JPS5942760Y2 - Synthesizer type tuning device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a sequential tuning control circuit synthesizer type tuning device, which speeds up the tuning operation even when an AFT circuit is provided, and quickly selects the correct signal. The purpose of the present invention is to provide a device that does the following.

FIG. 1 is a basic block diagram of a phase-locked loop frequency synthesizer type tuning device with an automatic frequency adjustment device, which is shown in US Pat. No. 4,025,953 and other documents.

First, this device will be explained.

In FIG. 1, 1 is a high frequency amplifier, 2 is a mixer, 3 is an intermediate frequency amplifier, 4 is a video amplifier, and 5 is a cathode ray tube, which constitute a normal television receiver.

A phase-locked loop (P
The output of the voltage-controlled oscillator 6 is applied to the mixer 2.

Therefore, the oscillator 6 is used as a local oscillator in a television receiver.

The frequency of the reference oscillator 11 divided by a second programmable frequency divider 12 is applied to the phase comparator 9, and the channel number signal output from the channel number counter memory 13 is applied to the first programmable frequency divider 8. A code converter 14 adds the code converted signal to the division ratio setting signal for each channel.

15 is a channel indicator.

When a channel consisting of channel number counter memory 13 is specified, the output of code converter 14 changes and the frequency division ratio of programmable frequency divider 8 changes depending on the channel.

A frequency-divided version of the output of the reference oscillator 11 is added to the phase comparator 9, and the phase-locked loop operates so that the frequency of the output of the programmable frequency divider 8 matches this frequency.

As a result, the oscillation frequency of the voltage controlled oscillator 6 changes, and the local oscillation frequency corresponding to the specified channel changes to the mixer 2.
In addition to this, channel selection will be performed.

There are two types of channel designation methods, one of which is a case where the number signal of the desired channel selection is input directly to the channel number counter memory 13 from a direct designation switch 16 such as a keyboard for channel designation.

In this case, the channel number signal is immediately converted by the code converter 14 and the designated channel is selected.

The other case is when a signal for specifying sequential channel selection is input from the sequential channel selection designation switch 17.

This input has an up direction signal and a down direction signal, but in either case, when this signal is input, a pulse is generated from the pulse generation circuit 18, this is added to the channel number counter memory 13, and the up direction signal is input. Depending on whether the signal is a down direction signal, the channel number signal in the counter memory 13 is changed by one channel.

For this reason, the frequency division ratio in the first programmable frequency divider 8 is also changed by l channels, and the tuner performs a sequential tuning operation in which the channel is sequentially shifted to the adjacent channel one channel at a time.

Then, a signal that has received a television broadcast signal is generated from a reception detection circuit, which will be described later, and the pulse generation in the pulse generation circuit 18 is stopped.This operation is repeated in step 1, and eventually the next signal is received in the up direction or down direction. Tuning is performed sequentially so as to stop at the channel where the signal is received.

Next, we will explain the parts that finely adjust the local oscillation frequency in each channel and detect whether or not a broadcast signal is received on that channel. 19 is a video carrier wave detection circuit, 20 is an audio carrier wave detection circuit, and 21 VIF A signal frequency discrimination circuit, 22 is a vertical synchronization signal detection circuit, 23 is a fine adjustment column circuit, 24 is an up/down counter, and the output of this up/down counter 24 is sent to the second programmable frequency divider 12 for setting the division ratio. The AFT circuit is configured such that it is added as a signal.

AFT operation is performed by video and audio carrier detection circuits 19.20.
The outputs of the frequency discrimination circuit 21 and the vertical synchronization signal detection circuit 22 are each compared with a reference voltage by a fine adjustment control circuit 23.
The result is logically operated to determine the counting direction of the up/down counter 24.

In other words, even if the division ratio of the first programmable frequency divider 8 is determined by the output of the code converter 14 and one of the channels is selected, the local oscillation frequency at that time may deviate from the accurate frequency required for reception. If the signal is not correctly received at that time, the up/down counter 24 is controlled in the up or down direction by the output of the frequency discrimination circuit 21 and the output of the vertical synchronization signal detection circuit 22, thereby controlling the up/down counter 24 in the up or down direction. AFT operation is performed to finely adjust the local oscillation frequency by changing the frequency division ratio of the 2 programmable frequency divider 12.

In addition, during sequential channel selection, each time the channel number signal in the channel number counter memory 13 changes and the channel moves, the up/down counter 24 is operated for a certain period of time to sweep within that channel, and the broadcast signal is sent to that channel. Detect whether or not exists.

