JP2001103023A - Fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FM receiver which facilitates digital processing and is capable of maintaining constant a ratio in the frequency characteristics of a main signal and a sub signal. SOLUTION: This FM receiver is provided with a correcting means 6, which has a correcting filter 63 that is calculated according to the characteristics of the main signal and the sub signal of a composite signal that is subjected to FM detection, corrects the frequency characteristics of the composite signal by the correcting means 6 and makes the frequency characteristics of the main signal and the sub signal flat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver.

[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 an FM receiver, an FM signal input from an antenna is mixed with high-frequency amplification and local oscillation to perform intermediate frequency conversion. Then, the converted FM-I
The F signal is supplied to an FM demodulation circuit, which is FM-detected by the FM demodulation circuit. The detected signal is separated into left and right LR signals by a demodulation circuit, and is discarded as an audio signal from a speaker or the like and output.

[0004]

By the way, the above-mentioned F
When the intermediate frequency conversion is performed on the M signal, a bandpass filter (B
PF) through the FM signal. With this bandpass filter (BPF), there is a problem that a flat frequency characteristic of the composite signal after FM detection cannot be obtained.

Conventionally, there has been a problem that the workability is complicated by changing the mixing ratio of the main signal and the sub-signal using an external resistor or the like.

The present invention has been made in view of the above-mentioned conventional problems, and provides an FM receiver capable of facilitating digital processing and maintaining a constant ratio between the frequency characteristics of a main signal and a sub-signal. The purpose is to:

[0007]

According to the present invention, there is provided a correction means calculated in accordance with the characteristics of a main signal and a sub-signal of a composite signal detected by FM detection, and the frequency characteristic of the composite signal is corrected by the correction means. In addition, the frequency characteristics of the main signal and the sub signal are flattened.

[0008] The correction means is characterized in that the correction is performed based on the characteristics of a band-pass filter used in the IF amplification processing section.

Further, the correction means corrects based on a phase characteristic of an anti-aliasing filter before conversion into a digital signal.

According to the above configuration, the ratio of the frequency characteristics of the main signal and the sub signal can be kept constant, so that stereo reproduction faithful to the original signal can be performed.

[0011]

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 receiving apparatus. FM according to the present invention
The receiver includes an antenna 1, a front end unit 2, an IF amplification unit 3, a limiter unit 4, an FM demodulation unit 5, a correction unit 6 and a stereo demodulation unit 7, which are features of the present invention.

[0012] The 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 amplifier 3 uses a ± 90 kHz band-pass filter (BPF) to mix with high-frequency amplification and local oscillation to perform intermediate frequency conversion.
Giving the IF signal to the limiter unit 4; As previously mentioned,
Due to the characteristics of the BPF in the IF amplifier 3, the frequency characteristics of the composite signal after the FM detection are not flat. The gain, selectivity, and various interference removal characteristics of the receiver are determined by the IF amplifier 2. Intermediate frequency can be image or IF
The frequency is 10.7 MHz in consideration of interference.

The limiter unit 5 removes noise and AM components caused 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 the FM wave, converts the FM wave 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. As described above, the characteristics of the main signal and the sub-signal of the composite signal are not flat. This is because the gain of the sub signal is lower than the gain of the main signal in the BPF.

Therefore, in the present invention, the frequency characteristics of the composite signal subjected to the FM detection are corrected by the correction means 6 to flatten the frequency characteristics of the main signal and the sub-signal. As will be described later, the correction means 6 includes a filter for correcting the frequency characteristic of the composite signal, corrects the composite signal, and supplies the corrected composite signal to the stereo demodulation unit 6. The stereo demodulator 6 separates and outputs an L signal and an R signal from a composite signal, and performs stereo demodulation by a switching method.

FIG. 2 shows a correcting means 6 which is a feature of the present invention.
FIG. 3 is a block diagram showing the configuration of FIG. As shown in FIG.
The M-detected composite signal is filtered by a low-pass filter (LPF) 61 as an anti-aliasing filter. The LPF 61 has, for example, the phase characteristics shown in FIG. 3, and the composite signal is phase-converted according to the phase characteristics. Then, the signal passing through the LPF 61 is converted into a digital signal by the analog / digital conversion circuit 62. Then, the digitized composite signal is supplied to the correction filter 63. The correction filter 63 takes into consideration the characteristics of each filter in advance, such as the characteristics of a band-pass filter used in the IF amplification processing unit 3 and a low-pass filter (LPF) 61 as an anti-aliasing filter before conversion into a digital signal. This is a digital filter in which the correction value is programmed.
3, the main signal and the sub-signal of the composite signal are flattened. The correction filter 63 can be configured to perform processing based on correction values in each band by a predetermined program using a DSP or the like.

As described above, the frequency characteristics of the main signal and the sub-signal can be kept constant by the correction filter 63. Then, a composite signal having a constant frequency characteristic ratio is provided to the stereo demodulation processing circuit 7, and a stereo reproduction signal faithful to the original signal is output from the stereo demodulation processing circuit 7.

If the characteristics of the BPF or the low-pass filter (LPF) 61 change, the correction value of the correction filter 63 can be easily changed by changing the program.

In the present invention, the circuits indicated by the blocks may be realized by 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.

[0020]

As described above, according to the present invention, the ratio of the frequency characteristics of the main signal and the sub signal can be kept constant, so that stereo reproduction faithful to the original signal can be performed.

[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 configuration of a correction unit 6 which is a feature of the present invention.

FIG. 3 is a diagram showing a phase characteristic of a low-pass filter (LPF) as an anti-aliasing filter before conversion into a digital 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 Correction means 7 Stereo demodulation part 61 LPF 62 A / D conversion circuit 63 Correction filter

Claims (3)

[Claims] A correcting means for calculating a frequency characteristic of the composite signal by correcting the frequency characteristic of the composite signal with a main signal and a sub-signal; An FM receiver characterized by flattening frequency characteristics. 2. The FM receiver according to claim 1, wherein the correction unit performs correction based on characteristics of a band-pass filter used in an IF amplification processing unit. 3. The FM receiver according to claim 1, wherein the correction unit performs correction based on a phase characteristic of an anti-aliasing filter before conversion into a digital signal.