JPH01109925A - Automatic gain control system - Google Patents

Abstract

PURPOSE:To prevent malfunction due to spurious noise by bringing a peak of correlation spike between positive or negative two threshold voltages. CONSTITUTION:A correlation spike outputted from a demodulator 13 is compared with positive or negative two threshold voltages given from a reference voltage generation section RV in response to the polarity by a comparator section CA. A count control section CC selects a clock from a clock selection section CL in response to the result of comparison and is given to a count section CU, where the signal is counted in positive or negative direction. A current corresponding to the count is generated by a gain control current generation section GC to control the gain of the variable gain amplifier 12 thereby bringing the correlation spike between the positive or negative threshold voltages. Thus, only the level of the peak of the correlation spike is caught to apply AGC, then the malfunction due to spurious noise of peaks of the correlation spike is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spread spectrum receiver, and more particularly to improvements in its automatic gain control method.

[Summary of the Invention] In a spread spectrum receiver, an AGC circuit of a variable gain amplifier that amplifies the output of a correlator is provided with a threshold voltage generation circuit to be compared with a correlation spike, and the circuit generates a threshold voltage according to the polarity of the correlation spike. The AGC circuit generates two positive and negative threshold voltages, and is controlled so that the peak of the correlation spike by the AGC circuit is between the two threshold voltages.

[Prior Art] An example of a conventional automatic gain control method adopted in a spread spectrum receiver is shown in FIG.

In the figure, 1 is a correlator, 2 is an IF amplifier, 3 is a correlation detector, and 4 is an AGC amplifier.

A received spread spectrum signal S is input to the correlator 1 , and its correlation output is given to the correlation detector 3 via the IF amplifier 2 .

The output of the correlation detector 3 is a correlation spike A as shown in FIG. When this correlation spike A is large, the output level of the AGC amplifier 4 becomes large, so the gain of the IP amplifier 2 is controlled to be lowered.

On the other hand, if the level of correlation spike A is small, AG
Since the output level of the O amplifier 4 is small, the gain of the IF amplifier 2 is controlled to be increased.

[Problems to be Solved by the Invention] In the case of a waveform like this correlation spike A, an AGC circuit that follows the peak value is normally used, but
The time constant of such an AGC circuit is.

It is designed to be short when charging and long when discharging. However, when the discharge time constant is lengthened, it responds quickly to fluctuations that increase correlated spikes, but responds slowly to fluctuations that decrease it, and even though the discharge time constant is lengthened, Since the discharge occurs little by little, the control voltage of the AGC constantly fluctuates, which has the disadvantage of causing malfunctions due to noise and spurious during periods when correlated spikes do not exist.

An object of the present invention is to provide an automatic gain control method in a spread spectrum receiver that performs gain control in response to only correlated spikes at high speed, without increasing the noise level or deteriorating the S/N ratio. .

[Means for Solving the Problems] In order to achieve the above object, the present invention correlates a spread spectrum signal received by a correlator with a reference signal,
In a spread spectrum receiver that supplies the correlation output to a demodulator via a variable gain amplifier, the correlation spike output from the demodulator is applied to two threshold voltages, either positive or negative, depending on its polarity. and controlling the gain of the variable gain amplifier in response to the comparison output so that the peak of the correlation spike is between the pressure or two negative threshold voltages.

[Operation] In the spread spectrum receiver of the present invention, the gain of the variable gain amplifier is controlled so that the correlation spikes output from the demodulator are between two positive and negative threshold voltages depending on their polarities.

Therefore, by capturing only the peak level of the correlation spike, A
Since GC is applied, spurious noise between the peaks of correlated spikes will not cause malfunctions.

[Examples] The present invention will be described below with reference to examples shown in the drawings.
FIG. 1 shows an embodiment in which the automatic gain control method of the present invention is applied to a spread spectrum receiver.
is a correlator, 12 is a variable gain amplifier, 13 is a demodulator, AG
C is an AGC circuit that controls the gain of the variable gain amplifier 12 in response to the output of the demodulator 13.

This AGC circuit includes a comparison section CA, a base voltage generation section RV,
It consists of a counting control section CC, a clock selection section CL, a counting section CU, and a gain control current generation section GC.

Thus, for example, the comparison section CA includes a comparator circuit 14 as shown in FIG. 2, and the reference voltage generation section RV has a threshold voltage generation circuit 15.

The counting control section CC has an absolute value circuit 16.16', a digital monomulti circuit 17.17', and a gate 18°18'.
, clock gates 19.19'.

The clock selection section CL consists of a clock switching circuit 25,
The counting unit CU includes an up/down counter 20 and a decoder 2
4, and the gain control current generating section GC has a D/A conversion circuit 2.
Consists of 3. Note that 21 is a data switching circuit, and 22 is a carrier sense circuit.

