JPH05102872A - Automatic level adjusting circuit - Google Patents

Abstract

PURPOSE:To automatically suppress the change of a passage loss generated by a temperature change at a band pass filter to respectively pass transmitting signals and pilot signals. CONSTITUTION:This automatic level adjusting circuit equipped with a pilot signal insertion part 30 on the transmission side and an automatic gain control amplifier 41, first and second band pass filters 43 and 44 to select the transmitting signals and the pilot signals and an automatic level control part 10 to control the automatic gain control amplifier 41 corresponding to a differential signal between the level of the obtained pilot signals and a reference voltage and to suppress the change of a transmission loss at a transmission line on the reception side is provided with a temperature detecting means 12 to detect the peripheral temperatures of the first and second band pass filters 43 and 44 and an operation processing means 13 to set the reference voltage for canceling the temperature characteristic difference to the automatic level control part 10 by calculating the temperature difference characteristic of the passage loss at the respective band pass filters 43 and 44 by fetching the peripheral temperature information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic level adjusting circuit (AL) for automatically compensating for changes in transmission loss in a transmission line.
C circuit).

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a configuration example of a high-frequency signal transmission device having a conventional automatic level adjusting circuit.

In the figure, the basic configuration of a high-frequency signal transmission device is a transmitter 2 arranged on the transmission side via a transmission line 20.
1 and modulator 22, and demodulator 23 arranged on the receiving side
And a receiver 24, between which high-frequency signals are transmitted.

By the way, the characteristics of the transmission line 20 change due to temperature changes and other factors, and the reception level of the high-frequency signal fluctuates as the transmission loss of the transmission line 20 changes.
Therefore, an automatic level adjustment circuit is used that controls the reception level to be constant and suppresses the characteristic change of the transmission line 20. The conventional automatic level adjustment circuit uses the transmitter 2 on the transmission side.
1 and a modulator 22, and a pilot signal insertion unit 30 inserted between the demodulator 23 and the receiver 24 on the receiving side.

In the pilot signal inserting section 30, the pilot signal generator 31 generates a pilot signal in a frequency band different from the transmission signal transmitted from the transmitter 21, and the pilot signal is passed through the fixed attenuator 32 to a predetermined value. Set to level. Further, only the frequency component of the pilot signal is extracted via the band pass filter 33, and the coupler 34
And superimposes it on the transmission signal and sends it to the modulator 22.

On the other hand, the signal demodulated by the demodulator 23 is input to the coupler 42 via the automatic gain control amplifier (AGC amplifier) 41 of the automatic level adjusting section 40. Coupler 42
Is a bandpass filter that divides the input signal into two parts, one of which is sent to the receiver 24 through a bandpass filter (BPF) 43 that passes only the frequency component of the transmission signal, and the other is a bandpass filter that passes only the frequency component of the pilot signal. (BPF)
It sends to the wave detector 45 via 44. The detector 45 detects the pilot signal and outputs a voltage corresponding to its reception level. The comparator 46 compares the reference voltage generated by the reference voltage generator 47 with the output voltage of the detector 45, and corresponds to the level variation of the pilot signal generated according to the change of the transmission loss of the transmission line 20. Get the differential voltage. The drive circuit 48 of the automatic gain control amplifier 41 adjusts the gain of the automatic gain control amplifier 41 so that the differential voltage output from the comparator 47 becomes zero, compensates for the level fluctuation of the pilot signal, and transmits it at the same time. The transmission loss of the transmission signal transmitted from the device 21 is compensated. In addition, the detector 4
5, comparator 46, reference voltage generator 47 and drive circuit 4
8 constitutes an automatic level control unit.

With such a configuration, fluctuations in the reception level caused by changes in the characteristics of the transmission line 20 are suppressed, and stable signal transmission can be realized.

[0008]

By the way, in the conventional automatic level adjustment circuit, the adjustment of the reception level of the transmission signal is performed as follows.
This is performed by a configuration that detects variations in the reception level of the pilot signal transmitted superimposed on it and compensates for it.
However, although the change in the transmission loss in the transmission line 20 can be sufficiently suppressed by the conventional configuration, the band pass filter 43 in the transmission path of the transmission signal after the coupler 42.
And the temperature characteristics of the band pass filter 44 in the passage of the pilot signal are different, the level adjustment based on the pilot signal cannot absorb the level fluctuation due to the difference of the temperature characteristics of the band pass filters 43 and 44. It was

According to the present invention, in addition to the function of suppressing the change of the transmission loss in the transmission line, the band-pass filter for passing the transmission signal and the pilot signal respectively automatically suppresses the change of the passage loss caused by the temperature change. It is an object of the present invention to provide an automatic level adjustment circuit capable of performing the above.

[0010]

According to the present invention, a transmitting side is provided with a pilot signal inserting section for superimposing a pilot signal on a transmission signal and sending it out to a transmission line, and a receiving side is provided with an automatic control for controlling the gain of the received signal. A gain control amplifier, a first band pass filter for selecting the transmission signal from the received signal and sending it to a receiver at a subsequent stage, a second band pass filter for selecting the pilot signal from the received signal, and the second Comparing the level of the pilot signal obtained through the band-pass filter with the reference voltage, and controlling the automatic gain control amplifier according to the obtained difference signal to suppress the change of the transmission loss in the transmission line. In an automatic level adjusting circuit including an automatic level control unit, temperature detecting means for detecting an ambient temperature of the first band pass filter and the second band pass filter; An arithmetic processing unit that takes in the ambient temperature information obtained by the detection unit to determine the temperature characteristic difference of the pass loss in each of the band pass filters, and sets a reference voltage that cancels the temperature characteristic difference in the automatic level control unit. It is characterized by having.

