JPH0636498B2 - FM stereo demodulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM stereo demodulator, and more particularly to an improved combination circuit of an FM demodulator and a stereo demodulator.

FIG. 1 shows a conventional FM stereo demodulator. Conventionally, an FM demodulator has one output terminal and a stereo demodulator has one or two output terminals. When the stereo demodulator is composed of two output terminals, as shown in FIG.
Output is the phase-locked loop {PLL (Phase-Locked Loop) circuit} of the stereo demodulator 6 via the coupling capacitor 4.
8 is provided to the first input terminal 10A formed on the side of 8 and is also provided to the second input terminal 10B formed on the side of the stereo decoder 14 via another coupling capacitor 12. The stereo decoder 14 has an output terminal 16 for extracting left and right stereo signals separated from the stereo composite signal.
R and 16L are formed.

According to this structure, the stereo composite signal demodulated by the FM demodulator is transmitted to the first and second input terminals 10A and 10B.
To the PLL via capacitors 4 and 12 individually.
Circuit 8 is a pilot signal (19K) in the stereo composite signal.
Hz) is detected to generate a switching signal of 38 KHz, which is a multiplied signal thereof, and is supplied to the stereo decoder 14. A stereo composite signal is given to the stereo decoder 14 from the second input terminal 10B, and the switching signal and the stereo composite signal are combined and the left and right stereo signals are separated and generated at the output terminals 16R and 16L. You can

However, in such stereo demodulation, PL
For the purpose of detecting the pilot signal, the L circuit 8 only needs to be provided with the 19 KHz component of the pilot signal in the stereo composite signal, and the audio signal component acts as an oscillating component with respect to phase synchronization, causing jitter, stereo monaural. This may cause inconvenience such as malfunction of the reproduction determination. Therefore, it is conceivable to reduce the capacitance of the coupling capacitor 4. However, since the coupling capacitor 4 also serves as the coupling capacitor for the stereo decoder 14, a capacitance of a certain value or more is required. When the capacitance is reduced, A high frequency component in the audio signal component is attenuated, resulting in deterioration of stereo separation.

As described above, the PLL circuit 8 is for detecting a pilot signal, and the stereo decoder 14 is for separating left and right stereo signals.
Since the FM demodulator 2 is configured with one output terminal, such inconvenience occurs and makes the configuration of the coupling circuit difficult.

Therefore, according to the present invention, an FM stereo demodulation realizing good stereo reproduction by individually inputting a stereo composite signal from the FM demodulator to the phase locked loop side and a stereo composite signal to the stereo decoder side. The purpose is to provide a device.

That is, the FM stereo demodulation device of the present invention synthesizes an FM demodulator (18) for extracting two demodulation outputs having different phases, and the other of the demodulation outputs obtained by inverting one of the demodulation outputs from the FM demodulator. And a first output combiner (diodes 25, 26, 3 to form a first stereo composite signal).
8 and transistors 30, 34, 42) to synthesize one of the demodulated outputs with the other of the demodulated outputs inverted to form a second stereo composite signal separately from the first stereo composite signal. 2 output combiner (diodes 25, 26, 36 and transistors 28, 32, 40)
And an output circuit (20) having the
A phase-locked loop (8) for receiving the first stereo composite signal from the output combining unit of the first stereophonic capacitor (48) and outputting a switching signal in synchronization with the pilot signal of the first stereo composite signal; The second stereo composite signal is received from the second output combining unit of the output circuit via the second capacitor (50) or the coil, and the switching signal is received from the phase locked loop. And a stereo decoder (14) for separating a stereo signal.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings.

FIG. 2 shows an embodiment of the FM stereo demodulator of the present invention, and the same parts as those of the FM stereo demodulator shown in FIG. In the figure, a stereo demodulator 2
An output circuit 20 is formed for the demodulation circuit 18 in order to individually take out the stereo composite signal corresponding to the PLL circuit 8 and the stereo decoder 14, and the output circuit 20 has a first circuit.
And second output terminals 22A and 22B are formed.
That is, diodes 25 and 26 are arranged with their anodes on the power supply line side between each amplification element of the differential circuit installed inside the demodulation circuit 18 and the power supply line to which the drive voltage Vcc is applied from the power supply terminal 24. The bases of the transistors 28 and 30 are commonly connected to the cathode of the diode 25, and the bases of the transistors 32 and 34 are similarly commonly connected to the cathode of the diode 26. The emitters of the transistors 28, 30, 32, 34 are commonly connected to the power supply line, and the diode 3 is provided between the collectors of the transistors 28, 30 and the reference potential point (GND).
6, 38 are connected to each other, and transistors 32, 34 are connected.
A transistor 40 between the collector of and the reference potential point,
42 is connected so that the emitter is on the reference potential point side.
The base of the transistor 40 is connected to the anode of the diode 36, the base of the transistor 42 is connected to the anode of the diode 38, and the collectors of the transistors 34 and 42 have the first output terminal 22A and the collectors of the transistors 32 and 40. The second output terminal 22B is formed. That is, demodulation outputs having different phases are individually added to the output circuit 20 from the demodulation circuit 18, and the diodes 25, 26, 38 and the transistor 3 are added.
Reference numerals 0, 34, and 42 denote a first output combining unit that inverts the demodulated output to one of the demodulated outputs to combine the first stereo composite signal, the diodes 25, 26, 36, and the transistor 2.
Reference numerals 8, 32, and 40 constitute a second output synthesizing unit which inverts the demodulated output to one of the demodulated outputs and synthesizes the second stereo composite signal separately from the first stereo composite signal.

