JPS6019692B2 - FM stereo receiver pilot signal removal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a demodulated right (referred to as R) signal from a composite signal.
Regarding a pilot signal removal circuit for an FM stereo receiver that automatically removes a pilot signal included in a signal (hereinafter referred to as L) and a left (hereinafter referred to as L) signal,
For example, even if the level of the pilot signal changes, it is automatically followed and the pilot signal of any level can be removed.

As is already known, in order to demodulate a pilot tone FM stereo signal, 3 subcarriers are obtained from the FM-detected composite signal, and these are used to convert the R signal and L signal from the composite signal. are separated.

However, as it is, a pilot signal of 1 HZ is included in the R signal and the L signal, which becomes a cause of deterioration of the S/N ratio.

Therefore, conventional methods have been proposed in which the pilot signal is attenuated by using a pilot signal blocking trap or a low-pass filter, or the pilot signal is canceled by using a signal at a certain level that is in reverse phase with the pilot signal. There is. However, in the former case, it is impossible to remove the pilot signal sufficiently;
Further, there are other disadvantages such as a phase rotation occurring in the Takagi portion of the demodulated signal. Furthermore, in the latter case, the pilot signal is canceled by a preset level, so if there is some variation in the transmission level of the pilot signal due to differences in receiving stations, the pilot signal will still remain in the demodulated signal. was there. The present invention is aimed at solving these difficulties, and will be described in detail above based on one embodiment shown in the drawings.

1 is a composite signal input terminal, 2 is an MPX demodulation circuit, 3 is a subcarrier generation section using a phase-locked loop (PLL), and like the general-purpose one, it includes a phase comparator 4, a low-pass filter (LPF), and a voltage-controlled oscillator ( VCO), 1
It consists of 2 frequency dividers 5 and 6.

7 is a control section for removing pilot signals, which includes an adder 8 for combining the R signal and L signal separated in the M-circle X demodulation circuit 2, a synchronous detector 9, and a low-pass filter (LP
F), a 1/2 frequency divider, and a voltage control amplifier (VCA). In FIG. 1, a composite signal that has been FM detected and input to input terminal 1 is input to subcarrier generation section 3 using a PLL.

This subcarrier generation section 3 is a voltage controlled oscillator (
A signal of 7 HZ oscillated from the VCO) is converted into a signal of 1 HZ by passing it through the 1/2 minute dividers 5 and 6. The phase is compared with the pilot signal of the arrival KHZ,
The error amount is detected.

This error passes through a low-pass filter (LPF) and becomes a control DC voltage that powers the voltage-controlled oscillator (VCO).
This completes the loop, and the loop operation is repeated until an accurate 7 HZ signal is obtained in synchronization with the 1 female HZ pilot signal, and the circuit is locked. In this state, a switching signal of 3 HZ is obtained from the 1/2 frequency divider 5 in the first stage, and this signal causes the M circle The R signal and L signal are separated from each other.

The separated R signal and L signal enter the next-stage de-emphasis circuit from the R channel output terminal 11 and the L channel output terminal 12, respectively, via an unillustrated amplifier or directly without passing through the amplifier. On the other hand, the R signal and L signal input to the adder 8 are combined here and input to one input terminal of the synchronous detector 9 at the next stage.

At this time, the other input terminal of the synchronous detector 9 has 1/2
From frequency divider 1 0, a second signal which is in phase with the pilot signal
Since a rectangular wave as shown in Figure 2 is injected, out of the composite signal that enters the synchronous detector 9, the 1HZ wave shown in Figure 2A is
Only the pilot signal components of are detected.

This detected signal is passed through a low-pass filter (LPF) at the next stage.
), high frequency components are removed and the DC voltage becomes a DC voltage with a level proportional to the level of the pilot signal, which enters one input terminal of a voltage controlled amplifier (VCA).

On the other hand, the other input terminal of this voltage control amplifier (VCA) is injected from the 1/2 frequency divider 10 with a rectangular wave signal as shown in FIG.
This signal is controlled in the amplifier (VCA) to a level corresponding to the voltage level of the signal applied from the low pass filter (LPF), and from this, the phase is opposite to the pilot signal and the level is controlled according to the voltage level of the same signal. A pilot cancellation signal is obtained.

This pilot cancellation signal is added to the composite signal injected from the terminal 1 in the M-circle X demodulation circuit 2, for example. By adding this pilot cancellation signal, the pilot signals included in the R signal and the L signal are canceled, and the R channel output terminal 11 and the L channel output terminal 12 each have an R signal that does not include the signal component of 1 carp HZ.
signal and L signal appear.

In the above embodiment, the pilot signal is a sine wave, whereas the cancellation signal is a rectangular wave with an opposite phase, so the difference component remains as a slightly higher frequency. However, this can be easily removed by adding a differential filter or a simple filter, and in the end, most of the pilot signal can be removed. As described above, the present invention cancels the pilot signal included in the R signal and the L signal by using a cancellation signal that is in opposite phase and has the same level as the pilot signal, so that the pilot signal is completely eliminated. Moreover, since the level of this signal for removal is controlled according to the level of the pilot signal included in the R signal and L signal, it is possible to change the channel selection, etc. Even if the level of the pilot signal changes due to some reason, the change automatically follows the change, and even the changed level of the pilot signal can be reliably removed.

Additionally, some conventional pilot signal removal devices require level adjustment and phase adjustment during the manufacturing process of FM stereo receivers, and in these cases, if the adjustment is insufficient, the pilot signal may be removed. Although there are drawbacks such as the inability to reliably remove or the occurrence of variations in the characteristics of the device, the present invention eliminates such problems at all, resulting in labor savings during manufacturing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the circuit according to the present invention, and FIG. 2 shows waveform diagrams for explaining the operation of the circuit. 2...MPX demodulator, 3...PLL,
7... Pilot signal removal control section, 8...
...Adder, 9...Synchronous detector, 10...
・...1/2 frequency divider, LPC... -Pass filter, VCA...Voltage control amplifier (level controller). Figure 1 Figure 2

Claims (1)

[Claims] 1 P tuned to the pilot signal in the composite signal
In an MPX demodulator that demodulates the right and left signals from the LL output signal, an adder for combining the right and left signals, the output of this adder is used as one input, and the P
a synchronous detector that extracts the pilot signal component appearing at the output of the adder using the output signal synchronized with the pilot signal provided from the LL as the other input; and a synchronous detector that extracts the pilot signal component appearing at the output of the adder; and a level controller for controlling the level of a signal synchronized with the composite signal, and the output of the level controller is combined with the composite signal as a pilot cancel signal.
Pilot signal removal circuit for M stereo receiver.