JPH0564893B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] A modulated microwave signal that is modulated with a baseband signal that has transmission information in a predetermined change in amplitude, such as multilevel QAM or SSB modulation, and that is transmitted along a transmission path. This is an AGC circuit used in a receiving circuit for microwave signals whose overall signal level fluctuates irregularly due to fading, etc. The output is amplified and detected by inputting a modulated carrier signal whose receiving level fluctuates. A peak hold circuit that stores the maximum value of the amplitude value at fixed time intervals sufficient to detect level fluctuations of the entire received signal, and a sample hold circuit that samples the stored maximum value and holds it until the next maximum value. The circuit is equipped with a high-speed data amplitude-modulated microwave signal that does not distort the amplitude component, but has good amplitude control operation against fluctuations in the overall level of the input signal due to fading, etc. AGC circuit that performs.

[Industrial application field]

The present invention modulates a high-frequency carrier signal with a baseband signal that has transmission information in a predetermined change in amplitude value, such as a signal subjected to multilevel QAM (quadrature amplitude modulation) or SSB modulation (single sideband amplitude modulation). The present invention relates to an automatic gain control (AGC) circuit that amplifies a modulated carrier wave input signal with a variable gain amplifier and automatically controls the gain of the amplifier so that the level of the output carrier wave becomes a constant value.

For example, the input multi-value QAM signal wave is a high-speed digital signal of a modulated carrier wave signal having an amplitude value and a phase value that change in a predetermined value of n, and the level of the entire multi-value QAM signal changes midway. The AGC of the amplifier for the received wave fluctuates irregularly due to fading, etc. that occurs in the wireless transmission path.
As a circuit, it does not respond to the original amplitude-modulated transmission signal of the input and does not cause distortion, and responds appropriately only to overall level fluctuations due to fading in the transmission path, etc. It is required that the output level be constant.

[Conventional technology]

The conventional AGC circuit converts the input carrier signal _Eio into a variable gain amplifier, as shown in the block diagram of Figure 5.
In a circuit that outputs an output carrier signal E _put after being amplified by an AGC AMP, a part of the output carrier signal E _put is detected by a detector DET having a time constant circuit CR, and the DC detection output of the detector DET is sent to a DC amplifier DC.
Variable gain amplifier AGC AMP with AWP amplification
In addition, the amplification gain of the variable gain amplifier AGC AMP is controlled to keep the amplitude of the carrier wave output _Eput constant.

[Problem that the invention seeks to solve]

When the conventional AGC circuit shown in FIG. 5 is used in a receiver that receives a modulated multi-value QAM microwave signal wave that has been multi-value QAM-modulated with high-speed data, the multi-value QAM microwave signal input to the receiver is Since high-speed data is transmitted using both predetermined amplitude changes and phase changes, the input multilevel QAM
The amplitude value of microwave signals is not constant;
It is a signal whose amplitude changes as determined by a modulation signal (data), and whose overall level fluctuates irregularly due to fading or the like in an intermediate transmission path.

Therefore, if the time constant CR of the AGC circuit's detector DET is selected to a small value in order to respond to fast fluctuations due to fading, etc. of the input level of the carrier wave signal of high-speed multilevel QAM, the response of the AGC operation becomes faster.
The control signal of the AGC circuit follows the amplitude change of the multilevel QAM signal, causing distortion in the predetermined amplitude change for each time slot of the signal (data) to be transmitted. Therefore, the time constant of the detector DET
The value of CR is approximately 10 timeslot of the transmission signal.
It must be more than doubled.

If the time constant CR is set to such a large value, a problem arises in that the control operation of the AGC circuit cannot follow fast fluctuations due to fading or the like in the input level of the multilevel QAM signal wave.

[Means for solving problems]

The problem with the above-mentioned conventional AGC circuit is that, as shown in the principle block diagram in Figure 1, a high-frequency carrier wave is modulated with a baseband signal that contains the information to be transmitted based on a predetermined amplitude change for each time slot. A carrier wave that is input as a modulated carrier signal that is a modulated high-frequency carrier signal and whose overall signal level fluctuates irregularly due to fading or the like in the transmission path, which is different from the change in the predetermined amplitude of the signal. A variable gain amplifier 3 that amplifies a signal with a gain that is varied by a control signal C and outputs an output carrier signal; and a variable gain amplifier 3 that outputs an output carrier signal by amplifying the signal with a gain that is varied by a control signal C; It consists of a peak hold circuit 1 that stores a maximum value large enough for each fixed time period, and a sample hold circuit 2 that samples the output of the peak hold circuit 1 at intervals of the fixed time period and holds the sampled value. This problem is solved by the present invention, which is configured to automatically control the amplification gain of the variable gain amplifier 3 using the control signal C so that the output value of the sample and hold circuit 2 is constant.

