JPS5851700B2 - 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 level amount of the pilot signal, but also eliminates the need for offset.
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 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 becomes the waveform of the R signal (or L signal).

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 19KHz.

) 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, three
The odd numbered peak values of the composite signal SC are sampled and the even numbered peak values of the composite signal SC are sampled and held using the 8 KHz sampling signal a.

As a result, waveforms AL and AR are obtained.

Next, by adding the composite signal SC to each of the waveforms AL and AR, waveforms BL and BR are obtained.

Considering the waveform BL here, for example, the peak value of the waveform AL immediately before the third sampling signal a is generated corresponds to the peak value of the composite signal SC when the second sampling signal a is generated. This peak value is a value lower than the L signal by the amount of the pilot signal.

Also, waveform A immediately before the fourth sampling signal is generated.
The peak value of L corresponds to the peak value of the composite signal SC at the time of generation of the third sampling signal a, but this peak value is higher than the L signal by the pilot signal valve.

Therefore, in the waveform BL obtained by adding the composite signal SC and the waveform AL, the wave height value immediately before the sampling signal a is generated is such that the influence of the height due to the pilot signal has been canceled here.

Therefore, the waveform CL obtained by sampling and holding the waveform BL with the sampling signal C that is output immediately before the sampling signal a is generated is a waveform obtained by sampling and holding the L signal.

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

It is desirable that the phase difference between the sampling signals a and C and the phase difference between the sampling signal b(!:d) be as small as possible, but since each pulse has the same width, the phase difference between the two pulses is It is necessary that the phase difference is such that the pulses do not overlap.

On the other hand, if the phase difference becomes large, distortion will occur in the output waveform, but if it is within a few degrees, there is no practical problem.

Therefore, it is desirable that the phase difference between the sampling signals a and C and the sampling signals S and d be 1 to 2 degrees.

The same is true for the waveform BR, and the waveform CR obtained by sampling and holding the waveform BR with the sampling signal d immediately before the sampling signal 2 is generated will be the same as the pilot signal if the influence of the pilot signal is canceled out. The R signal from which the 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 generation circuit that generates sampling signals a to d in synchronization with a pilot signal included in the composite signal SC;
PLL) and a plurality of frequency dividers as necessary.

3 and 4 are first sample and hold circuits which input the stereo composite signal SC, sample it, and output it to the ring signals a and b.
It samples and holds it, and outputs waveforms AL and AR.

This waveform output is added to the composite signal SC by adder circuits 5 and 6 to output waveforms BL and BR.

These waveforms BL and BR are transferred to the second sample and hold circuit 7,
8, the waveforms CL and CR are obtained by sampling with the sampling signals c and d.

If this is averaged, the L and R signals will be 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 of the pilot signal as in the conventional method, 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 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...Addition circuit, T, 8...
...Second sample and hold circuit.

Claims (1)

[Claims] 1 Synchronize the stereo composite signal with the pilot signal 38
a first sample-hold means for sampling and holding the first sampling signal of KHz; an adding means for adding the output of the first sample-hold means and the stereo composite signal; 1. A pilot signal removal device for an FM stereo receiver, comprising a second sample and hold means that samples and holds a second sampling signal whose phase is slightly ahead of that of the first sampling signal.