CN2329125Y - Tuner special for digital wired TV - Google Patents

Abstract

The utility model provides a tuner special for a digital wired TV, comprising a variable frequency tuning circuit, a filter circuit, an amplification circuit, and a demodulation circuit. The utility model has a connection relation that the output end of the variable frequency tuning circuit is connected with the input end of the filter circuit, the output end of the filter circuit is connected with the input end of the amplification circuit, and the output end of the amplification circuit is connected with the input end of the demodulation circuit. The utility model is a tuner special for digital wired TV, and has the advantages of compact circuit, small size, power supply interference resistance, and stable and reliable performance.

Description

The special-purpose tuner of digital cable TV

The utility model relates to a kind of tuner, particularly relates to the special-purpose tuner of a kind of digital cable TV.

Television reception is confidential to receive the TV signal of transmitting in space or the wired system, must be chosen in corresponding channel in 50MHz to the 750MHz frequency band through tuner, through low-converter radio frequency (RF) signal being become intermediate-freuqncy signal again sends into the lower part circuit and handles, its output is analog signal, and tuning and frequency conversion just is collectively referred to as traditional tuner.Technology from existing digital television receiver, all have one tuning, down-conversion QAM demodulation, MPEG II are separated the process of ginseng sign indicating number, and this plurality of processes is by independent devices and circuit are finished respectively separately at present, that is to say that the overall process that receives last digital bit stream output from analog signal realizes by the several separate device is common.

The purpose of this utility model is to provide a kind of and adds digital channel after second intermediate frequency output of original frequency conversion demodulator, the digital television signal demodulation that is modulated in the analog signal is come out, make it directly to export the special-purpose tuner of digital cable TV of 8 digital bit TV decoded datas.

The special-purpose tuner of the utility model digital cable TV is to realize like this, it comprises the frequency conversion tuning circuit, filter circuit, amplifying circuit and demodulator circuit, its annexation is, the input of the output termination filter circuit of frequency conversion tuning circuit, filter circuit output termination input amplifier, the input of the output termination demodulator circuit of amplification filtering circuit.The input of frequency conversion tuning circuit receives the TV signal of transmitting in the wired system, and the output of demodulator circuit output digital TV decoding data.Wherein, the frequency conversion tuning circuit is made of tuner; Filter circuit is made of inductance L 2, L3, L4, L5, capacitor C 5, C7, C19, C20, C21, C22; Amplifying circuit is made of amplifier U2 and peripheral circuit thereof; Demodulator circuit is made of demodulation chip U1 and peripheral circuit thereof.

The course of work of the special-purpose tuner of the utility model digital cable TV is, at first the radio frequency TV signal is input to the frequency conversion tuning circuit, be tuned at the frequency of some channels by it, this channel TV signal is received, by the secondary frequency conversion this frequency signal is become intermediate frequency (IF) TV signal, pass through low-pass filter circuit, after amplifying through amplifying circuit again, send into demodulator circuit, by analog-to-digital conversion, analog signal is become digital signal earlier, the digital television signal demodulation that will be modulated at then on second intermediate frequency (IF) signal is got off, pass through processing such as forward error correction again, output string number TV data.

The advantage of the special-purpose tuner of the utility model digital cable TV is integrated design; the circuit compactness; volume is little; to insert in the demodulator circuit in the tuner shielding box; not only not fragile, also prevented the power supply interference simultaneously, make it more reliable and more stable; integral structure is a totally enclosed type in addition, therefore is easier to protection.

Describe the utility model embodiment in detail below in conjunction with accompanying drawing.

