JPH0380607A - Satellite broadcast receiver - Google Patents

Abstract

PURPOSE:To obtain the superior satellite broadcast receiver which has small frequency variation with temperature and generates a small noise by applying the balanced outputs of a differential amplifier to both ends of the varactor diode of a resonance circuit. CONSTITUTION:The receiver is provided with a phase comparator 2 which compares the phases of an input FM-modulated signal and the output of a voltage-controlled oscillator with each other and the differential amplifier 15 inputs the balanced outputs 3 of the phase comparator 2 through a balanced type low-pass filter circuit 4. Further, the receiver has the varactor diode 8 which is applied with the balanced output voltages 6 and 16 of the varactor diode 8 at both ends and the resonance circuit of the voltage-controlled oscillator 11 formed of the varactor diode 8 and an inductance 10 connected thereto, and is further equipped with an FM demodulating circuit which is constituted by connecting them in a closed loop. Consequently, the satellite broadcast receiver which has small variation in oscillation frequency with temperature and has a demodulating circuit hardly generating a noise is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a satellite broadcasting receiver whose purpose is to perform highly stable FM demodulation.

BACKGROUND OF THE INVENTION In recent years, satellite broadcasting receivers are required to have high sensitivity and highly stable operation as equipment becomes smaller.

A conventional satellite broadcast receiver will be explained below.

FIG. 2 shows a block diagram of an FM demodulation circuit of a conventional satellite broadcasting receiver. In FIG. 2, 1 is an FM modulation signal input terminal, and the FM modulation signal is input to a phase comparator 2.

A balanced output 3 of the phase comparator 2 is input to a differential amplifier 5 via a balanced low-pass filter circuit 4, and one of the balanced outputs is outputted to an output terminal 7 as a demodulated output. Further, its output is applied to the cathode side of the variable capacitance diode 8 via the line 6. In addition, variable capacitance diode 8
The cathode side of is connected to one end of a tuning inductance 10 via a DC blocking capacitor 9, and a resonant circuit consisting of this variable capacitance diode 8 and tuning inductance 10 is further connected to a voltage controlled oscillator 11. The output of this oscillator 11 is passed through line 12 to phase comparator 2.
is input to.

The operation of the satellite broadcasting receiver configured in this manner will be described below. First, the FM modulation signal inputted from the input terminal 1 is phase-compared with the output of the voltage controlled oscillator 11 inputted through the line 12 in the phase comparator 2, and a balanced output 3 is generated. This balanced output 3 is subjected to a balanced low-pass filter 4 attenuating high frequencies to an arbitrary level, thereby suppressing high-frequency noise. The balanced output output from the low-pass filter 4 is amplified to a desired level by a differential amplifier 5, and the output of the differential amplifier 5 is taken out to an output terminal 7 with one side of the balanced output as a demodulated output. Further, this output changes the capacitance value of the variable capacitance diode 8 through the line 6, and changes the resonance frequency with the limiting inductance 10. The oscillation frequency of the voltage controlled oscillator 11 is controlled by the resonant circuit of the variable capacitance diode 8 and the tuning inductance lO. The oscillator output of the voltage controlled oscillator 11 is input to the phase comparator 2 through the line 12, but the above series of flows constitutes a closed loop, and the phase comparator 2
It operates so that the balanced phase difference output 3 of is “O”, but
As an instantaneous output, an FM demodulated signal that always follows the FM modulated signal at the input terminal 1 is obtained from the output terminal 7.

Problems to be Solved by the Invention However, in the conventional configuration described above, the output of the differential amplifier 5 drives the variable capacitance diode 8 in unbalanced operation, so the unbalanced output changes in DC offset due to temperature changes. , the oscillation frequency of the voltage controlled oscillator 11 changes depending on the temperature.

That is, as the output of the differential amplifier 5, an output signal having a waveform as shown at 31 in FIG. 4, for example, is obtained, and the line 6
is output to. At this time, the variable capacitance diode 8 has V
The outputs of (33) +V and (34) are applied. Therefore, due to temperature change, the DC offset voltage V, (
37), the voltage applied to the variable capacitance diode 8 is V.

(35) +V, (36), and ■. (37) will be offset and applied.

FIG. 3 shows a diagram for explaining the closed loop operation of the FM demodulation circuit having the above configuration. In FIG. 3, the vertical axis indicates the signal-to-noise ratio (C/N) of the FM modulated signal input to the input terminal l in FIG.

The horizontal axis shows the frequency deviation amount of the input FM modulation signal, fO shows the center frequency, and 21 and 22 show the points where noise occurs in the demodulated output, and as the input C/N decreases, one interval becomes It gets narrower. Further, in the case of a video signal in which the deviation of the input FM modulation signal is in the direction shown in 23, direction noise is likely to occur on the 21 side and black noise is likely to occur on the 22 side. Figure 3 (
fF-a in a) is the frequency at the center of the curves 21 and 22, and is called the free run of the demodulation circuit.
This is the oscillation frequency fF of the voltage controlled oscillator 11 when there is no input FM modulation signal at the input terminal 1 in FIG. Figure 3 (b
fF-b in ) indicates a state in which the frequency has changed due to the temperature change.

