KR20110051866A - Rf signal processing circuit - Google Patents

Abstract

PURPOSE: A circuit for processing an RF signal is provided to reduce noise due to the harmonics of an intermediate frequency component. CONSTITUTION: Filter units filter an operable frequency band among input RF signals. A signal selection unit creates an IF(Intermediate Frequency) signal through the RF signal of a selected frequency among the filtered RF signals. Saw filters(30,31) perform filtering and transferring of the IF signal. A demodulator demodulates the output signal of the saw filter.

Description

RF signal processing circuit {RF SIGNAL PROCESSING CIRCUIT}

The present invention relates to an RF signal processing circuit, and more particularly, to an RF signal processing circuit operating in an analog mode and a digital mode.

With the development of wireless communication technology, it is possible to transmit and receive audio and video signals far away. When transmitting audio signals and video signals, a communication frequency called an RF signal uses a signal of several hundred MHz to several Ghz. In the transmission equipment, the audio signal and the video signal are combined with the RF signal, and in the reception equipment, the RF signal and the audio signal and the video signal are separated. In this case, combining is called modulation and separating is called demodulation.

In general, an RF signal processing device amplifies an input RF signal, filters a signal of a desired frequency band, and then demodulates it. In this process, noise is inputted and amplified as much as possible, and RF signal amplification as necessary to improve the characteristics of the RF signal processing apparatus. There is automatic gain control function during internal operation of RF signal processing circuit. If the size of the input RF signal is too small, it is detected and amplified. If the input is too large, it is detected and reduced.

In general, instead of separating a signal having data from the input RF signal, the RF signal processing circuit converts the input RF signal into an intermediate frequency signal, and then demodulates the converted intermediate frequency signal. As the RF signal processing circuit processes an intermediate frequency signal in an internal process, a harmonic component of the intermediate frequency signal acts as a noise.

The present invention provides an RF signal processing circuit that can solve the noise phenomenon due to harmonics of the intermediate frequency signal.

The present invention provides a filter unit for filtering a range of an operable frequency band of an input RF signal; A signal selection unit generating an intermediate frequency signal by using an RF signal of a selected frequency among the RF signals filtered by the filter unit; A SAW filter provided to filter and transmit the intermediate frequency signal and capable of varying an operating frequency; And a demodulator for demodulating the signal output from the SAW filter, wherein the frequency of the intermediate frequency signal is selected so that the frequency of the harmonics is outside of the frequency band filtered by the filter unit. to provide.

In addition, the frequency of the selected frequency RF signal is 76.25MHz, the frequency of the intermediate frequency signal is characterized in that 37.5MHz.

According to the present invention, the RF signal processing circuit can reduce noise caused by harmonics of intermediate frequency components. Therefore, the operational reliability of the RF signal processing circuit is improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order to facilitate a person skilled in the art to easily carry out the technical idea of the present invention. do.

1 is a block diagram showing an RF signal processing circuit for explaining the present invention.

Referring to FIG. 1, the RF signal processing circuit includes input filter units 11, 12, 13, RF amplifiers 14, 15, 16, filter units 17, 18, 19, signal selector 20, The analog SAW filter 30, the digital SAW filter 31, and the analog demodulator 32 are included.

The input filter units 11, 12, and 13 transfer signals of a desired band among RF signals input through the antenna. The RF amplifiers 14, 15, and 16 amplify the signals transmitted from the input filter units 11, 12, and 13, respectively. The filter units 17, 18, and 19 filter the signals amplified by the RF amplifiers 14, 15, and 16, respectively. The reason why there are three input filter units, three RF amplifiers, and three filter units is to process RF signals in the VHF, UHFH, and UHFL bands, respectively.

In general, a television broadcast station can receive a radio wave by transmitting a radio wave of a very high frequency wave (VHF) and a very high frequency wave (UHF) to a viewer. In Korea, UHF television channels range from channel 13 (frequency 470-476 MHz) to channel 62 (frequency 764-770 MHz). Television broadcasts started using very high freqeuency (VHF) bands, or radio waves of 30 to 300 MHz (actually channel 1, ie from 90 to 96 MHz to channel 12, or 216 to 222 MHz). Due to the increase in the number of radio communication stations such as ships and ship stations, the radio waves cannot be handled by VHF alone.

In television broadcasting, a frequency band of 6 MHz, that is, an occupied bandwidth, is required, but in a radio communication that handles only an audio signal, a frequency bandwidth of 20 kHz is required. Therefore, the radio wave of the VHF band is used for radio communication other than the television, and the television has a high efficiency in radio wave assignment such that the radio wave of the UHF band can take a large number of channels. Therefore, television broadcasting is expected to move from VHF broadcasting to UHF broadcasting. As a transient state, the mixing of VHF broadcasting and UHF broadcasting is being performed. In order to receive UHF radio waves through the VHF receiver, UHF converter must be used for frequency conversion. However, an all-channel television product can receive both UHF and VHF broadcasting.

The signal selector 20 selects an RF signal of a predetermined frequency band among the input signals, generates and transmits the intermediate frequency signal IF. The signal selector 20 selects and transmits an RF signal of a predetermined frequency band, including a phase locked loop circuit 21, a mixing circuit 23, a VCO 22, and amplifiers 24 and 25. It is common to implement these circuits by including them in one chip. The power block 33 supplies stable power to the signal selector 20.

