JPH0418267Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a demodulation device that processes FM detection, AM detection, and stereo demodulation using a single IC. Regarding prevention of display malfunction.

[Conventional technology]

The demodulation device that performs FM detection, AM detection, and stereo demodulation includes a demodulation IC2 as shown in Figure 2.
, a mixer/detection section 4 that performs FM detection or AM detection after converting the high frequency input;
A stereo demodulation/display unit 6 that separates the stereo signal from the detection output from the detection unit 4 or passes the detection output other than the stereo signal and generates a stereo display output is installed on a single semiconductor substrate. It is something.

In this demodulation IC 2, a high frequency signal 10 applied to an input terminal 8 is applied to a mixer circuit (MIX) 12 as a frequency conversion means, and mixed with a local oscillation frequency from a local oscillation circuit (0SC) 14. After being converted to intermediate frequency (IF), FM/
It is amplified by an AM intermediate frequency amplification circuit (IF-AMP) 16. In FM reception mode, IF-AMP
The intermediate frequency output taken out from 16 is added to the FM detection circuit (FM-DET) 18 consisting of a quadrature detector etc., and the FM detection output is obtained from the intermediate frequency output. , the intermediate frequency output taken out from the IF-AMP 16 is applied to an AM detection circuit (AM-DET) 20, and an AM detection output is obtained from the intermediate frequency output.

Then, the FM detection output passes through the amplifier 22, and the AM detection output undergoes low frequency cutting by the capacitor 28 connected to the external connection terminals 24 and 26, passes through the amplifier 30, and then passes through the common signal path 32.
is inputted to the stereo demodulation/display section 6 from there. A capacitor 36 connected to external connection terminals 33 and 34 is inserted into the signal path 32, and the capacitor 36 is connected to the external connection terminals 33 and 34.
The DC component of each detection output is cut off by a capacitor 36.

The FM detection output or AM detection output input to the stereo demodulation/display unit 6 is passed through an amplifier 38 to a phase-locked loop (PLL) 40 and a synchronous detector 42.
and a stereo decoder (DEC) 44.

In the stereo mode, the PLL 40 outputs a switching signal synchronized with the pilot signal (19kHz) in the stereo composite signal given by the FM detection output and applies it to the synchronous detector 42 as a stereo detection means, and also outputs a switching signal of 38kHz. Output the signal and add it to DEC44. Therefore, in the stereo mode, the switching signal from the PLL 40 causes the DEC 44 to enter the stereo demodulation mode, separates the stereo signal from the stereo composite signal applied from the amplifier 38, and outputs the stereo demodulation output to the output terminals 46A and 46B. taken from.

In addition, in monaural mode, the DEC44 is in a signal passing state, and the monaural FM detection output or AM detection output added from the amplifier 38 is output to the DEC44.
4 and is taken out from output terminals 46A and 46B. 48 is a common output terminal 46A, 46
This represents the stereo demodulation output, monaural mode FM detection output, or AM detection output extracted from B.

Then, the synchronous detector 42 generates a phase comparison output as a detection output of the pilot signal depending on the switching signal from the PLL 40 and the presence or absence of the pilot signal in the FM detection output, and this phase comparison output is added to the trigger circuit 50. It will be done. In the stereo demodulation mode, the trigger circuit 50 is activated and its output causes the transistor 52 to conduct. Therefore, the external connection terminal 54 and the power supply terminal 5
Since an operating current flows through a transistor 52 to a light emitting diode (LED) 60 connected to the LED 60 through a resistor 58, the stereo demodulation mode is indicated by light emission from the LED 60.

[Problem that the invention attempts to solve]

By the way, in such a demodulator, the synchronous detector 42 may malfunction due to fluctuations in the output DC potential when the power is turned on or off or when switching between AM and FM, or due to low frequency components of the audio signal, resulting in stereo demodulation. There was a risk that LED 60 would light up in addition to the mode.

Therefore, this idea is based on such FM detection,
The present invention aims to provide a demodulator that prevents malfunctions in stereo demodulation display in a demodulation device that realizes AM detection, stereo demodulation, and stereo demodulation display using a single IC.

[Means for solving problems]

The demodulation device of this invention, as shown in FIG.
The FM detection output or the AM detection output is added to the stereo demodulation means (stereo demodulation/display unit 6) through the common signal path 32, and the FM detection output or AM detection output other than the stereo demodulation output is sent to the common output terminal 46A. , 46B, and stereo demodulation means (stereo demodulation/
In a demodulator, the stereo detection means (synchronous detector 42) is installed on the display section 6) side to detect a pilot signal from the FM detection output and generate a stereo display output.
2), the FM detection output is supplied through a signal path 64 which is independent of the signal path 32 and has a low frequency cutoff means (capacitor 62) inserted therein.

[Effect]

In this way, stereo demodulation means (stereo demodulation/
Separately from the signal path 32 that supplies FM detection output and AM detection output to the display section 6), a signal path 6 in which a low frequency blocking means (capacitor 62) is inserted.
4 through stereo detection means (synchronous detector 42)
Since the FM detection output is added to the FM detection output, the low frequency cutoff means (capacitor 62) blocks DC potential fluctuations and low frequency components, increasing the reliability of pilot signal detection for stereo detection. Malfunctions of demodulation display can be prevented.

