JPH02272808A - Reception device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a threshold level improvement type receiving apparatus which is particularly important in satellite broadcasting and satellite communications.

BACKGROUND OF THE INVENTION In recent years, receiving apparatuses for receiving satellite broadcasting are required to improve the threshold level due to the demand for smaller parabolic antennas and higher S/N in low C/N reception during rain attenuation.

An example of the above-mentioned conventional threshold improvement type receiving device will be described below with reference to the drawings.

FIG. 3 shows a block diagram of a conventional receiving device. In Figure 3, 1 is a mixer, 2 is a voltage controlled oscillator (
6 is an FM demodulator, 7 is a band pass filter (hereinafter abbreviated as BPF), 8 is a DC amplifier, 9 is a low pass filter (hereinafter abbreviated as LPF), a is an FM signal input terminal, and b is an FM signal input terminal. The demodulated signal output terminal and C are the tuning voltage input terminals.

This configuration is called the FMM feedback method.

The operation of the receiving device configured as described above will be described below.

The high frequency FM signal inputted upstream from the FM signal input terminal is applied to the mixer 1 . Further, the VCO 2 oscillates at a frequency corresponding to the DC voltage applied to the tuning voltage input terminal C, and its output is injected into the mixer 1. The mixer 1 obtains the frequency component of the difference between the two signals as an intermediate frequency FM signal.

In BPF7, excluding noise components other than the necessary band, F
The M demodulator 6 performs FM demodulation and extracts the baseband output. The LPF 9 removes unnecessary high-frequency noise in the baseband region, and the demodulated signal is guided to the demodulated signal output terminal through the DC amplifier 8.

At the same time, this demodulated signal is applied to a voltage control terminal provided separately from terminal C of the VCO 2 to FM modulate the vCO output signal. At this time, the FM signal input from terminal a and ■CO
mixer 1 so that the modulation signals of the output FM signals are in phase.
, BPF7, FM demodulator 6, LPF9, DC amplifier 8,
By configuring the loop of vC02, the frequency deviation of the intermediate frequency FM signal output from the mixer 1 can be compressed more than the frequency deviation of the FM signal input manually to the terminal a.

Therefore, the amplification of the occupied frequency band of the FM signal is reduced by the reduction in frequency shift, and the bandwidth of the BPF 7 can be narrowed accordingly. Narrowing the band of the BPF increases the C/N of the input signal of the FM demodulator with equal constraints, and improves the threshold level. (For example, [Easy to understand FM technology] co-authored by Yuya Ito and Akira Fujii, Sanpo Publishing 1)
Pages 40 to 144) Problems to be Solved by the Invention However, with the above configuration, when demodulating a wideband signal such as a video signal, the delay of the FMM feedback loop cannot be ignored. For a modulated signal whose frequency is twice the delay time of the loop as one cycle, the modulated signal of VCO2 and the modulated signal of the FM signal input to terminal a are opposite in phase, and the frequency deviation is not compressed but conversely. However, the amplitude frequency characteristic after demodulation has a problem in that a peak occurs and the amplitude frequency characteristic does not become flat. Also, the C of the FM signal input to terminal a
There is also a problem in that when the C/N deteriorates significantly, the C/N deteriorates further due to noise that goes around the loop.

In view of the above problems, the present invention provides an FM demodulator that can uniformly compress the frequency deviation of an FM signal even for a wideband modulated signal and improve the threshold level without using a loop. .

Means for Solving the Problems In order to solve the above-mentioned problems, the receiving device of the present invention provides a first
PF, an n frequency divider that divides its output by n (n is an integer), and a second frequency divider that matches the occupied frequency bandwidth of the FM signal after frequency division.
The BPF is equipped with a BPF and an FM [Il] unit that demodulates the output thereof.

Effect: With the above-described configuration, the present invention compresses the frequency deviation to 1/H over a wide band using the n frequency divider, so a loop such as FM negative feedback is not required, and the amplitude-frequency characteristics of the demodulated output are flattened. It is also possible to eliminate the influence of loop noise.

Embodiment Hereinafter, a receiving apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a receiving apparatus in a first embodiment of the present invention. In Fig. 1, 1 is a mixer, 2 is a VCO 13, 5 is a band pass filter (hereinafter abbreviated as BPF), 4 is an n frequency divider, and 6 is an FM
In the demodulator, a is an FM signal input terminal, and b is a demodulated signal output terminal.

