JPS637031A - Receiver - Google Patents

Abstract

PURPOSE:To effectively eliminate surrounding noise by designing a loop filter in relation to an equipment receiving a satellite broadcast wave so as to have a controllable time constant element to vary its band pass characteristic, thereby adjusting the value of the controllable time constant element depending on the reception state of a reception wave. CONSTITUTION:The loop filter 11 is connected among the collectors of transistors (TRs) Q3, Q5 and Q6, Q4. The loop filter 11 consists of the series connection of a resistor R6, capacitors C1, C2 and a diode D1 as a controllable time constant element, and both the terminals of said series circuit are connected to the common collector connecting points of the TRs Q3, Q5 and Q4, Q6 of a phase comparator 10. Thus, in supplying a control voltage obtained from a power supply divided by a variable resistor (not shown) via a control voltage terminal (h), the resistance of a pin diode D1 is change in response to the control voltage and the CR time constant of the loop filter is controlled to adjust the filter characteristic by the control voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a receiving device, for example, SHF for satellite broadcasting, etc.
The present invention is suitable for application to a receiving device that receives broadcast waves in the (Super high frequency) band.

B Overview of the Invention The present invention is based on PLL (Phase 1ocked 1
oop) - In a receiving device having an FM demodulation section,
By making it possible to adjust the filter characteristics of the loop filter, it is possible to obtain appropriate demodulation characteristics for the received wave.

C. Conventional technology Conventionally, for example, in satellite broadcasting and satellite communications operated in the United States, SHF (Super high
C-band and Ku-band radio waves belonging to the high frequency band are used. That is, the transmitting earth stations (e.g. broadcasting stations) have C-band and Ku-band frequencies (i.e. 6 CGH2) and 14 (G)l, respectively.

] )), a video signal, an audio signal, etc. are FM-modulated on a bass-spanned carrier wave, and the broadcast wave is transmitted to the satellite station, and the satellite station transmits the broadcast waves to 4 rcuz ) and 12 (GH2), respectively.
) frequency and broadcast to a receiving earth station (for example, a general home receiving device).

Problems to be solved by the invention D However, in practice, when receiving the C band, the C/N ratio of the received waves is generally low, and in addition to the fact that there are many nearby interference waves on the ground, Furthermore, since the modulation specifications (that is, the deviation specifications) are diverse, it is necessary for the receiving device to be able to cope with these various conditions.

In order to solve this problem, in conventional receiving devices, P
A system is used in which a baseband signal is demodulated by an FM demodulator having an LL (Phase 1 locked 1 loop) configuration. This FM demodulation section
By selecting the time constant of the loop filter constituting r to a relatively small value, it is possible to demodulate normal received waves with a wide band.

In this way, by using the FM demodulator having the PLL configuration, it is possible to stably demodulate baseband signals over a relatively wide band when there are practically standard reception conditions.

However, in reality, depending on the installation location of the receiving device, the C/
There is a risk that the N ratio will drop significantly and the amount of adjacent interference waves will increase significantly (for example, in the American C band, ±10 (Mll) from the receiving center frequency.

).In such a case, the FMa modulator may generate white noise and become unable to demodulate the received signal.

A receiving apparatus has been proposed in which two loop filters are switched and used depending on the state of the C/N ratio (Japanese Patent Application No. 182413/1982). However, by switching between two loop filters, each with specific filter characteristics, it is possible to obtain the optimum characteristics for the received wave, and to fine-tune the filter characteristics according to changes in the reception conditions. However, there were problems such as not being able to use the system, and it was still unsatisfactory in terms of user-friendliness.

The present invention has been made in consideration of the above points, and attempts to propose a receiving device that is easy to use for users by making it possible to adjust the filter characteristics of a loop filter in response to changes in reception conditions. It is something.

E Means for Solving Problem E To solve this problem, in the present invention, the phase comparison circuit 10 compares the received wave with the frequency output of the voltage controlled oscillator 130, and the phase comparison output is passed through the loop filter 11. In the received word W1, which has an FM demodulation unit 5 which transmits the FM demodulated output via the DC amplifier 12 and feeds back the FM demodulated output to the voltage controlled oscillator 13, the loop filter 11 It has a controllable time constant element D1 whose characteristics can be changed,
The value of the controllable time constant element D1 can be adjusted according to the receiving state of the received wave.

By adjusting the value of the F-acting controllable time constant element DI, the encounter characteristics of the relube filter II can be changed.

As a result, for example, when the C/N ratio of the received wave is low,
The value of the time constant is increased and the pass characteristic of the loop filter 11 is narrowed. In this way, only the main components of the tuned reception wave are sent out as the FM demodulation output, and surrounding noise etc. are effectively removed. Become.

Further, when the received wave is in a normal receiving state, the value of the time constant is made small and the pass characteristic of the loop filter 11 is made wide. This allows normal received waves with a wide band to be successfully demodulated.

Embodiment G An embodiment in which the present invention is applied to a receiving apparatus for receiving satellite broadcasting will be described in detail in the following drawings.

In FIG. 2, 1 indicates the receiving device as a whole. The receiving device 1 includes an outdoor unit including a parabolic antenna 2 and an S/IJ converter 3, and an indoor unit including a tuner section 4 and an FM demodulator 5.

