JPH05122192A - Automatic gain control circuit for spread spectrum receiver - Google Patents

Abstract

PURPOSE:To prevent the deterioration in a code synchronizing performance by maintaining the difference between the output peak value and the noise level of a convolver to the prescribed value, providing a switch element on the output side, and eliminating the output due to the delay wave other than the correlation output by a required wave signal to be outputted at constant time intervals. CONSTITUTION:A peak level detection device 22, a noise level detection device 23, and a differential detection device 24 detect the difference between the peak value of the output of a convolver 4 and the noise level. The gain of variable amplifiers 3 and 9 is controlled by the control voltage of a control voltage generator 25 to keep the difference to the prescribed value. The S/N of the output of the convolver 4 is optimized. A switch element is provided on the output side of the convolver 4 to be switched corresponding to the output intervals. Thus the output due to the delay wave other than the correlation output due to the desired wave signal to be outputted at the constant intervals is eliminated. Thus, the increase of the noise level in the receiving wave and the deterioration of the code synchronizing performance due to the powerful delay wave can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control circuit for a spread spectrum receiver, and more particularly to an automatic gain control circuit for improving the S / N ratio of the correlation output of a convolver or the like and eliminating the delayed wave output of the correlation output. The present invention relates to a gain control circuit.

[0002]

2. Description of the Related Art Conventionally, as an automatic gain control circuit in a receiving section of a spread spectrum communication device, one having a configuration shown in FIG. 2 or 3 is known.

FIG. 2 shows a reference signal generated by the first local oscillator 1, the first mixer 2 and the amplifier 3, the receiving antenna 5, the bandpass filter 6, the second local oscillator 7 and the second mixer. 8 and the reception signal obtained by the variable amplifier 9 are input to the convolver 4.
The correlation output from the detector is sent to the detector 11 via the amplifier 10, and the detected output is output to a code synchronization unit (not shown) for code synchronization. Based on the detection output, reception by the convolver 4 is performed. Control voltage generator 12 for controlling signal input
Have and. Hereinafter, they will be described in order.

First, the output of the first local oscillator 1 is spread by the spread code in the first mixer 2 into a constant band,
The signal is amplified by the amplifier 3 and supplied to the convolver 4 as the reference signal Sref.

On the other hand, the received wave received through the antenna 5 is removed by the bandpass filter 6 from unnecessary waves outside the band, and the second wave
It is converted to a predetermined frequency by the local oscillator 7 and the second mixer 8. Then, the converted reception wave is amplified by the variable amplifier 9 and supplied to the convolver 4 as a reception signal S _RX .

Here, the convolver 4 inputs the reference signal Sref and the received signal S _RX , and outputs the correlation peaks at regular intervals when the codes that spread these two input signals match.

The correlation peak output from the convolver 4 in this way is amplified by the amplifier 10, envelope-detected by the detector 11, and supplied to the code synchronization section.

The control voltage generator 12 includes a detector 11
Receives the detection output from and integrates it to generate a DC voltage V _C corresponding to the detection output.

The DC voltage V _C is used as a control voltage to control the gain of the variable amplifier 9 to control the reception signal input so as to keep the correlation peak output from the convolver 4 constant.

Further, in the configuration shown in FIG. 3, the control voltage generator 12 takes in the output signal of the variable amplifier 9, that is, the input received signal to the convolver 4, controls the variable amplifier 9 based on this value, and controls the convolver. The input to the convolver 4 is controlled so that the output (correlation peak) is kept constant.

That is, in FIG. 3, the received signal S _RX is
At the same time as input to the convolver 4, the control voltage generator 12
Is input to, the envelope detection and integration are performed, a DC voltage corresponding to the received signal power is generated, the gain of the variable amplifier 9 is controlled by this DC voltage, and constant power is supplied to the convolver 4.

As a result, the correlation peak output from the convolver 4 is kept constant regardless of the fluctuation of the received wave power.

