JPS63278430A - Detector for sca channel - Google Patents

Abstract

PURPOSE:To attain a small-sized device by detecting a signal of an auxiliary communication job channel directly from an FM stereo scopic composite signal so as to reduce the fine adjustment of the entire detector. CONSTITUTION:A local oscillation circuit 100 using a PLL circuit and a frequency divider circuit so as to output signals fa2, fb2 whose frequencies are coincident respectively with the frequencies fa, fb to be selected by a digital frequency modulation (FSK) carrier and a 1st detection circuit 300 detecting the presence and absence of a DC term in a beat component being a difference of frequency obtained through the multiplication between the fa2 signal and the FM stereo scopic composite signal so as to detect the presence and absence of the fa component in the FSK carrier are provided. Moreover, the 2nd detection circuit 400 detecting the presence and absence of a DC term in the beat component being the frequency difference through the multiplication of the fb2 signal and the FM stereo scopic composite signal to detect the presence and absence of the fb component of the FSK carrier is provided. Thus, the fine adjustment of the detector is decreased and the small-sized device is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a detection device for an SCA channel in an FM stereo composite signal.

[Conventional technology]

Currently, American FM stereo broadcasts range from 53 to 99 K.
S C where the frequency between llzO is the instantaneous frequency of the carrier wave
A (Subsidiary Communicatio
nAuthorization; auxiliary communications service) FM that multiplexes channels to create an FM stereo composite signal
Broadcasting is underway.

FIG. 2 shows the frequency spectrum of the FM stereo composite signal. In Figure 2, 10 parts of OK11z
The frequency band of ~15 K11z is the signal of the stereo main channel, the frequency band of 23 K11z to 53 K11z of the 20 part is the signal of the stereo circulation channel, and the 19 Knz of the part 6 between both channels is the pilot signal.

And the SCA channel signal is 53 KH of 40 parts
It is in the frequency band of z~99 IGlz. As a signal of this SCA channel, a certain digital signal is converted into a phase continuous F
S K (Frequency 5hirt Keyi)
When using a signal modulated by ng (digital frequency modulation) method, the conventional method of detecting the SCA channel signal from the FM stereo composite signal is to extract the SCA channel signal using a bandpass filter with a steep cutoff characteristic, and then A method of frequency detection for this is generally used. Figure 3 shows a block diagram of a conventional detection device, and Figure 4 shows the demodulation process. Input the FM stereo composite signal and first pass the steep band pass filter (BPF).
) 11, frequency components other than the SCA channel are cut and only the FSX signal of the SCA channel is extracted.

The waveform of the FSK signal is shown in A of FIG.

Next, the frequency detector 12 detects the FSX signal.
Devices for this frequency detection include, for example, Foster seesaw type, ratio type, quadra chair type, PLI, (
There are various types such as phase locked loop (phase locked loop) type and pulse count type, but each type of circuit is
A voltage corresponding to the frequency shift of the FSX signal is detected as shown in FIG. A timing signal for reading the positive or negative of this voltage is generated by the timing circuit 16 as shown in C in Figure 4 (
. Finally, using this timing signal, the identification circuit 16 reads the sign of the voltage and determines the sign, thereby demodulating it into the original digital signal and obtaining the demodulated signal D in FIG. 4.

[Problem that the invention seeks to solve]

When detecting an SCA channel signal from an FM stereo composite signal using the various conventional frequency detectors described above, a bandpass filter (
Unless a BPF is installed to cut frequency components other than the SCA channel, frequency detection of the SCA channel signal will not be possible due to the influence of the stereo channel frequency component.

This band-pass filter for extracting the SCA channel signal has a stereo channel frequency band (OIGIz~5
In order to attenuate the signal of 3K11z), it is necessary that the cutoff characteristic be steep and the amount of attenuation be large. However, in order to stably obtain this characteristic, for example, several stages of active filters must be arranged in series, which increases the circuit scale and becomes an impediment to miniaturization of the entire detection device.

Further, there were other problems such as delicate and difficult adjustment of resistors and capacitive elements.

SUMMARY OF THE INVENTION An object of the present invention is to provide a detector for SCA channel signals that requires less fine adjustment of the detector and can be downsized.