The analog SAW filter 30 filters and outputs the signal output from the signal selector 20, and the demodulator 32 demodulates the signal output from the analog SAW filter 30 to output the video signal V and audio. Output signals A and SIF. The digital SAW filter 31 filters the signal output from the signal selector 20 and transmits the filtered signal to the amplifier 25 provided in the signal selector 20. The amplifier 25 amplifies and outputs it, and a digital demodulator (not shown) demodulates it.

FIG. 2 is a frequency waveform diagram illustrating an operation of the RF signal processing circuit of FIG. 1.

Square X in FIG. 2 shows a frequency band through which an RF signal processing circuit is input and processed.

The RF signal processing circuit internally converts an externally input signal into an intermediate frequency signal IF and demodulates the converted signal. At this time, harmonics of intermediate frequencies adversely affect the signal processing operation. For example, in case of selecting 76.25Mhz in PAL method, 38.9Mhz is used as the intermediate frequency, and there is 77.8MHz signal which is 2 harmonics of IF signal (IF Frequency 38.9MHz X 2 = 77.8MHz). . Thus, when tuning to 76.25MHz, a beat component (77.8MHz-76.25Mhz = 1.55MHz) is produced. This bit component is a big problem because it appears as diagonal lines on the screen. In order to eliminate this, a trap circuit may be additionally provided in a line through which the intermediate frequency signal IF is transmitted.

However, the additional cost of the trap circuit is expensive, and the trap circuit may cause another problem. The present invention proposes an RF signal processing circuit which is not provided with a trap circuit and which can prevent noise caused by harmonics of an intermediate frequency.

3 is a block diagram showing an RF signal processing circuit according to a preferred embodiment of the present invention.

As shown in FIG. 3, the RF signal processing circuit according to the present embodiment includes an input filter unit 110, 120, 130, an RF amplifier 140, 150, 160, a filter unit 170, 180, 190, a signal selector 200, and a SAW filter 321. It includes a demodulating unit 320 provided.

The input filter unit 110, 120, 130 transmits a signal of a desired band among the RF signals input through the antenna. The RF amplifiers 140, 150, and 160 amplify the signals transmitted from the input filter units 110, 120, and 130, respectively. The filter units 170, 180, and 190 filter the signals amplified by the RF amplifiers 140, 150, and 160, respectively. The reason why there are three input filter units, three RF amplifiers, and three filter units is to process RF signals in the VHF, UHFH, and UHFL bands, respectively.

The signal selector 200 selects an RF signal of a predetermined frequency band among input signals, generates and transmits an intermediate frequency signal IF. The signal selector 200 selects and transmits an RF signal of a predetermined frequency band, including a phase locked loop 210, a mixing circuit 230, a VCO 220, and amplifiers 240 and 250. It is common to implement a circuit by including it in one chip.

The demodulator 320 filters a predetermined band by the SAW filter 321 provided therein, and demodulates the filtered signal and outputs the filtered signal. At this time, the SAW filter 321 provided inside the demodulator 320 filters the signal output from the signal selector 200 and transmits the signal to the amplifier 250 or outputs it to the outside (V, A, SIF). . In the RF signal processing circuit shown in FIG. 3, there is only one SAW filter 321 because the SAW filter of the DSP system can be changed in frequency. The demodulator 320 is implemented as one integrated circuit and is a demodulator using a built-in SAW filter capable of changing the frequency of a DSP method. Therefore, the frequency band that the SAW filter 321 filters depends on the mode in which the RF signal processing circuit operates.

As described above, when the frequency of the intermediate frequency signal IF is used as 38.9 MHz when the 76.25 MHz tuning is performed, a 1.55 MHz bit component exists.

However, in the RF signal processing circuit according to the present embodiment, when 37.5 MHz is used as the intermediate frequency signal IF when 76.25 MHz is tuned, the double harmonic of 37.5 MHz becomes 75 MHz to prevent the generation of bit components. As shown in Fig. 2, since 75 MHz is outside the range of the frequency band processed by the RF signal processing circuit, no bit component is generated.

As described above, the RF signal processing circuit according to the present embodiment includes a variable SAW filter and has a frequency at which harmonics of intermediate frequencies do not affect the frequency associated with the channel being processed, thereby acting as noise on the screen. The bit component can be removed.

Although the present invention has been described in detail with reference to exemplary embodiments above, those skilled in the art to which the present invention pertains can make various modifications to the above-described embodiments without departing from the scope of the present invention. Will understand. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims, as well as the appended claims.

1 is a block diagram showing an RF signal processing circuit for explaining the present invention.

2 is a frequency waveform diagram illustrating an operation of the RF signal processing circuit of FIG.

3 is a block diagram showing an RF signal processing circuit according to a preferred embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

110 to 130: input filter unit 140 to 160: RF amplifier

170 ~ 190: Tuning circuit 200: Signal selector

320: demodulator

Claims (2)

A filter unit for filtering a range of an operable frequency band among input RF signals; A signal selection unit generating an intermediate frequency signal by using an RF signal of a selected frequency among the RF signals filtered by the filter unit; A SAW filter provided to filter and transmit the intermediate frequency signal and capable of varying an operating frequency; And And a demodulator for demodulating the signal output from the SAW filter, wherein the frequency of the intermediate frequency signal is selected such that the frequency of the harmonics is outside of the frequency band filtered by the filter unit. The method of claim 1, The frequency of the selected frequency RF signal is 76.25 MHz, and the frequency of the intermediate frequency signal is 37.5 MHz.

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