[0013]

However, although it is possible to keep the output level of the convolver 4 constant in the above-mentioned automatic acquisition control circuit of the conventional example, since the transmitter is located far away, the received wave level is high. Fall down due to decay,
In some cases, the received waves cancel each other out due to multipath caused by reflectors, and the received wave level drops extremely.

In such a case, in order to keep the output of the convolver constant, the gain of the variable amplifier 9 in the receiving section must be greatly increased, and the noise level also increases accordingly, and the gain to the convolver 4 is increased. There is a possibility that the S / N ratio of the input wave deteriorates and the gain of the amplifier 9 becomes insufficient, resulting in a decrease in the convolver output level.

Further, since the S / N ratio of the input wave S _RX from the receiving section is deteriorated, the S / N ratio of the correlation peak which is the convolver output is deteriorated, and as a result, the efficiency of the convolver 4 is deteriorated. However, there is a drawback that the deterioration of the code synchronization performance is revealed.

Further, in the above conventional example, when an intense delayed wave other than the desired wave is input, the convolver output is larger in the delayed wave correlation output than in the desired wave correlation output. However, there is a drawback that the deterioration of code synchronization performance is introduced.

It is an object of the present invention to provide an automatic gain control circuit for a spread spectrum receiver capable of preventing the deterioration of the code synchronization performance due to the increase of the noise level in the received wave and the strong input of the delayed wave. To do.

[0018]

SUMMARY OF THE INVENTION The present invention detects a difference between a peak value of a correlation output by a convolver or the like and a noise level, and keeps the difference at a predetermined value by using a variable amplifier and a reference signal of a receiving section. By controlling the variable amplifier or the local oscillator of the generator, the S / N ratio of the correlation output is optimized.

Further, according to the present invention, a switch element is provided in the output stage of a convolver or the like, and the switching element is switched in correspondence with the correlation output interval, so that the correlation output other than the correlation output by the desired wave signal output at constant time intervals The output due to the delayed wave is removed.

[0020]

1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, components corresponding to those in FIG. 2 are designated by the same reference numerals, and the description will focus on the differences from the conventional one.

In the first embodiment, the difference from the configuration shown in FIG. 2 is that the difference between the peak value of the correlation output from the convolver 4 and the noise level is detected, and the reception is performed so that the difference becomes a predetermined value. This is to control the gain of the variable amplifier 9 of the control unit and the gain of the variable amplifier 3 of the reference signal generation unit.

As a configuration for performing such control, a peak level detector 22 for detecting the peak level of the convolver output, a noise level detector 23 for detecting the noise level, and a peak level and a noise level. A difference detector 24 for detecting a difference and the variable amplifiers 3 and 9
And a control voltage generator 25 for generating the gain control voltage.

Next, the operation of such a circuit will be described.
Since the basic operation until obtaining the convolver output is the same as that of the conventional example, the gain control of the variable amplifiers 3 and 9 will be described here.

The peak level detector 22 detects the peak value V _{S of} the convolver output detected by the detector 11. This is possible by normal peak detection.

The output of the detector 11 is input to the noise level detector 23, and the noise level V _N is detected by the noise level detector 23. This is to detect the noise level by cutting off only the normal peak portion of the convolver output and performing peak detection on the other portions.

Then, the difference detector 24 detects the difference V _d between the peak level and the noise level. The voltage V _d thus detected corresponds to the ratio of the signal of the convolver output to the noise, and the higher this voltage is, the better the S / N ratio of the convolver output is. Therefore, this difference voltage V _d
Sending level to a predetermined value V _o regulator control voltage V _c from the (control voltage generator 25) to each of the variable amplifier 3, 9 with the.

The control voltage V _c controls the gains of the variable amplifier 9 of the receiving section and the variable amplifier 3 of the reference signal generating section, and the differential voltage V _d becomes a predetermined value V _O.

FIG. 4 is a schematic diagram showing the outline of the gain (P _g ) and noise figure (NF) characteristics with respect to the current (I _c ) of the variable amplifier.

