Design Of Active Low-pass Filter In DVB-H Tuning Chip

Beginning from the invention of black and white television (TV), the development of TV hasgone through a long period of time. Driven by the technological innovation, TVs are capable ofproviding viewers with richer content, and become more and more popular. Nowadays, thedevelopment of television is entering a new stage: mobile digital TV (MDTV) which is acombination of TV and mobile phone. MDTV technologies will promote the development of thenext generation of wireless communications technology, and have broad market prospects.Among numerous standards of MDTV, digital video broadcasting-handheld terminal(DVB-H) has the most extensive market penetration rate and the most powerful industry researchand development team. The purpose of this thesis is to design a variable bandwidth activelow-pass filter which can be applied to DVB-H tuning chips.Firstly, the development status and the classification of filters are introduced. Then, theadvantages and disadvantages of OPAMP-RC, OPAMP-MOSFET-C, OPAMP-MOSFET-RC,Gm-C filters are analyzed. The Gm-C structure is employed in this thesis, due to its outstandingperformance. After the elaboration of the active device equivalent alternative method and signalflow chart method in cascaded Gm-C filter, ladder (LC) Gm-C filter, an eight-order ChebyshevGm-C active low-pass filter is designed using the active device equivalent alternative method.Due to the performance instability caused by process tolerances, the changes of ambienttemperatures, device aging, etc., an automatic frequency tuning circuit is needed to stabilize theperformance of the filter. After comparing the advantages and disadvantages of the automatictuning of the voltage-controlled oscillator (VCO), voltage-controlled filters, switched-capacitortechnology, a switched capacitor automatic tuning circuit is designed. As tuning chips are used indifferent frequency bands, the3dB bandwidth of the filter should be variable. Therefore, aftercomparing several commonly used methods of changing the filter bandwidth, a circuit forchanging the filter bandwidth is designed.The active low-pass filter designed in this work employs the TSMC90nm CMOS process.The simulated results show that the bandwidth of the proposed active low-pass filter is able toswitch among3MHz,3.5MHz, and4MHz. The linear input range is up to160mV, and the totalharmonic distortion is about0.6%. The supply voltage of the proposed filter is1.2V, and itspower consumption is between5-10mW. All performances satisfy the required systemperformance indexes.