KR930006667B1 - Wide band receiver using up-conversion and direct synchronization method - Google Patents

Abstract

The broadband receiving circuit for a television or a video tape recorder converts the received HF signal into the IF signal by up- conversion and demodulates the IF signal by the direct synchronous detection. The circuit comprises an automatic gain control section (100), a control section (200) for producing the selection control signal, first and second band selection section (300,400) for extracting VHF and UHF signals from the output of the automatic gain control section, a local oscillation section (500), an IF conversion section (600) for up-converting by mixing the local oscillation frequency with one from the outputs of two band selection sections, and a sync. detection section (700) for demodulating the video and audio baseband signals.

Description

Wideband Receiver Circuit Using Up-conversion and Direct Synchronization

1 is a block diagram of a conventional television signal receiving circuit.

2 is a block diagram of a broadband receiving circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

12: high frequency attenuator 14: AGC detector

16; Microcomputer 18: PLL circuit

20,22,48,72: 1st, 2nd, 3rd, 4th band pass filter

24, 40, 44: 1st, 2nd, 3rd pin diode switch

26,32,38,42,54,64: Amplifier

28: high pass filter 30: varactor filter

34,36: first and second oscillator 46: mixer

50: VCO 52,62: first and second synchronous detector

56,66: first and second low pass filter 58: baseband amplifier

60: 90 "or higher 68: Phase difference detector

70: loop filter 74: audio signal demodulator

100: gain control unit 200: control unit

300,400: first and second band selector 500: local oscillator

600: intermediate frequency conversion unit 700: synchronous detection unit

AT: Antenna

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wideband reception circuit using up-conversion and direct synchronization, and more particularly to channel selection in a wideband high frequency signal received in a system for receiving and processing wireless high frequency television signals. The present invention relates to a wideband reception circuit that modulates a signal in a frequency band according to the signal, up-converts to an intermediate frequency signal over a received high frequency signal band, and then directly synchronously detects and demodulates the signal into a baseband signal.

In systems that receive and process wireless high-frequency television signals, such as television and video tape recorders (VTRs), high-frequency tuners are typically single-down conversion heterodyne intermediate frequencies. (intermediate frequency) conversion method is adopted.

1 is a block diagram of a conventional television signal receiving circuit employing an intermediate frequency conversion method, and an input tuning circuit 1 for performing band selection by tuning a high frequency signal received through an antenna AT by predetermined control. And a high frequency amplifier (2) for automatically gain control of the high frequency signal of the selected band by an AGC (Automatic Gain Control) signal, and an inter-step tuning circuit for tuning a channel by tuning the amplified high frequency signal by a predetermined control (3). ), A local oscillator 4 for oscillating a local oscillation signal by a predetermined control, and a local oscillation signal of a local oscillator 4 of a high frequency signal of the selected channel, and converting it into an intermediate frequency signal ( a mixer (5), a phase locked loop (PLL) circuit 6 for controlling the input tuning circuit 1, the inter-stage tuning circuit 3, and the local oscillator 4, and the converted intermediate frequency signal. An intermediate frequency tuning circuit 7 for tuning An intermediate frequency amplifier 8 for amplifying an intermediate frequency signal, a demodulator 9 for demodulating a baseband signal from the amplified intermediate frequency signal, AGC detection of the baseband signal, and an AGC signal detected from the detected high frequency amplifier ( It consists of an AGC detector 10 provided in 2).

Referring to FIG. 1, the operation of the conventional receiving circuit will be described. First, the circuit of FIG. 1 tracks together with the local oscillator 4 using a tunable filter for the input tuning circuit 1 and the inter-stage tuning circuit 3. The high frequency signal tuned by the variable tuning filter is mixed with the local oscillation signal in the mixer 5 to convert to the intermediate frequency signal, and then amplified by the intermediate frequency as the intermediate frequency amplifier 8 through the intermediate frequency tuning circuit 7 and then demodulated. In (9), the baseband signal is demodulated.

