JPS6138893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a baseband signal synthesis circuit in a diversity reception system.

In non-line-of-sight communication systems, a diversity reception system is essential, and Ratio Squarer combining is the most excellent method for combining received signals.

Ratio Squarer synthesis in the baseband band uses a control signal corresponding to the S/N ratio (signal-to-noise power ratio) of the demodulated signal to attenuate and control the signal of the corresponding diversity route. The signal from the route with a good S/N ratio is emphasized, and the signal from the route with a poor S/N ratio is synthesized after being greatly attenuated. As a control signal corresponding to this S/N ratio, a voltage obtained by amplifying and detecting noise outside the baseband signal band or an AGC voltage corresponding to the received input electric field is used.

The attenuation circuit that performs Ratio Squarer uses a variable attenuation element such as a diode, and the control voltage changes the bias current of the diode and changes the amount of attenuation of the baseband signal. At this time, the control voltage is fed to the baseband signal, which deteriorates the S/N ratio particularly in the low frequency section of the baseband signal band, and limits the usable range of the low frequency section of the baseband.

FIG. 1 is a block diagram showing a conventional system.
Although this figure shows a double diversity configuration, the operation in the case of N-fold diversity (N2Q) is exactly the same. The diversity received signal is received by the receiving antennas 10 and 20, demodulated by the receivers 11 and 21, and converted into a baseband signal.
Connected to Squarer attenuators 12 and 22. on the other hand
The control voltage required for Ratio Squarer control is an AGC voltage or a voltage obtained by amplifying and detecting noise outside the baseband from control voltage generators 13 and 23 to a Ratio Squarer attenuator through low-pass filters 14 and 24. Connected. In these attenuators, the baseband signal is attenuated by the control signal so as to satisfy the Ratio Squarer characteristic. At this time, the control signal is combined with the baseband signal, and the S/N ratio of the low frequency region is It causes deterioration. Ratio of 2 routes
The signals subjected to the Squarer attenuation control are combined and become an output signal from the output terminal 30. The cutoff frequency of the low-pass filter is selected to be low in order to suppress the noise coupled to the baseband signal to the lowest possible frequency, but this increases the control operation time and reduces the noise generated during propagation. It must be limited to a value that can sufficiently follow Veedenck. There is a drawback that the control signal and weighted noise that have passed through this low-pass filter are coupled to the low-frequency part of the baseband signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a baseband signal synthesis circuit which eliminates the above-mentioned drawbacks.

The present invention uses a conventional synthesis circuit as a main circuit, adds an auxiliary circuit to it, and outputs a synthesis signal from the main circuit.
This baseband synthesis circuit is characterized in that the control signal coupled to the main circuit is removed by subtracting the synthesized control output synthesized by the auxiliary circuit in a differential circuit.

A detailed explanation will be given below with reference to the drawings.

FIG. 2 shows an embodiment of the invention, 10,20
is a receiving antenna, 12, 22 are Ratio Squarer attenuators, 13, 33 are control voltage generators, 14, 24
is a low-pass filter, 15, 25 is a synthesis auxiliary circuit, 31
is a differential circuit, and 30 is an output terminal. The diversity received signals are ratio squared controlled by control signals from the control voltage generators 13 and 23, and then combined and connected to the input terminal A of the differential circuit 31. As described above, the control signal is superimposed on the baseband signal in the low frequency range, and the S/N in the low frequency range is degraded.
The above-mentioned synthesis circuit is defined as the main synthesis circuit. On the other hand, the control voltage generators 13 and 23 in the synthesis auxiliary circuits 15 and 25
The control signal from the main synthesis circuit is supplied to the low-pass filters 14 and 24 that constitute the main synthesis circuit, and is also supplied to the auxiliary synthesis circuit. The synthesis auxiliary circuits 15 and 25 are
The low-pass filters 14 and 24 of the main synthesis circuit and the Ratio
A circuit that combines Squarer attenuators 12 and 22,
The control signal is connected to one input terminal B of the differential circuit by combining the voltages similar to those combined with diodes and superimposed on the baseband signal of the main combining circuit. However, since no baseband signal is supplied to the auxiliary synthesis circuits 15 and 25, the output of this circuit is a composite output signal containing only control signals.

The baseband signal on which the control voltages synthesized by the above-mentioned main synthesis circuit are superimposed and the control signals synthesized by the synthesis auxiliary circuit are subtracted in a differential circuit. Since the superimposed control signal has the same magnitude and the same amplitude as the outputs of both circuits, the in-phase signal is removed, and only the baseband signal becomes a differential output and is taken out from the output terminal. The differential circuit can be easily constructed by using, for example, a differential amplifier.

As described above, by adding a synthesis auxiliary circuit and a differential circuit, a synthesis circuit that is not affected by the Ratio Squarer control signal can be realized.

By adopting this method, the control signal does not affect the baseband signal in principle, so the S/N of the baseband low range can be improved without reducing the control operation time. There are benefits to expansion.

[Brief explanation of the drawing]

FIG. 1 shows a conventional Ratio Squarer baseband synthesis method, and FIG. 2 shows an embodiment of the present invention. In the figure, 10 and 20 are receiving antennas, 1
1 and 21 are receivers, 12 and 22 are Ratio Squarer
Attenuator, 13, 23 is a control voltage generator, 14, 2
4 is a low-pass filter, 15 and 25 are synthesis auxiliary circuits, 3
0 is an output terminal, and 31 is a differential circuit.

Claims (1)

[Claims] 1. In a baseband signal synthesis circuit that combines a plurality of diversity reception signals in a baseband band and generates a certain baseband signal, a plurality of control signals corresponding to the S/N ratio of the plurality of diversity reception signals are respectively generated. a plurality of first means for generating the diversity received signals; a second means for attenuating and controlling the diversity reception signals using the plurality of control signals and combining them; and a third means for combining the plurality of control signals. and fourth means for subtractively synthesizing the outputs of the second and third means and outputting the baseband signal.