JPH06112858A - Receiver - Google Patents

Abstract

PURPOSE:To reduce deterioration in the demodulation characteristic due to feedback of an undesired signal to an intermediate frequency amplifier circuit by using a filter having a different pass characteristic in the forward and reverse direction for an intermediate frequency filter of the receiver. CONSTITUTION:Part of power of an oscillation signal from a VCO in a PLL being a component of an FM demodulation circuit 21 in an IC 40 is leaked to an input section of an intermediate frequency amplifier circuit 9 in order to increase a passing loss in the reverse direction (from output to input) in comparison with a passing loss in the forward direction (from input to output) of an intermediate frequency filter 8. In this case, the feedback from the output to the input of the intermediate frequency filter 8 is prevented. Thus, when the PLL is in the lock state, the frequency of the signal inputted to a phase comparator in the PLL is equal to the frequency of the oscillation signal from the VCO. Thus, when the feedback quantity of the input to the intermediate frequency filter 8 is much, the filter characteristic is deteriorated, and then a differentiation phase characteristic, a differentiation gain characteristic, a group delay characteristic and a demodulation output frequency characteristic are deteriorated while the deterioration in the demodulation characteristic is reduced in this receiver.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving device such as an indoor unit of a satellite broadcast receiver for receiving signals from a broadcasting satellite or a communication satellite, and in particular, one tuner device can receive signals of different bandwidths. And a receiver.

[0002]

2. Description of the Related Art As a receiver using an intermediate frequency filter in a super-heterodyne system, a second converter section of a BS tuner, a UHF / VHF television tuner and the like are known. According to the conventional technology, the intermediate frequency filter uses a filter having a reversible characteristic in which the pass characteristic is the forward direction and the reverse direction, and eliminates the signal feedback between the input and output of the intermediate frequency filter and the characteristic deterioration due to the unnecessary signal from the demodulation circuit. There is no consideration for the configuration.

[0003]

In the conventional tuner device of the super-heterodyne system, the intermediate frequency filter uses a filter having a reversible characteristic in which the pass characteristic is the forward direction and the reverse direction. When the FM demodulation circuit is used, the oscillation signal of the VCO (voltage controlled oscillator) in the loop of the PLL leaks from the output side to the input side of the intermediate frequency amplifier circuit of the tuner device and deteriorates the characteristics. In particular, when a surface acoustic wave filter is used as the intermediate frequency filter, leakage of the VCO increases the amplitude ripple of the pass band characteristic and deteriorates the differential gain characteristic and the differential phase characteristic of the demodulation circuit. Furthermore, in a receiving device that receives two signals of two types of intermediate frequency bands by switching two filters having two bandwidths, the switching circuit becomes complicated in order to reduce this characteristic deterioration, and the input side of the intermediate frequency filter is Alternatively, if a filter switching circuit is provided on one side of the output side and the other side is directly connected, there is a limit to reduction of characteristic deterioration.

An object of the present invention is to solve the above problems and, for example, in a front end of a satellite broadcast receiver including a tuner unit and a PLL / FM demodulation unit, an oscillation signal of a VCO in a loop of a PLL is generated by a tuner device. Avoid leaking from the output side of the intermediate frequency amplifier circuit to the input side, and prevent the output side signal of the intermediate frequency filter from being fed back to the input side or the input side intermediate frequency amplifier circuit,
This is to obtain good demodulation characteristics.

[0005]

The above object is to provide a difference between the forward pass characteristic and the reverse pass characteristic of the intermediate frequency filter so that the reverse pass loss is larger than the forward pass loss. Is achieved in. Further, the intermediate frequency amplifier circuit including the intermediate frequency filter may be configured in a balanced type and may be balancedly connected to further improve. Further, in a receiving apparatus that receives two signals of two kinds of intermediate frequency bands by switching two filters having two bandwidths, this can be achieved by disposing two intermediate frequency filters.