The conventional method receives a wireless high-frequency television signal, tunes a broadcast frequency of a desired channel, and converts it into a single frequency conversion into a 45 MHz intermediate frequency signal through one frequency conversion. Therefore, the rejection problem of these signals has a great influence on the tuner performance according to the influence of the intermediate frequency signal component and the image component on the input terminal. That is, the frequency of the intermediate frequency signal of the mixer 5 is referred to as f _IF , the frequency of the local oscillation signal of the local oscillator 4 is referred to as f _LO , and the frequency of the input high frequency signal input through the antenna AT is f. _{If it is C} , the relationship as following Formula (1) is established.

f _IF = f _LO -f _C. … … … … … … … … … … … … … … … … … … … … (One)

If the frequency of the image component generated here is f _IM, f _IM is expressed as in Equation 2 below.

f _IM = f _C ± 2f _IF ... … … … … … … … … … … … … … … … … … … … … (2)

Since the frequency component of f _{IM which} is an image component as shown in Equation (2) is included in the television signal band, when it acts as an interference component at the input terminal, it has a problem that it acts as a disturbance signal to the channel tuned signal and adversely affects the TV quality. .

In addition, when the extracted intermediate frequency signal acts on the input terminal again, it acts as a disturbing wave, so that the rejection at the input terminal of the intermediate frequency signal component becomes bad.

Also, in the conventional circuit as described above, unlike the mechanical tuner of the past, the electronic tuner is configured by using a variable-capacitance diode as a tuner, so that there is no contact point and the function of remote control can be improved. However, since the individual devices are used to fabricate, it is difficult to form an integrated circuit (IC), and there are many difficulties in forming and manufacturing characteristics in the manufacturing process.

In addition, since a high frequency signal is converted into an intermediate frequency signal, a demodulation circuit needs to be added.

Accordingly, an object of the present invention is to provide a system for receiving a wireless high-frequency television signal, wherein the signal of a frequency band tuned according to channel selection is upconverted to a local oscillation frequency in which a channel frequency is added to a frequency higher than or equal to the reception high-frequency signal band, and then directly synchronized. By detecting and demodulating the baseband signal, it is possible to improve the image and intermediate frequency signal rejection characteristics, and to provide a receiving circuit that enables ICs of the tuner.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of a broadband reception circuit according to an embodiment of the present invention, and a gain adjusting unit 100 for automatically adjusting gain of a high frequency signal received through an antenna AT according to a demodulated baseband signal and tuning to a precursor channel. Band pass filtering of the control unit 200 for generating a control voltage signal and a selection control signal for selecting a signal of a band corresponding to channel selection, and the gain-adjusted signal of the gain control unit 100. A first band selector 300 which extracts first and second VHF band signals and selectively outputs one of the extracted first and second VHF band signals by a selection control signal of the controller 200; A second band selector configured to high pass filter the gain-controlled signal of the gain adjuster 100 to extract the UHF band signal, and then tune to the channel selected by the control voltage signal of the controller 200 ( 400 and before control of the control unit 200. The oscillation frequency is controlled by the signal, and one of the VHF and UHF local oscillation frequency signals oscillated by oscillating the VHF and UHF local oscillation frequency signals having a frequency obtained by adding a channel frequency according to the channel selection to a frequency higher than or equal to a received high frequency signal band. The local oscillator 500 which selects and outputs the selected control signal by the selection control signal of 200 and the output signals of the first and second band selection units 300 and 400 are selected and input by the selection control signal of the controller 200. An intermediate frequency converter 600 which up-converts the input signal by mixing with the local oscillation frequency signal of the local oscillator 500 to convert to an intermediate frequency signal, and then band-pass filters and removes adjacent channels and image components; Input the up-converted intermediate frequency signal of the intermediate frequency converter 600, and perform synchronous detection as a voltage controlled oscillation synchronization signal to synchronize with the input intermediate frequency signal. It consists of a synchronization detector 700 for demodulating the audio baseband signal.

In the configuration of FIG. 2, the gain adjusting unit 100 automatically adjusts the high frequency signal received through the antenna AT by the AGC signal to attenuate it when a strong signal is input, and the synchronous detector ( AGC detector 14 demodulating the video baseband signal demodulated in 700 and providing the AGC signal to the high frequency attenuator 12.

