JPH04373315A - Tuner for satellite broadcasting reception - Google Patents

Abstract

PURPOSE:To provide a tuner for satellite reception considerably decreasing noise power. CONSTITUTION:An intermediate frequency (IF) amplifier circuit 26 equipped with the plural steps of narrow band width to shift amplify an IF signal and to shift a normal IF band by a variable capacity diode is connected to the output of a mixer 25, the band width is apparently widened by shifting the IF pass band while following up the FM modulated frequency of the input signal, a PLL detection circuit 27 connected to the output of the above- mentioned IF amplifier circuit 26 executes PLL detection to the IF amplified signal, and a tuning voltage for the shift control of the IF pass band in variable tuner circuits 30 and 31 is outputted from the PLL detection circuit 27.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a tuner for receiving satellite broadcasting, and more particularly to a bandpass filter of an intermediate frequency amplifier circuit in a tuner for receiving satellite broadcasting or communication satellites in an ultra-high frequency band (hereinafter referred to as BS tuner). It is related to.

0002

[Background Art] A satellite broadcasting receiving system uses a BS antenna to receive radio waves in the 12 GHz band, for example, transmitted from a broadcasting satellite, and amplifies the weak radio waves received by a BS converter for easy signal processing and distribution. 1 GHz band frequency signal. Furthermore, after selecting a desired channel signal from the 1 GHz band converted signal with a BS tuner and obtaining an intermediate frequency (IF) signal of a normal television broadcast signal,
An FM demodulator extracts a video signal and an audio signal from the IF signal and demodulates or amplifies them respectively.

[0003] The above BS tuner, as shown in FIG.
High-pass filters (1) (2) are connected to the input terminals (Via) (Vib).
) and switching diodes (5) (6) connected via attenuators (3) (4) (7)
, a high frequency amplification circuit (10) having an AGC attenuator (8), a bandpass filter (9), etc., a frequency conversion circuit (10) having a mixer (11), a buffer amplifier (12), and a local oscillation circuit (13). 14) and IF amplifier (15) (1
an intermediate frequency amplifier circuit (18) having a bandpass filter (17) of a SAW filter connected to the output of the mixer (11) via a prescaler circuit (19) and a PLL synthesizer (20). It is connected to an FM demodulator (24) having a high-pass filter (21), an intermediate frequency AGC (22), a diode detector (23), and the like. Incidentally, there is also one that uses a PLL detection circuit as the FM demodulation section (24).

Here, as an item indicating the characteristics of the BS tuner, there is a ratio between a carrier signal and a noise signal, that is, carrier/noise (C/N), and the higher the ratio, the better. In particular, the noise power (Pn) in the intermediate frequency band is Pn=kT
B (where k: Boltzmann constant, T: absolute temperature, B: S
AW filter bandwidth). Therefore, the narrower the bandwidth (B), the more the noise power (Pn) decreases and the carrier/noise (C/N) improves. Currently, the bandwidth (B) is 27MHz in Japan, and its center frequency is 40MHz.
At 2.78MHz, carrier/noise (C/N) is 14
dB or more.

[0005]

Problem to be Solved by the Invention The problem to be solved by the present invention is that, in view of the above-mentioned conventional technology, since the intermediate frequency of the BS tuner is subjected to FM modulation, the single frequency is It moves temporally within the frequency band, but since the SAW filter of the bandpass filter (17) is fixed, the bandwidth (B
) becomes wider and the noise power (Pn) becomes larger.

[0006]

[Means for Solving the Problems] The present invention includes a mixer that mixes a high frequency input signal and a local oscillation signal and outputs an intermediate frequency signal; , the intermediate frequency passband is shifted by a variable tuning circuit, and the intermediate frequency passband is shifted in accordance with the FM modulation frequency of the input signal, and the intermediate frequency passband is shifted in accordance with the FM modulation frequency of the input signal. , connected to the intermediate frequency amplification circuit to widen and the output of the intermediate frequency amplification circuit,
The present invention is characterized by comprising a PLL detection circuit that performs PLL detection of the intermediate frequency amplified signal and outputs a tuning voltage for shift control of the intermediate frequency pass band of the variable tuning circuit.

