JPS5940323B2 - FM receiver - Google Patents

Description

[Detailed Description of the Invention] The present invention provides an excellent FM system that can always obtain the optimum tuning point even when the reception frequency fluctuates or the intermediate frequency fluctuates.
The purpose is to provide a receiver.

EMBODIMENT OF THE INVENTION Hereinafter, the FM receiver of this invention is demonstrated with the drawing of one Example.

In the figure, 1 is a quadrature detection FM detection circuit, 2 is a DC amplifier that amplifies the DC component of the output of the detection circuit 1, and 3 is a coil L1, capacitors CVI, C4, C
3. A local oscillation circuit including a variable capacitance diode D4 and the like. Q0, Q2, Q3, and Q4 are transistors constituting the first control means, Q5 is a transistor constituting the second control means, 02 is a charging/discharging capacitor, and 51 is a changeover switch. In addition, the ON terminal O of the changeover switch 51
N is connected to the output end of a muting circuit (not shown) via a diode D1.

In the above embodiment, since the FM detection circuit 1 is of the quadrature detection type, the voltage appearing at the reference voltage terminal a of the detection circuit 1 is not OV but a constant voltage (for example, 5 or 6 V).

Therefore, a DC output component appears at the DC output terminal of the detection circuit 1 so as to draw an s-curve with this constant voltage as a reference. Now, if the switch 51 is turned on to the off terminal OFF, the base of the transistor Q1 is grounded via the switch 51, so the transistor Q
1 is off, transistor Q2 is on, transistor Q3
is off, and transistor Q4 is on.

Therefore, in this case, current will flow from the +B power supply through resistor R5, diode D2, resistor R8, and transistor Q4, and capacitor C2 will have approximately resistor R5.
, R8 will be applied. In other words, current also flows through the transistor Q4 through resistors R6 and R8, but if the value of resistor R6 is made sufficiently larger than the value of resistor R5, the current flowing through resistor R6 becomes the current flowing through resistor R5. However, the voltage applied to the capacitor C2 becomes the value obtained by dividing the +B power supply by the resistors R5 and R8. Then, this voltage is constantly applied to the variable capacitance diode D4 that constitutes the local oscillation circuit 3 via the resistor R12, and the local oscillation circuit 3 is connected to the variable capacitance diode D4.
4, capacitor CVI, C4, and C3 at a frequency determined by coil L1. If we start the tuning operation in this state and change the value of the capacitor CV1, a DC output component will appear from the detection circuit 1 in an s-curve with the reference voltage as the center as described above, and this will be generated by the resistor. Applied to the base of transistor 05 via R9. Therefore, the transistor Q5, which is normally set to be off, turns on, and a current starts to flow through the resistor RlOl transistor Q5 and the resistor Rll. Therefore, the accumulated charge acts on the capacitor C2 to be discharged through the resistor RlO, the transistor Q5, and the resistor Rll, but in this case, since the value of the resistor RlO is set sufficiently large, the transistor Q5 is turned on.
The voltage applied to the variable capacitance diode D4 can be kept at a substantially constant value determined by the resistors R5 and R8 regardless of whether it is off or not. As a result, when the switch S1 is set to the OFF terminal, the tuning operation can be performed in the same way as a normal FM receiver. Next, the case where the switch S1 is turned on to the ON terminal will be described.

When the switch S1 is connected to the ON terminal 0N, a predetermined output appears only when in tune, and when detuned, the signal that appears at the output terminal of the muting circuit, which is substantially in ground units, is sent to the base of transistor Q1 via diode D1. Therefore, when detuning, the same operation as when the switch S is turned to the off terminal OFF occurs. Then, when the tuning region is entered and a predetermined output in the positive direction appears at the output terminal of the muting circuit, diode D1 is substantially turned off, and the +B lightning source is turned off by resistor R.
1 to charge the capacitor C1. Therefore, the voltage across capacitor C1 gradually increases, and after a certain period of time determined by resistor Rl and capacitor C1 has elapsed, transistor Q is turned on.
2 off, transistor Q3 on, transistor Q4
turn off. Therefore, in this state, diode D2 becomes reverse biased, and no current flows through resistor R5, diode D2, resistor R8, and transistor Q4. In this state, the +B power is exclusively applied to the capacitor C2 through the resistor R6. By the way, when the tuning region is entered and a predetermined output appears at the output end of the muting circuit, a DC output component forming an S curve centered on the reference voltage has already appeared from the detection circuit 1. Now, if the receiving frequency fluctuates while the tuning point is at the perfect tuning point, transistor Q5 will turn on and off according to the S curve of the output of the wave circuit, and will always be in perfect tuning regardless of the above fluctuations. Control it so that it becomes a point. In other words, if a DC output component greater than the reference voltage is now buried at the output end of the FM detection circuit 1 with a deviation from the perfect tuning point, the transistor Q5 turns on as described above and gradually removes the charge accumulated in the capacitor C2. is discharged through the resistor RlO, the transistor Q5, and the resistor Rll,
By lowering the voltage across capacitor C2, local oscillation circuit 3
control to increase the oscillation frequency. Furthermore, when the DC output component appearing from the output terminal of the FM detection circuit 1 is lower than the above reference voltage, the transistor Q5 is turned off and acts to charge the capacitor C2 through the resistor R6, increasing the voltage across the capacitor C2. The oscillation frequency of the local oscillation circuit 3 is controlled to decrease. In this way, when the switch S is turned on to the ON terminal ON, the transistor Q5 is turned on and off so that a perfect tuning point is always obtained. As is clear from the above embodiments, the present invention includes a first control means comprising transistors Ql, Q2, Q3, Q4, etc. controlled by the output of the muting circuit, and Using a charged capacitor and a second control means such as a transistor Q5 controlled by the DC component of the output of the FM detection circuit, the oscillation frequency of the local oscillation circuit is controlled by the voltage appearing across the capacitor. Even if a quadrature detection circuit is used as the FM detection circuit, it can effectively correct fluctuations in the reception frequency and always obtain the optimum tuning point, making it extremely advantageous in practice. be.

In the embodiment, a quadrature detection circuit is used as the detection circuit, but the same effect can be obtained even if a normal ratio detection circuit is used.

[Brief explanation of drawings]

The figure is a schematic electrical connection diagram of an embodiment of the FM receiver of the present invention. 1...FM detection circuit, 2...DC amplifier, 3...Local oscillation circuit, Ql, Q4...
- Transistor Q5 constituting the first control means...
...A transistor constituting the second control means.

Claims (1)

[Claims] 1. A first control means that is controlled by the output of the muting circuit and outputs a predetermined voltage during detuning, and outputs a voltage higher than the above voltage during tuning, and a capacitor that is charged by the output of this control means. and a second control means that is controlled by the DC component of the output of the FM detection circuit and configures a discharge circuit for the capacitor, and controls the oscillation frequency determining element of the local oscillation circuit by the voltage appearing across the capacitor. An FM receiver that is controlled and configured to always be in the optimal tuning state.