The operation of the receiving apparatus configured as described above will be described below with reference to FIGS. 1 and 2.

The high frequency FM signal inputted upstream from the FM signal input terminal is applied to the mixer 1, and the output of the local oscillator VCO 2 for tuning is also injected into the mixer 1 to obtain a fixed intermediate frequency f. is converted to fo is the center frequency of the FM signal at the intermediate frequency stage. Here, the peak-to-peak frequency deviation of the FM signal is Δfo
1. If the maximum modulation frequency is fIll, the occupied frequency bandwidth B of the FM signal is expressed by equation (1) according to Carson's law.

B-Δf o+ 2 f m・Old−・(1) Therefore, B
The PF3 requires a bandwidth shown by equation (1) centered around the frequency r0, and its amplitude-frequency characteristics are schematically shown in Figure 2(a).The output of this BPF3 is divided by n. 4 divides the frequency into 17n. Through this operation, the center frequency of the FM signal becomes f 0 /n, the peak-to-peak frequency deviation is compressed to Δf o /n, and the occupied frequency bandwidth B' of the FM signal becomes equation (2).

n Here, in order to obtain a normal demodulated output, the conditions shown in equation (3) are required for the frequency and frequency division ratio.

Note that a frequency divider that divides the frequency into an even number can be realized, for example, by simply connecting D flip-flop circuits of digital circuits in parallel, and if an ECL element is used, it is possible to handle input signals up to about 2 GHz. It is. In addition, although amplitude information is lost due to digitization, this is not a problem since amplitude information is not needed in the FM signal, and the circuit can be simplified because the amplitude limiter and AGC circuit that were conventionally required before the FM demodulator can be omitted. Also connected.

The FM signal frequency-divided by the n frequency divider 4 has a center frequency ' o
/n, the bandwidth is input to BPF5 expressed by equation (2). FIG. 2(b) schematically shows the amplitude frequency characteristics of the BPF 5. The signal passing through the BPF 5 is demodulated by the FM demodulator 6 and output to the demodulated signal output terminal.

As described above, according to this embodiment, the first BPF has a bandwidth equal to the occupied frequency bandwidth of the input FM signal.
, a frequency divider that divides the output by n, and a bandwidth equal to the occupied frequency bandwidth of the FM signal after frequency division. Since it is equipped with a narrow-band second BPF and an FM demodulator that demodulates its output, it realizes a threshold-improved receiving device with flat demodulation amplitude frequency characteristics over a wide band and without the effects of wrap-around noise due to loops. can do.

Effects of the Invention As described above, the present invention includes a first BPF having a bandwidth equal to the occupied frequency bandwidth of the input high frequency FM signal, an n frequency divider, and an occupied frequency band of the FM signal after frequency division. Since the second BPF has a bandwidth equal to the width of the first BPF and has a narrower band than the first BPF, and an FM demodulator that demodulates the output thereof, the demodulation amplitude frequency characteristic is flat over a wide band and can be controlled by the loop. It is possible to realize a threshold-improved receiving device that is not affected by feedback noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a receiving device in the first embodiment of the present invention, FIG. 2(a) is an amplitude frequency characteristic diagram of BPF 3 in FIG. 1, and FIG. 2(b) is an amplitude frequency characteristic diagram of BPF 5 in FIG. 1. The frequency characteristic diagram in FIG. 3 is a block diagram of a conventional receiving device. l...Mixer, 2...vCO13,5
...BPF, 4...n frequency divider, 6...
...FM demodulator, a...FM signal input terminal, b...demodulated signal output terminal. Name of agent: Patent attorney Shigetaka Awano, 2nd ward and α2 (b), dD Fu Ushi & buru

Claims (1)

[Claims] a first bandpass filter having a bandwidth matching the occupied frequency bandwidth of the input FM signal; and a frequency division by n (n is an integer) that divides the frequency of the FM signal after passing through the first bandpass filter. a second bandpass filter having a bandwidth matching the occupied frequency bandwidth of the divided FM signal, and an FM demodulator for demodulating the FM signal after passing through the second bandpass filter. A receiving device characterized by: