JPH0563594A - Frequency detection circuit - Google Patents

Abstract

PURPOSE:To reduce malfunction due to random noise when the C/N of a reception signal is deteriorated. CONSTITUTION:A mixer mixes a reception signal S1 with an oscillation signal Sv to apply frequency conversion. A band pass filter 2 eliminates an undesired signal component to allow only a desired intermediate frequency signal S2 to pass therethrough. A level detection section 3 detects a level of the intermediate frequency S2 to generate a DC voltage V1 proportional to the level. A level averaging processing section 4 averages a DC voltage V1 to output an averaging voltage Va. A sweep processing section 5 generates a sweep voltage Vs in which a voltage changes at least once for a prescribed range in response to the mean voltage Va. A voltage controlled crystal oscillation section (VCXO) 6 changes the frequency of the oscillation signal Sv in response to the sweep voltage Vs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a frequency detection circuit,
In particular, the present invention relates to a frequency detection circuit that controls a voltage controlled oscillator that generates a local oscillation signal in a receiver for satellite communication to detect the frequency of a desired signal.

[0002]

2. Description of the Related Art Conventionally, this type of frequency detection circuit is shown in FIG.
As shown in, the mixer 1 for mixing the received signal S1 with the oscillation signal Sv to convert the frequency, the band-pass filter 2 for removing unnecessary signal components and passing only the desired intermediate frequency signal S2, and the intermediate frequency signal S2. A level detector 3 that detects a level and generates a DC voltage V1 proportional to the level, and a sweep voltage generator 7 that generates a sweep voltage Vs whose voltage changes only once within a predetermined range centered on the DC voltage V1.
And a voltage controlled crystal oscillator (VCXO) 6 that changes the frequency of the oscillation signal Sv according to the sweep voltage Vs. With this configuration, the desired intermediate frequency signal S2 can be taken in and output from the bandpass filter 2.

[0003]

In the above-mentioned conventional frequency detecting circuit, when C / N of the received signal S1 is lowered,
Since the C / N of the intermediate frequency signal also deteriorates and the DC voltage output by the level detection unit fluctuates due to random noise, and the oscillation signal is swept only once, it malfunctions and the desired intermediate frequency signal is output. There is a problem that it becomes difficult to pull in.

An object of the present invention is to provide a frequency detection circuit which can reduce malfunctions due to random noise when the C / N of a received signal is lowered.

[0005]

A frequency detecting circuit of the present invention comprises a frequency converting means for mixing a received signal with an oscillating signal for frequency conversion, and a means for extracting only a desired signal from an output signal of the frequency converting means. A means for detecting the level of the extracted desired signal and outputting a voltage corresponding to the level,
Means for averaging the voltage according to the level and outputting the average voltage; means for changing the voltage at least once within a predetermined range centered on the average voltage to generate a sweep voltage; and depending on the sweep voltage. And a means for changing the frequency of the oscillation signal. Also, the sweep voltage generating means is configured to further average the average voltage and increase the number of sweeps to two times or more to generate the sweep voltage when the average voltage drops below a predetermined value. It

[0006]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The mixer 1 mixes a received signal S1 with an oscillating signal Sv to perform frequency conversion, and a desired intermediate frequency signal by removing unnecessary signal components. A bandpass filter 2 that passes only S2,
A level detector 3 for detecting the level of the intermediate frequency signal S2 and generating a DC voltage V1 proportional to the level;
A level averaging unit 4 for averaging the value of 1 over a certain period of time to output an average voltage Va, and a sweep voltage Vs whose voltage changes at least once within a predetermined range centered on the average voltage Va.
And a voltage controlled crystal oscillator (VCXO) 6 that changes the frequency of the oscillation signal Sv according to the sweep voltage Vs.

Here, the sweep control section 5 determines the average voltage V
When the value of a drops below a predetermined value, that is, when the C / N of the received signal drops, the average voltage Va is further averaged and the number of sweeps is increased to two or more. By doing so, the difference between the maximum value and the minimum value of the random noise can be suppressed and the difference from the signal can be clarified, so that malfunction due to noise can be reduced.

[0009]

As described above, according to the present invention, when the C / N of the received signal is lowered, the average voltage of the desired intermediate frequency signal level is further averaged to generate the sweep voltage, and the sweep frequency is increased. By increasing, it is possible to reduce malfunctions due to random noise.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an example of a conventional frequency detection circuit.

[Explanation of symbols]

 1 mixer 2 band filter 3 level detector 4 level average processor 5 sweep controller 6 voltage control crystal oscillator (VCXO) S1 received signal S2 intermediate frequency signal Sv oscillation signal Va average voltage Vs sweep voltage

Claims (2)

[Claims] 1. A frequency conversion means for mixing a received signal with an oscillating signal to perform frequency conversion, a means for extracting only a desired signal from an output signal of the frequency conversion means, and a level of the extracted desired signal is detected. A means for outputting a voltage according to the level; a means for averaging the voltage according to the level to output the average voltage; and a means for changing the voltage at least once within a predetermined range centered on the average voltage to obtain a sweep voltage. A frequency detecting circuit comprising: a generating unit and a unit that changes a frequency of the oscillation signal according to the sweep voltage. 2. The sweep voltage generating means, when the average voltage drops below a predetermined value, further averages the average voltage and increases the number of sweeps to two times or more to generate the sweep voltage. Claim 1 characterized by the above-mentioned.
The described frequency detection circuit.