JPS5851699B2 - 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 stereo receiver.

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

Conventionally, this has been achieved by adding the same level of a signal with the opposite phase to the pilot signal to cancel each other out, but this requires not only the level of the pilot signal to be detected, but also the offset. Problems such as misalignment and 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 38KHz.
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 L curve) waveform.

However, since a pilot signal is actually included, it is known that each peak value of the pressure 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 19 illusions.

) 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 pressure wave.
The signal or R signal must be demodulated.

Therefore, in this invention, first, the 7
All peak values of the composite signal SC are sampled and held using the 6 KHz sampling signal a.

Waveform A is thereby obtained. Next, when this waveform is sampled with a 38 KHz sampling signal 1 and a sampling signal d, which are out of phase with the sampling signal a, waveforms BL and BR are obtained, respectively.

Here, the waveform BL is the same as the waveform obtained by sequentially connecting the odd-numbered peak values of the composite signal SC, and a slight phase difference θ (900° in the example shown) 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 obtained when even-numbered peak values of the composite signal SC are sequentially connected, and has a slightly different phase difference. θ' (900 in the illustrated example) is generated.

Then, by adding waveform A and waveform BL, and waveform A and waveform BR, respectively, waveforms CL and CR are obtained.

Considering the waveform CL here, the phase difference θ is 1.
The peak value of waveform A corresponds to the third peak value of the composite signal SC, which is lower than the L signal by the pilot signal valve, whereas the waveform BL corresponds to the first peak value of the composite signal SC. This corresponds to the peak value of , which is higher than the L signal by the pilot signal valve.

Therefore, when adding these two waveforms A and BL,
The waveform CL between the phase differences θ is the sum of 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 third sampling signal a is output. Therefore, the influence of the height of the pilot signal is canceled out here.

Therefore, the sampling signal C generated between the phase difference θ
If the waveform CL is sampled and held, a waveform DL as shown by the dotted line in the middle of the waveform CL can be obtained.

This is essentially 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.

The same is true for the waveform CR.If you sample and hold the sampling signal e between the phase difference 07, the waveform CR
A waveform DR as shown by the middle dotted line is obtained, and for the same reason as described above, this is a waveform obtained by sampling and holding the R signal with the influence of height due to the pilot signal canceled out.

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 '4C is applied; 2 is a sampling signal generation circuit that generates sampling signals ae in synchronization with the pilot signal included in the composite signal SC;
B) and, if necessary, a plurality of branching units.

3 is a first sample and hold circuit which inputs the stereo composite signal SC, samples and holds it with the sampling signal a, and outputs a waveform A.

This waveform output is input to the second sample and hold circuits 4 and 5 as sampling signals.

The waveform BL is sampled and held by d.
, outputs BR.

These waveform outputs are converted into waveform A by adder circuits 6 and 7, respectively.
and outputs waveforms CL and CR.

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

If these waveforms CL and CR are sampled by the sample and hold circuits 8 and 9 using the sampling signal C2e, the waveform DL
, DR is obtained.

Should we average this? This means that the f% L and R signals have been demodulated.

As detailed above, according to the present invention, in order to remove the pilot signal from the stereo composite signal, it is not necessary to detect the level 14 of the pilot signal as in the conventional case, but simply sample and hold the signal and add it. It is possible to remove this problem, and furthermore, if necessary, it is possible to perform stereo demodulation.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram for explaining the operating principle of the invention, and FIG. 2 is a block diagram showing an embodiment of the invention. 1...Input terminal, 2...Sampling signal generation circuit, 3...First sample hold circuit, 4゜5...Second sample hold Circuit, 8, 9...Third sample hold circuit, 6
, 7...Addition circuit.

Claims (1)

[Claims] 1. Synchronizing the stereo composite means with the pilot signal 76
a first sample and hold means that samples the output of the first sample and hold means with a sampling signal of KH2; a third sample and hold means for sampling the output of the addition means with a sampling signal generated between the phase differences; A pilot signal removal device for an FM stereo receiver.