The first coupling element 44 is connected to the first output terminal 22A.
The input terminal 10A of the PLL circuit 8 is connected to the input terminal 10B of the stereo decoder 14 via the second coupling element 46, and the input terminal 10A of the PLL circuit 8 is connected to the second output terminal 22B.
The first coupling element 44 is composed of a capacitor 48 having a small capacity that allows the pilot signal component in the stereo composite signal to pass therethrough. The second coupling element 46 is composed of a capacitor 50 having a capacitance sufficient to pass an audio signal component in the stereo composite signal or a trap coil resonating with 19 kHz.

According to such a configuration, the stereo composite signal can be taken out from the output terminal of the FM demodulator 2, and the pilot signal component can be effectively given to the PLL circuit 8 via the first coupling element 44. Since the audio signal component can be attenuated by the first coupling element 44, the synchronous operation of the PLL circuit 8 is improved, and it is possible to prevent the occurrence of jitter and the malfunction during transient. Particularly, since the system is separate from the stereo decoder 14, the coupling element 44
The capacitor 48 may have a small capacity, for example,
It is possible to use a capacitive element or the like on the integrated circuit.

Further, the stereo composite signal taken out from the second output terminal 22B is given to the stereo decoder 14 via the second coupling element 46 which does not cause the attenuation of the audio signal component, and the deterioration of the stereo separation characteristic can be prevented.
In particular, the influence of the pilot signal can be eliminated by using a trap coil having a frequency selection characteristic of 19 KHz.

Further, the first output terminal 22A has an automatic frequency control (AF) (not shown) formed in the stereo demodulator 6.
Even if the output terminal formed for C) is also used, the same effect can be expected.

Further, in the exemplary embodiment, the first and second coupling elements 44, 46 are
However, the same effect can be expected by using a filter having a predetermined frequency pass characteristic in order to improve each signal processing. Furthermore, although the first and second coupling elements 44 and 46 are described as capacitors or trap coils in the embodiment, a filter having a predetermined frequency pass characteristic may be used in order to perform good signal processing.

As described above, according to the present invention, an output circuit is provided which individually synthesizes and extracts the first and second stereo composite signals from the demodulated outputs of the FM demodulator having different phases,
By giving the corresponding first or second stereo composite signal to the phase-locked loop and the stereo decoder respectively, it is possible to prevent the occurrence of jitter due to the audio signal component to the phase-locked loop and the malfunction at the time of transient, and to the stereo decoder. Can remove the influence of the pilot signal component, can obtain good stereo separation characteristics without attenuating the audio component.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional FM stereo demodulator, and FIG. 2 is a circuit diagram showing an embodiment of the FM stereo demodulator of the present invention. 2 ... FM demodulator 8 ... Phase locked loop 14 ... Stereo decoder 18 ... Demodulation circuit 20 ... Output circuit 25, 26, 38 ... Diode (first output combining unit) 30, 34, 42 ... Transistor (first output combining unit) 25, 26, 36 ... Diode (second output combining unit) 28, 32, 40 ... Transistor (second output combining unit) 48 ... First capacitor 50 ... … Second capacitor

Claims (1)

[Claims] 1. An F for extracting two demodulated outputs having different phases.
Of the demodulated output together with the M demodulator and the first output combiner that combines the demodulated output from the FM demodulator with the other of the demodulated output inverted from one of the demodulated outputs to form a first stereo composite signal. An output circuit including a second output combining section that combines the other of the demodulated outputs inverted to one to form a second stereo composite signal separately from the first stereo composite signal, and this output circuit A phase-locked loop that receives the first stereo composite signal from the first output combining unit via a first capacitor, and outputs a switching signal in synchronization with a pilot signal of the first stereo composite signal; Receiving the second stereo composite signal from the second output combiner of the circuit via the second capacitor or coil and receiving the switching signal from the phase locked loop; Serial FM stereo demodulation device characterized by comprising a stereo decoder for separating a stereo signal from the stereo composite signal.