JPH028441Y2 - - Google Patents

Description

[Detailed explanation of the idea] (b) Industrial application fields The present invention relates to an automatic sweeping receiver.

(b) Prior art Conventionally, the device has a sweep stop signal input terminal, and stops the sweep operation when a DC signal of a predetermined level or higher, for example, a signal meter output of a predetermined level or higher is applied to this input terminal from a reception input signal level detection circuit. An automatic sweep receiver equipped with an automatic sweep control circuit having the function of

FIG. 1 is a circuit diagram showing a conventional example of this type of automatic sweep receiver.

In Figure 1, 1 is an integrated circuit (IC) for an AM receiver (for example, LA1245), and this IC includes an AM radio frequency amplification (RF) circuit 2, a local oscillation circuit (OSC) 3,
A mixing circuit (MIX) 4, an intermediate frequency amplification (IF) circuit 5, a detection circuit 6, a reception input signal level detection circuit that generates a DC signal according to the magnitude of the reception input signal level, such as a signal meter drive circuit 7, and an automatic It has a built-in gain control (AGC) circuit 8, etc.
9 is the smoothing circuit of the AGC circuit 8, and the detection output terminal 1
0 and the AGC signal input terminal 11, and a capacitor C1 connected between the connection point 12 of the resistors R1 and R2 and the ground 13.
It is composed of. 14 is a signal meter output terminal from the signal meter drive circuit 7. 15 is an integrated circuit (e.g.
TC9147P), (STP1) and (STP2) are sweep stop signal input terminals, and the sweep operation stops when both input terminals reach high level. (C2) is a capacitor for grounding the alternating current portion of the signal meter output from the signal meter output terminal 14 to prevent the automatic sweep control circuit in the IC 15 from malfunctioning. D1 is a backflow prevention diode, R3 is a current control resistor, R4 is a load resistor for signal meter output, and SVR1 is a variable resistor for voltage adjustment.

By the way, the signal meter output terminal 14 is connected to the sweep stop signal input terminal STD of the automatic sweep control circuit.
1. The sweep operation is stopped when the voltage applied to STP2 reaches a high level of a predetermined level (for example, 2.5V) or higher.

However, in the case of the circuit shown in Figure 1, if a rapid tuning operation is performed, the AGC will not work before the tuning point and the meter output will rise momentarily and a peak will appear, and the automatic sweep will occur at the peak before the tuning point. The drawback was that the control circuit malfunctioned and the sweep operation stopped.

For this reason, the applicant of the present application previously proposed a circuit as shown in FIG. 2 in Japanese Patent Application No. 162,713/1983. That is, we have proposed a circuit in which a series circuit 16 consisting of a resistor R5 and a diode D2 is connected in parallel to the smoothing circuit 9 between the detection output terminal 10 of the IC1 and the AGC signal input terminal 11.

In the case of the circuit shown in FIG. 2, when the received input signal level rapidly increases near the tuning point during the sweep operation, the diode D2 becomes conductive and the smoothing circuit 9 is short-circuited. Therefore, the rising operation of the AGC circuit 8 becomes faster, and the peak of the signal meter output before the tuning point is suppressed. Therefore, when a peak occurs before the tuning point, the sweep stop signal input terminal STP of IC15
1. Since the voltage applied to STP2 does not reach a high level higher than a predetermined level, the automatic sweep control circuit does not stop the sweep operation. Then, when the voltage applied to the sweep stop signal input terminals STP1 and STP2 reaches a high level as the tuning point approaches, the automatic sweep control circuit operates to stop the sweep operation.

However, in the case of the circuit shown in FIG. 2, there is a drawback that the distortion of the detected output signal becomes large in the low range of the detected output signal during normal reception (during tuning). That is, during normal reception, the detection output terminal 10 and the AGC signal input terminal 11
The DC potential is almost the same as that of , but the low frequency (about 100
Hz or less) appears at the detection output terminal 10, since only one diode constitutes the series circuit 16 between the detection output terminal 10 and the AGC signal input terminal 11, the detection output signal The positive peak diode D2 conducts. Therefore, current flows from the detection output terminal 10 to the AGC signal input terminal 11 via the resistor R5 and diode D2, the gain of the high frequency (RF) circuit 2 decreases, and the detection output signal of the detection output terminal 10 becomes as shown in Fig. 3. This results in a distorted output waveform.