Fig. 1: the utility model circuit block diagram

Fig. 2: the utility model circuit connection diagram

The special-purpose tuner of the utility model digital cable TV comprises the frequency conversion tuning circuit, filter circuit, amplifying circuit and demodulator circuit, its annexation is, the input of the output termination filter circuit of frequency conversion tuning circuit, filter circuit output termination input amplifier, the input of the output termination demodulator circuit of amplification filtering circuit.The input of frequency conversion tuning circuit receives the TV signal of transmitting in the wired system, and the output of demodulator circuit output digital TV data.Wherein, the frequency conversion tuning circuit is made of tuner U3 (ALPStuner); Filter circuit is by inductance L 2, L3, L4, L5, and capacitor C 5, C7, C19, C20, C21, C22 and resistance R10, R18 constitute; Amplifying circuit is by amplifier U2 (CLC446), and capacitor C 9, C10, C11, C12 and resistance R 13 constitute; Demodulator circuit is by demodulation chip U1 (L64768), resistance R 1, R2, R3, R4, R5, R6, R7, R9, R11, R12, R15, R16, R17, R19, R20 and capacitor C 1, C2, C3, C4, C6, C8, C13, C14, C15, C16, C17, C18, C, C, C, C, C15, C16, C17, C18, formation.Its annexation is, the input termination radiofrequency signal output of U3, its output pin 35 connects R18 one end, ground connection mouth pin 34,12,10,3 connects simulation ground, power supply input pin 13,6,4 connects+the 5V power supply, power supply input pin 5 connects the tuning power supply input pin 11 of 9V power supply and connects+the 24V power supply, another termination of resistance R 18 connects C19 and L2 one end respectively, L2 another termination L3 and C20 one end, L3 another termination L4 and C21 one end, another termination of L4 L5 one end, C19, C20, another termination simulation ground of C21, C22, another termination of L5 C5, C7 one end, C5, the C7 other end are through resistance R 10 ground connection.After above filtering, signal is sent into amplifying circuit; U2 positive input pin 3 connects the C5 and the C7 other end, the negative input pin 2 of U2 is connected by R6 with 6 of input pins, again through R13 ground connection, U2 positive supply input pin 7 connects+the 5V power supply, negative supply input pin 4 connects-the 5V power supply, and+5V power supply and negative 5V power supply be the parallel circuits ground connection by C9 and C10 and parallel circuits and C11 and C12 respectively.Signal is delivered to demodulation chip U1 analog input pin 34 through R8, C6 and C8 parallel circuits after above amplifying circuit amplifies; U1 and power supply input pin 3,13,21,26,28,38,44,49,53,62,68,78,86,96 and 81 connect the 3.3V power supply, parallel circuits through C1, C2 and C3 connects digitally simultaneously, the U1 test allows a mouthful pin 4 also to connect the 3.3V power supply, U1 earth terminal pin 2,7,14,22,29,39,63,69,74,79,87,98,93,45 and 52 connects digitally, U1 automatic gain control (AGC) delivery outlet pin 18 feeds back to the AGC input pin 33 of U3 through R19, is used for the gain of control of conversion tuner.Simultaneously a termination C25 one end and L6 one end of R20, another termination of L6 C24 anode and+the 5V power supply, another termination U1 of R20 ... pin 18, another termination of C24 negative terminal and C25 digitally.U1 analog power and thresholding power supply input pin 36 and 37 connect L1 one end and the while connects simulation ground through the parallel circuits of C17 and C18, another termination of L1 3.3V power supply, and connect digitally through C15 and C16 parallel circuits simultaneously, U1 simulation reference current input pin 35 connects simulation ground through R7.U1 reference voltage end pin 32 connects the 3.3V power supply through R3, and U1 negative reference voltage end pin 33, analog power and thresholding power ground end pin 30 and 31 connect simulation ground simultaneously.The output of U1 passage allows mouthful pin 82 and analog to digital conversion (ADC) power supply to disconnect pin 27 simultaneously digitally.The PLL numeral lower margin 98 of U1 connects digitally, and PLL simulation lower margin 100 connects simulation ground.U1 operator scheme Mode1 and Mode0 pin 5 and pin 95 connect+the 5V power supply through R2 and R1 respectively, are equivalent to put this two pin high potentials, and the auxiliary input bus pin 24 of U1 is connect simulation ground.The phase-locked loop low-pass filtering mouth pin 99 of U1 connects R15 and C13 one end, another termination of R15 C14 one end, another termination simulation ground of C13 and C14.(UPD0～UP07) pin 46～56 connects the microcomputer parallel port to U1 microprocessor control bus, (AD0～AD3) pin 56～60 connects the microcomputer address bus to address mouth, (EXT-OUT1, EXT-OUT2) pin 76 and 77 connects clock line (SCL) pin 6 and address wire (SDA) pin 8 of U3 respectively to auxiliary output bus.(CO0～CO7) pin 67～73 is exported 8 digital bit TV data by the channel data mouth at last.

Claims (2)

1, the special-purpose tuner of a kind of digital cable TV, comprise the frequency conversion tuning circuit, it is characterized in that also including filter circuit, amplifying circuit and demodulator circuit, its annexation is, the input of the output termination filter circuit of frequency conversion tuning circuit, filter circuit output termination input amplifier, the input of the output termination demodulator circuit of amplifying circuit.

2, the special-purpose tuner of digital cable TV as claimed in claim 1 is characterized in that the frequency conversion tuning circuit is made of tuner U3; Filter circuit is made of inductance L 2, L3, L4, L5, capacitor C 5, C7, C19, C20, C21, C22; Amplifying circuit is made of amplifier U2 and peripheral circuit thereof; Demodulator circuit is made of demodulation chip U1 and peripheral circuit thereof.

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