JPH0533078Y2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Field of Industrial Application The present invention relates to a radio receiver using an integrated circuit having at least an FM multiplex circuit having a VCO circuit and an intermediate frequency amplification circuit for AM.

(b) Prior Art Conventionally, as shown in, for example, Japanese Utility Model Publication No. 62-30351, in radio receivers, AM,
An integrated intermediate frequency amplification circuit and detection circuit for FM is used. Also, recently, even more
Attempts are being made to integrate FM multiplex circuits as well. However, the free-running oscillation frequency of the VCO circuit used in the FM multiplex circuit is affected by issues such as the stability and shape of the oscillator (the smaller the oscillation frequency, the worse the oscillation accuracy and the larger the shape). , n (integer)×
Since it is set around 456KHz, if the AM intermediate frequency amplifier circuit and FM multiplex circuit are integrated, the AM intermediate frequency is 450KHz.
or 455KHz and 456K of FM multiplex circuit
The drawback was that it generated beats at Hz, causing deterioration in S/N characteristics, distortion rate, etc. during AM.

(c) Problems to be solved by the invention In consideration of the above-mentioned drawbacks, the invention uses an integrated circuit having at least an FM multiplex circuit having a VCO circuit and an intermediate frequency amplification circuit for AM. , prevent the occurrence of beats,
This improves the S/N characteristics, distortion rate, etc.

(d) Means for solving the problem The radio receiver of the present invention has a switching element connected to the oscillator pin of the integrated circuit, which grounds the oscillator pin when the switching means is switched to the AM side. It is something.

(E) Effect Since the present invention is configured as described above, the VCO circuit of the integrated circuit becomes inactive during AM, thereby preventing the occurrence of beats.

(f) Embodiments Examples of the present invention will be described based on the drawings. 1
is an integrated circuit, and the following circuits are integrated.

That is, 2 is a frequency amplification circuit for AM, which amplifies the signal from the pin at high frequency. 3 is an AM mixing circuit which mixes the signal from the high frequency amplifier circuit 2 and the signal from the local oscillation circuit 4, and outputs an intermediate frequency signal of 450 KHz. Reference numeral 5 denotes an intermediate frequency amplification circuit for AM, which amplifies the intermediate frequency signal from the mixing circuit 3. Reference numeral 6 denotes an AM detection circuit, which performs AM detection on the signal from the intermediate frequency amplification circuit 5 and outputs it to a subsequent low frequency amplification circuit (not shown) via a pin. 7 is a high frequency amplification circuit for FM, which amplifies the signal from the pin at high frequency. 8 is a mixing circuit for FM, which mixes the signal from the high frequency amplifier circuit 7 and the signal from the local oscillation circuit 9. 10 is
This intermediate frequency amplification circuit for FM amplifies the intermediate frequency signal from the mixing circuit 8. Reference numeral 11 denotes an FM detection circuit, which performs FM detection on the signal from the intermediate frequency amplification circuit 10. Reference numeral 12 denotes an FM multiplex circuit which demodulates the signal from the detection circuit 11, divides it into L and R signals, and outputs the signals to a low frequency amplifier circuit (not shown) downstream from the pin, and as is well known, it is a phase comparator circuit. 13, DC amplifier 14, VCO circuit 15,
It is composed of a frequency divider 16 that divides the frequency by 12, a frequency divider 17 that divides the frequency by 2, and a switching circuit 18. The above is the configuration of the integrated circuit 1.

19 is the FM multiplex circuit 12;
This is an oscillator connected to the 15 oscillator pin of the VCO circuit, and is used to bring the free-running oscillation frequency of the VCO circuit 15 close to 456KHz.
20 is a transistor whose collector is connected to a pin via a capacitor 21 and whose emitter is grounded. 22 is a switch that opens and closes in conjunction with a selection switch (not shown) for selecting AM or FM, and one end is connected to the transistor 2 through a resistor 23.
Connect to the base of 0 and connect the other end to the power supply of about 1.5V 24
is connected to.

The selection switch 22 is set to select AM when closed, and in AM mode, the pin of the integrated circuit 1 is grounded. Therefore, during AM, the VCO circuit 15 becomes inactive, thereby preventing the occurrence of beats.

Furthermore, the oscillation frequency of the VCO circuit is 456KHz.
Needless to say, not only that, but also frequencies that are integral multiples of that frequency can be applied.

(g) Effects of the invention Since the invention is configured as described above, during AM, the VCO circuit of the integrated circuit becomes inoperable and oscillation around n×456KHz stops, causing the beat This can be prevented and the S/N characteristics, distortion rate, etc. can be improved. Also, transistors can be used as switching elements.
The operating voltage for disabling the VCO circuit can be set low, providing a high degree of freedom in design, and there is no need to provide a special pin on the integrated circuit for disabling the VCO circuit.

[Brief explanation of the drawing]

The drawing is a block circuit diagram of the radio receiver of the present invention. 1... integrated circuit, 5... intermediate frequency amplification circuit, 1
2...FM multiplex circuit, 15...VCO
Circuit, 19...Resonator, 20...Transistor (switching element), 22...Switch (switching means).

Claims (1)

[Scope of utility model registration request] FM multiplex circuit with VCO circuit and
an integrated circuit having at least an intermediate frequency amplification circuit for AM; and an integrated circuit connected to an oscillator pin of the integrated circuit.
In a radio receiver having an oscillator that brings the free-running oscillation frequency of the VCO close to n (integer) x 456 KHz, and a switching means that operates in response to switching between AM and FM, the oscillator pin of the integrated circuit A radio receiver characterized in that a switching element is connected to ground the oscillator pin when the switching means is switched to the AM side.