Therefore, the up/down counter 24 has its up/down direction controlled by an external control signal, and when it counts within a predetermined range 1, it automatically reverses the counting direction and repeats within the predetermined range. It is designed to sweep.

When a broadcast signal having a predetermined electric field strength or more is received as a result of the sweep, a detection output is generated from the video carrier detection circuit 19, and the panel generator 18 is stopped by that output and the channel selection state is entered.

When there is no broadcast signal, control is performed to sweep a predetermined frequency range of that channel for a predetermined time and then move to the next channel.

The button 24 is an operation delay circuit, and the output of a new channel is output from the channel number counter memory 13.
After the PLL operation by the programmable frequency divider 8 is completed (after 300 m5ec), the AFT and sweep operation is started, and the up/down counter 24 is operated for a certain period of time so that the sweep operation is performed only for a predetermined time (328 m5ec) thereafter. It is intended to make it possible.

In this manner, this device has the advantage of performing a channel selection operation and being able to receive all channels with a relatively simple configuration, but has the following drawbacks.

That is, during sequential channel selection, the channel number signal in the channel number counter memory 13 is sequentially changed to sequentially change the reception channels, and the presence or absence of a received broadcast signal is detected by sweeping for each channel, and when no signal is present, the next Therefore, in a situation such as the current UHF broadcast band where broadcast signals exist only on a very small number of channels out of a large number of channels and on channels that are far apart from each other, , it takes a considerable amount of time to move from one broadcast receiving channel to the next, and during that time, as the local oscillation frequency changes, there may be noise signals that do not reach the specified electric field strength. The drawback is that an unsightly image may appear on the screen of the cathode ray tube.

Therefore, an object of the present invention is to provide a device that shortens the period during which unsightly images such as those described above appear in such a device, and allows the selection of the next channel 1 to be performed at high speed. A detection circuit is provided to detect whether or not a signal is received, and when a detection signal indicating that a broadcast signal is not received is output from this detection circuit, the next channel is switched on without performing AFT or sweep operation. It was moved to .

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. 2 showing the main parts thereof.

The buttons in FIG. 2 and the same parts as those in FIG. 1 will be described with the same reference numerals.

The fine adjustment control circuit 23 detects whether the outputs of the video carrier detection circuit 19, the audio carrier detection circuit 20, the vertical synchronization signal detection circuit 21, and the frequency discrimination circuit 22 have a reference voltage for each detection. Comparison circuit 2 for
6 to 30 are provided.

Comparing circuits 26 to 28 generate high-level outputs when the detection outputs of the respective signals are generated.

The comparison circuit 29 generates a high level output when the frequency discrimination output is above a predetermined level, and the comparison circuit 30 generates a high level output when the frequency discrimination output is above a predetermined level.

Therefore, when high-level outputs are generated from all of these comparison circuits 26 to 30, it is when the television signal is correctly tuned to the frequency and received, so at that time, low-level outputs are generated from the gate 31. This causes the up/down counter 24 to stop counting.

This is the AFT operation.

On the other hand, in this device, in order to control the operation of the up/down counter 24, a switch circuit 32 is further provided, and a gate 33 and a switch 34 are provided in this part.

The switch 34 is used to manually command whether or not to perform the AFT operation button and the sweep operation.
If the switch 34 is opened, no clock pulses are applied to the up/down counter 24, and neither the AFT operation nor the sweep operation is performed, and these operations are performed only when the switch 34 is closed.

In addition to the clock pulse, the gate 33 also has a fine control circuit 2.
In addition to the output of No. 3 and the control output of the operation time control circuit 25, the detection output from the video carrier detection circuit 19 is also added.

And the button for this device is Q of the video carrier wave detection circuit 19.
is made low to widen the bandwidth, and no matter which channel is pressed, a detection output is generated as long as a signal of a predetermined electric field strength or higher exists within the assigned frequency range of that channel.

However, if the band width is widened in this way, the fine adjustment circuit 2
Since this is not suitable for detecting the center frequency for 3.3, a level-shifted output is added to the comparator circuit 26.

With this configuration, the sequential channel selection switch 17 now commands sequential channel selection, and the channel number counter memory 13
Suppose you are moved to the next channel.

Of course, it is assumed that the switch 34 is closed.

