JPH0352309A - Satellite broadcast receiver - Google Patents

Abstract

PURPOSE:To prevent noise from being generated even when an FM signal wave with a large frequency shift is inputted by applying frequency conversion to an input signal with a signal of a voltage or current controlled oscillator, applying FM demodulation and feeding back the result to the voltage or current controlled oscillator via an amplitude expansion amplifier so as to control its oscillating frequency. CONSTITUTION:A 2nd intermediate frequency outputted from a 2nd intermediate frequency band pass filter 4 is inputted to a 2nd frequency converter 20, in which the signal is frequency-converted into a 3rd intermediate frequency with an oscillation signal from a voltage or current controlled oscillator 21 and inputted to an FM demodulation circuit 5. Part of the demodulation output from the FM demodulation circuit 5 is inputted to an amplitude expansion amplifier 23. Thus, even when an FM signal with a large frequency shift is inputted, the overmodulation portion is expanded by an amplitude expansion amplifier 23 to increase the FM negative feedback quantity by an FM negative feedhack loop. Thus, the FM shift of the overmodulation part is compressed and the production of noise at transient response causing overmodulation hardly occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a satellite broadcasting receiver whose purpose is to perform FMffj tuning with low noise. BACKGROUND OF THE INVENTION In recent years, satellite broadcasting receivers are required to operate with high sensitivity and low noise as equipment becomes smaller.

The conventional satellite broadcast receiver is explained below. Figure 4 is a block diagram of a conventional satellite broadcasting receiver. In Figure 4, 1 is a first intermediate frequency input terminal, 2 is a frequency converter, 3 is a local oscillator, and 4 is a second intermediate frequency band filter. vessel,
5 is an FM demodulation circuit, and 6 is a demodulation output terminal. This FM demodulation circuit 5 has a configuration as shown in FIG. 5 or 6. In FIG. 5, 7 is a second intermediate frequency input terminal, 8 is a phase comparator, 9 is a low-pass filter, 10 is a DC amplifier, and 11 is a voltage or IA current controlled oscillator. In addition, in FIG. 6, 12 is an FM/AM converter, 13 is an A
It is an M detector. The operation of the satellite broadcasting receiver configured in this way will be explained below. First, the first
The first intermediate frequency inputted from the intermediate frequency input terminal 1 is mixed with the oscillation signal of the local oscillator 3 set to the desired tuning frequency by the frequency converter 2, and is mixed with the 6th frequency, which becomes the second intermediate frequency, 2, signals outside the desired band are attenuated by a second intermediate frequency band filter 4, and FMaL
The signal is input to the control circuit 5. The signal demodulated by the FM demodulation circuit 5 is output from the demodulation output terminal 6. Here, FM
The operation of demodulation circuit 5 will be further explained. Figure 5 is a block diagram of a phase synchronized FM demodulation circuit.
The second intermediate frequency FM signal inputted from the second intermediate frequency band filter 4 to the phase comparator 8 through the terminal 7 is phase-compared with the oscillation signal from the voltage or current controlled oscillator 11,
The phase difference output is subjected to a low-pass filter 9 attenuating unnecessary Takashiro noise components, amplified in amplitude by a DC amplifier 10, and then input to a voltage or current controlled oscillator 11 as a frequency control signal. This closed loop circuit operates so that the phase difference signal of the phase comparator 8 becomes "zero", but it produces a phase difference output between the signal from the input terminal 7 and the signal from the voltage or current controlled oscillator 11 as an instantaneous signal. This is directly extracted as an FM demodulated signal. Figure 6 is a block diagram of a slope detection circuit or a similar detection method. The second input from the second intermediate frequency band filter 4 to the FM/AM converter 12 through the terminal 7
The intermediate frequency FM signal is tuned to the seventh frequency due to the resonance characteristics of the tuned circuit.
As shown in the figure, an amplitude modulated wave is output by converting ΔV/Δf along the curves 14 and 15 and on the straight line 16, which is the combined characteristic, and the AM detector 13 detects the amplitude modulated wave. The demodulated output is obtained. Problems to be Solved by the Invention However, in the configuration of the conventional example described above, when a video signal having a transient response as shown in FIG. 8, especially when a white character is modulated as overmodulation due to superimposition, In the phase-locked FM demodulation circuit, the oscillation frequency of the voltage or current controlled oscillator 11 cannot follow a transient response with a large frequency deviation, and the phase comparator 8 will output an unstable output. , this had the problem of being output as demodulation noise. In addition, in the slope detection circuit shown in Figure 6 or a similar detection method, signals with a large frequency shift as shown in Figure 8 are subjected to FM/AM conversion in a region with poor linearity, so the demodulated output is This had the problem of causing nonlinear distortion and noise. The present invention solves the above-mentioned conventional problems, and is capable of demodulation without generating noise even when an FM signal wave with a large frequency shift is input, such as when a video @ signal is frequency modulated as overmodulation. The purpose is to provide a satellite broadcasting receiver with a circuit. Means for Solving the Problems In order to solve the above problems, the satellite broadcasting receiver of the present invention has the following features:
means for converting the frequency of an input signal using a signal from a voltage or current controlled oscillator; means for FMfi modulating the signal output from the frequency converting means; and amplitude expansion for expanding the amplitude of the FMei modulated signal from an arbitrary level. It is equipped with means for feeding back to the voltage or current controlled oscillator via an amplifier and controlling its oscillation frequency. Effect With the above configuration, even when an FM signal with a large frequency shift is input, such as when a white character is frequency-modulated as overmodulation due to superimposition, the overmodulation part is expanded by the amplitude expansion amplifier. However, by increasing the amount of FM negative feedback by the FM negative feedback loop,
It is possible to compress the amount of FM deviation in the overmodulation part, thereby making it difficult to generate noise during transient response that results in overmodulation. EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a satellite broadcasting receiver according to an embodiment of the present invention. In FIG. 1, 1 is a first intermediate frequency input terminal, 2 is a frequency converter, 3 is a local oscillator, 4 is a second intermediate frequency band filter, 5 is an FMfi modulation circuit, and 6 is a demodulation output terminal. Furthermore, 20 is a second frequency converter interposed between the second intermediate frequency band filter 4 and the FM demodulation circuit 5, and 21 is a voltage or current controlled oscillator connected to the second frequency converter 20. , 22 is a DC amplifier that inputs the output of the amplitude expansion amplifier 23, into which the demodulated output is input, to the voltage or current controlled oscillator 21. This amplitude expansion amplifier 23 expands the amplitude of an input signal above a certain level. The operation of the satellite broadcasting receiver configured in this way will be explained below. The operation from the first intermediate frequency input terminal 1 to the second intermediate frequency bandpass filter 4 is the same as the conventional one. The second intermediate frequency output from the second intermediate frequency bandpass filter 4 is input to the second frequency converter 20, where it is frequency-converted by the oscillation signal from the voltage or current controlled oscillator 21 and converted into a third intermediate frequency. converted to frequency, FM
The FM demodulation circuit 5 input to the 6tli circuit 5 is similar to the conventional example shown in FIG. 5 or 6, and the demodulated output is obtained at the output terminal 6. A part of this demodulated output is input to the amplitude expansion amplifier 23. FIG. 2 is a circuit diagram showing a specific example of the amplitude expansion amplifier 23. In FIG. 2, 27 is a demodulation signal input terminal, 28 is a DC amplification transistor, 29 is a load resistor,
30 is an emitter current setting resistor, 31 is a switching transistor for amplitude expansion, 32 is a current limiting resistor, 33.
34 is an amplitude expansion voltage setting resistor, 35 is a power supply terminal, 36
is the output terminal. Next, we will explain the operation of this circuit. When the [1 output input to the transistor 28 exhibits a transient response characteristic due to pre-emphasis as shown in FIG. The base-emitter voltage is set to the voltage set at 34, transistor 31 becomes conductive, and a current limited by resistor 32 flows. resistance 32
The collector current of the transistor 28 increases due to the current flowing through the transistor 28, and the collector voltage decreases due to the load resistor 29. In other words, the voltage gain increases. In this state, as shown in FIG. 3, the level difference between 40 and 41 in FIG. 8 is expanded to the level difference between 46 and 47 in FIG. 3, and this signal is output from the output terminal 36. This swing is 1! ! #The output signal of the long amplifier 23 is sent to the DC amplifier 2
2 to drive a voltage or current controlled oscillator 21 through F
The M-modulated oscillation signal is input to the second frequency converter 20. The oscillation signal at this time is FM modulated by a signal expanded above a certain level shown in Figure 3, and the first
It is in phase with the input signal from input terminal 1 in the figure,
The FM deviation of the third intermediate frequency output from the second frequency converter 20 is compressed in the transient response portion as shown in FIG. 9 due to the increased amount of FM negative feedback. Effects of the Invention As described above, according to the present invention, a means for converting the frequency of an input signal using a voltage or a signal from a t-current controlled oscillator, a means for demodulating the signal output from the frequency converting means, and an FM By providing means for controlling the oscillation frequency of the voltage or current controlled oscillator via an amplitude expansion amplifier that expands the amplitude of the demodulated signal from an arbitrary level, the video signal may be frequency modulated as overmodulation, etc. Even if an FM signal with a large frequency shift is input, the amount of feedback is increased, which compresses the amount of FM shift in the transient response part, making it difficult for noise to occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a satellite broadcasting receiver according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of an amplitude amplifier, and FIG.
The figure is a waveform diagram of the amplitude-expanded demodulated signal, Figure 4 is a block diagram of a conventional satellite broadcasting receiver, and Figure 5 is a phase synchronized FM
A block diagram of the demodulation circuit, FIG. 6 is a block diagram of slope detection or a similar detection method, FIG. 7 is a waveform diagram for explaining FM/AM conversion using the slope detection method, and FIG. 8 is a block diagram of the demodulation circuit.
The figure is a FM1Rfi signal waveform diagram of the input signal, and FIG. 9 is a demodulation signal waveform diagram illustrating how the FM deviation amount of the transient response portion is compressed and output.

Claims (1)

[Claims] 1. Means for converting the frequency of an input signal using a signal from a voltage or current controlled oscillator, means for FM demodulating the signal output from the frequency converting means, and expanding the amplitude of the FM demodulated signal from an arbitrary level. A satellite broadcasting receiver comprising means for feeding back the voltage or current controlled oscillator through an amplitude expansion amplifier to control its oscillation frequency.