The controller 200 controls the tuning of the micro-computer 16 which generates channel tuning data according to the channel tuning key input and the second band selection unit 400 by the channel tuning data. A signal for controlling the frequency of the local oscillation frequency signal of 500 is generated as the control voltage signal, and the band signal selection of the first band selection unit 300, the local oscillation unit 500, and the intermediate frequency conversion unit 600 is controlled. And a PLL circuit 18 for generating a signal to be generated as the selection control signal.

The first band selector 300 includes a first band pass filter 20 for extracting a first VHF band signal by band pass filtering the gain-adjusted high frequency signal of the high frequency attenuator 12 and the gain of the high frequency attenuator 12. A second band pass filter 22 which extracts the second VHF band signal by bandpass filtering the adjusted high frequency signal, and one of the first and second VHF band signals to the voltage level of the selection control signal of the PLL circuit 18; And a first pin diode switch 24 for selective output, and an amplifier 26 for amplifying the selected VHF band signal.

The second band selector 400 high pass filter 28 extracts the UHF band signal by high pass filtering the gain-controlled high frequency signal of the high frequency attenuator 12, and the PLL circuit 18 from the extracted UHF band signal. And a varactor filter 30 that tunes to the channel selected according to the voltage level of the control voltage signal, and an amplifier 32 that amplifies the tuned UHF band signal.

The local oscillator 500 oscillates the oscillation frequency by the control voltage signal of the PLL circuit 18, and oscillates the UHF and VHF local oscillation frequency signals each having a frequency obtained by adding a channel frequency according to channel selection to a frequency above a received high frequency signal band. A PLL of one of the first and second oscillators 34 and 36, an amplifier 38 for amplifying the oscillated UHF local oscillation frequency signal of the first oscillator 34, and the UHF and VHF local oscillation frequency signal. And a second pin diode switch 40 for selectively outputting according to the voltage level of the selection control signal of the circuit 18, and an amplifier 42 for amplifying the selected local oscillation frequency signal.

The intermediate frequency converter 600 includes a third pin diode switch 44 for selectively outputting the output signals of the first and second band selectors 300 and 400 according to the voltage level of the selection control signal of the PLL circuit 18; A mixer 46 which converts the output signal of the third pin diode switch 44 with the local oscillation frequency signal of the local oscillator 500 to up-convert and converts it into an intermediate frequency signal, and a band pass of the converted intermediate frequency signal And a third band pass filter 48 for filtering to remove adjacent channels and image components.

The synchronous detection circuit 700 includes a voltage controlled oscillator (VCO) 50 for voltage-controlled oscillation of a synchronous signal synchronized with an intermediate frequency signal output from the third band pass filter 48 by a control voltage, and the third band. A first synchronous detector 52 for synchronously detecting the intermediate frequency signal output from the pass filter 48 as the synchronous signal oscillated by the VCO 50, an amplifier 54 for amplifying the synchronously detected signal, and the amplification A first low pass filter 56 for extracting the video baseband signal by low pass filtering the received signal, a baseband amplifier 58 for amplifying the video baseband signal, and the VCC 50. The 90 ° phase shifter 60 shifts the phase of the synchronization signal oscillated at 90 °, the intermediate frequency signal band-pass filtered by the third band filter 48, and the 90 ° phase shifter 60. A second synchronous detector 62 for mixing signals and the second synchronous detector 62 An amplifier 64 for amplifying an output signal of the second signal; and a second low pass filter 66 for low-pass filtering the output signal of the amplifier 64 to be equal to a band of the output signal of the first low pass filter 56. And a phase difference detector 68 for detecting a phase difference by comparing the phases of the output signals of the first and second low pass filters 56 and 66 and outputting the detected phase difference signal, and performing low pass filtering on the phase difference signal. A fourth filter which extracts an audio band signal by bandpass filtering the loop filter 70 provided to the VCO 50 as a control voltage of the low frequency component after removing the high frequency component and the output signal of the amplifier 64; And a band pass filter 72 and an audio signal demodulator 74 for demodulating the audio baseband signal from the output signal of the fourth pass band filter 72.