[0007]

[Operation] According to the above technical means, the bandwidth of the bandpass filter in the intermediate frequency amplifier circuit is made narrow and variable, and the bandwidth is shifted to follow the input signal, thereby making the narrow bandwidth appear wider. do.

[0008]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In the figure, (25) is a mixer, (26) is an intermediate frequency (IF) amplifier circuit, and (27) is a PLL detection circuit. The mixer (25) mixes the high frequency input signal and the local oscillation signal and outputs an IF signal. IF amplifier circuit (2
6) are amplifiers (28) (29) and variable tuning circuit (30)
(31), and the variable tuning circuits (30) and (31) each include a coil formed by silver plating copper wire and a variable capacitance diode to increase Q (selectivity), or The bandwidth (B) is narrowed by providing two to several stages of the IF passband, and the IF passband is shifted and controlled by a variable capacitance diode. Then, as described later, the tuning voltage for controlling the variable capacitance diode is changed to an appropriate operating voltage by the operational amplifier (34) as needed from the output of the PLL detection circuit (27), and then applied to each variable tuning circuit (30) (31). Add.

[0009] The PLL detection circuit (27) is an amplifier (35)
(36), PLL oscillator (37), and phase comparator (3
8) and an IF input via an amplifier (35).
The signal and the PLL oscillation signal are synchronized by a phase comparator (38), and when the frequency deviates, the voltage changes to the video signal (VID).
EOOUT) and behaves similarly to the IF signal. Therefore, this voltage is applied to the variable capacitance diodes of the variable tuning circuits (30) and (31) via the operational amplifier (34) as a tuning voltage for shift control of the IF passband, and is applied to the variable capacitance diodes of the variable tuning circuits (30) and (31) to adjust the IF passband by following the FM modulation frequency of the input signal. is shifted to make its bandwidth (B) appear wider. at the same time,
Since the bandwidth itself is narrow, noise power is reduced. Note that when the bandwidth (B) is halved (13.5 MHz in Japan), the carrier/noise (C/N) is improved by at least 3 dB and becomes as high as 18 dB.

0010

According to the present invention, since the IF pass band of the BS tuner is narrowed and shifted to follow the input signal, the narrow IF pass band is apparently widened, and the IF pass band of the BS tuner is narrowed and shifted to follow the input signal. is amplified, the threshold level is greatly improved, and the performance is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts showing an embodiment of a satellite reception tuner according to the present invention.

FIG. 2 is a block diagram showing a specific example of a BS tuner.

[Explanation of symbols]

25 Mixer 26 Intermediate frequency amplification circuit 27 PLL detection circuit 30, 31 Variable tuning circuit

Claims (3)

[Claims] 1. A mixer that mixes a high frequency input signal and a local oscillation signal to output an intermediate frequency signal; and a mixer that is connected to the output of the mixer, amplifies the intermediate frequency signal, and uses a variable tuning circuit to pass the intermediate frequency signal. an intermediate frequency amplification circuit which has a bandpass filter with a shifted band and a narrow bandwidth, and which shifts an intermediate frequency passband to follow the FM modulation frequency of an input signal to make the bandwidth appear wider; A satellite broadcast receiver characterized by comprising a PLL detection circuit connected to the output of the amplifier circuit, which performs PLL detection of the intermediate frequency amplified signal and outputs a tuning voltage for shift control of the intermediate frequency pass band of the variable tuning circuit. tuner. 2. A tuner for satellite broadcast reception, wherein the variable tuning circuit according to claim 1 is formed by forming coils and variable capacitance diodes in multiple stages. 3. A tuner for satellite broadcast reception, wherein the coil included in the variable tuning circuit according to claim 1 is formed by silver plating a copper wire.