KR950000104Y1 - Carrier detection system - Google Patents

Abstract

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Description

Carrier detection device

1 is a block diagram of a conventional carrier detection device.

2 is a configuration of a carrier detection device according to the present invention.

3 is a frequency characteristic diagram of each filter for explaining the present invention.

* Explanation of symbols for main parts of the drawings

100: low power narrowband frequency modulation intermediate frequency circuit

200: comparator 210: narrowband filter

230: comparison means 231: DC conversion means

232: reference voltage generating means 300: low pass filter

The present invention relates to an apparatus for detecting a high frequency carrier received from a wireless telephone, and more particularly, to an apparatus for stably detecting a carrier without interference of an adjacent channel.

In FIG. 1, which shows a conventional carrier detection apparatus, a low power narrow band frequency modulation intemidiate frequency (hereinafter abbreviated as "LPN FM IF") circuit 100 is a local oscillator ( 10), mixer 20, limiter amplifier 30, demodulator 40, low frequency (hereinafter, abbreviated as "AF") amplifier 50, filter amplifier 60, squelch circuit ( 70) and a filter 80.

In FIG. 1, a signal input to terminal (A) of the LPN FM IF circuit 100 is mixed in the mixer 20 together with an oscillation signal generated by the local oscillator 10 and connected to the mixer 20 ( 80).

The filter 80 filters the applied mixed signal and then supplies it to the limiter amplifier 30.

The signal passing through the limiter amplifier 30 is separated into a carrier frequency signal and a frequency signal in the demodulator 40, and the low frequency signal is applied to the AF amplifier 50 connected to the demodulator 40 to be a low frequency amplified signal.

The amplified signal is output from the (B) terminal of the LPN FM IF circuit 100 and input to the terminal C of the LPN FM IF circuit 100 via the capacitor C1 and the resistor R1 connected in series.

The capacitor C1 and the resistor R1 are adjusted to pass a frequency of several tens of KHz.

An internal filter amplifier 60, an external resistor R2, and a capacitor C2 are connected between the (C) and (D) terminals of the LPN FM IF circuit 100.

Here, the resistor R2 and the capacitor C2 are feed back means, whereby the gain and frequency characteristics are adjusted to suppress high frequency amplification.

As a result, only a few tens of KHz of noise in the low frequency frequency signal is converted into a direct current component by a double voltage means consisting of capacitors C3 and C4 and diodes D1 and D2.

The DC-converted noise is adjusted to a potential level by the resistors R3 and R4 and applied to the internal squelch circuit 70 through the (E) terminal of the LPN FM IF circuit 100.

Since one terminal of the squelch circuit 70 is fixed internally at 1.5 V, the sensitivity of carrier detection is adjusted by adjusting the potential level input to the terminal E. FIG.

However, in the conventional apparatus having the above-described configuration, the characteristics of the filter may not be excellent and may be disturbed by a strong low frequency signal, and the carrier detection level may be changed due to noise caused by adjacent channels, thereby preventing accurate detection. .

Therefore, the present invention has been devised to solve the above-mentioned problems of the prior art, and the dual filtering through the low pass filter and the narrow band filter minimizes the detection error caused by the interference of the low frequency strong signal and the high frequency signal and the adjacent channel signal. It is an object of the present invention to provide a carrier detection device capable of accurately detecting a carrier signal.

Means for achieving the object of the present invention is a low pass filter for low-passing the signal output from the low-frequency amplifier of the LPN FM IF circuit, and the signal passing through the low pass filter so as to block adjacent channels and ambient noise, etc. The band-pass filter and the comparison means for rectifying the signal passing through the narrow-band filter and comparing the reference voltage to output a carrier wave will be described in detail with reference to the accompanying drawings.

2 is a configuration diagram of a carrier detection device of the present invention and is composed of an LPN FM IF circuit 100 and a comparator 200 as shown therein.

The comparator 200 has a filtering function and a comparison function, and includes a narrow band filter 210 and a comparison means 230.

In FIG. 2, the same reference numerals are given to the same components as those in FIG. 1, and accordingly, description of the operation of the LPN FM IF circuit 100 will be omitted.

The low frequency amplified signal output from the terminal (B) of the LPN FM IF circuit 100 is applied to the comparator 200 through the parallel resistor R1 and the capacitor C1 which are the low pass filter 300.

The first-filtered signal at parallel resistor R1 and capacitor C1 is second-filtered again at narrowband filter 210 comprising resistors R2 (R3) (R4) and capacitors (C2) (C3). do.

This narrowband filter 210 is connected between the (C) and (D) terminals of the LPN FM IF circuit 100.

Here, the carrier detection can be narrowband because it detects the high frequency noise signal from the mixed signal of the low frequency signal and the high frequency frequency noise signal, and discriminates the active channel and the unused channel and the coverage area according to the magnitude of this level. It is good to design so that.

The detection noise signal passing through the narrowband filter 210 is converted into a DC component by the diode D1 resistor R5 and the capacitor C4 and applied to the inverting terminal (-) of the comparator 90.

Comparator 90, resistors R6, R7, R8, R9 and capacitor C5 form comparator 230.

In the comparison means 230, the resistors R6, R7, R8, R9 and capacitor C5 make a reference voltage of the comparator 90 and supply the reference voltage to the non-inverting terminal (+).

Therefore, if the DC component noise signal applied to the inverting terminal (-) has a larger potential than the reference voltage supplied to the non-inverting terminal (+) of the comparator 90, the carrier wave (CD) is detected to confirm that the channel is already in use. There is a number.

Referring to FIG. 3, (a) is a frequency characteristic diagram of a conventional wide band filter, (b) is a frequency characteristic diagram of a low pass filter 300, and (c) is a narrow band filter 210. Is the frequency characteristic diagram of (d) is the frequency characteristic diagram of the result of filtering low and narrow band.

In the conventional case, as shown in (a) of FIG. 3, a wideband filter passes through a wide frequency range, so that signals due to many cautions and adjacent channels are passed to generate noise. As shown in FIG. 2, since the passband is narrow and the adjacent channel and the ambient noise are blocked, only the carrier is detected more accurately.

As described in detail above, the present invention is not connected to the squelch circuit, but the first low pass filtering through the direct low pass filter and the second narrow band filtering through the narrow band filter to prevent the interference of strong low frequency signals and the adjacent channel and ambient noise. There is an effect that can detect a very stable carrier that blocked the back.

Claims (2)

A low pass filter 300 which is not connected to the terminals E and F of the squelch circuit 70 and low-passes the signal output from the low frequency amplifier 50 of the low power narrow band frequency modulation intermediate frequency circuit 100; And a narrowband filter 210 for narrowband passing the signal passing through the low pass filter 300 to block adjacent channels and ambient noise, and rectifying the signal passing through the narrowband filter 210 to a reference voltage. And a comparing means (230) for comparing and outputting a carrier wave. The method of claim 1, wherein the comparison means 230 is a DC conversion means 231 for converting the signal passing through the narrow-band filter 210 into a half-wave rectification to a DC component, and obtained by the DC conversion means 231 And a reference voltage generating means (232) for generating a reference voltage to be input to the comparator (90).