[Effect]

The peak hold circuit 1 of the present invention is sufficient to not respond to a predetermined change in the amplitude value for each time slot of the baseband signal obtained by detecting the output carrier wave E _put of the variable gain amplifier 3. However, it is sufficient to respond to and detect the overall irregular level fluctuations of the output carrier wave _Eput , which is the peak value at regular intervals of several tens to hundreds of time slots. Then, the stored maximum value of the amplitude is reset to be erased at regular intervals. The sample and hold circuit 2 samples the output of the peak and hold circuit 1 at fixed time intervals of the same several tens to hundreds of time slots, avoiding the influence of the reset of the peak and hold circuit, and outputs the signal stored in the peak and hold circuit 1. Since the maximum value of the amplitude is held until the maximum value of the next sample comes, when the output of the sample hold circuit 2 is applied as a control signal to the variable gain amplifier 3, the gain of the variable gain amplifier 3 becomes equal to that of the multilevel QAM signal wave. It does not follow individual changes in signal amplitude for each time slot, but only for fluctuations due to fading or the like in the maximum value of the signal amplitude for every several tens to hundreds of time slots.

Therefore, the AGC operation of the variable gain amplifier 3 performs a satisfactory AGC operation that outputs a carrier signal at a constant level for a high-speed multilevel QAM signal wave in which the level of the entire input signal fluctuates irregularly, and This eliminates the problem of causing distortion to changes in amplitude, which is the transmission information of the high-speed received carrier signal.

〔Example〕

FIG. 2 is a block diagram showing the configuration of an automatic gain control circuit according to an embodiment of the present invention, FIG. 3 is a waveform diagram for explaining the operation of this embodiment, and FIG. 4 is a diagram showing the automatic gain control circuit of this embodiment. Circuit peak hold circuit (Figure A)
and a circuit diagram of the sample and hold circuit (Figure B).

Output carrier signal of variable gain amplifier 3 in Fig. 2
A part of E _put is detected by the diode of the peak detector 11 of the peak hold circuit 1, and the output carrier
A detection voltage proportional to the peak amplitude of E _put , which is the sum of the variable amplitude value originally determined for each time slot of the baseband signal and the fluctuation value where the overall signal level fluctuates due to fading, etc. A proportional detected voltage is obtained across the resistor R. The detection output of the peak detector 11 is sent to the operational amplifier OP AMP of the voltage hold circuit 12 in order to detect a level fluctuation value in which the level of the entire signal fluctuates due to fading, etc., and extract the maximum value thereof. is input to the + input terminal of

The output of the operational amplifier OP AMP is connected to its own - input terminal and at the same time charges the capacitor C1.

The capacitor C1 is charged one after another by the output V _put 1 of the operational amplifier OP AMP and held at its maximum value, but the reset switch SW _p connected across the capacitor C1 detects the level fluctuation of the entire signal. It is reset at regular time intervals of tens to hundreds of time slots large enough for the purpose.

This reset operation of the capacitor C1 is performed by sending a control signal to the peak hold circuit at fixed time intervals, that is, at intervals of tens to hundreds of time slots, which are sufficiently large for one time slot, as shown in FIG. 3A. Since this is done by a reset pulse, the charging voltage of the capacitor C1 will represent the maximum value of the carrier wave signal output _Eput for each tens to hundreds of time slots.

The charging voltage of this capacitor C1, that is, the output voltage V _put 1 of the peak hold circuit 1 is input to the + input terminal of the operational amplifier AMP-1 of the sampling circuit 21 of the next sample hold circuit 2,
The output of AMP-1 is turned on for sampling.
Voltage hold circuit 22 via switch SW-1
The capacitor C2 is charged. The output of AMP-1 is also connected to the operational amplifier of voltage hold circuit 22.
Input to the + input terminal of AMP-2.

