JPS6233778B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an incoming signal level detection circuit that improves the linearity of incoming signal level versus detected output level.

In wireless communication using microwaves, millimeter waves, etc., in order to monitor the communication status, it is necessary to detect the level of an incoming signal on the receiving side, and the following methods are available for this purpose.

One method is to detect the output signal of a suitable variable gain amplifier among a plurality of variable gain amplifiers in the receiver and use this as a detection output signal of the incoming signal level. This method has the disadvantage that the linearity of the incoming signal level versus the detected output signal is poor, causing inconvenience to the monitor.

There is also a method of connecting a logarithmic amplifier to the output of the level detection circuit to improve linearity, but this method results in a complicated circuit configuration and high cost.

The present invention was devised in view of the drawbacks of the conventional circuits as described above, and its purpose is to utilize the reciprocity between the incoming signal level versus detection output signal characteristic and the incoming signal level versus automatic gain control signal characteristic. It is an object of the present invention to provide an incoming signal level detection circuit that improves the linearity of the incoming signal level versus detected output signal characteristic and contributes to improving the monitoring function.

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an incoming signal level detection circuit embodying the invention. In this circuit 1, 2, 3, 4,
5 is an amplifier, and 6, 7, and 8 are variable attenuators. The input of the first stage amplifier 2 is connected to an input terminal 9. A detector 10 and an automatic gain control circuit 11 are connected in this order between the output of the final or fourth stage amplifier 5 and the gain control input of each variable attenuator 6, 7, 8. Further, the output of the automatic gain control circuit 11 is connected to one input of the combining circuit 12. The other input of the synthesis circuit 12 is connected to the output of a level detection circuit, such as a detection circuit 13, which is connected to the output of the third stage amplifier 4. The synthesizing circuit 12 is, for example, a differential amplifier circuit, and is a circuit that synthesizes one input signal and an inverted signal of the other input signal and outputs the synthesized signal.

Next, the operation of the circuit of the present invention having the above configuration will be explained.

An incoming signal arriving at the input terminal 9 is amplified by the amplifier 4 via the amplifier 2, the variable attenuator 6, the amplifier 3, and the variable attenuator 7. The output signal is supplied to the level detection circuit 13 and also to the variable attenuator 8.

The signal supplied to the level detection circuit 13 is subjected to detection processing, for example, detection, to generate a detection output level signal for the incoming signal. This detection output level signal has a second level relative to the incoming signal level.
It has characteristics as shown by curve L1 in the figure.

On the other hand, the output signal supplied to the variable attenuator 8 is further amplified by the amplifier 5 and then supplied to the detector 10. The detection output signal is the automatic gain control circuit 11
from which an automatic gain control signal is generated and applied to the gain control inputs of the variable attenuators 6, 7, 8 and to one input of the combining circuit 12. This automatic gain control signal has characteristics as shown by curve L2 in FIG. 2 with respect to the incoming signal level.

Both signals mentioned above are combined in the combining circuit 12. To explain this specifically, differential amplifier circuit 1
The detection output signal applied to the inverting input of circuit 12 is effectively inverted and added to the automatic gain control signal applied to the non-inverting input of circuit 12. Repeat this operation as a second
To explain using a diagram, the operation corresponds to combining a curve L3 and a curve L2, which represent a signal with the polarity of the detection output signal represented by the curve L1 inverted, to form a curve L4. From this, it is clear that
The linearity of the output signal of the combining circuit 12, ie the detection output signal of the circuit of the invention, with respect to the incoming signal level is significantly improved. In addition, when a differential amplifier is used as a synthesis circuit, it can perform polarity reversal by itself as described above, and it also allows for load conditions (for example, impedance,
level) can be selected arbitrarily.

In the above embodiment, an example was explained in which a differential amplifier circuit is used as a combining circuit, but the signal supplied to the other input is supplied to an inverting circuit, and the output signal and the signal supplied to one input are connected to each other by a resistor. It may also be configured to be supplied to a sum circuit.

Further, the detection circuit may have a configuration of a peak detection circuit, an average value detection circuit, or an envelope detection circuit.

As is clear from the above description, according to the present invention, the following effects can be obtained.

The linearity of the incoming level detection characteristic is improved.

Therefore, the threshold value of the incoming signal level monitor circuit can be set accurately, and sensitivity can be kept constant, so that highly accurate monitoring can be performed over a wide range of incoming signal levels. or,
In a communication system that applies automatic transmission gain control determined according to the incoming signal level, transmission control can be performed with few errors.

[Brief explanation of the drawing]

FIG. 1 is an incoming signal level detection circuit diagram of the present invention;
FIG. 2 is a characteristic curve diagram of incoming signal level versus various output levels. In the figure, 4 and 5 are amplifiers, 11 is an automatic gain control circuit, 13 is a level detection circuit, and 12 is a synthesis circuit.

Claims (1)

[Claims] 1. In an incoming signal level detection circuit having an amplifier, a level detection circuit connected to the output of the amplifier, an automatic gain control circuit connected to the output of the amplifier, the level detection circuit and the automatic gain An incoming signal level detection circuit comprising a combining circuit that inverts one of the output signals of the control circuit and combines the inverted signal with the other signal. 2. The incoming signal level detection circuit according to claim 1, wherein the combining circuit is constructed of a differential amplifier circuit.