[0011]

According to the present invention, the automatic level control section does not fix the reference voltage as a reference for level comparison of pilot signals, but the first band pass filter for passing the transmission signal and the second band pass for passing the pilot signal. Set the reference voltage that cancels the difference in the temperature characteristics of the filter.

That is, the arithmetic processing means fetches the ambient temperature of each band pass filter detected by the temperature detecting means,
By determining and setting the reference voltage that cancels the difference in the temperature characteristics of each band pass filter, the level of the pilot signal can be converted into the level of the transmission signal for level adjustment. Therefore, it is possible to absorb the difference in the temperature characteristics of the band pass filters while monitoring the pilot signal, and reliably suppress the change in the transmission loss of the transmission signal in the transmission path.

[0013]

1 is a block diagram showing the configuration of an embodiment of the present invention. The present embodiment will be described based on the configuration of the high-frequency signal transmission device used in the description of the prior art. Therefore, the basic configuration including the transmitter 21, the modulator 22, the demodulator 23, and the receiver 24 connected via the transmission path 20, the pilot signal generator 31, the fixed attenuator 32, the bandpass filter (BPF) 33, and The pilot signal insertion unit 30 including the coupler 34, the automatic gain control amplifier (AGC amplifier) 41, the coupler 42, and the bandpass filters (BPF) 43 and 44 are the same as those in the conventional case.

The feature of this embodiment is that in the automatic level control section of the automatic level adjusting section 10 provided on the receiving side, the detector 45, the comparator 46 and the drive circuit 4 are first provided.
Although 8 is the same as the conventional one, the reference voltage generated by the reference voltage generator 11 can be changed by external control. Further, a temperature detector 12 that detects the ambient temperature of the bandpass filters 43 and 44 is provided, and as a calculation processing unit that controls the reference voltage generated by the reference voltage generation unit 11 according to the temperature information obtained by the temperature detector 12. , Arithmetic processing unit (CP
U) 13 and the memory 14.

In this embodiment, the temperature characteristic data of the pass loss of each of the band pass filters 43, 44 is stored in the memory 14 in advance, and the arithmetic processing unit 13 obtains each of the band pass filters 43, 44 obtained by the temperature detector 12. It is characterized in that corresponding temperature characteristic data is read from the memory 14 in accordance with the ambient temperature of 44, and a reference voltage for canceling the difference in the pass loss in each band pass filter is calculated.

Therefore, according to the configuration of this embodiment, the reference voltage generator 11 generates the reference voltage that the arithmetic processing unit 13 cancels the difference in the temperature characteristics of the band pass filters 43 and 44.
By setting to, even if automatic level adjustment is performed with reference to the level of the pilot signal, it is possible to reliably suppress fluctuations in the level of the transmission signal indirectly.

The present invention is particularly effective in an optical transmission system in which a change in transmission loss due to a change in temperature is large, but in that case, the modulator 22, the transmission line 20, and the demodulator 23 are respectively electrically / optical. It becomes a converter, an optical fiber cable, and an optical / electrical converter.

[0018]

As described above, according to the present invention, in a high-frequency signal transmission device or other transmission system that transmits a high-frequency signal with low loss, it is possible to reliably suppress a level change due to a temperature change in a transmission line and a receiving end. Therefore, the reception level of the transmission signal can be made extremely stable.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration example of a high-frequency signal transmission device including a conventional automatic level adjustment circuit.

[Explanation of symbols]

 10 Automatic Level Adjustment Unit 11 Reference Voltage Generator 12 Temperature Detector 13 Calculation Processing Unit (CPU) 14 Memory 20 Transmission Line 21 Transmitter 22 Modulator 23 Demodulator 24 Receiver 30 Pilot Signal Insertion Unit 31 Pilot Signal Generator 32 Fixed Attenuator 33 Band pass filter (BPF) 34 Coupler 40 Automatic level adjusting unit 41 Automatic gain control amplifier (AGC amplifier) 42 Coupler 43,44 Band pass filter (BPF) 45 Detector 46 Comparator 47 Reference voltage generator 48 Drive circuit

Claims (1)

[Claims] 1. A transmission side is provided with a pilot signal insertion section for superimposing a pilot signal on a transmission signal and sending it out to a transmission line, and a reception side is provided with an automatic gain control amplifier for controlling the gain of the reception signal, and a reception signal It is obtained via a first band pass filter for selecting the transmission signal and sending it to a receiver at a subsequent stage, a second band pass filter for selecting the pilot signal from the received signal, and a second band pass filter. An automatic level control unit for comparing the level of the pilot signal and the reference voltage, and controlling the automatic gain control amplifier according to the obtained difference signal to suppress the change of the transmission loss in the transmission line. In the automatic level adjusting circuit, a temperature detecting unit that detects the ambient temperature of the first band-pass filter and the second band-pass filter, and the ambient temperature obtained by the temperature detecting unit. Arithmetic processing means for fetching temperature information to determine a temperature characteristic difference of the pass loss in each of the band pass filters, and setting a reference voltage for canceling the temperature characteristic difference in the automatic level control unit. Automatic level adjustment circuit.