JPS59153335A - Receiver for am and fm - Google Patents

Abstract

PURPOSE:To simplify the constitution by inserting and coupling a high pass filter comprising a coupling capacitor between an output section of an AM detector and an input section of a stereophonic demodulating circuit so as to reduce the number of capacitors. CONSTITUTION:The capacitor 18 is inserted between the output of an FM detecting circuit 14 and the input of a stereophonic demodulating circuit 6 and they are coupled together. The high-pass filter 22 comprising the capacitor 18 and a resistor 20 is inserted between the output of the AM detecting circuit 16 and the input of the stereo demodulating circuit 6 and they are coupled together. Through the constitution above, only one coupling capacitor is enough as the coupling capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AM-FM receiver, and particularly to an AM-FM receiver.
This invention relates to improvements in M detection circuits.

FIG. 1 shows a detection circuit section of a conventional AM-FM receiver. In a ΔM-FM receiver that outputs the AM detection output as an audio signal through a stereo demodulation circuit in the same way as the FM detection output, the FM detector 2 and the AM
Coupling capacitors 8 and 10 with different capacities are individually inserted and coupled between the detector 4 and the stereo demodulation circuit 6, and the output terminal 12 of the stereo demodulation circuit 6 receives an FM detection output or an AM detection output. It is configured to selectively take out ij=. In this way, the FM detector 2 or AM detector 4
A coupling capacitor 8.10 is connected between the and the stereo demodulation circuit 6.
are inserted separately because the demodulation frequency characteristics of the FM detector 2 and AM detector 4 are different.If the capacitances of these coupling capacitors 8.10 are C1 and C2, then F
The capacitance CI of the two M detectors is set to be large enough to be unaffected by the input impedance of the stereo demodulation circuit 6.
Since the capacitor C2 on the detector 4 side constitutes a high-pass filter, it needs to be set to a smaller capacitance than the capacitor C1 (CI>C2).

Inserting the coupling capacitors 8.10 individually in this way means that when each detector 2.4 and the stereo demodulation circuit 6 are configured with an integrated circuit, the coupling capacitors 8.10 are connected to external terminals (pins). However, there are drawbacks such as the need for additional equipment and the equipment itself being expensive.

An object of the present invention is to provide an AM-FM receiver that reduces the required number of capacitors and has a simplified configuration.

This invention provides an AM-F in which the AM detection output is passed through a stereo demodulation circuit and extracted as an audio output.
In the M receiver, a capacitor is inserted between the output 81 of the FM detection circuit (and the input section of the stereo demodulation circuit) to couple the two, and the output section of the AM detection circuit and the input section of the stereo demodulation circuit The present invention is characterized in that a high-pass filter including the capacitor is inserted between the capacitor and the capacitor to couple the two.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the AM-FM receiver of the present invention, in which the same parts as the circuit of FIG. 1 are given the same reference numerals.

In the figure, an FM detection circuit 14 and an AM detection circuit 16 are obtained by adding an output circuit to the output side of the conventional FM detector 2 and AM detector 4 to make the output DC potentials the same.

That is, when a capacitor 18 is inserted between the output side of this FM detection circuit 14 and the input side of the stereo demodulation circuit 6 and the two are coupled, the AM detection circuit 16
A high-pass filter 22 composed of the capacitor 1B and a resistor 2o is inserted between the output side of the stereo demodulation circuit 6 and the input side of the stereo demodulation circuit 6, and the two are coupled.

With this configuration, the number of coupling capacitors is reduced to one, and the configuration can be simplified compared to a conventional coupling circuit. Furthermore, since the output side of the FM detection circuit 14 and the output side of the AM detection circuit 16 are connected via the resistor 20, the number of terminals (pins) in the case of an integrated circuit is greater than that of a conventional circuit. can be configured with less. In particular, resistance 2
The coupling between the FM detection circuit 14 and the AM detection circuit 1G is weakened by o, so that they are not affected by the FM signal during AM detection, and the same applies to the reverse case.

FIG. 3 shows a specific embodiment of the FM detection circuit 14 and AM detection circuit 16 in the present invention. In the figure, the input terminal 30 of the FM detection circuit 14 and the AM detection circuit 1
The input terminal 32 of No. 6 receives an FM signal converted from the intermediate frequency signal g1 (from the intermediate frequency signal G1) and a .DELTA.M multiplied signal.

