JPS5833733B2 - Pilot signal removal device for FM stereo receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pilot signal removal device for an FM receiver.

As is well known, the stereo composite signal received by the FM receiver includes a pilot signal that is synchronized with the subcarrier.
During demodulation, it is required to remove this pilot signal.

Conventionally, this has been done by adding the same level amount of a signal with the opposite phase to the pilot signal to cancel each other out, but this method not only requires detecting the pilot signal level amount, but also requires offset deviation ,
Problems such as drift occur.

The purpose of this invention is to remove pilot signals stably and reliably.

The present invention is characterized in that the pilot signal is removed by utilizing the fact that a phase shift occurs between the input and output before and after sample and hold.

First, the operating principle of this invention will be explained.

As shown in Figure 1, the stereo composite signal SC is 38KH2
If the pilot signal is omitted, for example, the curve obtained by connecting odd-numbered peak values will be the waveform of the L signal (or R signal), and if the even-numbered peak values are connected, The curve obtained in this case has an R curve (or one curve) waveform.

However, since a pilot signal is actually included, it is known that each peak value of the positive wave has a height difference with respect to the waveform of the L or R signal.

This height is the same for odd numbers (even numbers are the same) because the pilot signal is 19KH2.

) will occur alternately at the peak values.

Therefore, in actual demodulation, the influence of the height due to the pilot signal is removed from the peak value of the positive signal.
The signal or R signal must be demodulated.

Therefore, in this invention, first, three
With the sampling signal a of 8KH2, the odd-numbered peak values of the composite signal SC and the even-numbered peak values of the sampling signal are sampled and held.

This results in a waveform ALAR.

Next, when both of these waveforms are sampled with a 38 KHz sampling signal C and a sampling signal d, which are out of phase with the sampling signal a, a waveform BL is obtained.

BR is obtained.

Here, the waveform BL is the same as the waveform L obtained by sequentially connecting the odd-numbered peak values of the composite signal SC, and a slight phase difference θ (900 in the illustrated example) occurs.

In addition, since the waveform BR has a phase delay of 1800 with respect to the sampling signal, it is the same as the waveform R when even-numbered peak values of the composite signal SC are sequentially connected, but it is slightly smaller than the waveform R. A phase difference θ' (900 in the example shown) is generated.

Next, waveform AL and waveform BL, and waveform AR and waveform BR
By adding these, waveforms CL and CR are obtained.

Considering the waveform CL here, the peak value of the waveform AL between the phase difference θ corresponds to the third peak value of the composite signal SC, and this value is lower than the L signal only outside the pilot signal. On the other hand, the waveform BL corresponds to the first peak value of the composite signal SC, and this value is higher than the L signal except for the pilot signal.

Therefore, when these two waveforms AL and BL are added, the waveform CL between the phase difference θ is the amplitude value of the L signal when the first sampling signal a is output, and the amplitude value of the L signal when the first sampling signal a is output. This value is the sum of the amplitude value of the L signal when it is output, and the influence of the height caused by the pilot signal is canceled out by this value.

Therefore, the sampling signal e generated between the phase difference θ
If waveform CL is sampled and held by , waveform DL is obtained, but this is a waveform obtained by sampling and holding the L signal.

Therefore, by averaging these, the L signal from which the pilot signal has been removed will be demodulated.

Even if the waveform CR is ℃・(Similarly, if you sample and hold the sampling signal f between the phase difference
R is obtained, but for the same reason as described above, this is a waveform obtained by sample-holding the R signal in a state in which the effects of height due to the pilot signal are cancelled.

If this is also averaged in the same way as the waveform DL, an R signal from which the pilot signal has been removed will be demodulated.

An embodiment of the present invention based on the above-mentioned operating principle will be described with reference to FIG.

1 is an input terminal to which a stereo composite signal SC is applied; 2 is a sampling signal generating circuit that generates a sampling signal a''-□f in synchronization with a pilot signal included in the composite signal SC; The tank bottom is controlled by a phase-locked loop (PLL) and, if necessary, a plurality of frequency dividers.

3 and 4 are first sample and hold circuits which input the stereo composite signal SC, sample and hold it with the sampling signal ab, and output a waveform ALAR.

This waveform output is input to the second sample and hold circuit 56, where it is sampled and held by the sampling signal cd and outputs the waveform BLBR.

These waveform outputs are each added to the waveform AL by the adder circuit 78.
, AR and waveform CL.

Output CR.

As described above, the value between the phase difference θ 07 of this waveform is the value obtained by removing the pilot signal from the stereo composite signal SC.

If the waveforms CL and CR are sampled by the sample and hold circuit 910 using the sampling signals e and f, the waveform DL
, DR is obtained.

If this is averaged, the L and R signals will be demodulated.

Note that the stereo composite signal may sometimes include interfering pulses.

If you sample and hold this as it is, the correct waveform D
LDR cannot be obtained (obviously).

In order to prevent this, a disturbance pulse detection circuit 11 is provided,
This will detect the interfering pulse contained in the stereo composite signal.

The time setting circuit 12 is triggered by this detection signal, and the gate circuits 13 and 14 are closed by a signal output for a certain period of time.

During this closed period, the sampling signal e or f is not applied to the sample and hold circuits, so the sample and hold circuits 9 and 10 continue to hold and output the previous hold value.

This avoids the harmful effects of interference pulses.

Note that the gate circuit may be installed so as to prevent the sampling signal cd from being applied to the sample and hold circuits 5 and 6.

As described in detail above, according to the present invention, in order to remove a pilot signal from a stereo composite signal, it is not necessary to detect the level amount of the pilot signal as in the conventional method, but simply sample and hold the signal and add it. This can be removed, and if necessary, stereo demodulation is also possible.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram for explaining the operating principle of this invention.
FIG. 2 is a block diagram showing an embodiment of the invention. 1... Input terminal, 2... Sampling signal generation circuit, 3, 4... First sample hold circuit, 5, 6... Second Sample hold circuit, 7, 8... Addition circuit, 910...
-Third sample and hold circuit.

Claims (1)

[Claims] 1 Synchronize the stereo composite signal with the pilot signal 38
A first sample and hold means samples and holds the first sampling signal of KI (Z), and the output of the first sample and hold means is synchronized with the pilot signal and has a phase difference with the first sampling signal. a second sample hold means for holding a sample with a certain second sampling signal; an addition means for adding the outputs of the first and second sample hold means; and an addition means for adding the outputs of the respective first and second sample hold means; and a third sample and hold circuit that samples and holds a third sampling signal generated between the phase differences of the second sampling signal.
Pilot signal removal device for M stereo receiver.