As is clear from the figure, the curves 21 and 22 are fF-b
The deviation is 23 because it is moving with respect to fO according to
Since the black level side of the video signal in the direction shown approaches the curve 22, black noise is likely to occur. Similarly, when fF changes in the opposite direction to fF-5 due to temperature change, white noise is likely to occur.

When the oscillation frequency fry of the voltage controlled oscillator 11 changes due to temperature changes in this way, there is a problem in that noise is likely to occur as the C/N deteriorates.

The present invention solves the above-mentioned conventional problems, and aims to provide a satellite broadcasting receiver having a demodulation circuit whose oscillation frequency changes little due to temperature changes, and therefore hardly generates noise. .

Means for Solving the Problems In order to solve the above problems, the present invention provides a phase comparator that compares the phases of an input FM modulation signal and a voltage controlled oscillator output, and a balanced output of this phase comparator. A variable capacitance diode to which the balanced output voltage of the differential amplifier is applied via a band-pass filter circuit, and an inductance connected to this variable capacitance diode. and a resonant circuit of the voltage controlled oscillator, and an FM demodulation circuit configured by connecting these in a closed loop.

Effect: With this configuration, the output of the differential amplifier, which is a balanced output with little voltage difference change due to temperature changes, is applied to both ends of the variable capacitance diode, so there is no DC offset change, and therefore there is no noise in the demodulated output. can be made less likely to occur.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows F of a satellite broadcasting receiver in one embodiment of the present invention.
A block diagram of an M demodulation circuit is shown. In FIG. 1, l is an FM modulation signal input terminal, 2 is a phase comparator, 3 is a balanced output of the phase comparator 2, and 4 is a balanced low-pass filter circuit into which the balanced output 3 is input, This is the same as the conventional one shown in FIG. 15 is a differential amplifier to which the output of the low-pass filter circuit 4 is input, and its balanced outputs 6 and 16 are output from output terminals 7 and 17. The balanced outputs 6 and 16 are applied to the card side and the anode side of the variable capacitance diode 8.

The card side of this variable capacitance diode 8 is connected to one end of a tuning inductance via a DC blocking capacitor 9. 18 is a DC blocking capacitor connected to the card side of the variable capacitance diode 8. Furthermore, a resonant circuit consisting of a variable capacitance diode 8 and a tuning capacitor 10 is connected to a voltage controlled oscillator 11. This oscillator 11
The output of is input to the phase comparator 2 through line 12.

Regarding the satellite broadcast receiver configured in this way.

The operation will be explained below. The operation from the FM modulation signal input terminal 1 to the differential amplifier 15 is the same as the conventional one.

Signals 6 and 16 output from the differential amplifier 15 are balanced outputs of waveforms 31 and 32 as shown in FIG. 4, and are applied to both ends of the variable capacitance diode 8.

This variable capacitance diode 8 and tuning inductance 10
The oscillation frequency of the voltage controlled oscillator 11 is controlled by a resonant circuit consisting of the following. The subsequent operations are the same as in the conventional example.

In FIG. 4, 31 is the waveform of the output signal 6 in FIG. 1, and 32 is the waveform of the other output signal 16. In this case, the output of the differential amplifier 15 changes due to temperature to the waveform shown on the right side. Like■. Even if it changes by (37), the voltage applied to the variable capacitance diode 8 is V□ (33) = V,
(35) and is not affected by changes in V, (37).

As described above, according to this embodiment, by directly applying the balanced output of the differential amplifier to both ends of the variable capacitance diode,
The oscillation frequency does not change even when the DC offset changes due to temperature changes, making it difficult to generate noise when C/N deteriorates.

Effects of the Invention As described above, according to the present invention, by applying the balanced output from the differential amplifier to both ends of the variable capacitance diode of the resonant circuit, an excellent structure with less frequency fluctuation due to temperature change and less noise generation is achieved. It is possible to realize a satellite broadcasting receiver.

[Brief explanation of drawings]

FIG. 1 shows F in a satellite broadcasting receiver according to an embodiment of the present invention.
A block diagram of the M demodulation circuit, FIG. 2 is a block diagram of a conventional satellite broadcasting receiver, FIGS. 3(a) and (b) are diagrams for explaining the closed loop operation of the FM demodulation circuit, and FIG. 4 is a diagram of the present invention. FIG. 3 is a diagram for explaining the operation of the FM demodulation circuit in the satellite broadcasting receiver when the temperature changes. ■...FM modulation signal input terminal, 2...phase comparator,
4...Low pass filter circuit, 15...Differential amplifier, 6, 16...Balanced output, 7.17...Demodulated signal output terminal, 8...Variable capacitance diode, 9, 18...
DC blocking capacitor, 10... Tuning capacitor,
11...Voltage controlled oscillator.

Claims (1)

[Claims] 1. means for inputting the balanced output of a phase comparator that compares the phases of the input FM modulation signal and the output of the voltage controlled oscillator to a differential amplifier via a balanced low-pass filter circuit; means for applying an output to both ends of the variable capacitance diode, and means for controlling the oscillation frequency of the voltage controlled oscillator by a resonant circuit consisting of the variable capacitance diode and an inductance connected thereto; A satellite broadcasting receiver in which an FM demodulation circuit is constructed by connecting a bandpass filter circuit, a differential amplifier, a resonant circuit, and a voltage controlled oscillator in a closed loop.