(c) Purpose of the invention In view of the above, the object of the present invention is to obtain an automatic sweep receiver that prevents the detection output signal from being distorted during normal reception.

(d) Embodiment of the invention FIG. 4 is a circuit diagram showing an embodiment of the invention. In FIG. 4, for the same parts as in FIGS. 1 and 2, the same figure numbers as in FIGS. 1 and 2 will be used.

In the circuit shown in Figure 4, the detection output terminal 10 of IC1
and the AGC signal input terminal 11, a series circuit 16' consisting of a resistor R5 and two diodes D2 and D3 with their cathodes facing the AGC signal input terminal 11 side.
are connected.

In this way, in the circuit of FIG. 4, the series circuit 16'
Since two diodes are used for the detection output terminal 10, during normal reception, when a low frequency detection output signal with an amplitude of 1.0V or more appears at the detection output terminal 10, the diode D2, D3
is not conductive. Therefore, at this time, the detection output terminal 10
Since no current flows from the AGC signal input terminal 11 to the AGC signal input terminal 11, the gain of the radio frequency (RF) circuit 2 does not decrease. Therefore, the detection output signal at the detection output terminal 10 has an output waveform without distortion as shown in FIG.

Further, when the received input signal level suddenly increases as the tuning point approaches the tuning point during the sweep operation during tuning, the diodes D2 and D3 become conductive and the smoothing circuit 9 is short-circuited.
Therefore, the rising operation of the AGC circuit 8 becomes faster,
The peak of the meter output (VSM) before the tuning point is suppressed. Therefore, when a peak occurs before the tuning point, the sweep stop signal input terminal STP1 of IC15,
The voltage applied to STP2 is at a predetermined level (approximately 2.5V)
Since the level does not reach the above high level, the automatic sweep control circuit does not stop the sweep operation. Then, as it approaches the tuning point, the sweep stop signal input terminals STP1 and STP
Only when the voltage applied to 2 reaches a high level does the automatic sweep control circuit operate and stop the sweep operation.

In the embodiment shown in FIG. 4, an example was explained in which two diodes were used in the series circuit 16'.
Depending on the characteristics of IC1, etc., three or more diodes may be used.

(e) Effects of the invention As described above, according to the automatic sweep receiver according to the invention, distortion of the detected output signal can be prevented with an inexpensive and simple circuit configuration.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams showing the main parts of a conventional automatic sweep receiver, Figure 3 is a detection output waveform diagram when the circuit in Figure 2 is used, and Figure 4 is an automatic sweep receiver according to the present invention. FIG. 5 is a circuit diagram showing the main parts of the sweep receiver, and is a detection output waveform diagram when the circuit shown in FIG. 4 is used. 8...AGC circuit, 9...Smoothing circuit, R5...
Resistor, D2, D3...diode.

Claims (1)

[Scope of utility model registration request] Has a smoothing circuit connected to the detection output terminal
It has an AGC circuit, a reception input signal level detection circuit that generates a DC signal according to the magnitude of the reception input signal level, and a sweep stop signal input terminal, and the input terminal is supplied with a predetermined level from the reception input signal level detection circuit. In an automatic sweep receiver equipped with an automatic sweep control circuit having a function of stopping the sweep operation when the above DC signal is applied, a series circuit consisting of a resistor and a plurality of diodes is connected in parallel to the smoothing circuit of the AGC circuit. Automatic sweep reception characterized in that the smoothing circuit is connected to the circuit and the smoothing circuit is short-circuited based on the detection output signal when the receiving input signal level suddenly changes, and low-frequency distortion of the detection output signal is prevented during normal reception. Machine.