[Means for solving problems]

1- In order to achieve the record, the SCA channel signal detection device of the present invention uses a PLL circuit and a frequency dividing circuit to detect the FSK carrier frequency (faSf) of the SCA channel from the 191tG]z pilot signal in the FM stereo composite signal.
b) A local oscillator circuit that creates signals (fa2, fb2) whose frequencies match The first detection circuit detects the presence or absence of the fa acid component of the FSX carrier wave, and the presence or absence of the DC term in the beat component, which is the difference between the phase continuous FSK synchronized with the fb2 signal and the FM stereo composite signal, is used to detect the presence or absence of the FSK carrier wave. It is characterized by providing a second detection circuit for detecting the presence or absence of the fb acid component.

[Effect]

In the present invention, the carrier frequency (fa, f
b) is 3 of the pilot signal frequency (19KHz)
, 5x, 4x, and 4.5x i.e. 66, 5 Knz
, 76 Knz, and 85.5 KHz, and the modulation rate is 17 m (m==1.
2.3,...), the SCA channel signal can be extracted from the FM composite signal using a steep bandpass filter as in the past. However, it is possible to directly detect the SCA channel signal from the FM composite signal using a smaller low-pass filter that can be easily fine-tuned.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

First, to explain the FSX modulation method of digital signals in the SCA channel, the FSK carrier frequency (ra, rb) of the SCA channel is
3.5 times, 4 times, and 4.5 times the pilot signal frequency (19 KI]z) from 53Knz to 99 TGIz), i.e. 66.5 KHz, 76 KHz
, and 85,5 KF]z, and the modulation speed is 19/m K11z (m= 1.2.3,
...) is an FSX modulation method in which the digital signal modulated is synchronized with the pilot signal.

The upper three rows A, B, and C of FIG. 5 show these relationships. For example, f a=76N(z, f b=66
．． 5. If m=1, 19 K11 shown in A of Figure 5
In synchronization with the z pilot signal, 76 KJIz according to the 71 high level and low level of the digital signal shown in Figure 5B.
(fa) Toro A waveform with a continuous phase of 6.5 KHz (f b ) is the FSK carrier wave, and is the waveform C in FIG. 5. The FSX carrier wave can be expressed as follows.

AXSIN (2πfat+θa) (high level period)
AXSIN (2πfbt 10b) (low level period)
A; Carrier amplitude, θaνθ1) = Q or π first
The figure is a block diagram of a detection device for an SCA channel. The local oscillation circuit 100 includes a multiplier phase comparator (PC) 101
．． Low pass filter (L P F ) 102, amplifier (
Affix) 103, voltage controlled oscillator (VCO) 104
, frequency dividing circuits 105, 106, and 107. Among them, a multiplier phase comparator 101, a low-pass filter 102, an amplifier 103, a voltage controlled oscillator 104, and a frequency dividing circuit 105 constitute a PLL circuit. The free running frequency of the voltage controlled oscillator 104 is the F S X of the SCA channel.
The frequency (rO) is twice the least common multiple of the carrier frequencies (fa, fb). The purpose of doubling is to make the frequency-divided waveform the target waveform.

This fO is divided by the frequency dividing circuit 105 to produce a signal (F c ) of 191 (Hz) shown in B in FIG. When input, the phase of the 19 KHz Fc signal is locked to the phase of the pilot signal present in the FM stereo composite signal by the operation of the PLL circuit.The pilot signal is shown in A of FIG. The output signal rO of the frequency dividing circuit 106,
and frequency division circuit 107 to obtain the FSX carrier frequency (fa
, fb) have the same frequency. Signal (fa2
．． fb2). At this time, the respective counters in the frequency dividing circuit 106 and the frequency dividing circuit 107 are reset simultaneously so that the initial phases of the applied signals (fa2, fb2) are matched. C and D in Figure 6 are these fa
2, which shows the phase of fb2. For example, fa
=76KI(z, f b=66.5Kitz. Also, the pilot signal + l;' C9fa2.f
When b2 is expressed by the formulas, they are as follows.

Note that 11;'c, fa2, and fb2 are square waves, but they are calculated as cosine waves.