In the configuration of FIG. 2, the first VHF band signal output from the first band pass filter 20 is a low band signal among the VHF band signals, and the second VHF band signal output from the second band pass filter 22 is The VHF band signal is a high band signal. The PLL circuit 18 is a circuit for generating a control voltage signal and a selection control signal having a different voltage level depending on an input data value. The PLL circuit 18 is a PLL frequency synthesizer IC manufactured and sold by TOSHIBA, Japan. TD6359p can be used.

Hereinafter, an operation example of FIG. 2 according to the present invention will be described in detail.

Now when the power is "on" and the wireless high-frequency television signal is received through the antenna AT of FIG. 2, the high frequency signal received through the antenna AT is attenuated by the high frequency attenuator 12 which attenuates when a strong signal is received. do. The gain-adjusted signal is band-pass filtered by the first and second band path filters 20 and 22 to be separated into a first VHF band signal as a low band signal and a second VHF band signal as a high band signal, and then a first pin diode switch. It is input to (24). In this case, the first and second VHF band signals are, for example, band signals of two channels-six channels and seven channels-13 channels, respectively. The gain-adjusted signal is also input to the high pass filter 28 and high pass filtered so that the UHF band signal is extracted and input to the varactor filter 30.

In the above state, when channel tuning data is generated in the microcomputer 16 by a key input according to a channel tuning key operation of the user, the PLL circuit 18 generates a control voltage signal according to the channel tuning data to generate the varactor filter 30. ) And the first and second oscillators 34 and 36, and generate a selection control signal to the first, second and third pin diode switches 24, 40 and 44. Accordingly, the first pin diode switch 24 selects and outputs one of the first and second VHF band signals, and the varactor filter 30 outputs the tuned UHF band signals by tuning to a desired channel. The VHF band signal selected by the first pin diode switch 24 and the UHF band signal tuned by the varactor filter 30 are respectively amplified by the amplifiers 26 and 32 and then input to the third pin diode switch 44 and selected. The output is selected by the control signal.

On the other hand, in the first and second oscillators 34 and 36, UHF and VHF local oscillation frequency signals each having a frequency higher than or equal to a received high frequency band are oscillated. The frequency of the oscillated UHF and VHF local oscillation frequency signals is controlled by a control voltage signal. do. For example, when 63 channels are tuned to the frequency of the local oscillation frequency signal, the frequency of the UHF local oscillation frequency signal of the first oscillator 34 becomes 2㎓63 plus the frequency corresponding to the channel. The UHF local oscillation frequency signal is input to the second pin diode switch 40 via the amplifier 38 and the VHF local oscillation frequency signal is input to the second pin diode switch 40 as it is. Then, the second pin diode switch 40 selects and outputs one of the UHF and VHF local oscillation frequency signals by the control voltage signal, and the output local oscillation frequency signal is amplified by the amplifier 42 and input to the mixer 46. .

The mixer 46 mixes the VHF band signal or UHF band signal selected by the third pin diode switch 44 and the VHF local oscillation frequency signal or UHF local oscillation frequency signal output from the amplifier 42, and then the intermediate frequency signal. Output converted to. At this time, if the voltage level of the selection control signal is output from the PLL circuit 18 so that the UHF band signal is selectively output from the third pin diode switch 44, the UHF local oscillation is generated from the second pin diode switch 40 by this voltage level. The frequency signal is selected and output. That is, the UHF local oscillation frequency signal is mixed with the UHF band signal, and the VHF local oscillation frequency signal is mixed with the VHF band signal.

Since the frequency of the intermediate frequency signal converted as described above is several GHz, the image rejection is much improved because the frequency is different from the frequency of the high frequency television signal input through the antenna AT, which is several times MHz. The effect of the signal input stage on the image quality is much reduced.

The intermediate frequency signal is simultaneously applied to the first and second synchronous detectors 52 and 62 of the synchronous detector 700 through a third band pass filter 48 that removes the inver channel and the image component. The first synchronous detector 52 performs synchronous detection by mixing the input intermediate frequency signal with the synchronous signal oscillated by the VCO 50. Accordingly, the baseband signal is demodulated, and the demodulated baseband signal is extracted by the first low pass filter 56 through the amplifier 54, and the extracted video baseband signal is a bassband amplifier 58. Amplified output. At this time, as the AGC detector 14 detects the baseband signal, the AGC signal is provided to the high frequency attenuator 12 to adjust the gain of the received high frequency signal.

