JPS6051310A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To prevent the malfunction of automatic gain control for interference waves and measure wide-band transmission characteristics. CONSTITUTION:In case of normal transmission of a signal, a switch 106 is connected to the side of a contact (a) because an output voltage does not appear in a detector 109, and an automatic gain control circuit is operated by the output of a voltage detector 107 which detects the output signal of a filter 103 tuned to a signal band center frequency, and therefore, interference waves are attenuanted by the filter 103 even if there are interference waves of adjacent channels or the like, and the malfunction due to interference waves is not generated. In case of measurement of wide-band transmission characteristics, a measured signal is inputted to a filter 104 tuned to a point shifted from the signal center frequency because the measured signal is swept, and this signal is detected by the detector 109, and the output voltage appears in the detector 109. At this time, if an input power is high, the switch 106 is connected to the side of a contact (b) by an automatic gain control voltage 4 and the output voltage of the detector 109, and the input of a gain controlling amplifier is connected to a detector 108, and therefore, the band of the input of the detector is not limited.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic gain control circuit, and more preferably,
Automatic gain control that prevents automatic gain control from malfunctioning due to interference waves in main intermediate frequency amplifiers with automatic gain control used in microwave communication heterodyne repeaters, etc., and also has a function that allows measurement of broadband transmission characteristics without trouble. It is related to circuits.

If an adjacent frequency causes a malfunction of automatic gain control due to the selection of the frequency arrangement used in a microwave heterodyne repeater, etc., the output level detection circuit for detecting the output level of the automatic gain control circuit of the main intermediate frequency amplifier will not detect interference waves from the adjacent frequency. One possible method is to install a narrowband filter tuned to the intermediate frequency in the output detection circuit for automatic gain control so as not to detect the signal. However, when measuring transmission characteristics over a wide band by having a bandpass filter, the measurement signal is band-limited by the attenuation characteristics outside the bandpass filter's band, and the detection level of the detector decreases, automatically The squelch operated during this time, making it impossible to measure broadband characteristics.

The present invention has been made in view of the above circumstances. Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, prevent automatic gain control malfunction due to interference waves in a main intermediate frequency amplifier with automatic gain control, and provide broadband transmission. An object of the present invention is to provide a novel automatic gain control circuit whose characteristics can be measured.

In order to couple the above objects, the automatic gain control w! according to the present invention! In the output detection circuit for automatic gain control of the main intermediate frequency amplifier with automatic gain control used in tFi, microwave heterodyne repeaters, etc., there is a first detection circuit tuned to the intermediate frequency center frequency, and a first detection circuit tuned to the intermediate frequency center frequency, and a first detection circuit tuned to the intermediate frequency center frequency. a first detection circuit tuned to frequencies apart from each other, a third detection circuit with wideband characteristics, and a detection output of the first detection circuit and an automatic gain control voltage to detect the first transverse wave circuit and the third detection circuit. and switching means for switching the output of the detection circuit.

Next, a preferred embodiment of this invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, one embodiment of the circuit according to the present invention includes a main intermediate frequency amplifier 10/, a gain control amplifier 10, an intermediate frequency band filter 103, IO'l, a switch 706,
It is configured to include a switching control circuit IO3' and detectors IO'l-109.

The detector lθ7 is connected to a filter /θ3 tuned to the center frequency of the intermediate frequency signal band, and its output during signal transmission operation detects, for example, a multiple telephone signal wave /l, as shown in Figure 2. Become something. Father, the detector IOT does not have a filter, so the detected output does not have any frequency characteristics. Detector 109
is a point arbitrarily distant from the center frequency of the signal band (Figure 1/
The filter 104I is connected to a filter 104I which is tuned to the characteristic of the filter 104I, and its output signal is output only when a signal falls within the band of the filter /θl.

Next, as shown in FIG. 1, the switch 104 is connected to the above-mentioned wave detectors 107 and 101, and its output is connected to the input of the gain control amplifier 10. The switching control circuit 10j for controlling the switching device 104 receives the gain control voltage l and the output of the detector/θji as inputs, and controls the switching device 104 by the input voltages of both. Switching control circuit/(As the operation of H, the detector 10
When there is no output voltage of 9 or the gain control voltage is low! (
When the input signal power of the main intermediate frequency amplifier /θ/ is low, the switch IOT is connected to A in the figure, and when the output voltage of the detector /θ is high and the gain control voltage DA is high ( When the input signal power of the main intermediate frequency amplifier /θ/ is high), the switch 104 is selected to be connected to the point in the figure.

During normal signal transmission, since no output voltage appears in the detector 109, the output signal of the filter 103 connected to the switching niot Fiα side and tuned to the signal band center frequency is detected by the voltage detector IO'L'fc. Since the automatic gain control circuit is operated by the output of 1, even if there is an interference wave from an adjacent channel (OH), the interference wave is attenuated by the filter 103, and is automatically controlled by the input power of the signal wave without being transversely waved. Since the gain control circuit operates, there will be no malfunction due to interference waves.

Also, since the measurement signal is swept when measuring broadband transmission characteristics, filter 1 tuned to a point far from the center frequency is used.
A measurement signal enters into 044, is detected by the wave detector 109, and the output voltage of the wave detector 109 K appears. Also, when the input power is high at this time, the p switch 104 is connected to the b side according to the output voltage of the automatic gain control overloader and transverse wave detector 109, and the gain control amplifier input is connected to the wave detector 101. The detector input makes it possible to measure wideband transmission characteristics without being band limited. Further, even if the interference wave has a frequency that enters the filter/θq, the automatic gain control circuit will malfunction when the signal input power is low and the input levels of the interference wave and the signal are reversed. In this case, since the gain control amplifier is low, the switch iob is connected to the a side, so that the automatic gain control circuit will not malfunction due to interference waves.

From the above, according to the present invention, during signal transmission, the automatic gain control function is not hindered by interference waves caused by frequency allocation and operates normally, and furthermore, wideband transmission characteristics can be measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic gain control circuit according to the present invention. /θl...main intermediate frequency amplifier, lθco...automatic gain control amplifier, 103...filter tuned to the center frequency of the signal band, 1041...center frequency of the signal band) distant point Filter tuned to 10! ...switching controller,
104...Switcher, 109-/n9...Detector FIG. 2 is a diagram showing the frequency relationship of the filter used in the present invention. /l...signal wave, lko...interference wave, /,? ... Selection characteristics of filter 103, /+ ... Selection characteristics of filter 10 % Fraudulent applicant NEC Corporation Agent Patent attorney Yutabe Kumagai

Claims (1)

[Claims] In an output detection circuit for automatic gain control of a main intermediate frequency amplifier with automatic gain control used in a microwave heterodyne repeater, etc., a first detection circuit tuned to the intermediate frequency center frequency and a first detection circuit tuned to the intermediate frequency center frequency, and a first detection circuit tuned to the intermediate frequency center frequency are used. A first detection circuit tuned to nine frequencies apart, a third detection circuit with broadband characteristics, and a detection output of the first detection circuit and an automatic gain control voltage. 9. An automatic gain control circuit characterized by comprising a switching means for switching the output of the detection circuit of No. 3.