In general, a transistor, an FET, etc., changes non-linearly, unlike the current value at which the maximum gain is obtained and the current value at the point of the best noise figure. Further, in FIG. 1, the gain and the noise figure of the variable amplifier 9 of the receiving unit are G ₁ , N
Let F ₁ be the gain and noise figure of the variable amplifier 3 in the reference signal generation section be G ₂ and NF _2, and the gain and noise figure of the convolver 4 and the amplifier 10 at the subsequent stage be G ₃ , NF ₃ and G.
₄ and NF ₄ , the overall noise figure from the receiver to the convolver 4 is approximately NF ₁ + (NF ₃ −1) / G ₁ + (NF ₄ −1) / (G ₁ · G ₃ ). , Mainly determined by the noise figure NF ₁ and the gain G ₁ of the variable amplifier 9 in the receiving section.

Similarly, the overall noise figure from the reference signal generator to the convolver 4 is approximately NF ₂ + (NF ₃ -1) / G ₂ + (NF ₄ -1) / (G ₁ · G ₃ ). , Which is mainly determined by the noise figure NF ₂ and the gain G ₂ of the variable amplifier 3 of the reference signal generator.

That is, the S / N ratio of the convolver output is controlled by controlling the gains of the two variable amplifiers 3 and 9 to appropriate values and maintaining the output voltage of the difference detector 24 at a preset value of V _0. Will be optimally maintained despite variations in the received wave level.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

In the above embodiment, the reference signal is controlled by controlling the gain of the variable amplifier 3. However, the fixed type amplifier 3 is provided without using the variable amplifier, and the noise figure is optimized for the gain. It is possible to control the S / N ratio of the reference signal generator in an optimum state by fixing the value to a value and controlling the output power from the first station instead.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

The third embodiment differs from the first and second embodiments in that a high-frequency switch element is provided in the convolver output to eliminate the output of the delayed wave other than the correlation output of the desired wave signal. It is a thing.

In FIG. 6 as well, components corresponding to those in FIG. 2 are designated by the same reference numerals, and the description will focus on the differences from the prior art.

The third embodiment differs from the configuration shown in FIG. 2 in that the output side of the convolver 4 (amplifier 10
High-frequency switch 33 operated by voltage input to the output stage)
And a switching circuit generator for generating a switching signal based on the timer circuit 35 for obtaining the timing of the desired wave signal from the detection output of the detector 11, and a high frequency switching device 33. Switching is performed according to the interval of the desired wave signal, and the output due to the delayed wave is removed.

FIG. 7 is a waveform diagram showing the correlation output V _CONV of the convolver 4 and the output signal of the detector 11.

The correlation output V _CONV shown in FIG. 7A is a known output interval t given by the transmission rate of information to be transmitted.
Have _one . Also, the width t ₂ of the correlation output V _CONV is known. Then, the correlation output V _CONV is sent to the detector 11 via the high frequency switching unit 33, becomes a detection signal shown in FIG. 7B, and is sent to the code synchronization unit.

FIG. 8 is a waveform diagram showing a waveform when a delayed wave due to multipath is received at the correlation output V _CONV of the convolver 4.

FIG. 8A shows a state in which the correlation output of the delayed wave component due to the multipath is delayed by Δt from the correlation output of the desired wave component. When the largest correlation output peak is detected by envelope detection to synchronize the codes, the delay waves cause the peak intervals to shift, which makes it difficult to synchronize the codes.

Therefore, the high frequency switch 33 is switched in accordance with the interval of the correlation output due to the desired wave component to remove the correlation output component due to the delayed wave.

FIG. 9 is a waveform diagram showing how the correlation output component due to the delayed wave is removed.

The correlation output including the delayed wave component shown in FIG. 9 (a) is in the through state when the switching signal S ₁ of the switching signal generator 34 shown in FIG. 9 (b) is on, It is sent to the detector 11. That is, the high frequency switch 33
Functions as an attenuator when the switching signal S ₁ is off and attenuates the correlation output, while when the switching signal S ₁ is on, the correlation output is in a through state and the correlation output is passed to the detector 11 side.

