JPS5910817Y2 - receiver tuning circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver tuning circuit in which a local oscillator is phase-locked to a reference oscillator.

In a conventional FM receiver in which a local oscillator is phase-synchronized with a reference oscillator, as shown in FIG. It is mixed with the signal from local oscillator 6.

The intermediate frequency signal thus obtained is selectively amplified by an intermediate frequency amplifier 4 and then detected by an FM detector 5 to obtain an audio signal.

On the other hand, the signal from the local oscillator 6 is phase-compared with the signal from the reference oscillator 10 by a phase comparator 7, and converted into a DC signal by a DC amplifier 8 and a low-pass filter 9 to control the local oscillator 6.

As described above, the well-known phase-locked loop 12 is implemented.

When the FM receiver finishes receiving, turns off the power, and turns on the power again, the local oscillation frequency gradually increases and becomes almost constant at the free-run frequency.

On the other hand, since the above-mentioned phase-locked loop normally has a pull-in width of about 10 to 20 KHZ, if the local oscillation frequency is located outside the pull-in range near the frequency corresponding to the frequency of the signal desired to be received, phase locking is not achieved.

It is also possible to synchronize to a frequency corresponding to an adjacent station.

The present invention has been made with the aim of eliminating the above-mentioned drawbacks, and the local oscillator frequency is varied within an appropriate range until the local oscillator is phase-locked to the target frequency.
This is forcibly phase-synchronized to the target frequency.
A detailed explanation will be given below according to the drawings.

FIG. 2 shows one embodiment of the present invention.

In the figure, parts having the same functions as those in FIG. 1 are given the same reference numbers and their explanations are omitted.

The intermediate frequency signal from the intermediate frequency amplifier 4 is transmitted to the tuning detector 1
7 and the output from low pass filter 9 is applied to a synchronous detector 18.

Outputs from the tuning detector 17 and the synchronization detector 18 are applied to an AND circuit 16.

The output of the AND circuit 16 is applied to the sweep oscillator 14 via the sweep control circuit 15.

In the above, the sweep oscillator 14 varies the oscillation frequency of the local oscillator 6, and as a result, the local oscillator 6 is forced to repeatedly sweep a range of approximately ±40 KHz around the free oscillation frequency.

The sweep period may be determined according to the pull-in time of the phase-locked loop 12, and is set to about 0.5 to 2 Hz, for example.

The tuning detector 17 generates a signal by detecting that the local oscillator 6 approaches the frequency corresponding to the signal desired to be received. For example, during tuning, the tuning detector 17 uses the fact that an intermediate frequency output is generated to generate an intermediate frequency A detection signal is generated when the output of the circuit exceeds a predetermined level.

Furthermore, the synchronization detector 18 is configured to generate a signal when the local oscillator 6 is synchronized. For example, in this embodiment, the output of the phase detector 7 fluctuates when synchronization is lost. The output signal is generated only when there is no signal.

AND circuit 16 generates a signal when signals are simultaneously obtained from both tuning detectors 18, operates sweep control circuit 15, and stops oscillation of sweep oscillator 14.

According to the above structure, when the power is turned off after listening and then turned on again, the local oscillator 6 will be turned off by ±4 as shown in FIG.
It rises while fluctuating in a range of about 0KHZ, and finally begins to fluctuate around the free run frequency.

As a result, even if the free-run frequency is outside the pull-in range of the target frequency for phase locking, the local oscillator 6 is synchronized with the reference oscillator 10 as a result of the above-described fluctuations.

Therefore, a detection signal is obtained from the synchronization detector 18, and when a broadcast is received, the output of the intermediate frequency circuit 4 exceeds a predetermined level, and a detection signal is obtained from the tuning detector 17.

As a result, the sweep oscillator 14 stops oscillating, and the local oscillator 6
is fixed and stable at the frequency corresponding to the desired signal to be received.

On the other hand, if the local oscillator 6 is phase-locked to a frequency different from the target frequency, the signal you want to receive cannot be received, and you will receive, for example, 100 KHz above and below the desired signal. Since no signal is distributed, the input to the tuning detector 17 does not exceed a predetermined level, and therefore no tuning detection signal is generated, so the sweep continues without stopping and finally corresponds to the desired signal to be received. Synchronize to local oscillation frequency.

AND circuit 16 and sweep control circuit 1 in the above embodiment
5. A specific example of the sweep oscillator 14 is shown in FIG.

In FIG. 4, the sweep oscillator 14 consists of a low frequency oscillator made up of transistors T1 and T2, and an integration circuit made up of an output circuit of a transistor T3 and a resistor R capacitor C3. occurs.

? The integrating circuit integrates the square wave and converts it into a triangular wave.

Thereafter, the signal passes through the output circuit and appears at the output terminal 19 to control the local oscillator 6 and vary the oscillation frequency.

The AND circuit 16 is composed of transistors T4 and T5, diodes D1, D2, D3, D4, resistor R1, etc., and drives the sweep control circuit 15 according to the human power level of the input terminals 20, 21, 22.

The sweep control circuit 15 includes a transistor T6 and a reed relay RL4, and drives switches S1 and S2.

The open/close states of switches S1 and S2 with respect to the levels of input terminals 20, 21, and 22 are shown in the table below.

As described above, when the terminal 20 is at the H level, the sweep is stopped only when the terminal 21 is at the power supply level, that is, the H level, and the terminal 22 is at the ground level, that is, the L level.

Now, the output of the synchronization detector 17 is applied to the terminal 21, and the output of the synchronization detector 18 is applied to the terminal 22.

Here, the tuning detector 17 uses a detector whose H level ground becomes an L level during tuning, and the synchronization detector 18 uses a detector whose ground becomes a low level, that is, an L level and an H level during phase synchronization.

As described above, when the power is turned on or if the synchronization is lost for some reason, the terminal 20 is always connected to the power supply and is at a high level, that is, the H level, and the local oscillator 6 starts to fluctuate according to the level of the terminals 21 and 22. , when the phase is synchronized to the frequency corresponding to the desired signal to be received, switches S1 and S are activated as shown in the previous table.
2 is opened by reed relay RL, and no sweep signal is generated, and local oscillator 6 continues to oscillate stably at a predetermined frequency.

Note that the synchronization detector 18 may detect that it is within the synchronization pull-in range by counting the local oscillation frequency.

As described above, the present invention is advantageous in that it is possible to easily obtain a local oscillation frequency corresponding to the desired receiving frequency.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing a conventional FM receiver, Fig. 2 is a block diagram showing an example of an FM receiver according to the present invention, and Fig. 4 is a block diagram showing an example of an FM receiver according to the present invention.
The figure is a circuit diagram embodying a part of the block in the embodiment of FIG. 2, and FIG. 3 is a diagram showing the movement of the output frequency of the local oscillator in the present invention.

Claims (1)

[Scope of utility model registration request] In a receiver tuning circuit comprising a local oscillation circuit in which the local oscillator is phase-synchronized with a reference oscillator, means for reciprocating the oscillation frequency of the local oscillator circuit up and down around its free run frequency; means for detecting that the local oscillation frequency is synchronized with the reference oscillator;
means for detecting that the receiver is tuned to an input high-frequency signal and a tuned output of a predetermined level or higher is obtained; and stopping the sweep of the local oscillator only when the outputs of the two detection means are simultaneously obtained. 1. A receiver tuning circuit comprising: means.