[0006]

In the present invention, compared with the forward direction (input to output) pass loss of the intermediate frequency filter, the reverse direction (output to input)
In order to increase the pass loss of the filter, the signal level of the filter output signal is smaller in the backward direction propagating toward the input in the filter than the intermediate frequency filter with the same forward characteristic and reverse characteristic. Become. The signal propagating in the opposite direction becomes a kind of co-channel interference and is added at the filter input to deteriorate the amplitude characteristic or the output S / N of the tuner section. Therefore, the fact that the signal level propagating in the opposite direction is small can reduce the deterioration of the demodulation characteristics. In addition, in a receiving device that switches two filters having two bandwidths to receive signals of two types of intermediate frequency bands, in addition to the above interference, a signal propagating in the opposite direction is selected through a filter that does not select. Since there is an interfering component that leaks into the existing filter, this interfering component can also be reduced by setting the characteristics of each intermediate frequency filter to the above characteristics.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the following description, AGC will be referred to as Automa.
tic Gain Control, PLL is Pha
It is an abbreviation for se Locked Loop.

FIG. 1 is a circuit block diagram showing a first embodiment of a receiving apparatus of the present invention, showing a front end for receiving a high frequency signal and outputting a baseband signal. The input signal to the input terminal (1) is amplified by the high frequency amplifier circuit (2). A variable tuning filter (3) for suppressing unnecessary waves is arranged at the subsequent stage of the high frequency amplifier circuit (2), and the tuning voltage from the tuning circuit (31) is applied to the variable tuning filter (3) and the pass band center frequency is applied. To change. In the subsequent stage, a high frequency amplification circuit (4) with variable amplification gain, a mixer circuit (5), a first intermediate frequency amplification circuit (7) with variable gain, an intermediate frequency filter (8), a second intermediate frequency amplification circuit. A frequency conversion circuit is configured by connecting (10) and inputting a signal from a local oscillation circuit (6) that oscillates a desired frequency by the tuning voltage from the tuning circuit (31) to the mixer circuit (5).
The intermediate frequency signal is output to the FM demodulation circuit (20), and the baseband signal is obtained from the output terminal (21). Tuning circuit (3
1) is a circuit for generating a tuning voltage according to the tuning data input to the terminal (30). Also, the detection circuit (10)
The output level of the second intermediate frequency amplifier circuit (9) is detected by the high frequency amplifier circuit (4) with variable amplification gain in the AGC circuit (11) so that the input level of the demodulation circuit (20) becomes a constant value. , A variable gain first intermediate frequency amplifier circuit (7),
The amplification gain of the second intermediate frequency amplifier circuit (9) is controlled.
In this embodiment, the second intermediate frequency amplifier circuit (9) and the AGC are used.
The circuit (11), the detection circuit (10), and the demodulation circuit (21) are integrated in the same IC (40), and the intermediate frequency filter (8) has a lower passband signal loss from the input terminal to the output terminal. A surface acoustic wave filter with a large amount of passband signal attenuation from the output terminal to the input terminal is used.

According to the configuration of this front end, in order to make the passage loss in the reverse direction larger than the passage loss in the forward direction of the intermediate frequency filter (8), the FM demodulation circuit (20) in the IC (40) is installed. When a part of the power of the oscillation signal of the VCO in the configured PLL leaks into the input part of the second intermediate frequency amplifier circuit (9), it is necessary to feed back the output from the intermediate frequency filter (8) to the input. Can be suppressed. Therefore, when the PLL is in the locked state, the signal input to the phase comparator in the PLL loop and the oscillation signal of the VCO have the same frequency, and if the amount of feedback to the input of the intermediate frequency filter (8) is large, the filter characteristics deteriorate. However, the differential phase characteristic, the differential gain characteristic, the group delay characteristic, and the demodulation output frequency characteristic deteriorate, but in the embodiment of the present invention, such demodulation characteristic deterioration is small.

FIG. 2 is a diagram showing a second embodiment of the present invention, in which the intermediate frequency filter of the first embodiment is replaced with an intermediate frequency filter (8-1) having a first pass bandwidth. It is another embodiment in which an intermediate frequency filter (8-2) having a pass band width of 2 is connected in parallel. The intermediate frequency filter (8-1) and the intermediate frequency filter (8-2) are elastic surfaces having a larger amount of passband signal attenuation from the output terminal to the input terminal than the loss of the passband signal from the input terminal to the output terminal. You are using a wave filter. One of the intermediate frequency filter (8-1) and the intermediate frequency filter (8-2) is selected by a switching circuit (50) on the input side of each filter, and the switching circuit (50) is controlled by a tuning circuit. The control signal from (31) is used.

