is set to f, to f6, which is considerably closer to the center frequency fO than the conventional pull-in range of fL to fH. This makes it possible to bring the frequency at the time of pull-in when performing continuous frequency adjustment closer to the center frequency fo, so that even if there is some frequency fluctuation thereafter, it will not deviate significantly from the center frequency fo.

Even when using the AFC control voltage as shown in FIG. 2, the AFO operation holding range is exactly the same as the conventional ft-f
It goes without saying that this is widely held to be the case.

Also, if the control voltage for AFC is temporarily de-fed to the reference voltage 10 and the AFO operation is started from this reference voltage 10, the pull-in range becomes fL-fH,
It can be entrained over a wide frequency range.

Therefore, when discontinuous frequency adjustment is performed, such as when changing channels, or when the power is turned on, the AFC control voltage is temporarily de-fed to the reference voltage Vo, so that the frequency can be reliably pulled in even if it is slightly off.

Next, an embodiment of a specific configuration for generating an AFC control voltage having such characteristics to perform automatic frequency control and its operation will be described with reference to Figs.

In the figure, reference numeral 1 denotes a local oscillator circuit, 2 denotes a mixing circuit, and 3 denotes a video intermediate frequency amplifier circuit, which are the same as those in a normal television receiver.

Reference numeral 4 denotes a frequency discrimination circuit which detects the frequency of the video intermediate frequency signal, and generates a frequency discrimination output A at a voltage higher than the reference voltage Vo in the range of lower frequencies up to a lower limit frequency fL, centered on a reference voltage Vo at a center frequency fo, as shown by vA in FIG. 4A, and at a voltage lower than the reference voltage Vo in the range of frequencies higher than the center frequency fo up to an upper limit frequency fH.

This frequency discrimination output is output by one of the transistors 5 and 6 which constitute a differential amplifier.
4A. On the other hand, the polarity is inverted by transistor 7 as shown by (4) in FIG. 4A, and then the polarity is inverted by transistor 7 and then supplied to the base of the other transistor 6.

An AFC control voltage, which will be described later, is taken from the collector of this transistor 6 and supplied to the local oscillator circuit 1 .

Reference numeral 8 denotes a detection circuit which detects whether the frequency of the signal in the video intermediate frequency amplifier circuit 3 is between an upper limit frequency fH and a lower limit frequency fL when there is no AFC operation, and which detects, for example, the presence or absence of a sync signal extracted by a sync separation circuit in the subsequent stage, or the presence or absence of a frequency discrimination output as shown in FIG. 2A, thereby generating a detection output which becomes high level within the upper and lower limit frequency range fH-fL as shown in FIG. 4B.

This detection output is applied to the base of transistor 9, causing its collector to produce an output which becomes a low level when fH-fL, as shown in FIG. 4D, and is further applied to the bases of transistors 10 and 11, causing their respective collectors to produce outputs which become a high level when fH-fL, as shown in FIG. 4E and F.

The collector output F of transistor 11 is further supplied to the collector as well as the base of transistor 12 to produce an output which goes low at fH-fL as shown in FIG.

Furthermore, 13 indicates the upper limit frequency fH of the signal frequency in the video intermediate frequency amplifier circuit 3 when there is no AFO operation.
A detection circuit for detecting whether the frequency is between 57.25 MHz and a slightly higher frequency f'H, for example, by detecting a signal of 57.25 MHz from the video intermediate frequency amplifier circuit 3.
As shown in FIG. 3C, a detection output that is at a high level in the range fH to f'H from the upper limit frequency fH to the frequency f'H is generated.

It should be noted that this detection output VC is obtained by detecting the audio carrier. In addition, a detection output V'c due to a video carrier can be obtained at a lower frequency, but the detection output V'c is not used here.

This detection output C is applied to the base of transistor 140, and an output which becomes low in the range of <fH-f'H, the range of vc, and the range of v'c, as shown in FIG. 4H, is generated at its collector. This output is applied to the base of transistor 15, and the collector current becomes fH-f'H, as shown in FIG.
It blocks the signal in the range of VLC and the range of VLC, and allows it to flow in other ranges.

Incidentally, 16 is a constant current transistor.

Next, an operation for performing continuous frequency adjustment in such a configuration will be described.

First, in the frequency range lower than fL, transistor 9
, 14 are cut off, and transistors 10, 11, 12, 15
When the frequency discrimination outputs VA and V'A are both equal to the reference voltage Vo, the transistor 5 is cut off and the transistor 6 is turned on.
Since the base bias voltage of is set as shown in FIG. 4J, the AFO control voltage from the transistor 6 becomes a low level VL as shown in FIG.

