JPS5929004B2 - automatic channel selection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic tuning device that automatically changes the oscillation frequency of a local oscillation circuit to receive a desired station, and in particular, by making the rate of change of the oscillation frequency variable, The aim is to achieve reliable reception and shorten the tuning time.

In conventional automatic channel selection devices, the search speed was constant, so if the search speed was increased, the station passing immediately after the start of the channel selection operation would be passed through, making reception impossible. If the speed is slowed down, it has the disadvantage that it takes too much time to receive reception at a desired station.

In addition, conventional automatic channel selection devices generally generate a search stop signal when reception of a desired station is achieved, and since the search stop signal has a predetermined time delay, overshooting occurs. It had the following drawback.

The present invention has been made in view of the above points, and will be described below based on embodiments and with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which a signal received by an antenna 1 is amplified by a radio frequency amplification circuit 2, converted to an intermediate frequency by a mixing circuit 3, and then converted to an intermediate frequency by an intermediate frequency amplification circuit 4. The signal is amplified by the detector circuit 5, then amplified by the low frequency amplifier circuit 6, and applied to the speaker 7.

A voltage-controlled oscillation circuit 8 is connected to the mixing circuit 3, and the oscillation frequency of the oscillation circuit 8 changes depending on the value of the applied DC voltage.

The DC voltage applied to the oscillation circuit 8 is D-
It is supplied from the A converter 9.

The D-A converter 9 converts one digital signal obtained from the up-down counter 10 into a DC voltage (analog signal), and generates a DC voltage according to the number of output pulses from the up-down counter 10. You can.

11 is a selection circuit for selecting the counting speed of the up-down counter 10; when the selection circuit 11 is in the first state, a low-speed pulse from the low-speed pulse generation circuit 12 is applied to the up-down counter 10 as a clock pulse; When the selection circuit 11 is in the second state, switching control is performed so that the high-speed pulse from the high-speed pulse generation circuit 13 is applied to the up-down counter 10 as a clock pulse.

14 is a control circuit for switching the mode of the selection circuit 11, and the control circuit 14 includes an operation switch 15 for instructing up search or down search, and a timer 16 that operates according to the operation of the operation switch 15. and,
It is connected to a detection circuit 17 that detects the S curve signal which is the output signal of the detection circuit 5, and depending on the states of the operation switch 15, timer 16 and detection circuit 17,
It can be switched to the first state or the second state.

The timer 16 is provided so that the control circuit 14 generates a control signal that maintains the selection circuit 11 in the first state for a predetermined period from when the operation switch 15 is operated. The signal is transmitted to the control circuit 14
It acts preferentially on

Further, a detection circuit 17 detects the S curve signal of the detection circuit 5.
teeth.

A zero level at the midpoint of the S-curve signal and between stations, a direct current voltage of a predetermined level or higher at the first peripheral edge of the S-curve signal, and a negative DC voltage of a predetermined level or higher at the second peripheral edge of the S-curve signal. It discriminates, does not generate an output when the level is zero, and generates a predetermined output signal when a positive or negative DC voltage equal to or higher than the predetermined level is generated.

Next, the operation will be explained.

To start the automatic channel selection operation, first press the operation switch 15.
is operated to put the switch 15 into the up search state or down search state.

If the operating switch 15 is now placed in the up search state, a signal indicating the up search state is generated from the switch 15 and acts on the timer 16 and the control circuit 14.

Therefore, a signal is applied from the control circuit 14 to the selection circuit 11 such that the timer 16 operates and the selection circuit 11 enters the first state in which it selects the low-speed pulse from the low-speed pulse generation circuit 12. An up signal is applied to the up/down counter 10 from 14 .

As a result, the up/down counter 10 performs up-counting using the low-speed pulse as a clock signal.

As mentioned above, since the up/down counter 10 counts the speed according to the low-speed clock signal, the DC voltage which is the output signal of the DA converter 9 also changes at a low speed, and therefore the oscillation circuit operates as a local oscillator. The output oscillation frequency of 8 also changes at a low speed, achieving a low speed search.

When a predetermined period of time has elapsed, the operation of the timer 16 is stopped, and the control circuit 14 begins to apply a control signal to the selection circuit 11 in accordance with the signal directly applied from the operation switch 15.

By the signal directly applied from the operation switch 15,
The control circuit 14 generates a control signal that puts the selection circuit 11 in the second state.

When the second state is reached, the selection circuit 11 begins to pass the high-speed pulse from the high-speed pulse generation circuit 13, and the up/down counter 10 performs up-counting using the high-speed pulse as a clock signal.

Therefore, the output DC voltage of the D-A converter 9 changes at high speed, and the output oscillation frequency of the oscillation circuit 8 also changes at high speed, achieving a high-speed search.

Regardless of whether it is a high-speed search or a low-speed search.

When a broadcasting station is present, a signal is generated from the detection circuit 17, and the control circuit 14 generates a control signal that sets the selection circuit 11 to the first state.

As shown in FIG. 2, when a broadcasting station having S curve characteristics with the frequency fo as the center frequency exists during the search, the detection circuit 17 having a predetermined detection level (VSL) detects the S curve characteristic with the frequency fo as the center frequency.
Point A of the curve characteristic is detected and a priority signal is generated, and in response, the control circuit 14 generates a control signal that puts the selection circuit 11 in the first state.

Therefore, during a high-speed search, the selection circuit 11 is switched, and during a low-speed search, the oscillation frequency of the oscillation circuit 8 changes at a low speed while remaining unchanged during a low-speed search.