According to the configuration of the present front end, the reverse direction pass loss is larger than the forward direction pass loss of each of the intermediate frequency filters (8-1) and (8-2). When selecting (8-1), the desired signal appearing at the output of the intermediate frequency filter (8-1) is switched from the output of the intermediate frequency filter (8-2) to the switching circuit (50).
The signal level leaking into the intermediate frequency filter (8-1) via the input of can be reduced. In the surface acoustic wave filter, since the in-band ripple of the pass band frequency characteristic increases due to the above-mentioned signal leakage and the demodulation characteristics such as the group delay characteristic deteriorate, the deterioration of the demodulation characteristics can be reduced by using the present invention. In addition, the same effect as that of the first embodiment shown in FIG. 1 can be obtained.

FIG. 3 is a diagram showing a third embodiment of the present invention, in which the intermediate frequency filter of the first embodiment is replaced with an intermediate frequency filter (8-1) having a first pass bandwidth. It is another embodiment in which an intermediate frequency filter (8-2) having a pass band width of 2 is connected in parallel. The intermediate frequency filter (8-1) and the intermediate frequency filter (8-2) are elastic surfaces having a larger amount of passband signal attenuation from the output terminal to the input terminal than the loss of the passband signal from the input terminal to the output terminal. You are using a wave filter. One of the intermediate frequency filter (8-1) and the intermediate frequency filter (8-2) is selected by a switching circuit (51) on the output side of each filter, and the switching circuit (51) is controlled by a tuning circuit. The control signal from (31) is used.

According to the configuration of the present front end, the reverse pass loss is larger than the forward pass loss of each of the intermediate frequency filters (8-1) and (8-2). When selecting (8-1), the desired signal appearing at the output of the switching circuit (51) is input from the switching circuit (51) through the input of the intermediate frequency filter (8-2) to the intermediate frequency filter (8-1). ) Can be reduced. In the surface acoustic wave filter, since the in-band ripple of the pass band frequency characteristic increases due to the above-mentioned signal leakage and the demodulation characteristics such as the group delay characteristic deteriorate, the deterioration of the demodulation characteristics can be reduced by using the present invention. In addition, the same effect as that of the first embodiment shown in FIG. 1 can be obtained.

FIG. 4 shows a fourth embodiment of the present invention. Figure 4
Is a variable gain first intermediate frequency amplification circuit (7), variable gain second intermediate frequency amplification circuit (9), intermediate frequency filter (8), demodulation circuit (20) of the first embodiment of the present invention. ) Is composed of a balanced circuit, and the gain is variable between the first intermediate frequency amplification circuit (7), the intermediate frequency filter (8), the variable gain second intermediate frequency amplification circuit (9), and the demodulation circuit (20). It is another embodiment in which the connection between circuits is a balanced type.

According to the configuration of this front end, in addition to the effect shown in the first embodiment, the amount of feedback of the VCO due to spatial coupling or the like is reduced by making the inter-circuit connection a balanced type, and further the demodulation characteristic is obtained. Deterioration can be reduced.

FIG. 5 shows a fifth embodiment of the present invention. Figure 5
Is a variable gain first intermediate frequency amplifier circuit (7) according to the second embodiment of the present invention, a switching circuit (52), a variable gain second circuit.
Intermediate frequency amplifier circuit (9), intermediate frequency filter (8-
1) (8-2), the demodulation circuit (20) is composed of a balanced circuit, and a variable gain first intermediate frequency amplifier circuit (7), a switching circuit (52), an intermediate frequency filter (8-1) (8) −
2), another embodiment in which the circuit connection between the second variable frequency intermediate frequency amplifier circuit (9) and the demodulation circuit (20) is a balanced type.

According to the configuration of this front end, in addition to the effect shown in the second embodiment, the amount of feedback of the VCO due to spatial coupling or the like is reduced by making the inter-circuit connection a balanced type, and further the demodulation characteristic is obtained. Deterioration can be reduced.

