Control circuit for integral high frequency head between digital cable television and digital terrestrial television

Abstract

The invention relates to a control circuit for an integral high frequency head between a digital cable television and a digital terrestrial television. The control circuit comprises a radio frequency switcher, which belongs to GaAS IC, wherein the radio frequency switcher acts as a radio frequency single-pole double-throw switch specially used for switching between an input signal of the digital cable television (DVB-C) and the input signal of the digital terrestrial television (DMB-TH); when S2 is a high level (5V), the signal of DVB-C is communicated and the signal of DMB-TH is cut off; when S3 is the high level (5V), the signal of DMB-TH is communicated and the signal of DVB-C is cut off; a 75 ohm impedance matching network consists of C3, L1, C4, R4, R5 and L2; and the signal is amplified by a broadband amplifying circuit consisting of Q1 by 15dB to resist the insertion loss of a forestage circuit. Therefore, convenient switching between the signals of the digital cable television (DVB-C) and the digital terrestrial television (DMB-TH) is realized.

Description

technical field [0001] The invention relates to an integrated tuner for digital cable television (DVB-C) and digital terrestrial television (DMB-TH), in particular to a control circuit of the tuner. Background technique [0002] In the prior art, there is no integrated tuner compatible with digital cable television (DVB-C) and digital terrestrial television (DMB-TH). Digital cable television (DVB-C) and digital terrestrial television (DMB-TH) use different DVB-C tuner and DMB-TH tuner to solve. This results in that the same receiver can only be used for DVB-C or DMB-TH, but cannot simultaneously receive digital cable TV (DVB-C) and digital terrestrial TV (DMB-TH) programs. [0003] There are three main technical issues: [0004] First. How to conveniently switch between digital cable television (DVB-C) signals and digital terrestrial television (DMB-TH) signals; [0005] Second. Since the signal amplitude of digital cable television (DVB-C) varies little and the signal am...

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Problems solved by technology

[0005] Second. Since the signal amplitude of digital cable television (DVB-C) varies little and the signal amplitude of digital terrestrial television (DMB-TH) varies greatly, the automatic gain control (AGC) characteristic of DVB-C is different from that of DMB-TH. The control (AGC) features are different and difficult to be compatible;

[0006] Third. Since the digital cable TV (DVB-C) 64QAM signal symbol rate is 6.98Mbaud, the code rate reaches 41.34, so the phase noise performance requirements of the tuner are higher, and the signal gain requirements are relatively low; while digital terrestrial TV ( DMB-TH), which requires high signal gain, which makes it difficult to design the signal gain and phase noise of the tuner

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