At this time, if there is a received signal on that channel and a detection output is generated from the video carrier detection circuit 19, the gate 33 becomes conductive and a clock pulse is applied to the up/down counter 24, as described above. A sweep operation is performed on that channel as in the case of .

If high level outputs are generated from all of the comparison circuits 26 to 30 during the sweep, the fine adjustment control circuit 23 determines that the tuning is correctly tuned to the television signal, and the output of the gate 31 becomes low level, causing the gate 33 AFT operation is performed to interrupt the up/down counter 24 and stop the counting operation of the up/down counter 24.

If no output is generated from the fine adjustment control circuit 23 even after the sweep operation, the signal is determined not to be a television signal, and after the sweep operation time determined by the operation time control circuit 25, the up/down counter 2
4, and moves to the next channel.

On the other hand, when moving from channel to channel, if there is no received signal with a predetermined electric field strength or higher in the channel/channel and no detection output is generated from the video carrier detection circuit 19, the signal is immediately pressed without pressing the sweep operation button or AFT operation. The pulse generating circuit 18 is controlled to move to the next channel.

After that, by repeating this operation, sweep operation and AF are performed only on channels where signals of a predetermined electric field strength or higher exist.
T operation is performed, channels that do not exist are immediately skipped, the channel is moved to the next channel, and then the television signal is stopped at the channel where the television signal is correctly received.Sequential tuning is performed.

Therefore, according to such a device, it is possible to eliminate the waste of conventionally performing sweep and AFT operations even on channels where there is no received signal, and it is possible to eliminate the waste of conventionally performing sweep and AFT operations even on channels where there is no received signal. Even if the number of channels available is small, pressing the button can quickly select a channel with the next television signal.

In the above embodiments, the presence or absence of a received signal is determined by pressing a button for each channel using the output of the video carrier detection circuit. There is no one thing you can do.

As described in detail above, in the present invention, a button is pressed on a synthesizer type channel selection device having an AFT function, and the AFT operation is performed during sequential channel selection only on channels where received signals with a predetermined electric field or higher are present. Therefore, 1
from one broadcast reception channel to the next broadcast reception channel 1
This makes it possible to perform high-speed channel selection by shortening the time required for channel selection, and to reduce the display of unsightly images during that time.

[Brief explanation of drawings]

Figure 1 is a basic block diagram of a synthesizer type tuning device.
FIG. 2 is a circuit diagram of a main part of a synthesizer type tuning device according to an embodiment of the present invention. 2...Mixer, 6...Voltage controlled token, 7...Prescaler, 8...First
Programmable frequency divider, 9... Phase comparator, 1
0...Low pass filter, 11...Reference oscillator, 12...Second programmable frequency divider, 13
...Channel number counter memory, 14...
... Code converter, 17 ... Sequential tuning designation switch, 18 ... Pulse generation circuit, 19 ...
...Video carrier detection circuit, 20...Audio carrier detection circuit, 21...Frequency discrimination circuit, 22
...Vertical synchronization signal detection circuit, 23...
Fine adjustment control circuit, 24... Up/down counter, 25... Operating time control circuit, 26, 27, 2
8, 29, 30... Comparison circuit, 31...
・Gate, 32...Switch circuit, 33...
...Gate, 34...Switch.

Claims (1)

[Scope of utility model registration request] a voltage-controlled local oscillator for a tuner; a first programmable frequency divider that divides the oscillation output of the local oscillator;
Comparing the phases of a reference oscillator, a second programmable frequency divider that divides the oscillation output of the reference oscillator, and a divided output of the first programmable frequency divider and a divided output of the second programmable frequency divider. A phase comparator, a low-pass filter that smoothes the comparison output of this phase comparator and applies it to the local oscillator as an oscillation frequency control voltage, and a reception channel by switching the division ratio that is pressed to the first program frequency divider. a sequential channel selection control circuit that sequentially changes the channel number counter memory one channel at a time so as to sequentially change the division ratio of the first program branching unit one channel at a time; a counter that finely adjusts the reception frequency by changing a frequency division ratio in a programmable frequency divider; an AFT circuit that detects a frequency shift in the output signal of the tuner and controls the counter so as to correct the frequency shift; a carrier wave detection circuit that detects the output signal of the tuner and generates a detection output when a broadcast signal having a predetermined electric field strength or more is received and stops the switching operation of the channel number counter memory; A synthesizer type tuning device comprising a switching circuit that switches between the AFT circuit and the counter so that the AFT circuit controls the counter only when an output is generated.