JPS5912841Y2 - stereo receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM stereo receiver, and particularly to improving the degree of separation between outputs of two low frequency channels in the receiver.

When FM broadcasting becomes multi-channel, a major problem on the receiver side is the ability to eliminate interference from adjacent interference waves.

Particularly, the worst situation is interference from adjacent 200 KHz, and in current receivers, this situation causes a significant drop in the S/N ratio during stereo reception.

The following has been confirmed as the cause of this.

First, the beat frequency 200 is the difference between the desired wave and the interference wave.
KHz appears mixed in the output of the FM detector.

During stereo operation, a switching type stereo demodulator operates, and this switching frequency is 38.
The fifth harmonic frequency of 190 KHz and the above beat frequency of 200 KHz generate a 10 KHz beat, and this beat component is the S/N of the low frequency output at the receiver.
This is the main factor causing the ratio to decline.

Of course, since both the desired wave and the interference wave are actually modulated, this 10 KHz beat spreads over the entire low frequency band.

Here, as a known means for removing this 10 KHz beat, a low-pass filter or a notch filter having an attenuation pole near 200 KHz is connected immediately after the FM detector to sufficiently attenuate the 200 KHz beat. It has been confirmed that this is sufficiently effective in improving the S/N ratio of the demodulated output.

However, the amplitude and phase characteristics of this filter reduce the degree of separation of the stereo demodulated signals.

In general, regarding the influence of amplitude characteristics, if the gain difference between the main and sub channels in the composite signal is 1 dB, the degree of separation will decrease by about 15 dB, and regarding the phase characteristics, if the phase difference between both channels is 1 degree, the degree of separation will be reduced by about 5 dB. resulting in deterioration of

Therefore, although there are differences in degree depending on the configuration of the filter, a decrease in the degree of separation is unavoidable.

Therefore, the present invention focuses on the fact that even if a filter is inserted, if the separation degree is adjusted again at the low wave stage at that point, the separation degree will return to almost its original state. By setting the adjustment amount to optimize the degree of separation at each time, and switching the adjustment amount in conjunction with the on/off operation of the filter, good stereo reproduction output can be obtained in any case. This is how it was done.

The present invention will be explained below based on the accompanying drawings showing one embodiment thereof.

In Figure 1, 1 is an FM detector, 2 is a 200 KHz
3 is a stereo demodulator, and 4 is a separation adjustment circuit. For example, a circuit using a losstalk cancellation method as shown in FIG. 2 is used.

First, referring to FIG. 2, 41 and 42 are crosstalk canceling transistors, each of which has a left channel signal Lin from the stereo demodulator 7 at its base,
A right channel signal Rin is applied.

Reference numeral 43 denotes a variable resistor for setting a separation adjustment amount, and by adjusting this, a left channel output signal Lout and a right channel signal Rout which are pure from the respective collector outputs can be obtained.

Further, in FIG. 1, 5 is an on/off switch for the filter 2, and 6 is an adjustment amount switch that is linked to the changeover switch 5.
The variable resistor 43 and the variable resistor 44 used when the filter 2 is turned on are switched.

Note that 7 is an on/off switching command device for the filter 2, and the changeover switches 5 and 6 are switched by this output.

Therefore, in the above configuration, when there is no beat disturbance, the changeover switches 5 and 6 are switched to the opposite state from that shown in the figure.
The FM detector 1 and the stereo demodulator 3 are directly connected, and a variable resistor 43 is used as the variable resistor of the separation degree adjustment circuit 4.

When beat disturbance occurs, selector switches 5 and 6 are
is switched to the state shown in the figure, a filter 2 is inserted between the FM detector 1 and the stereo demodulator 3, and a variable resistance Peking Opera is used.

Generally, when a gain difference occurs between the main and subchannels of the synthetic liquid due to the insertion of filter 2, the separation will be approximately the same amount over the entire band as shown in the normal state a to b, as shown by b in Figure 3. Since the degree of separation deteriorates, the degree of separation is readjusted in the degree of separation adjustment circuit 4 to return from b to C and almost to a.

In addition, when the degree of separation deteriorates due to phase, the amount of deterioration varies depending on the frequency, as shown in a to d in Fig. 4.
Since the user is sensitive to the degree of separation in the midrange when listening, it is effective to adjust from d to e so that the midrange is improved the most.

As explained above, according to the present invention, it is possible to improve the S/N ratio during beat disturbance by providing a separation adjustment circuit that can switch between two adjustment amounts depending on whether the filter is used or not. At the same time, deterioration of stereo separation can be prevented.

In addition, by removing interference signals with a beat removal filter after FM detection, the degree of freedom in filter characteristics is increased.
It is possible to minimize the phase difference by allowing the amplitude difference between the main and sub-channels of the stereo composite signal, and by adjusting the degree of separation during stereo demodulation, the degree of separation can be improved to almost the level without a filter. can do.

Note that the degree of separation adjustment circuit is not limited to that shown in FIG.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a stereo receiver according to an embodiment of the present invention, Fig. 2 is a basic wiring diagram of a separation adjustment circuit in the receiver, and Figs. 3 and 4 explain the operation of the receiver. FIG. 1...FM detector, 2...Beat removal filter, 3...Stereo demodulator, 4...
... Separation adjustment circuit, 5, 6 ... Changeover switch, 43.44 ... Variable resistor for setting separation degree adjustment amount.

Claims (1)

[Scope of utility model registration request] a beat removal filter installed between a detector and a stereo signal demodulator; and a switching means for determining whether to connect the detected signal directly to the stereo signal demodulator or to connect the detected signal to the demodulator through the filter. and a stereo demodulated signal separation and adjustment circuit that operates in conjunction with the switching means and can switch between two adjustment amounts.