FIG. 6 shows a sixth embodiment of the present invention. Figure 6
Is a variable gain first intermediate frequency amplifier circuit (7), a variable gain second intermediate frequency amplifier circuit (9), and an intermediate frequency filter (8-1) (8- 2), the switching circuit (53) and the demodulation circuit (20) are composed of a balanced circuit, and a variable gain first intermediate frequency amplification circuit (7), intermediate frequency filters (8-1) (8-2), and switching Circuit (5
3) is another embodiment in which the circuit connection between the variable gain second intermediate frequency amplifier circuit (9) and the demodulation circuit (20) is a balanced type.

According to the configuration of the present front end, in addition to the effect shown in the third embodiment, the amount of feedback of the VCO due to spatial coupling or the like is reduced by making the inter-circuit connection a balanced type, and further the demodulation characteristic is obtained. Deterioration can be reduced.

[0020]

According to the present invention, the intermediate frequency filter of the receiving device, which frequency-converts the input signal and band-limits by the intermediate frequency filter, passes the reverse pass loss larger than the forward pass loss. Because of the characteristics, the signal level of the signal output from the filter propagating in the opposite direction in the filter toward the input can be reduced. Therefore, it is possible to reduce a failure due to an unnecessary signal propagating in the opposite direction, that is, deterioration of the output S / N of the tuner section and deterioration of demodulation characteristics. Further, in a receiving device which receives two kinds of intermediate frequency band signals by switching two filters having two bandwidths, an unnecessary signal propagating in the opposite direction leaks to the selected filter via a filter that does not select. It can alleviate complicated obstacles. Therefore, miniaturization of the receiving device and enhancement of the function having the 2IF bandwidth switching function not only increase the degree of freedom in the circuit layout and the board pattern design but also realize the simplification of the circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a third embodiment of the present invention.

FIG. 4 is a block diagram showing a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a fifth embodiment of the present invention.

FIG. 6 is a block diagram showing a sixth embodiment of the present invention.

[Explanation of symbols]

 1, 21 ... Terminals, 2 ... RF amplifier circuit, 3 ... Variable tuning filter, 4 ... Gain variable RF amplifier circuit, 5 ... Frequency mixing circuit, 6 ... Local oscillation circuit, 7, 9 ... Gain variable IF amplifier circuit, 8 ... Intermediate frequency filter, 10 ... Detection circuit, 12 ... AGC circuit, 20 ... Demodulation circuit, 30 ... Control terminal attenuator, 31 ... Channel selection circuit, 40 ... IC.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaki Noda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Ltd.

Claims (4)

[Claims] 1. A frequency conversion circuit comprising an input high frequency amplification circuit, a fixed or variable tuning band pass filter, a frequency mixing circuit and a local oscillation circuit, and an intermediate frequency amplification for amplifying a frequency-converted signal (intermediate frequency signal). It has an intermediate frequency filter placed between the circuit and the intermediate frequency amplifier circuit, inputs channel selection data, and outputs a tuning voltage corresponding to the input signal frequency to a variable tuning bandpass filter and a local oscillator circuit. A tuner device having a station circuit, a demodulation circuit for demodulating an output signal of the tuner device, and means for detecting an output level of the tuner device and controlling an amplification gain of the tuner device according to the output level of the tuner device are provided. In the receiving device, the pass characteristics in the pass band of the intermediate frequency filter are shown as input terminal to output terminal and output terminal to input terminal. The receiving device is characterized in that the attenuation amount from the output terminal to the input terminal is larger than the attenuation amount from the input terminal to the output terminal. 2. The receiving apparatus according to claim 1, wherein the intermediate frequency filter comprises two band pass filters having a first pass band width and a second pass band width, and a first pass band width A receiver comprising means for selectively switching the second pass band width. 3. The receiving device according to claim 1, wherein:
A receiving device, characterized in that the intermediate frequency amplifier circuit, the intermediate frequency filter, and the demodulation circuit are configured by a balanced type circuit, and the respective circuits are connected in a balanced manner. 4. The surface acoustic wave filter according to claim 1, wherein a unidirectional electrode is used as an electrode for converting an electric signal into a surface acoustic wave as an intermediate frequency filter. A receiving device using a (SAW filter).