JPH0132429Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention is an FM/AM receiver, in particular, equipped with an automatic sweep control circuit, which reduces the sweep speed when the received input signal exceeds a predetermined level during automatic sweep of the FM band. This relates to FM/AM receivers.

Prior Art FIG. 1 is a circuit diagram of the main parts of a conventional FM/AM receiver.

In Figure 1, 1 is a large-scale integrated circuit (LSI) (for example, TC9147P) used in a PLL synthesizer type FM/AM receiver and has a built-in PLL circuit and automatic sweep control circuit. First to third control signal input terminals STP ₁ , STP ₂ , to which control signals for controlling operations are applied;
Equipped with STP ₃ . Among them, the first and second control signal input terminals STP ₁ and STP ₂ are used to control the sweep operation during FM, and the third control signal input terminal
STP ₃ is used to control the sweep operation during AM.

In other words, during FM, the first and second control signal input terminals
A sweep operation is performed when a low level control signal is applied to STP ₁ and STP ₂ , and a sweep operation is performed when a high level control signal is applied to the first control signal input terminal (sweep speed control signal input terminal) STP ₁ . Speed is 1/
2 to ensure that the next sweep operation is stopped. When high-level control signals are applied to both the first and second control signal input terminals STP ₁ and STP ₂ , the sweep operation is stopped. (For example, when an antenna input of approximately 30 dBμV is applied to a 300 Ω antenna terminal and the antenna input is within ±35 KHz from the perfect tuning point, the sweep operation will stop.) In addition, a third control signal input terminal is provided to prevent malfunctions due to noise etc. during FM reception.
I try to add a high level signal to STP ₃ . On the other hand, during AM, the third control signal input terminal
An intermediate frequency signal is applied to STP ₃ , and the AM intermediate frequency is directly counted so that the automatic sweep operation stops within the range of 450KHz±3KHz. A low level control signal is applied to the first and second control signal input terminals STP ₁ and STP ₂ .

In order to control the above-mentioned sweep operation, the circuit shown in FIG. 1 uses four transistors _Q1 to _Q4 . That is, during FM, the transistor _Q2 is fixed in the off state, and it is turned on and off by the signal appearing at the output terminal 2 of a signal meter drive circuit (not shown) using a received input signal level detection circuit, e.g., a light emitting diode (LED) display. controlled transistor
Q ₃ and Q ₄ connect the first control signal input terminal of LSI1
A low level or high level control signal is applied to STP ₁ , and the second control signal input terminal STP is controlled by the FM muting signal appearing at the output terminal ₃ of the FM muting circuit (not shown). A low level or high level control signal is applied to ₂ . Further, a high-level control voltage divided by resistors R ₁ and R ₂ is applied to the third control signal input terminal STP ₃ .

On the other hand, during AM, it is added to amplifier 4 from terminal 6,
The AM intermediate frequency (IF) signal amplified by the amplifier 4 is applied to the third control signal input terminal STP ₃ . or
At AM, transistor Q ₂ is on, transistor Q _{3 is} on.
and fix transistor _Q4 on respectively,
A low level control signal is applied to the first control signal input terminal STP ₁ of the LSI 1. Furthermore
During AM, the FM muting signal appearing at the output terminal 3 of the FM muting circuit is at a high level, so transistor _Q1 is turned on, and the IC
A low-level control signal is also applied to the second control signal input terminal _STP2 of No.1.

In FIG. 1, D ₁ is a reverse current prevention diode, 5 is a power supply line, S ₁ is a band selection switch, and R ₃ and R ₄ are base resistances of transistor Q ₁ .

Problems with the prior art In the conventional circuit shown in Figure 1, the sweep operation must be controlled using four transistors, which has the disadvantage of increasing the number of parts, making the circuit more complex, and increasing costs. .

Purpose of the invention The object of the invention is to provide an FM/AM receiver that eliminates the above drawbacks by reducing the number of transistors used to control the sweep operation.

Embodiment of the invention FIG. 2 is a circuit showing an embodiment of the invention.
Note that for the same parts as in FIG. 1, the same figure numbers as in FIG. 1 will be used.

In the circuit of FIG. 2, two transistors Q ₅ ,
_Q6 is used to connect the first control signal input terminal of LSI1.
A low level or high level control signal is applied to STP ₁ . In other words, the base is the first resistor.
A first stage transistor with an emitter grounded type connected to the output terminal 2 of the signal meter drive circuit via _R5 , and whose collector is connected to the FM side fixed terminal of the band selection switch _S1 via a second resistor _R6 .
_Q5 , the base of which is connected to the collector of transistor _Q5 through a third resistor _R7 , and a fourth resistor
It is connected to the AM side fixed terminal of the band switching switch _S1 via _R8 , and its collector is connected to the first control signal input terminal _STP1 , and is also connected to the power supply line 5 via the fifth resistor _R9 . A low-level or high-level control signal is applied to the first control signal input terminal _STP1 using a second-stage transistor _Q6 having a grounded emitter configuration. The other configurations are the same as the circuit shown in FIG.