The mote switching circuit 24 includes the respective emitters of a transistor 36 connected to a constant current source 34 that regulates the operating current of the FM detector 2, and a transistor 40 connected to a constant current source 38 that regulates the operating current of the AM detector 4. are connected in common, and a constant current source 42 is inserted between the emitter and a reference potential point to regulate the sum of the operating currents. A reference bias power supply 44 that applies a reference bias voltage Ve is connected to the base of the transistor 36, and a reference bias power supply 44 that applies a reference bias voltage Ve is connected to the base of the transistor 40.
- A control input terminal 46 is formed to apply a control voltage Vc for AM switching.

Further, in the output circuit 26 of the FM detector 2, diodes 5o and 52 are provided between the FM detector 2 and a power supply terminal 48 to which the drive voltage Vcc is applied. each diode 5
The bases of transistors 54 and 56 are individually connected to the cathode of 0.52, and the diode 50 and transistor 56 constitute a current inverting circuit;
The transistor 54 also constitutes a current inversion circuit.

The emitter of each transistor 54.56 is connected to the power supply line connected to the power supply terminal 48, and a 1-run lister 58.6o is connected between the collector of each transistor 54.56 and the reference potential point. is inserted. 1-
Base-collector of runlister 58 and transistor 6
The bases of transistors 58 and 60 constitute a current inversion circuit.

On the other hand, the output circuit 28 is composed of diodes 62, 64 and transistors 66, 68, 70, 72, and has the same structure as the output circuit 26.

The power supply terminal 73 is supplied with a drive voltage V similar to that of the power supply terminal 48.
cc is applied.

The output terminal 74 of the FM detection circuit 14 is formed at the collector of the 1-run lister 56.60, while the output terminal 76 of the AM detection circuit 16 is formed at the collector of the transistor 68.72, and at each output point. There is resistance 7 between
A common bias power supply 82 is connected via 8.80.

In the above configuration, the control voltage Vc is applied to the control input terminal 46.
When the value of is made higher than the reference bias voltage Vs of the bias power supply, the transistor 40 becomes active and the AMM detector becomes active. In this case, a signal current flows from the output of the AMM detector to the transistor 70.72 via the diode 62.64 and the transistor 66.68, and the AM detection output can be taken out from the output terminal 76.

Further, when the control voltage Vc is lowered than the reference bias voltage VB, the transistor 36 is activated and the F
The MM detector becomes operational. The output of the FMM detector is then connected to the diode 50.52 and the transistor 54.5.
6 into the transistors 58 and 60, and as a result of current combination, an FM detection output can be taken out from the output terminal 74.

That is, the AM detection output and the FM detection output are controlled to have an opposite phase relationship when a signal current is generated and when a signal current is not generated, and their outputs are determined.

In such an operating state, a resistor 78.8 is connected to the collector of the transistor 6o, 72 of each output circuit 26.28.
A DC bias is applied from a common bias power supply 82 through the output terminal 0, and each output point is maintained at the same DC level. As a result, as mentioned above, from FM mode to AM mode,
Alternatively, when switching from AM mode to FM mode, since there is no fluctuation in the DC potential, it is possible to reliably prevent the generation of abnormal sounds, such as popping noises, caused by the switching.

Since the output points of each output circuit 26 and 28 are connected to the common bias power supply 82 in this way, as shown in FIG.
8 to the stereo ijj lta circuit 6, and the output section on the AM detection circuit 16 side can be connected to the stereo demodulation circuit 6 via the high-pass filter 22 including the capacitor 18.

Further, as shown in FIG. 4, a similar effect can be expected by inserting a low-pass filter 88 composed of a resistor 84 and a capacitor 86 between the AM detection circuit 16 and the high-pass filter 22.

As explained above, according to the present invention, by coupling the FM detection circuit, the AM detection circuit, and the stereo demodulation circuit, the coupling capacitor can be omitted and the configuration can be simplified. Interference can also be removed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional AM-FM receiver.
′! FIG. 82 is a block diagram showing an embodiment of the AM-FM receiver of the present invention, FIG. 3 is a circuit diagram showing an AM-FM detection circuit, and FIG. 4 is a block diagram showing another embodiment of the present invention. be. 2...FM detector, 4...AMM detector 14...
・FM detection circuit, 16...AM detection circuit, 18...
・Capacitor, 22...High-pass filter. Figure 1

Claims (1)

[Claims] In an AM/1"M receiver in which the AM detection output is passed through a stereo demodulation circuit and extracted as audio output, a capacitor is installed between the output section of the FM' detection circuit and the input section of the stereo demodulation circuit. A high-pass filter including the capacitor is inserted between the output section of the AM detection circuit and the input section of the stereo demodulation circuit to couple the two. A receiver for M-FM characterized by the following.