Next, when the frequency is in the range from the lower limit frequency fL to the center frequency fO, the transistor 9 is turned on and the transistor 1 is turned on.
Since I0, I1 and I12 are cut off, a voltage as shown in FIG. 4J is applied to the bases of transistors 5 and 6, and transistor 14 is conductive only in the range of V'c and transistor 15 is cut off only in the range of V'C.

Therefore, at this time, the transistors 5 and 6 are at the lower limit frequency f
Near L and the center frequency fo, they are in the active region, and in the central part other than that, both are cut off within the range of V'c, and in other ranges, transistor 5 is turned on and transistor 6 is turned off, and an AFC control voltage similar to the frequency discrimination output A is generated at the collector of transistor 6, as shown in FIG. 4K.

It should be noted that VH is the collector voltage when the transistor 6 is cut off, and is approximately equal to the power supply voltage (+B) here.

In addition, when the frequency is in the range from the center frequency fo to the upper limit frequency fH, the transistors 9 and 14 are conductive and the transistors 10, 11, 12, and 15 are conductive, and the collector of the transistor 6 is supplied with the fourth current due to the voltage relationship opposite to that described above.
As shown in FIG. K, an AFO control voltage similar to the frequency discrimination output VA is generated.

Furthermore, in the frequency range from the upper limit frequency fH to a higher frequency f'H, transistor 9 cuts off and transistors 10, 11 and 12 conduct, but transistor 14 conducts, causing transistor 15 to cut off and a high-level vH AFO control voltage is generated at the collector of transistor 16, as shown in FIG. 4K.

When the frequency is in the range higher than f'H, the AFO control voltage returns to the original level L.

In this way, an AFO control voltage as explained in FIG. 2 can be obtained at the collector of transistor 6, and by applying this to local oscillator circuit 1, good AFO operation as described above can be achieved.

In the specific example of the device shown in Figures 3 and 4, in the frequency range higher than the upper limit frequency fH, the AFO control voltage is generated at a high level VH only up to frequency f'H, and is returned to a low level vL again for frequencies above that frequency. This is because, when there is a frequency gap between the lower limit frequency of the adjacent channel and the lower limit frequency of the adjacent channel, it is necessary to keep the voltage at a low level in the frequency range below the lower limit frequency of the adjacent channel.

This is not necessary when the upper limit frequency fH of one of the adjacent channels is the same as the lower limit frequency fL of the other adjacent channel or exceeds each other's frequencies fL and fH.

Furthermore, it goes without saying that the means for generating the detection output Vo in the frequency range higher than the upper limit frequency fH may be any means, such as using a tuning circuit tuned to a frequency farther away than the frequency of the single carrier in the case of a single carrier signal.

Next, a specific circuit configuration for controlling the control voltage for AF0 to the reference voltage Vo when switching channels and when the power is turned on in such an apparatus will be described with reference to FIG.

In FIG. 5, the same parts as those in FIG. 3 are designated by the same reference numerals and their explanations are omitted.

First, 17 is a detection circuit for detecting when a channel is changed.
When a channel is changed, a switch 20 is closed by a cam 19 attached to a channel change shaft of a tuner 18, a capacitor 22 is charged via a diode 21, and a positive pulse is generated via a resistor 23.

A detection circuit 24 detects when the power is turned on, and detects the rising edge of the power supply voltage generated by a power supply circuit 25 using a capacitor 26 and a resistor 27, and generates a positive pulse via a resistor 28 when the power is turned on.

Further, 29 is a switch for manually defeating NFC operation, which supplies a positive voltage via resistor 30 .

These pulses and voltages for NFC defeat are applied to the base of transistor 31, and the collector output is applied to the bases of transistors 32 and 33. Furthermore, the collector output of transistor 33 is applied to the bases of transistors 34 and 35.
In addition to the base of transistor 35, transistors 36 and 37 are switched by this transistor 35.

The transistors 38 to 41 form a feedback circuit that maintains the output control voltage at the reference voltage Vo during the defeat.

In this configuration, when the AFO defeat pulse or voltage is not applied to the base of transistor 31, transistor 31 is in a cutoff state, transistors 32 and 33 are in a conductive state, and transistor 34 is in a turned-on state.
, 35 are cut off, transistors 36 and 37 are conductive, and transistors 38, 39, 40, and 41 are cut off, and the same NFC operation as in the case of FIG.