The comparator circuit 14 uses four comparators 4a to 4d, and the child terminals of the comparators 4a and 4b are given the output of the demodulator 3, and one terminal is given the threshold voltages ■ and ■ of the threshold voltage generation circuit 15. . Also, comparators 4c, 4
The output of the demodulator 3 is applied to one terminal of d, and the threshold voltages 1 and 2 of the circuit 15 are applied to the child terminals.

The absolute value circuits 16 and 16' are composed of, for example, OR circuits, each of which is given the comparison outputs of the respective comparators.
．． 18' and the up and down input terminals U of the up-down counter 10 via clock gates 19 and 19'.
This leads to P and DOWN.

The output of the counter 10 is sent to the D/D via the data switching circuit 21.
The signal is applied to the A conversion circuit 13, and the gain of the variable gain amplifier 12 is controlled by the output of the circuit.

Now, in the configuration shown in FIG. 1, the correlation spike output from the demodulator 13 is compared with two positive or negative threshold voltages given from the reference voltage generation section RV according to its polarity in the comparison section CA. Depending on the comparison result, the counting control section CC selects a clock from the clock selection section CL and supplies it to the counting section CU to count in the positive or negative direction. A current corresponding to this count value is generated by the gain control current generator GC, thereby controlling the gain of the variable gain amplifier 12 so that the correlation spike is between a positive or negative threshold voltage. Hereinafter, the above-mentioned operation will be further explained based on the embodiment shown in FIG.

In FIG. 2, as shown in FIG. 3, for example, the spread spectrum modulated data from the correlator 11 continues to be 1 or 0, and changes at a cycle of T/2. In this case, intermittent high-frequency correlation spikes are output with a period of T. However, T is one period of a PN code used for data spectrum spreading. This correlation spike is amplified by a variable gain amplifier 12. , demodulated by the demodulator 13 to obtain the baseband signal (2) shown in FIG.

The comparator 14 includes a threshold voltage generation circuit 1
5, the threshold voltage v2+■,v shown in FIG.
l+■, vl-■, and v2-■ are supplied.

When the baseband signal ■ exceeds v1+, v3■ is output, and when it exceeds v2+, v4■ and v3@ are output.

Also, if the baseband signal ■ falls below vl-, ■
2■ is output and if it is less than v2-, v1■ and v2
■ is output.

In the absolute value circuit 16, v4■ and v1■ are connected to the absolute value circuit 1.
V3■ and V2■ are input to 6'.

Perform an OR operation on each to obtain a signal (■) and a signal (■).

This relationship is shown in FIG.

The intended operation of the AGC circuit in Figure 2 is to set the positive peak of the baseband signal ■ to the middle of the threshold levels v1+ and v2+, and the negative peak to the threshold level v1-, based on these signals. The purpose is to control the variable gain amplifier so that the gain is in the middle of v2-.

As shown in FIG. 6, the digital monomulti circuits 17 and 17' use the signals ■ and ■ as triggers to obtain pulse signals @ and ■ of τ1. Here, τ1 is as shown in FIG.
Corresponding to the case where the correlated spikes continue with period T/2, T/
There is a case where τ1<T and a case where the correlated pulse continues with a period T and a corresponding case where T/2<τ1<2T, and the clock switching circuit 25 switches the digital monomulti time clock ■. This allows you to choose. This is because if the outputs (2) and (2) of the digital mono multi-circuit are less than one cycle of the correlation peak, the AGC may malfunction due to noise.

This is because if the number of cycles is two or more, the operation of the AGC becomes slow.

The gates 18 and 18' transmit the signal O and the signal ■ to the gates 18 and 18 by the control signal input during receiver adjustment.
', and keep the signals ■ and ■ as shown in Table 1.

Table 1 Clock gates 19 and 19' output signals ■ and ■ of gates 18° and 18', and UP count prohibition signal ■ and DOWN.
Count inhibit signal inhibit signal power Controls the count clock (■) and outputs an UP pulse (■) and a DOWN pulse (■) as shown in Table 2.

Table 2 The up/down counter 20 uses UP pulse ■ and DOWN pulse
A counting operation is performed using pulse (2) as a trigger, and N-bit binary data is output.

When adjusting the receiver, the data switch 21 switches the output to data O according to the input control signal, and sets the gain of the variable gain amplifier 12 to a fixed value.

The D/A conversion circuit 23 converts the N-bit output of the data switch into analog and supplies it to the variable gain amplifier 12 to control the gain. For the D/A conversion operation of the D/A conversion circuit 23, it is preferable to use a nonlinear D/A converter in order to correct the control characteristics of the variable gain amplifier 12 and perform linear control.

Note that the counter 20 operates as a ring counter, and all N pitches of the output may become KI O'' at the next up pulse of 1'', or conversely, all N pitches may become KI O'' from the state of all 'O'' until the next down pulse. It would be undesirable if all of them became "1".

