JPH04151925A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution remarkably by holding a peak value of a synchronizing control signal in a phase locked loop for a pseudo noise code so as to apply gain control to a received signal. CONSTITUTION:A correlation device 5 obtains a product of two input signals, integrates the product for a prescribed time at two adjacent phases of a pseudo noise code to obtain both of differences thereby forming a synchronization use control signal. A loop filter 6 extracts only the required component from a correlation output, the component enters a voltage controlled oscillator 7 to control a clock of a pseudo noise code generator 8 thereby forming a phase lock loop of the pseudo noise signal. Upon the receipt of a signal modulated by an information signal, a phase of a pseudo signal synchronized is deviated every time the information signal changes at a receiver side, the phase locked loop is operated to make the deviation zero and the original signal is demodulated based on a threshold level. Thus, a peak level of an output of a loop filter is used as a gain control signal to simply add a gain control function.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic gain control circuit, and more particularly, to a spread spectrum (spread spectrum) method using phase modulation of a pseudo-noise (PN) code.
The present invention relates to an automatic gain control circuit in a SS) type receiver. For example, it is applied to spread spectrum (SS) receivers and wireless communications.

■ As a gain control method in a conventional spread spectrum (SS) receiver, the received spread signal and the reference spread signal are correlated, and the correlation output or its peak value is used to control the gain of the amplifier. It is common to do this. An example of this is JP-A-64-10746. In this example, a matched filter or a convolver is used as a correlator to obtain a correlation output, and a correlation peak is detected and smoothed to obtain a gain control signal. However, this conventional method requires separate correlators for synchronization control and gain control. In the above example, a correlator is required even before demodulation, and the circuit configuration is complicated.

The gain control circuit in a conventional spread spectrum receiver uses a gain control correlator (matched filter,
A separate correlator is required for 1 demodulation, and in the case of a synchronous type, another correlator is also required for synchronization, resulting in a complicated circuit configuration.

This results in increased costs and manufacturing difficulties.
SUMMARY OF THE INVENTION The present invention was made in view of the actual situation such as "double series", and it is an object of the present invention to provide a gain control circuit with a simple configuration by using a correlator for synchronization also for gain control, and furthermore, to provide a gain control circuit with a simple configuration.
The purpose of this invention is to provide an automatic gain control circuit for use in a demodulation system in which demodulation and gain control are performed using a sum of +yI.

In order to achieve the purpose described in Section 1, we have developed a form of spread spectrum (PN) modulation that modulates the phase of a pseudophonic (PN) code.
An automatic gain control circuit used in a SS) system receiver includes an automatic gain control amplifier that amplifies the received signal, and a correlator that correlates the amplified received signal with the output of a pseudo-noise (PN) code generator. , a loop filter that converts the correlation output from the correlator into a control signal, a voltage controlled oscillator that is controlled by the control signal from the loop filter, a peak hold circuit that extracts a peak value from the control signal from the loop filter; The present invention is characterized by comprising an automatic gain control filter that smooths the peak value taken out by the peak hold circuit and uses it as a gain control signal for the amplifier. Hereinafter, the present invention will be explained based on examples.

FIGS. 1(a) and 1(b) are configuration diagrams for explaining an embodiment of a transmitter/receiver using an automatic gain control circuit according to the present invention, FIG. 1(a) is a transmitter, and FIG. 1(b) is a FIG. 2 is a configuration diagram of a receiver. In the figure, l is a clock generator, 2 is a pseudo noise (PN
) code generator, 3 is a variable delay circuit, 4 is an AGC (automatic gain control) amplifier, 5 is a correlator, 6 is a loop filter, 7
is a voltage controlled oscillator, 8 is a pseudo-noise (PN) code generator,
9 is a peak hold circuit, 10 is an AGC (automatic gain control) filter, and 11 is a comparator.

The parts that are only related to gain control are the peak hold circuit, AGC filter, and AGC amplifier, but to explain the operation, it is necessary to explain the entire modulation and demodulation system.
FIG. 1 shows the overall configuration of the transceiver.

First, a modulation and demodulation method using phase modulation of a pseudo-noise (I) code will be described. In the transmitter, a pseudo-noise (PN) code generator 2 is driven by a clock from a constant clock oscillator 1, and its output is passed through a variable delay circuit 3, where the delay time is varied and phase modulated by a digital information signal, and the signal is transmitted. Signal. - On the other hand, in the receiver, the received signal is amplified, enters the correlator 5, and performs a correlation operation with the same pseudo-noise (PN) code as that on the transmitting side. The correlator 5 basically calculates the product of two human input signals, integrates this over a certain period of time, performs this with two adjacent phases of the pseudo-noise (P N ) code, calculates the difference between the two, and calculates the second A control signal for synchronization is created as shown in the figure.

Note that, as described later, it is also possible to realize the characteristics shown in FIG. 2 with one correlator. Correlation output is loop filter 6
Only the necessary signal components are extracted and input to the voltage controlled oscillator 7, and the tarock of the pseudo-noise (PN) code generator 8 is controlled to form a pseudo-noise (PN) code locking loop.