In addition, the synchronous signal output from the VCO 50 is shifted by 90 ° by the 90 ° phase shifter 60, mixed with the input intermediate frequency signal by the second synchronous detector 62, and then the amplifier 64 and the second low pass. The filter 66 is input to the phase detector 68 as a signal having the same band as the output signal of the first low pass filter 56. The phase difference detector 68 detects a phase difference between the output signals of the first and second low pass filters 56 and 66, generates a phase difference signal according to the detection, and outputs the phase difference signal to the loop filter 70. In the loop filter 70, since the phase difference signal is low-pass filtered, only a low frequency component is fed back to the VCO 50 as a control voltage.

The phase difference is eliminated by precisely synchronizing so that the synchronization signal oscillated in the VCO 50 is controlled and locked by the phase difference signal indicating the phase difference, and the output signal of the baseband is exactly synchronized with the input signal.

The synchronous detection process in the synchronous detection unit 700 will be described with reference to the following equation. First, if the signal input to the first synchronous detector 52 is an AM (Amplitude Modulation) signal, this signal V (t) is expressed by Equation 3 below.

V (t) = [Vc + kVm (t)] x (cosω _C t + ø ₁ ). … … … … … … … … … … … (3)

The output synchronizing signal Vo (t) of the VCO 50 is expressed by the following equation (4).

Vo (t) = cos (ω _C t + ø ₂ ). … … … … … … … … … … … … … … … … … … (4)

Therefore, the output signal V ₁ (t) of the first synchronous detector 52 on the I-phase side becomes as follows.

V ₁ (t) = V (t) × Vo (t)

= [Vc + kVm (t)] × cos (ω _C t + ø ₁ ) × cos (ω _C t + ø ₂ )

= 1/2 [Vc + kVm (t)] × {cos (2ω _C t + ø ₁ + ø ₂ ) + cos (ø ₁ = ø ₂ )} (5)

When a signal such as Equation (5) passes through the first low pass filter 56, the 2ω _C component is removed in Equation (5). Therefore, the output signal V ₁ '(t) of the first low pass filter 56 is expressed by the following expression (6).

V ₁ '(t) = 1/2 [Vc + kVm (t)] x cos (Ψ _1- ø ₂ ). … … … … … … … … … … (6)

Here, if the input signal of the first synchronous detector 52 and the output signal of the VCO 50 are correctly synchronized, φ ₁ = φ ₂ in Equation 6 above, and thus the final output is 1/2 [Vc + kVm (t) ] Only the baseband component remains, and the desired signal is output.

On the other hand, if the synchronization signal oscillated and output from the VCO 50 and the phase shifted by 90 ° in the 90 ° phase 60 is Vo '(t), the synchronization signal Vo' (t) is expressed by Equation 7 below.

Vo (t) = sin (ω _C t + ø ₂ ). … … … … … … … … … … … … … … … … … … … … (7)

Therefore, the output V _Q (t) of the second synchronous detector 62 on the Q-phase side becomes as shown in Equation 8 below.

V _Q '(t) = 1/2 [Vc + kVm (t)] × {cos (2ω _C t + ø ₁ + ø ₂ ) + sin (ø ₁ -ø ₂ )}. … (8)

When the signal of the above expression (8) passes through the second low pass filter 66, the 2ω _C component is removed. Therefore, the output signal V _q '(t) of the second low pass filter 56 is expressed by the following expression (9).

V _q '(t) = 1/2 [Vc + kVm (t)] x sin (Φ _1- ø ₂ ). … … … … … … … … … … (9)

If the phase difference signal detected by the phase difference detector 68 for the synchronous locking of the VCO 50 is V _C (t), the phase difference signal V _C (t) is expressed by Equation 10 below.

