JPH0136739B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a code detection circuit used in spread band communication systems and the like.

In spread band communication radio equipment, demodulation is performed while shifting the phase of the receiver's spreading code.
When the spreading codes are synchronized, carrier reproduction is performed and the noise level of the receiver is reduced, so that this reduction in the amount of noise is detected and dispersion detection with the transmitting side is performed. However, in this method, it was necessary to provide a trimmer to adjust the detection threshold level of the noise detection circuit.

SUMMARY OF THE INVENTION An object of the present invention is to provide a code synchronization detection circuit which does not require the above-mentioned trimmer and which facilitates synchronization acquisition even when the input electric field strength is weak.

This will be explained below along with examples. FIG. 1 shows a radio device using a code synchronization detection circuit according to an embodiment thereof, in which 1 is an antenna, 2 is a band wave circuit, 3 is a high frequency amplification circuit, and 4 is a high frequency amplification circuit 3.
5, 7, and 14 are amplifier circuits; 6 is a band-limiting circuit; and 8 is a amplifier circuit based on the output of the amplifier circuit 7; , 7 and control the mixing circuit
AGC circuit, 9 is TAU-DITHER
Detection circuit, 10 is a clock circuit, 11 is a code generation circuit, 13 is a local oscillator, 15 is a frequency discrimination circuit, 16 is a high-pass circuit, 17 is a noise amplification circuit, 18 is a rectifier circuit, 19 is the output of the rectifier circuit 22 20 is a low frequency amplifier circuit, 21 is a speaker, 22 is a rectifier circuit, 23 is a comparison circuit that compares the output of the rectifier circuit 22 and the set value set by the volume controller 26; A comparison circuit 24 is a switching circuit.

Next, the operation of this embodiment will be explained. A received signal input from the antenna 11 is band-limited by a band wave circuit 2, amplified by a high frequency amplifier 3, and then mixed with a local oscillation balanced modulation signal, which is the output of a balanced modulation circuit 12, by a mixing circuit 4. The local oscillation balanced modulation signal is generated by driving the code generation circuit 11 by the clock generation circuit 10 to generate a specific code string, and then generating this signal by subjecting the output signal of the local oscillation circuit 13 to balanced modulation. It is something. When functioning as a frequency modulation type receiver, the function of the code generation circuit 11 is stopped and the system of the balanced modulation circuit 12 and local oscillation circuit 13 functions as a local oscillator.

Further, in the case of the band spread method, the mixing circuit 14 functions as a type of correlator. Now, if the synchronization between the code on the transmitting side and the code on the receiving side is not established, the output signal that has passed through the amplifier circuit 7 of the amplifier circuit 5 and the band limiting circuit 6 is subjected to spread modulation with the code on the receiving side. Therefore, the signal that has passed through the amplifier circuit 14 and is demodulated by the frequency discrimination circuit 15 contains many noise components. On the other hand, if the spreading codes on the transmitting and receiving sides are uniform, the carrier is regenerated in the mixing circuit 4, and the noise in the frequency discrimination circuit 15 is suppressed. Therefore, if you monitor this noise component,
Detection of synchronization will occur. For this purpose, a high-pass circuit 16 is connected to remove the audio component of the demodulated signal, and this is amplified by a noise amplification circuit 17. Next, the rectifier circuit 18 converts it to a DC level, and the comparator 19 determines the amount of noise by determining this level. That is, when the amount of noise is large, the threshold level of the comparator 19 is exceeded and asynchronous information is output. As a result, the clock generation circuit 10 adds or removes a clock so as to shift the phase of the code output from the code generation circuit 11. If synchronization is not established in this way, the phase of the code changes sequentially.

Next, when synchronization is achieved, noise is suppressed, comparator 19 outputs information indicating the establishment of synchronization, and the phase correction operation performed by clock generation circuit 10 is stopped. Once synchronization is established, the current clock tracking function operates, and in order to ensure this amplitude modulation, the AGC circuit 8 operates to prevent the radio section from being saturated.