Next, we will discuss the principle of demodulation. If we receive a signal modulated by an information signal as shown in Figure 3 (a),
On the receiving side, each time the information signal changes, the phase of the previously synchronized pseudo-noise (P N ) code shifts, and the synchronization loop works to reduce the shift to zero. As a result, the loop filter output is as shown in Figure 3. (b). Therefore, the third
If the signal in figure (b) exceeds a certain threshold value, 1. If a comparator or the like with hysteresis is used so that the value becomes O when the value falls below a certain threshold value, the original signal can be demodulated as shown in FIG. 3(C). Now, here there is a proportional relationship between the strength of the received signal and the correlation output, and as shown in Figures 2 and 3 (b)
There is also a proportional relationship between the correlation output and the peak value of the loop filter output. Therefore, by using the peak value of the loop filter output as the gain control signal, a gain control function can be added with a very simple configuration. This allows a single correlator to perform all three functions: code synchronization, automatic gain control, and signal demodulation. Although not specifically mentioned in the previous explanation, it goes without saying that the present invention can be applied not only to wired communication but also to wireless communication and optical communication by providing a frequency conversion section and a photoelectric conversion section in the middle of the circuit. .

FIGS. 4(a) and 4(b) are diagrams showing other embodiments of the transmitter/receiver using the automatic control circuit according to the present invention.
) is a configuration diagram of a transmitter, and Figure (b) is a configuration diagram of a receiver. In the figure,
12 is a crystal oscillator, 13 is a pseudo-noise (PN) code generator, 14 is an exclusive OR (EXOR) circuit, 15 is a delay circuit, I6 is a logic circuit, 17 is an AGC (automatic gain control) amplifier, and 18 is a correlation 19 is a multiplier, 20 is an integrator, 2
1 is a loop filter, 22 is a voltage control generator, 23 is a pseudo-noise (PN) code generator, 24 is a buffer amplifier, 2
5 is a diode, 26 is a filter, and 27 is a comparator.

Pseudo-noise (PN) code generator 1 with the output of crystal oscillator 12
3 is driven, and the exclusive OR of the output and the clock is taken to convert the pseudo noise (PN) code into Manchester code. Then, this output is divided into those that are passed through the delay circuit 15 and those that are not, and these are switched by a digital information signal and used as a transmission signal. On the other hand, in the receiver, AGC
The received signal passed through the amplifier 17 and the spread signal from the pseudo-noise (PN) code generator 23 are manually despread by a correlator 18 consisting of a multiplier 19 and an integrator 20, and the characteristics shown in FIG. 2 are obtained. Get the correlation output with This correlation output is passed through a loop filter 21 as a control signal for a voltage controlled oscillator 22, and the clock of a pseudo-noise (PN) code generator 23 is controlled to achieve code synchronization. In addition, the output of the loop filter 21 is taken out through the buffer amplifier 24 so as not to affect others, and it is divided into two parts, one of which is connected to the diode 2.
AGC by the peak value detection circuit by 5 and filter 26
It is used as a control signal to control the gain of the AGC amplifier 17.

The other signal is input to a comparator 27 with hysteresis to reproduce the information signal. In an embodiment of the present invention, Manchesterized pseudo-noise (PN) codes and ordinary pseudo-noise (P
N) Since the code's cross-correlation characteristics are utilized, a single correlator achieves the three functions of synchronization, demodulation, and gain control.

The embodiments have been described above, and in all the examples so far, the AGC amplifier has been arranged before the correlator. However, since it is sufficient to obtain a correlation output of the required strength, the GO amplifier may be placed after the correlator or after the loop filter. In this case, the signals before and after the loop filter are low frequency signals, which facilitates manufacturing and reduces costs. In addition, in the transmitter shown in Fig. 4,
Although only positive peaks are extracted as a peak detection method, it is possible to rectify the signal through an absolute value circuit before detecting the peak and detect negative peaks as well.

As is clear from the above description, according to the present invention, the automatic gain control circuit of the present invention uses a pseudo-noise (PN) code in a spread spectrum demodulator that digitally modulates the phase of a pseudo-noise (PN) code. ) Since the gain of the received signal is controlled by holding the peak value of the synchronization control signal in the code synchronization loop, the peak hold circuit, filter, and
Gain control is possible by simply adding a simple circuit consisting of a GC amplifier. Therefore, there is no need for a correlator just for gain control as in the prior art, and the circuit configuration can be greatly simplified, leading to lower costs and improved reliability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining an embodiment of a transmitter/receiver using an automatic control circuit according to the present invention, FIG. 2 is a diagram showing a synchronization control signal, and FIG. 3 is a diagram showing the principle of demodulation. FIG. 4, an explanatory diagram, is a diagram showing another embodiment of a transmitter/receiver using an automatic gain control circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... Clock generator, 2... Pseudo-noise (PN) code generator, 3... Variable delay circuit, 4... AGC (automatic interest control) amplifier, 5... Correlator, 6... ...Loop filter, 7...Voltage controlled oscillator, meter...Pseudo noise (
P N ) code generator, 9... peak hold circuit,
10...80C (automatic gain control) filter, 11...
·comparator.

Claims (1)

[Claims] 1. In an automatic gain control circuit used in a spread spectrum (SS) receiver that modulates the phase of a pseudo-noise (PN) code, an automatic gain control amplifier that amplifies the received signal, and an automatic gain control amplifier that amplifies the received signal; a correlator that correlates the output with a pseudo-noise (PN) code generator, a loop filter that converts the correlation output from the correlator into a control signal, and a voltage-controlled oscillator that is controlled by the control signal from the loop filter; It is characterized by comprising a peak hold circuit that extracts a peak value from a control signal from the loop filter, and an automatic gain control filter that smoothes the peak value extracted by the peak hold circuit and uses it as a gain control signal for the amplifier. automatic gain control circuit.