KR100232965B1 - Reducing circuit of interference of balanced modulator in using direct spread system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference reduction circuit of a balanced modulator used in a direct spread system. In general, in order to demodulate a direct spread signal, an interference signal that is likely to occur in this process must be replaced with a signal having a baseband bandwidth. However, the present invention has a problem in that the operation of the receiver cannot be properly performed by recognizing the original signal, but the present invention improves the carrier suppression capability of the balance modulator used as a correlator in a direct spreading system, thereby improving the receiver even in a critical interference signal. It is possible to ensure interference cancellation by maintaining the condition.

Description

Interference Reduction Circuit of Balanced Modulator for Direct Diffusion System

1 is a waveform change spectrum after a directly spread signal is correlated.

2 is a block diagram of a conventional correlator circuit.

3 is a spurious generated signal spectrum due to interference.

4 is a signal conversion diagram based on a signal product of a code modulated local oscillation frequency.

5 is a circuit diagram of the present invention.

* Explanation of symbols for main parts of the drawings

a: direct spread signal b: baseband signal

T: period f: frequency

10 ~ 14: 1st ~ 5th Balanced Modulator (DBM) 15,16: Code Generator

17: buffer amplifier A: receiving input signal

B: Correlator output signal C: Bandpass filter output signal

The present invention relates to an interference reduction circuit of a balance modulator used in a direct spread system, and more particularly, to improve a carrier suppression capability of a balance modulator (DBM) that is frequently used as a correlator in a direct spread system. The present invention relates to an interference reduction circuit of a balanced modulator (DBM) used in a direct spreading system to reduce interference with a received signal.

In general, a direct spread signal in which a carrier is directly modulated and spread by a code used in digital communication has a shape spreading over a wide band as shown in FIG. 1 (a) to demodulate the received signal into an original signal. This requires switching to a signal (b) of baseband (baseband) bandwidth (this is called MAP). It is said to correlate and an INTERFERENCE signal can be generated during this process.

Referring to the drawings in detail, FIG. 2 is a conventional correlator circuit, which is a phase-modulated direct spread signal (①) of an ultra high frequency (UHF) band and a code modulated local oscillation frequency (④) which is another input signal. ) Is input to the first balance modulator 10, and the output (⑤) of the first balance modulator 10 becomes a single tone signal having correlated information.

On the other hand, the code modulated local oscillation frequency (④) is a mixed signal of the local oscillation frequency (②) and the code modulation signal (③). It is input to the first balance modulator 10.

However, if the carrier suppression capability of the second balanced modulator 11 used here is poor, the waveform of the code modulated local oscillation frequency ④ becomes third as a result of the code imbalance caused by the interference signal, thereby converting this spurious signal to the original. Since the signal is recognized as a signal, the spurious signal acts as a jamming signal, and the tracking loop of the carrier is not locked so that the receiver cannot be properly operated.

The present invention is to solve the above problems, it is characterized in that the interference can be ensured to ensure that the receiver remains intact even in the case of fatal interference signal.

That is, the present invention improves the carrier suppression capability of the balance modulator used as a correlator of a direct spreading system, and uses a wide band signal as an input signal, such as a CDMA (Code Division Multiple Access) cellular system. Applicable

Hereinafter, described in detail with reference to the accompanying drawings.

4 is a signal conversion diagram based on a signal product of a code-modulated local oscillation frequency of a direct spreading correlator for the purpose of understanding the present invention. When (A-2) comes in together, the spread signal is correlated and outputted on condition that the code modulated local oscillation frequency and the pattern and timing of the code match (B-1), but the interfering signal is spread to a low level signal (B-2).

When the signal passes through the bandpass filter, the original signal is reduced in both sidebands, resulting in a good signal-to-noise ratio (C-1), but the interference signal is further reduced (C-2) and remains a noise component.

5 is a circuit of the present invention for preventing an unlock due to signal leakage, and includes first and second code generators 15 and 16 for generating codes, the first code generator 15 signal, and a local oscillation frequency. A fourth balanced modulator 13 for mixing a modulated signal to form a code modulated signal, and a third balanced modulator for lowering a carrier by mixing a code modulated local oscillation frequency that is an output of the fourth balanced modulator 13 with a high input signal; (12), a buffer amplifier (17) for separation and amplification between the third balance modulator (12) and the fifth balance modulator (14), and the output of the QVJ amplifier (17) to a second code generator (16). And a fifth balance modulator 14 for further lowering the carrier by mixing with the signal and a bandpass filter (BPF) for removing all spurious components around the signal carrier.

The present invention configured as described above is as follows.

The first code generator 15 is mixed with the local oscillation frequency to produce a code modulated local oscillation frequency, which is the third balanced modulator 12 when the code modulated local oscillation frequency signal and the code of the high received input signal are synchronized. The output of is equal to B in FIG. Here, if the carrier suppression capability of the third and fourth balance modulators 12 and 13 is reduced, a spreading signal having spurious appears at point ⓐ as shown in FIG. 3 so that the interference signal is recognized as an original signal. The leakage of the third balance modulator 12 is masked as if the (A-2) signal of FIG. 4 is diffused into the (B-2) signal by the second code generator 16, and thus the fifth balance modulator 14 There is a weak stress on the input. In the fifth balance modulator 14, the outputs of the second code changer 16 and the third balance modulator 12 are multiplied, and since they are synchronous, the original signal can be re-mapd to the desired bandwidth, and at the same time the first mixing ( Residual components due to the spurious signal of 12) are spread so that all spurious components around the signal carrier are removed when passing through the BPF.

Therefore, by using this method, it is possible to obtain a suppression of about 60 (dB) as a whole in the reality that the carrier suppression capability of one balance modulator is only about 30 (dB).

As described above, the present invention has the effect of ensuring interference cancellation so that the receiver can remain in the dead state even in the case of fatal interference signals.

Claims (2)

In a direct spreading system, a fourth equilibrium for generating a code modulated signal by mixing the first and second code generators 15 and 16 for generating a code, the first code generator 15 signal, and a local oscillation frequency is generated. A third balance modulator 12 for lowering a carrier by mixing a modulator 13, a code modulated local oscillation frequency that is an output of the fourth balance modulator 13, and a high input signal, and the third balance modulator 12 And a fifth amplifier for further lowering the carrier by mixing the buffer amplifier 17 for separation and amplification between the fifth balance modulator 14 and the output of the buffer amplifier 17 with the signal of the second code generator 16. An interference reduction circuit of a balance modulator for use in a direct spreading system, characterized by comprising a balance modulator (14) and a bandpass filter (BPF) for removing all spurious components around the signal carrier. The second code generator (16) according to claim 1, wherein the second code generator (16) causes the leakage of the third balance modulator (12) to exist as a weak stress and at the same time to be input to the fifth balance modulator (14). 15) is designed to be input to the fourth balance modulator (13), the interference reduction circuit of the balance modulator for use in a direct spreading system, characterized in that the design of the two code generator mixing circuit.