JP2699698B2 - Receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus, and more particularly to a receiving apparatus for moving a microwave whose reception input level fluctuates.

[0002]

2. Description of the Related Art As shown in FIG.
A low noise amplifier 21 for amplifying the input microwave signal with a fixed gain, a mixer 22 and a local oscillator 23 for converting the microwave signal into an intermediate frequency signal, and an AGC amplifier 24 for amplifying the intermediate frequency signal to a constant level. , AGC
And a gain control circuit 25 for controlling the gain of the amplifier 24.

For example, if the gain of the low noise amplifier 21 is set to 20 db and the variable gain range of the AGC amplifier 24 is set to 50 db, the level of the input signal becomes -80 to -3.
Even if it changes to 0 dbm, the output level of the AGC amplifier can be kept constant at -10 dbm.

In the above-mentioned conventional receiving apparatus, the level fluctuation of the input microwave signal is -80.
Up to about -30 dbm can be tolerated.
By the way, recently, in the operation of this type of receiving apparatus, the case where the distance to the transmitting apparatus changes from a long distance to a close distance as seen in a marathon relay or the like has increased.
For this reason, it has become necessary to be able to receive a signal whose input level varies greatly from about -80 to -10 dbm.

However, in this case, even if the gain variable range of the AGC amplifier is increased to about 70 db, when the input level of the microwave signal increases to about -10 dbm, the gain of the low noise amplifier is about 20 db. Because there is
There is a problem that the signal level input to the mixer becomes excessively large at +10 dbm, and high-order intermodulation occurs in the mixer, causing distortion in the signal.

An object of the present invention is to provide a receiving apparatus capable of preventing a mixer from receiving an excessive input when the level of a received input signal increases.

[0006]

According to the present invention, there is provided a receiving apparatus comprising: a low-noise amplifier for controlling a gain in accordance with a first control signal to amplify a received input signal; A mixer for controlling the gain in accordance with a second control signal to amplify the intermediate frequency signal, and the first and second amplifiers in accordance with the level of the received input signal.
And a gain control circuit for transmitting a second control signal.
Wherein the received input signal level is equal to or less than a predetermined value.
Under the above so that the low noise amplifier has the maximum gain
A first control signal is transmitted and the output of the AGC amplifier is output.
Sends the second control signal so that the power level becomes constant
And when the received input signal level exceeds a predetermined value,
So that the signal level input to the mixer does not become excessive
The first control signal for reducing the gain of the low noise amplifier.
And the output level of the AGC amplifier is constant.
The second control signal is transmitted so that

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The low noise amplifier 11 varies the gain according to the control signal C1 and amplifies the input microwave signal. The mixer 12 and the local oscillator 13 convert a microwave signal into an intermediate frequency signal. The AGC amplifier 14 controls the control signal C
The intermediate frequency signal is amplified to a constant level by varying the gain according to (2). The gain control circuit 15 controls the control signals C1, C2
And send it.

[0009] Here, for example, the maximum gain of the low noise amplifier 11 is set to 20 db, the variable gain range of the AGC amplifier 14 is set to 50 db, and the received input signal is -80 to-
It is assumed that the level varies up to 10 dbm.

When the input signal level is low, for example, at -80 dbm, the gains of the low noise amplifier 11 and the AGC amplifier 14 are set to the maximum gains of 20 db and 70 db by the control signals C1 and C2, respectively.
In this case, the input level to the mixer 12 is -60 dbm
And no distortion occurs in the mixer. Now, assuming that the conversion loss of the mixer is 10 db, the output of the AGC amplifier 14 is 0 dB.
dbm.

When the input signal level is from -80 dbm to -30
In the range up to dbm, the gain of the low noise amplifier 11 is set to the maximum of 20 db to obtain a good S / N,
The gain of the C amplifier 14 is controlled by the control signal C2.
Now, when the input signal level is −30 dbm, the mixer 1
The input level to 2 is -10 dbm. At this level, no distortion occurs in the mixer. AGC amplifier 14
By setting the gain to 20 db, an intermediate frequency signal having a constant level of 0 dbm can be output.

When the input signal level exceeds -30 dbm, control is performed by the control signal C1 so that the gain of the low noise amplifier 11 is reduced. In this case, the gain control circuit 15
Detects that the input signal level has exceeded a predetermined value from the value of the control signal C2, sends out the control signal C1, and outputs the control signal C1.
The gain of the low-noise amplifier 11 is controlled in a range from 20 db to 0 db so that the input level does not exceed -10 dbm.

Here, when an FET is used as the amplifying element of the low noise amplifier 11, the gain changes by about 15 db in one stage of the FET by changing the gate voltage of the FET. Therefore, gain control of about 30 db can be performed by two stages of FETs.

By controlling the gain of the low-noise amplifier when the input signal level exceeds a predetermined value, it is possible to prevent an excessive input to the mixer while maintaining a good S / N.

[0015]

As described above, according to the present invention, a low-noise amplifier capable of varying the gain is provided, and the gain of the low-noise amplifier is controlled when the input signal level exceeds a predetermined value. Over-input to the mixer can be prevented while maintaining a high S / N ratio, a stable and good reception output can be obtained even for a reception signal with a high input level, and in a situation where the reception input level varies greatly. Operation becomes possible.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating an example of a conventional receiving device.

[Explanation of symbols]

 11 Low Noise Amplifier 12 Mixer 14 AGC Amplifier 15 Gain Control Circuit C1, C2 Control Signal

Claims (1)

(57) [Claims] A gain control means for controlling a gain according to a first control signal;
A low-noise amplifier for amplifying a received input signal, a mixer for converting the output of the low-noise amplifier to an intermediate frequency signal, and an AGC amplifier for controlling the gain according to a second control signal to amplify the intermediate frequency signal; According to the level of the received input signal.
Gain control for transmitting the first and second control signals
And a gain control circuit, the gain control circuit comprising:
When the level is below a predetermined value, the low-noise amplifier has a maximum gain.
The first control signal is transmitted so that
In order to keep the output level of the AGC amplifier constant, the second
And the received input signal level is a predetermined value.
Exceeds the signal level input to the mixer
Before reducing the gain of the low noise amplifier to avoid
Sending out the first control signal and controlling the AGC amplifier.
The second control signal is transmitted so that the output level becomes constant.
Receiving device, characterized in that the output.