The output voltage V _put 2 of the operational amplifier AMP-2 is connected to its own - input terminal, and at the same time is connected to the - input terminal of the operational amplifier AMP-1 via a series resistance circuit of the resistor R1 and the resistor R2 of the sampling circuit 21. is input. Also, resistors R1 and R2 of the series resistance circuit
The connection point is the off switch for sampling.
It is connected to the input side of the on switch SW-1 via SW-2. The on switch SW-1 and the off switch SW-2 for sampling are driven by a sampling pulse controlled by a sample hold circuit as shown in FIG. 3B, but the period of the sampling pulse is determined by the peak hold circuit. Same as the period of the reset pulse, the output voltage V _put 1 of the peak hold circuit 1 is sampled at fixed time intervals of several tens to hundreds of time slots, charges the capacitor C2, and is held as a DC voltage.

The DC voltage held in the capacitor C2 is output as a DC output V _put 2 from the output terminal of the operational amplifier AMP-2, and is applied to the variable gain amplifier 3 as an AGC control signal to control the gain of the amplifier 3.
Performs AGC operation.

The control signal V _put 2 of the variable gain amplifier 3 of the AGC circuit of this embodiment is the output carrier wave signal E _put of the AGC circuit.
Of the peak-detected amplitude, the DC voltage V _put 1, which is the maximum value between several tens to hundreds of time slots, which is sufficient to detect the level fluctuation value of the entire signal due to fading, etc., is determined by the number of the same period. Since the sample values are sampled at regular intervals of ten to hundreds of time slots, the DC output V _put 2, which is the control signal for the AGC circuit of this embodiment, is the amplitude distortion of the signal for each time slot of the conventional AGC circuit. Compared to the response using the output voltage of a detector with a time constant CR that takes into account the control signal, a faster response with a response time of 1/10 to 1/100 or less can be obtained, and the input signal level is faster due to fading etc. Satisfying AGC that follows changes
take action. On the other hand, since the control signal V _put 2 does not follow individual amplitude changes for each time slot of the input carrier signal E _io , it does not distort the amplitude components of multi-value QAM signal waves, etc.
There is no problem of amplitude distortion as in conventional AGC circuits for QAM or SSB modulated microwave signals.

〔Effect of the invention〕

As explained above, according to the present invention, the conventional
It can respond to fast fluctuations in the level of the input carrier signal due to fading etc. with a response time of 1/10 to 1/100 of the AGC circuit, and it can also respond to multilevel QAM signals and SSB signals obtained by detecting the output carrier signal. This has the effect of providing a good automatic gain control circuit that does not adversely affect the predetermined amplitude change for each time slot of the modulated microwave signal. Also, when used as an AGC circuit for SSB modulated signal waves,
This eliminates the need for pilot signal insertion and branch circuits, which were required in the conventional example, and provides the advantage of simplifying the circuit.

[Brief explanation of the drawing]

FIG. 1 is a principle block diagram showing the structure of an automatic gain control circuit according to the present invention, FIG. 2 is a block diagram showing the structure of an automatic gain control circuit according to an embodiment of the present invention, and FIG. 3 is a block diagram showing the structure of an automatic gain control circuit according to an embodiment of the present invention. A waveform diagram for explaining the operation of the automatic gain control circuit, FIG. 4 is a circuit diagram of the peak hold circuit and sample hold circuit of the automatic gain control circuit according to the embodiment of the present invention, and FIG. 5 is a circuit diagram of the automatic gain control circuit of the conventional example. FIG. 3 is a block diagram showing the configuration of the circuit. In FIGS. 1 and 2, 1 is a peak hold circuit, 11 is a peak detector, 12 is a voltage hold circuit, 2 is a sample hold circuit, 21 is a sampling circuit, and 22 is a voltage hold circuit.

Claims (1)

[Claims] 1 A modulated high-frequency carrier signal in which a high-frequency carrier wave is modulated with a baseband signal having information to be transmitted with a predetermined change in amplitude for each time slot, and the above-mentioned specifications are applied due to fading, etc. in the transmission path on the way. An amplifier 3 that amplifies a carrier signal inputted as a modulated carrier signal in which the level of the entire signal varies irregularly in addition to the change in the amplitude of the signal, with a gain variable by a control signal C, and outputs an output carrier signal. , a peak hold circuit 1 that stores a maximum value for each fixed time that is large enough to detect the level fluctuation of the entire signal among the amplitude values obtained by detecting the output carrier signal of the amplifier 3; It consists of a sample hold circuit 2 which samples the output of the peak hold circuit 1 at intervals of the predetermined period of time and holds the sampled value. An automatic gain control circuit characterized in that the amplification gain of No. 3 is automatically controlled.