Pilot signal: AXSIN (2π fpt)
Fc: BXCO8(2π fct)fa
2: BXCO3(2g fat+π/
2) fb2: BXCO3 (2π fbt
+π/2) fc+ fp; 19 to 11z A; Bye 07
The amplitude of the signal [3; the amplitude of fa2trb2] is then input to the first detection circuit 600 consisting of a multiplier phase comparator (PC) 301, a low-pass filter (LPF) 302, an amplifier (Amp) 606, and an identification circuit 304. The multiplier phase comparator 601 receives the I''M composite signal and f
The a2 signal is input and a beat component, which is the difference in frequency between the two signals, is obtained from the output. Here, if an fa acid component of the FSK carrier frequency exists in the FM composite signal, a beat component whose frequency difference is zero for that period, that is,
In other words, a positive or negative DC term is output. This waveform is
Shown in D of the figure. Further, the amplitude (Da) of this DC term can be expressed by the following equation.

Da=(AXB/2)XSIN(θa-π/2)θa
= From Q or π Da-4AX[3/2)XSIN(±7r/2)=ShiA
XB/2 and the beat components other than the amplitude (Da) of this DC term are cut by a low-pass filter 602, and the amplifier 303
After amplifying the signal, the signal is sent to the identification circuit 604. The output waveform of amplifier 606 is shown at E in FIG. In the identification circuit 604, a certain positive and negative threshold voltage (10) is set and the input voltage is compared with the value vth. However, the absolute value of the DC term (Da) amplified by the amplifier 604 is By exceeding the threshold, the presence of the DC term (Da) is detected, and the detection signal Sa changes from low level to high level. This Sa multiplied signal is shown in F in FIG. This detects the presence or absence of the fa acid component in the FSX carrier wave in the FM stereo composite signal.

In addition, with a similar operation, a multiplier phase comparator (I'C)
401, low pass filter (LPF) 402, amplifier (
Amp) 403 and an identification circuit 404, the FM composite signal and the fb2 signal are input to the multiplier phase comparator 401, and the fb2 signal of the FSX carrier wave is input.
The presence or absence of an acid component is detected and the detection signal Sb is set to high level.

The sb multiplied signal is shown in G in FIG.

Finally, a timing signal for reading the high level and low level of the detection signals Sa and Sb is sent to the fifth timing circuit 201.
The timing signal is used to generate detection signals Sa and S in the logic circuit of the decoder 202.
By reading b and determining the sign, the original digital signal shown in (■) in FIG. 5 is obtained.

In this way, from the pilot signal to the FSX of the SCA channel
The principle of the present invention is to generate a signal having the same frequency as the carrier wave, and perform detection by multiplying this by an FM composite signal and detecting the presence or absence of a DC output.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, since the SCA channel signal can be directly detected from the FM stereo composite signal, there is no need to provide a steep band-pass filter as in the prior art. For this reason, there is little fine-tuning of the entire detection device, making it possible to downsize it, and even when it is integrated into an IC, it is effective in that it requires fewer external parts.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration in an embodiment of the present invention, Fig. 2 is a frequency spectrum diagram of an FM stereo composite signal, Fig. 3 is a block diagram showing a conventional detection device, and Fig. 4 is a block diagram showing the FSK demodulation. FIG. 5 is a waveform diagram of FSX demodulation of the present invention, and FIG. 6 is a waveform diagram of a signal generated from the local oscillation circuit. 100... Local oscillation circuit, 600... First detection circuit, 400... Second detection circuit. Figure 2! J1yLIIL [kHzl Figure 3 Figure 5

Claims (1)

[Claims] In a device that detects an SCA channel from an FM stereo composite signal using a phase-continuous FSK modulation method synchronized with a pilot signal, a PLL circuit and a frequency divider circuit are used to detect each possible frequency (fa, fb) of the FSK carrier wave. A local oscillation circuit that outputs signals (fa2, fb2) with matching frequencies, and detecting the presence or absence of a DC term in a beat component that is a difference in frequency obtained by multiplying the fa2 signal and the FM stereo composite signal. a first detection circuit that detects the presence or absence of the fa component of the FSK carrier wave; and a first detection circuit that detects the presence or absence of a DC term in the beat component, which is a frequency difference obtained by multiplying the fb2 signal and the FM stereo composite signal. In some cases, the FSK
A detection device for an SCA channel, comprising: a second detection circuit that detects the presence or absence of an fb component of a carrier wave.