Next, if you are receiving with frequency modulation method,
A noise component among the signal components output from the frequency discrimination circuit 15 is amplified and converted into direct current by a rectifier circuit 22 as in the band spread method, and then this level is detected by a comparator 23. That is, in the frequency modulation method, when the amount of noise is small, it means that a carrier signal has arrived. Therefore, at this time, the switching circuit 24 operates, supplies power to the low frequency amplifier circuit 20, amplifies the audio signal, and outputs audio from the speaker 21. The rectifier circuit 22 is different from the spread band type rectifier circuit 18 because the spread band type uses a small time constant to speed up synchronization, whereas the frequency modulation type uses a small time constant to prevent fluctuations due to fading, etc. This is because it is necessary to take a large time constant.

Figure 2 shows comparison circuits 19, 20, volume 25,
26 shows a specific configuration of a portion including 26. In the same figure, 37 and 38 are comparison circuits, 40 and 4
8 and 49 are resistors, 44 to 46 are analog switches, 41 is a volume control, 47 is a switch, 50 is an inverter, 39 is a terminal to which a reference voltage is applied, 42 is a terminal for inputting a band spread signal, and 43 is for inputting a frequency modulation signal. This is the terminal.

Next, the operation will be explained. Comparison circuit 37 is connected to terminal 42
The comparison circuit 38 inputs a spread band system signal from a terminal 43, and inputs a frequency modulation system signal from a terminal 43 thereof. Also, each comparison voltage is at terminal 39.
The voltage supplied to the circuit is divided by resistance and supplied. First, in the frequency modulation method, since the switch 47 is open, the control signal passing through the inverter 50 turns on the analog switch 45, so the resistor 40
The voltage divided by the volume controller 44 is sent to the comparator circuit 38.
is supplied to Next, in the case of the spread band method, the switch 47 is turned on and the analog switches 44, 46 are turned on.
conducts. Therefore, the voltage controlled by the volume 41 is connected to the comparison circuit 37, and therefore the level for synchronization acquisition is controlled by the volume. On the other hand, the voltage divided by the resistors 48 and 49 is input to the comparator circuit 38, and a comparison voltage of the comparator circuit that controls the switching circuit 24 for operating the low frequency amplification circuit is supplied.

That is, in the spread band method, the volume works to control the level of synchronization acquisition, and the so-called squelch level is fixed by resistors 48 and 49.

Furthermore, when the input power to the receiver is large, the inversion level of the comparator circuit 19 should be set high to prevent erroneous synchronization, but when the input power is small, the inversion level should be set low to prevent erroneous synchronization. It is necessary to improve the sensitivity and facilitate synchronization acquisition. That is,
The inversion level of the comparison circuit 19 should be varied depending on the input power of the receiver, and the volume 25 plays this role.

As is clear from the above description, the present invention has the feature that synchronization can be easily acquired without impairing operability when using a spread band method using a volume.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a code synchronization detection circuit according to an embodiment of the present invention, and FIG. 2 is a specific wiring diagram of the main parts thereof. 16...High-pass circuit, 19, 23, 37, 3
8...Comparison circuit, 20...Low frequency amplification circuit, 2
4...Switching circuit, 41...Volume.

Claims (1)

[Claims] 1 The received spread band modulated signal is mixed with the output of a separately provided balanced modulator, and the resulting output is discriminated by a frequency discriminator to obtain an audio signal, and the noise is removed from the output of the frequency discriminator. and when the level is reduced to a first predetermined level,
Stop adding or subtracting clocks to the balanced modulator and the controlling code generator so that the output of the balanced modulator is synchronized with the received spread band modulated signal, and the output of the frequency discriminator is When the level of the obtained noise is different from a second predetermined level, a squelch is applied to a low frequency amplification circuit provided after the frequency discriminator;
A code synchronization detection circuit characterized by comprising means for commonly setting a second predetermined level.