On the other hand, when a channel is changed, the power is turned on, or the AFO defeat is performed manually, and an AFO defeat pulse or voltage is applied to the base of transistor 31, the on/off state of each of transistors 31 to 41 is reversed, so that transistor 34 becomes conductive, thereby shorting transistor 15 and preventing the transmission of signal H, transistor 35 becomes conductive and transistors 36 and 37 become blocked, thereby preventing the transmission of signal B, and transistor 32 becomes blocked and transistors 38 to 41 become conductive, thereby performing a feedback operation to set AFC control voltage K to reference voltage Vo.

As a result, when the channel is changed, when the power is turned on, and when the AFC is manually defeated, the control voltage is set to the reference voltage Vo.

Thereafter, when the channel is switched or the power is turned on, the defeet pulse to the transistor 31 disappears after a predetermined pulse width time has elapsed, so that each of the transistors 31 to 41 is inverted again and performs the AFC operation as described above.

For this reason, since the AFO operation starts from the reference voltage Vo, the acquisition frequency at this time is wide, fL-fH, as described above, and acquisition can be performed reliably even if the frequency is slightly deviated.

In the embodiment of FIG. 5, the pull-in range is widened both when changing channels and when the power is turned on.
If necessary, it may be made wider only in one of the two cases, and the channel switching detection circuit, power-on detection circuit, and control voltage control circuit may be designed in any circuit configuration other than those described above that can achieve the same effect.

Furthermore, even in the case of a television receiver or the like in which the frequency detection output is generated only in the range from frequency fL to frequency fh as shown in FIG. 6A, this device can obtain an AFO control voltage as shown in FIG. 6K similar to the above-mentioned case as shown in FIG. 6, thereby narrowing the pull-in range during continuous frequency adjustment and widening the holding range.

Since the detailed operation is almost the same as that described above, the same reference numerals are used and the description is omitted.

Furthermore, in this case, when discontinuous frequency adjustment is performed, for example, when changing channels or when the power is turned on, the AFC control voltage of the output of the transistor 6 is temporarily de-fed to the reference voltage Vo and then changed from Vo. In this case, the pull-in range is from the lower limit frequency fL to the upper limit frequency fL.
It can be expanded to a wide range up to H and can be retracted reliably.

As described above, according to the present invention, it is possible to obtain an automatic frequency control device that performs stable and accurate NFC operation by narrowing the pull-in range when performing continuous frequency adjustment while maintaining a wide holding range during NFC operation.

[Brief description of the drawings]

FIG. 1 shows a conventional automatic frequency control device.
FIG. 2 is a characteristic diagram of the AFO control voltage used in an automatic frequency control device according to an embodiment of the present invention. FIG. 3 is a block diagram of the main parts of the device. FIG. 4 is a characteristic diagram for explaining the operation of the device. FIG. 5 is a block diagram of the device. FIG. 6 is a characteristic diagram of the AFO control voltage used in an automatic frequency control device according to an embodiment of the present invention.
1, J, and K are characteristic diagrams for explaining the operation of an automatic frequency control device in another embodiment of the present invention. 1: local oscillator circuit; 2: mixer circuit; 3: video intermediate frequency amplifier circuit; 4: frequency discrimination circuit; 5, 6, 7:
Transistor, 8 . . . Detection circuit, 9, 10, 11, 12
...Transistor, 13 ...Detection circuit, 14, 15, 1
6: transistor; 17: channel switching detection circuit; 18: tuner; 19: cam; 20: switch; 21: diode; 22: capacitor; 23:
......Resistor, 24......Power-on detection circuit, 25......Power supply circuit, 26......Capacitor, 27. 28......Resistor, 3
1 to 41...Transistor.

Claims (1)

[Claims] 1. An automatic frequency control device which controls frequency using a control voltage which varies within a first voltage region on the upper limit frequency side and within a second voltage region on the lower limit frequency side, with respect to a reference voltage at the center frequency, within a range of an upper limit frequency and a lower limit frequency, each of which is a fixed frequency away from a center frequency, and which controls frequency by fixing the control voltage to a fixed voltage in the second voltage region in a frequency range higher than the upper limit frequency and fixing the control voltage to a fixed voltage in the first voltage region in a frequency range lower than the lower limit frequency, and which controls frequency by temporarily setting the control voltage to the reference voltage at least either when power is turned on or when discontinuous frequency switching is performed.