Furthermore, if a signal exceeding the detection level (VSH) of the detection circuit 17 is detected during the continuation of the low-speed search [point B
], a second priority signal is generated from the detection circuit 17.

Then, the control circuit 14 receives the twelfth priority signal and receives the twelfth priority signal.
It continues to generate a control signal to the selection circuit 11 to maintain the first state, and also generates a down signal to the up/down counter 10.

As a result, the oscillation frequency of the 2/1 oscillation circuit 8 decreases at a low speed so that the up/down counter 10 performs low-speed down counting in the down direction.

After some time has elapsed, the detection circuit 17 again detects one peripheral edge (point C) of the S-curve characteristic.

Then, the detection circuit 17 again generates a signal informing the control circuit 14 that the point C has been detected.

Then, the control circuit 14 stops generating the down signal to the up/down counter 10, and therefore the oscillation circuit 8
The frequency change also stops.

The above operating state is illustrated in FIG. 3.

In FIG. 3, to is when the operation of the operation switch 15 starts, tl is when the timer 16 stops operating, t2 is the time when one peripheral edge of the S curve characteristic [point A in the second diagram] is detected, and t3 is the other peripheral edge. The time when [second figure point B] is detected, and t4 is the time when one peripheral edge part [second figure point C] is detected.

Regarding the down search, the same operation as the above-mentioned up search is performed.

If you want to do a down search. Operate the operation switch 15 to generate a down signal, perform a low-speed down search by the action of the timer 16 for a predetermined period of time from the start of the operation, and then
A high-speed down search is performed until one peripheral edge of the curve characteristic is detected, and then a low-speed down search and a low-speed up search are performed, and the search operation is stopped.

A detailed description of the down search will be omitted since it is substantially the same as the up search except for the direction.

The timer 16 generally sets the time, but in the present invention, the timer 16 is a counter that counts a predetermined number of clock signals applied to the counter 10 or clock signals correlated to the clock signal. Any method that detects a predetermined time after the operation switch 15 is operated is included.

The first feature of the present invention is that the output oscillation frequency of the oscillation circuit 8 is changed at a low speed for a predetermined period from the start of operation of the operation switch 15.

and. By performing a low-speed search for a predetermined period from the start of operation, there is a great advantage that it is possible to prevent search errors in nearby stations due to operational delays, delays until the voltage-controlled oscillation circuit stabilizes, etc.

In a preferred embodiment, the slow search is 24 ms
/digit (requiring 24 m5 of time per count of the counter) for 500 m5.

A second feature of the present invention is that after the low-speed search,
The point is to switch to high-speed search.

Since the search circuit becomes stable after a predetermined period of time has elapsed, the advantage is that the search time can be shortened.

Therefore, in the present invention, after the low-speed search period has elapsed,
It performs high-speed searches and takes full advantage of the above advantages.

In a preferred embodiment, the fast search is performed using 3TrL
The speed is s/digit.

Furthermore, the third feature of the present invention is that one peripheral edge of the S-curve characteristic is detected and the search is switched back to low-speed search, and the other peripheral edge of the S-curve characteristic is detected and the search direction is switched.

This is done in view of the fact that in a correct reception state, there is a pair of peripheral edges on the S curve characteristic, and in order to distinguish between a correct reception state and a case where it is not.

In other words, even if a signal that can be considered as one edge of the S-curve characteristic is detected for some reason, the search operation will not stop unless there is another edge of the S-curve characteristic. The search operation can be stopped only in the correct reception state.

At that time, if another peripheral part of the S-curve characteristic is not detected even after a predetermined period of time has passed after detecting one peripheral part of the S-curve characteristic, applying a circuit that returns to the high-speed state again can shorten the search time. useful for.

After the 0 point of the S-curve characteristic (Fig. 2) is detected, the oscillation frequency of the oscillation circuit 8 can be adjusted by a frequency fine adjustment circuit (not shown), thereby achieving perfect reception. be done.

Incidentally, if the station selected as described above is unnecessary, the search may be performed by operating the operation switch 15 again, or if the search stop signal is not given for a predetermined period of time after selecting the station. The search may be started automatically again.

As described above, the automatic tuning device according to the present invention can achieve accurate and quick tuning, and is particularly effective when used in car radios.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an automatic tuning device according to the present invention, FIG. 2 is a characteristic diagram for explaining the operation of the detection circuit shown in FIG. 1, and FIG. FIG. 2 is a characteristic diagram for explaining in detail. Explanation of main drawing numbers, 8...Oscillation circuit, 10...
...up/down counter, 11...selection circuit, 14...control circuit, 15...operation switch.

Claims (1)

[Claims] 1. In an automatic tuning device that automatically changes the oscillation frequency of a local oscillation circuit to search for a broadcast station,
a first search stage that includes a detection circuit that generates an output signal according to the character characteristics and a timer, and that changes the oscillation frequency in one direction at a low speed from the start of operation until a predetermined period set by the timer elapses; and a second search stage in which the oscillation frequency is changed at high speed in the same direction during a period from the end of the first search stage until the detection circuit detects one peripheral edge of the figure-8 characteristic, and the second search stage a third search stage in which the oscillation frequency is varied at low speed in the same direction from the end of the third search stage until the detection circuit detects the opposite peripheral edge of the figure-eight characteristic; a fourth search stage in which the oscillation frequency is varied at a low speed in the opposite direction until reaching the vicinity of the -periphery of the figure-8 characteristic; and a fourth search stage in which the change in the oscillation frequency is stopped after the fourth search stage is completed. An automatic channel selection device consisting of 5 search stages.