〔Example〕

FIG. 1 shows an embodiment of the demodulator of this invention.

As shown in FIG. 1, this demodulation device supplies a first FM detection output between a synchronous detector 42 as a stereo detection means installed in the stereo demodulation/display unit 6 and the FM-DET 18. signal path 3
2, a signal path 64 in which a capacitor 62 as a low frequency cutoff means is inserted is installed, and the FM-
The second FM detection output from DET18 is connected to signal path 6.
4 to the synchronous detector 42. The FM-DET 18 can be configured, for example, by a quadrature detector, and in the quadrature detector, two detection outputs are first and second.
FM detection output can be output simultaneously.

The capacitor 62 installed in the signal path 64 is
It has a capacitance that blocks low frequency components and allows the pilot signal of the stereo composite signal to pass through, and can be constituted by, for example, a capacitive element on the demodulating IC 2 of about 100 pF.

Therefore, the high frequency signal 10 applied to the input terminal 8 is applied to the MIX 12 as a frequency conversion means, mixed with the local oscillation frequency from the OSC 14 and converted to an intermediate frequency IF, and then converted to an intermediate frequency IF.
Amplified by AMP16.

By the way, in AM reception mode, IF-AMP1
The intermediate frequency output taken from 6 is AM-DET
20, and the AM detection output is obtained from the intermediate frequency output. This AM detection output is subjected to a low frequency cut via a capacitor 28, and furthermore,
Capacitor 3 in signal path 32 through amplifier 30
After the direct current component is removed by 6, it is applied to the PLL 40 and DEC 44 via the amplifier 38.

In addition, in FM reception mode, the intermediate frequency output taken out from IF-AMP16 is transmitted to FM-DET18.
The first and second FM detection outputs are obtained from the intermediate frequency output. The first FM detection output is passed through the amplifier 22, and after the DC component is cut off by the capacitor 36 in the signal path 32, it is applied to the stereo demodulation/display unit 6, and the second FM detection output is , after the low frequency components are removed via the capacitor 62 of the signal path 64,
It is added to the synchronous detector 42.

Since the stereo composite signal includes a pilot signal, the PLL 40 outputs signals of 19 kHz and 38 kHz, for example, in synchronization with the pilot signal.
Outputs a Hz switching signal. The 19 kHz switching signal is applied to the synchronous detector 42, and the 38 kHz switching signal is applied to the DEC 44. Therefore, the switching signal from the PLL 40 puts the DEC 44 into stereo demodulation mode, separates the stereo signal from the stereo composite signal applied from the amplifier 38, and the stereo demodulated output is taken out from the output terminals 46A and 46B.

At this time, the synchronous detector 42 generates a phase comparison output as a detection output of the pilot signal depending on the switching signal from the PLL 40 and the presence or absence of the pilot signal in the FM detection output, and this phase comparison output is sent to the trigger circuit 50. Added. The trigger circuit 50 is activated by this phase comparison input.
The trigger output causes transistor 52 to conduct. Therefore, in the stereo demodulation mode, an operating current flows through the LED 60 through the transistor 52, and the stereo demodulation mode is indicated by the light emission of the LED 60.

In addition, in monaural mode, the DEC44 is in a signal passing state, and the monaural FM detection output or AM detection output added from the amplifier 38 is output to the DEC44.
4 and is taken out from output terminals 46A and 46B. At this time, since there is no pilot signal due to the stereo composite signal, the synchronous detector 42
The detection output is canceled and the LED 60 does not light up.

In this way, the common output terminals 46A, 46B
A stereo demodulation output, a monaural FM detection output, or an AM detection output can be extracted from the stereo demodulation output, and the stereo demodulation mode can be displayed using the LED 60.

[Effect of idea]

As explained above, according to this invention, in addition to the signal path that supplies FM detection output and AM detection output to the stereo demodulation means, the FM detection output is sent to the stereo detection means through a signal path in which a low frequency cutoff means is inserted. Therefore, the low frequency blocking means can block low frequency components such as DC potential fluctuations and AM detection output, increasing the reliability of pilot signal detection for stereo detection.
Malfunctions of stereo demodulation display can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the demodulator of this invention, and FIG. 2 is a block diagram showing a conventional demodulator. 2...Demodulation IC, 4...Mixer/detection section, 6
... Stereo demodulation/display section, 32, 64 ... Signal path, synchronous detector as stereo detection means, 6
2... Capacitor as a low frequency blocking means.

Claims (1)

[Claim for Utility Model Registration] FM detection output or AM detection output is added to the stereo demodulation means through a common signal path, and stereo demodulation output or FM detection output or AM detection output other than the stereo demodulation output is taken out from the common output terminal. In addition, in the demodulation device, the stereo detection means is installed on the stereo demodulation means side for detecting a pilot signal from the FM detection output to generate a stereo display output, the stereo detection means being independent of the signal path and A demodulator characterized in that an FM detection output is supplied through a signal path in which a low frequency cutoff means is inserted.