The antenna 2 is composed of, for example, a parabolic main reflector, a sub-reflector, and an electromagnetic horn, and the received waves received here are transmitted to a frequency band of the SHF band (for example, 6 (G■2) to U HF (Ult
ra high frequency) band (
For example, the signal is converted to t (GHz)) and guided to an indoor unit via a coaxial cable or the like.

The received wave converted into the UHF frequency band is supplied to the tuner section 4 of the indoor unit. The received waves selected here are
Low frequency band of UHF band (e.g. 400 (MH2)
) and is supplied to the FM demodulator 5, whereby F
The M-demodulated FM demodulated output is output to the output terminal a.

Here, as shown in FIG.
It is constituted by a PLL circuit consisting of a CO (voltage controlled oscillator) 13.

The received wave inputted from the input terminal is sent to the phase comparator circuit 10.
The phase comparison output is compared in phase with the frequency output of the VCO 13, and this phase comparison output removes noise and high frequency components, passes through the loop filter 11 that determines the pass characteristic, and is further outputted as an FMfiffl output from the output terminal a via the DC amplifier 12. At the same time, it is fed back to the VCO 13.

At this time, the loop filter 11 is configured such that a time constant indicating its filter characteristics can be adjusted by a control voltage externally applied to a control voltage terminal by means of a controllable time constant element DI.

The phase comparator circuit is, for example, a double-balanced differential amplifier circuit, as shown in FIG.
, and Q4, QS and Q6, and transistors Q,
and the common base connection terminal fc of Q6, and the transistor Q
VCO1 between the common base connection terminal d of 4 and Q.
Receives frequency output of 3.

Furthermore, QI and Qt, which are NPN bipolar transistors, are connected to the emitter common connection terminals of the transistors Q3 and Qa, Qs and Q6, respectively, and receive the received wave given from the tuner unit 4 between their base connection terminals b1 and b2. .

Thus, the phase comparison circuit 10 compares the phases of the two by multiplying the frequency output of the VCO 13 and the received wave of the tuner section 4, and performs a phase comparison between the output terminals f and 8 connected to the collectors of the transistors Q3 and Q. It is configured to send output.

A loop filter 11 is connected between the collectors of the transistors Q3, Qs and Q6, Q4. The loop filter 11 has a resistor R6, a capacitor C, , C, and a pin diode D1 as a controllable time constant element connected in series. , 4, are connected to the common collector connection point of Qh.

The midpoint of the connection between the capacitor C1 and the pin diode D1 of the loop filter 11 is connected to the control voltage input terminal via the resistor R1, and the midpoint of the connection between the pin diode D1 and the capacitor C3 is grounded through the resistor R8. .

With this, for example, by supplying a control voltage obtained by dividing the power supply with a variable resistor (not shown) through the control voltage terminal, the resistance value of the pin diode D1 can be adjusted in response to the control voltage. By changing the CR time constant of the loop filter, the filter characteristics can be adjusted by controlling the control voltage.

In the above configuration, when trying to receive a received wave with a low C/N ratio well, for example, if the voltage supplied to the control voltage input terminal is reduced, the DC resistance of the pin diode D increases, and this This increases the time constant of the loop filter and narrows the pull-in range as a filter characteristic itself.

Therefore, the detection band of the FM demodulator can be narrowed, and thus the FM
The S/N ratio of demodulated output can be improved.

Conversely, when receiving a received wave with a high C/N ratio, normal detection characteristics can be obtained by setting the time constant of the loop filter to a small value to the extent that truncation noise etc. are not noticeable in the FM demodulation output. .

According to the above configuration, since the filter characteristics of the loop filter 11 can be changed continuously, the C of the received wave is
When a receiver is set up in an area with a low /N ratio, an area with terrestrial interference, or an area where the modulation characteristics differ depending on the receiving channel, it is possible to arbitrarily set the filter characteristics suitable for the received waves in each area. Can be selected.

Furthermore, when adjusting filter characteristics, for example, when receiving television broadcasts, visually check the screen of the television receiver. The user can easily select filter characteristics that are good for the received wave.

In the above embodiment, a configuration was used in which the resistance value was changed by controlling the voltage applied to the bin diode D1 as a controllable time constant element for changing the CR time constant of the loop filter 11. As a constant element,
The present invention is not limited to this, and for example, a configuration in which the capacitance is changed using a voltage variable capacitance diode may be used, and in short, the CR time constant may be changed by the control voltage.

H Effects of the Invention As described above, according to the present invention, the filter characteristics of the PLL loop filter can be continuously changed and controlled according to the reception status of the received waves, making it easy for the user to use. A receiving device can be easily realized.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing details of a phase comparator circuit and loop filter of a receiving device according to the present invention, FIG. 2 is a block diagram showing a schematic configuration of the receiving device, and FIG. 3 is a detailed configuration of the FM demodulation device. It is a block diagram. j... Receiving device, 5... FM demodulation section,
10... Phase comparator circuit, 11... Loop filter, 12... DC amplifier, 13...
...VCO (voltage controlled oscillator).

Claims (1)

[Claims] The received wave is compared with the frequency output of the voltage-controlled oscillator in the phase comparison circuit, and the phase comparison output is passed through a loop filter and sent out as an FM demodulation output via a DC amplifier. In a receiving device having an FM demodulation unit configured to feed back an FM demodulation output to the voltage-controlled oscillator, the loop filter has a controllable time constant element whose pass characteristic can be changed, and the loop filter has a controllable time constant element whose pass characteristic can be changed. A receiving device characterized in that the value can be adjusted depending on the reception state of the received wave.