Therefore, the cycle of the switching signal S ₁ is _{adjusted to} the interval t ₁ of the correlation output V _CONV , and the ON timing of the switching signal S ₁ is adjusted to the timing of the desired wave.
Further, by setting the on-pulse width t ₃ of the switching signal S ₁ to t ₃ <t ₂ with respect to the width t ₂ of the correlation output V _CONV , as shown in FIG. The removed correlation output can be obtained.

FIG. 10 is a waveform diagram showing the switching operation of the high frequency switching unit 33.

The switching signal S ₁ shown in FIG. 10A is maintained in the ON state after the power is turned on until the first correlation output is obtained. As a result, the first correlation output is the detector 11
And the detection output V _det shown in FIG. 10B is input to the timer circuit 35. This activates the timer circuit 35 and, as shown in FIG.
Switches on the timer output S ₂ from the off timing corresponding to the interval t ₁ of _CONV (t _m), the switch signal generator 3
The switching signal S ₁ of 4 is turned on. Then, from the second correlation output, the switching circuit S ₁ is on / off controlled by the unique operation of the timer circuit 35 in accordance with the interval t ₁ of the correlation output V _CONV . That is, the on-pulse width t ₃ and the off-pulse width (t ₁ −t ₃ ) of the switching signal S ₁ are set in the timer circuit 35 together with the first off-time t _m .

As the high frequency switch means, PI
You may use the thing which can change an attenuation rate by voltage like an N diode.

[0049]

As described above, according to the present invention,
By detecting the difference between the peak value of the correlation output and the noise level, and controlling the receiving unit and the reference signal generating unit to make this difference a predetermined value, the correlation is always maintained regardless of fluctuations in the input level of the received wave. The output S / N ratio can be optimized to a predetermined value, and code synchronization can be performed by using the correlation output under the optimum S / N ratio.

Further, according to the present invention, the switch means is provided in the output stage of the convolver or the like, and the switch means is switched in correspondence with the correlation output interval, so that the correlation output by the desired wave signal output at every constant time interval. Outputs due to delayed waves other than the above can be removed, and code synchronization can be performed using an appropriate correlation output.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a block diagram showing another conventional example.

FIG. 4 is a schematic diagram showing an outline of a gain with respect to a current and a noise figure characteristic of the variable amplifier.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

FIG. 7 is a waveform diagram showing the correlation output of the convolver and the output signal of the detector in the third embodiment.

FIG. 8 is a waveform diagram showing a waveform when a delayed wave due to multipath is received as a correlation output of the convolver in the third embodiment.

FIG. 9 is a waveform diagram showing how a correlated output component due to a delayed wave is removed in the third embodiment.

FIG. 10 is a waveform diagram showing a switching operation of the high frequency switching device in the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st local oscillator, 2 ... 1st mixer, 3, 10 ... Amplifier, 4 ... Convolver, 5 ... Receiving antenna, 6 ... Band filter, 7 ... 2nd local oscillator, 8 ... 2nd mixer, 9 ... Variable amplifier, 11 ... Wave detector, 22 ... Peak level detector, 23 ... Noise level detector, 24 ... Difference detector, 25 ... Control voltage generator, 33 ... High frequency switching device, 34 ... Switching signal generator, 35 ... Timer circuit.

Claims (2)

[Claims] 1. A spread spectrum receiver that inputs a received signal and a reference signal to a correlator to obtain a correlation output, performs code synchronization by the correlation output, and demodulates the received signal. Correlation output difference detection means for detecting the difference between the maximum value of the signal and the noise level value is provided, and the reception section of the reception signal and the generation of the reference signal are set so that the output of the difference detection means becomes a desired value. An automatic gain control circuit for a spread spectrum receiver having a control means for controlling the section. 2. A spread spectrum receiver that inputs a received signal and a reference signal to a correlator to obtain a correlation output, performs code synchronization by this correlation output, and demodulates the received signal. An automatic gain control circuit for a spread spectrum receiver, comprising switch means for turning on and off the output of the correlator at regular intervals in accordance with the output cycle.