JPS5926681Y2 - stereo demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stereo demodulation circuit for an FM receiver, and more particularly to a stereo demodulation circuit that is an improved blending circuit for left channel signals and right channel signals.

A conventional stereo demodulation circuit is configured as shown in FIG. 1, for example.

The composite signal applied to the input terminal IN is sent to amplifier 1.
A 38 KHz switching signal that is phase-synchronized with the 19 KHz pilot signal in the composite signal is created in phase-locked loop (PLL circuit) 2, and the 38 KHz switching signal from PLL circuit 2 is used as the main signal in the composite signal. The composite signal of the signal and the sub-signal is switched by the switching demodulation circuit 3, and the right signal e is output to the right signal output terminal R1.

R and the left signal e to the left signal output terminal L1.

L and the right signal output terminal R1 of the switching circuit 3.
A mixing circuit for mixing the right signal and the left signal, for example, the field effect transistor 4, is connected between the left signal output terminal and the left signal output terminal, and the voltage applied to the external terminal C is applied as the gate voltage of the field effect transistor 4. The signal was directly blended with the left signal.

However, the conventional stereo demodulation circuit as described above directly blends the output signals from the switching demodulation circuit, and therefore has the disadvantage that the blending element requires good linearity.

The present invention has been made in view of the above, and an object of the present invention is to eliminate the above-mentioned drawbacks and provide a stereo demodulation circuit with a simple configuration.

According to the present invention, this purpose is achieved by providing a phase shift circuit for changing the phase of a pilot signal by an external signal on the input side of a PLL circuit for generating a stereo demodulation switching signal, and changing the external signal to perform stereo separation. This is achieved by varying the intensity and obtaining a blending effect.

The present invention will be explained below with reference to examples.

FIG. 2 is a block diagram of an embodiment of the present invention.

In Figure 2, 1 is an amplifier that amplifies the composite signal, and 2 is an amplifier that amplifies the 19 KHz pilot signal.
3 is a PLL circuit for obtaining an 8 KHz switching signal, and 3 is a 38 KHz switching signal from PLL circuit 2 that switches the composite signal of the main signal and sub signal in the composite signal to output the right signal and the left signal. This is a switching demodulation circuit that emits an output.

The PLL circuit 2 consists of a phase comparator 6, a low-pass filter 7, a DC amplifier, an 8.76 KHz voltage controlled oscillator 9, a frequency divider 10 and 11, and is phase-locked to the 19 KHz pilot signal input to the phase comparator 6. 38KHz
The switching signal is obtained from ÷the output of the frequency divider 10.

Further, 5 is a phase shift circuit consisting of a capacitor 12, a resistor 13, and a field effect transistor 14 connected in series with the resistor 13, and the voltage applied to the external signal terminal C is applied to the gate of the field effect transistor 14. 19 which outputs to the PLL circuit 2 according to the external signal applied to the external signal terminal C.
The phase of the KHz pilot signal is shifted by 0° to 45°.

Therefore, the composite signal applied to the input terminal IN is amplified by the amplifier 1, and the 19 KHz pilot signal is amplified from 0° to 45° by the external signal applied to the external signal terminal C.
is input to the PLL circuit 2 with its phase shifted.

Therefore, 38
The phase of the KHz switching signal is synchronized with the 19 KHz pilot signal input to the PLL circuit 2.

Now the composite signal f(ω) is f(ω)=(L+R)+(L-R)cosωt+Pco
It is expressed as sTt.

where P is the level of the pilot signal, ω is the angular frequency of the subcarrier and ω=2π×38KHz, and L and R are the left and right channel signals.

When the phase shift angle of the phase shift circuit 5 is set to +0 degrees, the pilot signal input to the PLL circuit 2 is as follows.

This pilot signal generates 38 in the PLL circuit 2.
The KHz switching signal g(ω) is as follows.

By this switching signal g(ω), the composite liquid of the main signal and the sub signal is switched in the switching demodulation circuit 3, and the right signal output terminal R of the switching demodulation circuit 3
The output appearing in 1 is as follows.

Of these, O The deio ingredients are It is.

Therefore, the right output signal e appears at the right output terminal RT of the switching demodulation circuit 3.

The principal component M of R is as follows.

Here, if the phase shift angle θ is changed from 0 to +45°, co
Since s2θ changes from 1 to O, 1'-CO52θ changes from 1 to 0 in response to a change in the phase shift angle θ, and the main component M is determined by the shift of the 19 KHz pilot signal by the phase shift circuit 5. As the phase angle θ increases from 0 to 45°, the right channel signal decreases, and the left channel signal as a leakage component increases.

Therefore, when the phase shift angle θ=45°, the switching demodulation circuit 3
The principal component M appearing at the right output terminal RT is as follows, resulting in monaural demodulation.

Further, when the phase shift angle θ=0°, the main component M appearing at the right output terminal R7 of the switching demodulation circuit 3 becomes, and normal stereo demodulation is performed.

The demodulated output appearing at the left output terminal L1 of the switching demodulation circuit 3 can also be derived in the same way, but since it is similar to the above derivation, the explanation will be omitted.

Next, as described above, the phase shift angle of the phase shift circuit 5 can be controlled by an external signal applied to the external signal terminal C.

Therefore, for example, an external signal may be applied manually, or the electric field strength to the FM receiver is detected, and when the electric field strength is weak, the phase shift angle of the phase shift circuit 5 is increased to increase the blend amount. Good too.

Alternatively, a noise component in the received signal (for example, a noise component in the intermediate frequency output, a noise component in the FM detection output, etc.) may be detected and used as the external signal.

As explained above, according to the present invention, a phase shift circuit that changes the phase of a pilot signal by an external signal is provided at the input end of a PLL circuit that generates a switching signal, and the phase shift circuit changes the phase of a pilot signal by changing the external signal to create a right channel signal and a left channel signal. Since the amount of blending with the signal is changed, the configuration of the stereo demodulation circuit is simple, and even when the phase of the pilot signal is continuously changed by using a field effect transistor in the phase shift circuit, the distortion rate can be reduced. Deterioration has little effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional stereo demodulation circuit. FIG. 2 is a block diagram of a stereo demodulation circuit according to an embodiment of the present invention. 2...PLL circuit, 3...Switching demodulation circuit, 5...Phase shift circuit, C...
External signal terminal.

Claims (1)

[Scope of utility model registration request] In a stereo demodulation circuit including a switching demodulation circuit and a phase-locked loop for generating a stereo demodulation switching signal, a phase shift circuit for changing the phase of a pilot signal by an external signal is provided on the input side of the phase-locked loop, A stereo demodulation circuit characterized by changing the degree of stereo separation by changing the signal to obtain a blending effect.