JP2001094522A - Stereo demodulator of fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FM receiver which facilitates digital processing. SOLUTION: According to a sine wave generated in a 38 kHz sine wave generating circuit 61 and synchronizing with a pilot signal, an LR separate signal generating circuit 62 generates a LR switching separate signal, which is supplied as a switching signal to an LR separating circuit 63; and the LR separating circuit 63 multiplies an FM detection signal by the switching separate signal composed of the sine wave to calculate the right and left separate signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver, and more particularly to a stereo demodulator using a switching system.

[0002]

2. Description of the Related Art FM broadcasting is used in ultra-short-wave broadcasting for the purpose of higher-quality audio broadcasting than medium-wave broadcasting and short-wave broadcasting. In ultra-high-frequency FM broadcasting, modulation and demodulation are usually performed using a pilot tone system. In the demodulation system of the pilot tone system, demodulation is performed by a switching system or a matrix system.

In this switching method, voltages of two envelopes of a baseband signal are sequentially extracted by a switching signal.
The left signal and the right signal are reproduced by inserting a low-pass filter of z.

As the switching signal, a 38 kHz square wave is used in consideration of detection sensitivity. The demodulation switching signal for the left signal and the right signal is represented by gL.
(T) and gR (t) can be expressed by the following Equation 1.

[0005]

(Equation 1)

Switching is to multiply the voltage f (t) of the baseband signal for FM modulation represented by the following equation 2 in the pilot tone system by g _L (t) and g _R (t), The left and right signal outputs L _out and R _out are as shown in the following Expression 3.

[0007]

(Equation 2)

[0008]

(Equation 3)

Further, in order to improve the channel separation characteristic, a left and right separated signal can be obtained by subtracting a value represented by the following equation (4).

[0010]

(Equation 4)

[0011]

By the way, digital processing of each circuit of the FM receiver has been promoted using a digital signal processor or the like. As described above, a 38 kHz square wave is used as a switching signal, but it is difficult to perform stereo demodulation using a square wave formed by digital processing at a low sampling frequency.

SUMMARY OF THE INVENTION An object of the present invention is to provide an FM receiving apparatus which can be easily digitally processed in view of the above-mentioned conventional problems.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a stereo demodulator in an FM receiving apparatus for performing LR separation of an FM detection signal using a switching signal, in a 38 kHz sine wave synchronized with a pilot signal created by a sine wave creating means. Generating a LR switching separation signal based on the wave;
The LR separation signal is supplied to the LR separation unit as a switching signal, and the LR separation unit multiplies the switching detection signal formed of a sine wave by the FM detection signal to calculate a left / right separated signal.

By using a sine wave as a switching type switching signal, stereo demodulation can be performed efficiently.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the FM receiver. The FM receiver according to the present invention includes an antenna 1, a front end unit 2, an IF amplification unit 3, a limiter unit 4, an FM demodulation unit 5, and a stereo demodulation unit 6.
And

An FM radio signal is captured by the antenna 1,
The signal is given to the front end unit 2. The front end unit 2 selects and amplifies the input radio signal, performs frequency conversion to obtain an intermediate frequency, and converts the signal into an IF amplifying unit 3.
Give to. The IF amplification unit 3 mixes the high frequency amplification and the local oscillation to perform intermediate frequency conversion, and converts the converted FM.
Giving the IF signal to the limiter unit 4; The gain, selectivity, and various interference removal characteristics of the receiver are determined by the IF amplifier 2. The intermediate frequency should be 1 in consideration of image and IF interference.
It is 0.7 MHz.

The limiter unit 5 removes noise and AM components generated by multipath from the input FM-IF signal, adjusts the amplitude to a constant amplitude, and adds the signal to the FM demodulator 5. The limiter section 6 produces an excellent SN ratio unique to FM and an effect of suppressing an interfering signal.

The FM demodulation unit 6 detects and extracts a modulation signal from an FM wave, converts the FM signal into an AM wave, and then detects and demodulates the AM wave. And the original FM wave, and a quadrature detection method or Pd that obtains a demodulated signal from the bead signal
There is a detection method using LL.

Then, the FM detection signal is sent to the stereo demodulation unit 6.
Given to. The stereo demodulator 6 separates an L signal and an R signal from a combined signal and takes out the signal. In the present invention, as described later, stereo demodulation is performed by a switching method.

FIG. 2 is a block diagram showing the stereo demodulator 6 according to the present invention. As shown in FIG. 2, the FM detection signal is supplied to a sine wave generation circuit 61 composed of a PLL and an LR separation circuit 63. The sine wave generation circuit 61 is a PLL
Thus, a sine wave of 38 kHz is created, and the created sine wave is given to the LR separation signal creation circuit 62. The sine wave creation circuit 61 can be configured to create a sine wave by a predetermined program using, for example, a DSP.

The LR separation signal creation circuit 62 is a 38k synchronous with the pilot signal created by the sine wave creation circuit 61.
As shown in FIG. 3, a sine wave of 38 Hz is a half wavelength of 38 kHz.
The LR separation signal is provided to the LR separation circuit 63 as a switching signal. And L
The R separation circuit 63 multiplies the positive and negative sine waves by the signal after FM detection, and extracts a low frequency component. The extracted low-frequency signal is extracted by the degree-of-separation adjustment circuit 64 to calculate a left-right separated signal.

The L / R separation signal generated by the LR separation signal generation circuit 62 can be expressed as shown in the following Expression 5.

[0023]

(Equation 5)

Equation 2 in the pilot tone system
The voltage f (t) of the baseband signal for FM modulation indicated by
Is multiplied by g _L (t) and g _R (t) shown in the above formula 5, and when separated by the LR separation circuit 63, the left and right signal outputs L _out and R _out are as shown in the following formula 6 become.

[0025]

(Equation 6)

From the above equation (6), a left / right separation (channel separation) of about 18 dB is obtained in this case.
This is about 5 dB better than when a square wave is used as the switching signal described above.

Further, in order to improve the channel separation characteristics, the left and right separated signals can be obtained by subtracting the signal represented by the following equation 7 by the separation degree adjusting circuit 64.

[0028]

(Equation 7)

In the present invention, the circuits indicated by the blocks may be realized by using individual circuits. However, a digital signal processor which performs the processing indicated by the block circuits by appropriate programming is used. The present invention may be realized.

[0030]

As described above, according to the present invention, a stereo demodulation can be performed efficiently by using a sine wave as a switching type switching signal, and a theoretical separation characteristic using a square wave is used. About 5d
B improves.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an FM receiver.

FIG. 2 is a block diagram showing a stereo demodulation unit 6 according to the present invention.

FIG. 3 is a waveform diagram showing a switching signal used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Front end part 3 IF amplification part 4 Limiter part 5 FM demodulation part 6 Stereo demodulation part 61 Sine wave creation circuit 62 LR separation signal creation circuit 63 LR separation circuit 64 Separation degree adjustment circuit

Claims (1)

[Claims] 1. A stereo demodulator in an FM receiving apparatus for performing LR separation of an FM detection signal using a switching signal, based on a 38 kHz sine wave synchronized with a pilot signal created by a sine wave creation means. A signal is generated, and the LR separation signal is supplied to the LR separation unit as a switching signal. The LR separation unit multiplies the switching separation signal composed of a sine wave by the FM detection signal to calculate a left-right separated signal. F
Stereo demodulator in M receiver.