Next, the operation of the circuit shown in FIG. 2 will be explained.

During FM, in a completely detuned state, a low level control signal is applied to both the first and second control signal input terminals STP ₁ and STP ₂ of the LSI 1 to perform a sweep operation. When the received input signal approaches the tuning point and exceeds a predetermined level (for example, when the 300Ω antenna terminal
This is when an antenna input of 25 to 26 dBμV or more is added, and at this time it is usually close to the range of ±150KHz from the perfect tuning point. ) The signal appearing at the output terminal 2 of the signal meter drive circuit becomes high level, transistor Q ₅ is turned on, transistor Q ₆ is turned off, and the first control signal input terminal of LSI 1 is turned on.
A high level control signal is applied to STP ₁ and the sweep speed is reduced to 1/2. When the tuning point is further approached (in the range of ±35KHz from the complete tuning point), the signal appearing at the output terminal 3 of the FM muting circuit (not shown) becomes low level, transistor Q ₁ is turned off, and the second transistor of LSI 1 is turned off. Control signal input terminal
A high level control signal is applied to STP ₂ .
In this way, the first and second control signal input terminals of LSI1
When high-level control signals are applied to both STP ₁ and STP ₂ , the sweep operation stops. Also, the third control signal input terminal STP ₃ is connected to a resistor as in the case of Fig. 1.
A high level control signal (voltage of about 5V) separated by R ₁ and R ₂ is applied.

On the other hand, during AM, the base of the transistor Q ₆ is connected from the power supply line 5 to the band selection switch S ₁ and the resistor R _8.
Since voltage is applied through the transistor
_Q6 is fixed on, and a low level control signal is applied to the first control signal input terminal _STP1 of LSI1. Also, as in the case of the circuit in Figure 1, LSI1
A low-level control signal is applied from the collector of the transistor Q ₁ to the second control signal input terminal STP ₂ of the LSI 1, and the third control signal input terminal STP ₃ of the LSI 1
An AM intermediate frequency signal is applied from the amplifier 4 to . When the frequency of the signal applied to the third control signal input terminal STP ₃ is outside the range of 450KHz±3KHz, the sweep operation is performed, and when it falls within the range of 450KHz±3KHz, the sweep operation is stopped.

Note that the amplifier 4 will not operate unless the input signal level is above a predetermined level, and the antenna input during AM should be above a predetermined level (for example, about 90 dBμV/m or higher).
Otherwise, the configuration may be such that the sweep operation does not stop.

In this manner, in the circuit shown in FIG. 2, a low level or high level control signal can be applied to the first control signal input terminal STP1 of the LSI ₁ by using the two transistors _Q5 and _Q6 . In total, the three transistors Q ₁ , Q ₅ , and Q ₆ can control the sweep operation in exactly the same way as in the conventional circuit.

Effects of the invention According to the invention, the number of transistors that control the sweep operation can be reduced, and the circuit can be simplified and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the main parts of a conventional FM/AM receiver, and FIG. 2 is a circuit diagram showing the main parts of the FM/AM receiver according to the present invention. 1...LSI, 2...Output terminal of signal meter drive circuit, 3...Output terminal of FM muting circuit, 5...Power supply line, STP ₁ ...Sweep speed control signal input terminal, S ₁ ...Band switching Switch, _Q5 , _Q6 ...Transistor, _R5 to _R9 ...Resistor.

Claims (1)

[Claims for Utility Model Registration] (1) A receiving input signal level detection circuit that generates a first level DC control signal at an output terminal when the received input signal is at a predetermined level or higher, and a sweep speed control signal input terminal. and the first input terminal is connected to the input terminal.
In an FM/AM receiver equipped with an automatic sweep control circuit that has a function of decelerating the sweep speed when a level DC control signal is applied, and a band switching switch whose common terminal is connected to the power supply line, a first transistor with an emitter-grounded configuration, the base of which is connected to the output terminal of the received input signal level detection circuit via a first resistor, and the collector of which is connected to the FM side fixed terminal of the band selector switch via a second resistor; The base is connected to the collector of the first transistor via a third resistor, and the AM side fixed terminal of the band selection switch is connected via a fourth resistor, and the collector is connected to the sweep speed control signal input terminal. and a second transistor connected to the power supply line via a fifth resistor. The FM/AM receiver is configured such that the first level DC control signal is applied to the sweep speed control signal input terminal to reduce the sweep speed. (2) The FM/AM receiver according to claim 1, wherein the first level DC control signal is a high level DC control signal.