V _C (t) = V ₁ '(t) × V _Q ' (t)

= 1/4 [Vc + kVm (t)] ² × cos (ø ₁ -ø ₂ ) × sin (ø ₁ -ø ₂ )

= 1/8 [Vc + kVm (t)] ² × sin2 (ø ₁ -ø ₂ )

= 1/8 [Vc + kVm (t)] x sin2θ (since θθ = ø _1- ø ₂ ). … … 10

The 90 ° phase shifter 60, the second synchronous detector 62, the amplifier 64, the second low pass filter 66, the phase detector 68, the loop through the loop formed of the filter 70, the VCO (50) ) Is controlled so that φ ₁ -φ ₂ = 0 so that the phase difference between the output signal V _O (t) of the VCO 50 and the input signal V (t) of the second synchronous detector 62 is eliminated.

Meanwhile, the signal passing through the second synchronous detector 62 is input to the audio signal demodulator 74 through the fourth band pass filter 72 which detects the audio component through the amplifier 64, thereby extracting the audio signal.

As described above, the present invention is a system for receiving a wireless high-frequency television signal, and after directly converting a signal of a frequency band tuned according to channel selection to a local oscillation frequency in which a channel frequency is added to a frequency higher than a reception high frequency signal band, and then directly As a circuit for demodulating the baseband signal by synchronous detection, the image and intermediate frequency signal rejection characteristics can be improved, and the IC of the tuner can be realized.

Claims (3)

In a wideband reception circuit using an up-conversion and direct synchronization scheme of a system for receiving wireless high-frequency television signals, a gain adjusting unit (100) for automatically controlling gain of a high frequency signal received through an antenna (AT) according to a demodulated baseband signal. And a control voltage signal for tuning the tuning channel and a selection control signal for selecting a signal of a band corresponding to the channel tuning, and a gain-controlled signal of the gain adjusting unit 100. A first band selector 300 which extracts the first and second 2VHF band signals by band pass filtering and selectively outputs one of the extracted first and second VHF band signals by a selection control signal of the controller 200; A second band selector 400 for high-pass filtering the gain-controlled signal of the gain adjuster 100 to extract a UHF band signal, and then tuning to a channel selected by the control voltage signal of the controller 200; Prize The oscillation frequency is controlled by the control voltage signal of the control unit 200, and the VHF and UHF localized by oscillating the VHF, UHF local oscillation frequency signal having a frequency in which the channel frequency according to the channel selection is added to a frequency above the received high frequency signal band. The local oscillator 500 selects and outputs one of the oscillation frequency signals by the selection control signal of the controller 200, and one of the output signals of the first and second band selectors 300 and 400 of the controller 200. The input signal selected by the selection control signal and mixed with the local oscillation frequency signal of the local oscillation unit 500 are up-converted and converted into an intermediate frequency signal, followed by band pass filtering to remove adjacent channels and image components. Synchronization of a voltage controlled oscillator to input the intermediate frequency converter 600 and the upconverted intermediate frequency signal of the intermediate frequency converter 600 and to synchronize with the input intermediate frequency signal. The synchronous detector as a video call and up-conversion and direct broadband reception circuit using a synchronous manner, characterized in that consists of a synchronization detector 700 for demodulating the audio baseband signal. The method of claim 1, wherein the control unit 200 controls the tuning of the second band selection unit 400 by the microcomputer 16 for generating channel tuning data according to the channel tuning key input and the channel tuning data. The first band selector 300, the local oscillator 500, and the local oscillation frequency converter 600 generate a signal for controlling the frequency of the local oscillation frequency signal of the local oscillator 500 as the control voltage signal. And a PLL circuit (18) for generating a signal for controlling the band signal selection as the selection control signal. The UHF of claim 2, wherein the local oscillator 500 has an oscillation frequency controlled by a control voltage signal of the PLL circuit 18 and has a frequency in which a channel frequency according to channel selection is added to a frequency above a received high frequency signal band. And first and second oscillators 34 and 36 for oscillating the VHF local oscillation frequency signals, an amplifier 38 for amplifying the output UHF local oscillation frequency signal of the first oscillator 34, and the UHF and VHF. A second pin diode switch 40 for selectively outputting one of the local oscillation frequency signals according to the voltage level of the selection control signal of the PLL circuit 18, and an amplifier 42 for amplifying the selected local oscillation frequency signal. A wideband reception circuit using up-conversion and direct synchronization.

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