The decoder 24 decodes the output of the counter, and outputs an UP count prohibition signal ■ when all N bits are 1'', and a DOWN count prohibition signal when all N bits are ``O'', and outputs a clock gate circuit. 19.19' is controlled;
UP count from all N bits “1” to all N bits “0” and from all N bits “O” to all N bits tt
I Prohibits counting down to II.

Further, the carrier sense circuit 22 compares the output of the counter with the data ■, and outputs a carrier sense signal ■ when the value of the output of the counter is larger than the data ■.

The clock switching circuit 25 switches the clock 1■ and the clock 2■ according to the control signal ■ and the carrier sense signal, and outputs the time clock ■ as shown in FIG.

Therefore, this AGC circuit operates as described above, and is shown in Table 2.
When the state is A or D, a DOWN pulse is issued and the DOW
It performs N counts and operates to increase the gain of the variable gain amplifier. This is when the baseband signal (2) exceeds the threshold voltage v1+ and does not fall below v1-, and the level of the baseband signal (2) is low.

Also, in state C or OFF, it outputs an UP pulse, performs an UP count, and operates to lower the gain of the variable gain amplifier. This is when the baseband signal is above the threshold voltage v2+ and below v2-, and the level of the baseband signal is high.

In this way, the state B or E in Table 2 is finally reached.
Or it becomes H, and in this state, the counter value does not change, so the gain of the variable gain amplifier also does not change, and the positive peak of the baseband signal ■ is at the threshold level ■1.
+ and v2+, and the peak on the negative side is between the threshold levels vl- and v2-, and the intended operation of the AGC circuit shown in FIG. 2 can be achieved.

The AGC circuit of FIG. 2 has two threshold voltages on the positive side and the negative side, respectively, in order to use correlation spikes of both positive and negative polarities as input, and also has an absolute value circuit 16.16.
', but if the correlated spikes are only positive or negative waveforms, there are only two threshold voltages for either polarity, and the absolute value circuit 16.16' is not required. is clear.

In addition, although we have talked about a circuit using an up-down counter here, it is possible to process this using software using a CPU, as well as an up-down counter, and to perform the same operation using a bidirectional shift register. is possible.

[Effects of the Invention] As explained above, according to the present invention, in a spread spectrum receiver, it is possible to provide an AGC method that prevents malfunctions due to noise, allows the control range to be set freely, and does not require adjustment, and is practical. The effects are enormous.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS.
The figures are waveform diagrams for explaining the operation, the eighth one is a block diagram showing a conventional automatic gain control circuit, and FIG. 9 is a waveform diagram for explaining the operation. 11...correlator, 12...variable gain amplifier. 13... Demodulator, CA... Comparison section, RV... Reference voltage generation section, CC... Counting control section, CL... Clock selection section, CU... Counting section, GC... Gain control current generator.

Claims (7)

[Claims] (1) In a spread spectrum receiver that correlates a spread spectrum signal received by a correlator with a reference signal and provides the correlation output to a demodulator via a variable gain amplifier, The output correlation spike is compared with two positive or negative threshold voltages depending on its polarity, and the gain of the variable gain amplifier is controlled in response to the comparison output so that the peak of the correlation spike is the positive or negative threshold voltage. An automatic gain control scheme characterized in that the gain is between two threshold voltages. (2) In a spread spectrum receiver that correlates a spread spectrum signal received by a correlator with a reference signal and provides the correlation output to a demodulator via a variable gain amplifier, The output correlated spike output is compared with two positive or negative threshold voltages depending on its polarity, and the counting operation of the reversible counting means is controlled by the comparison output, and the counting operation of the variable gain amplifier is controlled in response to the counting output. An automatic gain control method, characterized in that the gain is controlled so that the peak of the correlation spike is between the two positive or negative threshold voltages. (3) In a spread spectrum receiver that correlates a spread spectrum signal received by a correlator with a reference signal and provides the correlation output to a demodulator via a variable gain amplifier, Compare the output correlated spike output with two threshold voltages, positive or negative depending on its polarity, and be triggered by the comparison output,
The counting operation of the reversible counting means is controlled by the output of the mono multi-circuit that continues to generate an output for a predetermined period of time, and the gain of the variable gain amplifier is controlled in response to the counting output, so that the peak of the correlation spike is determined to be positive or negative. An automatic gain control scheme characterized in that the gain is between two threshold voltages. (4) The automatic gain control method according to claim 3, wherein the output generation time of the monomulti circuit is set to be longer than the period of the correlation spike. (5) The automatic gain control method according to claim 3, wherein the output generation time of the monomulti circuit can be controlled by an external signal. (6) The automatic gain control method according to claim 2, wherein the counting output is D/A converted, and the gain of the variable gain amplifier is controlled in response to the converted output. (7) The automatic gain control system according to claim 6, wherein the count output is D/A converted by a nonlinear D/A converter that compensates for nonlinear characteristics of the variable gain amplifier.