Design Of Channel Selection Filter In Digital TV Tuner

The function that choosing wanted signal from numerous interferences of mobile TV Tuner is guaranteed by its excellent channel selection property. Focusing on issues such as linearity and noise optimization, multiple bandwidth, variable gain, cutoff frequency tuning and so on, this thesis presents a channel select filter used in TV Tuner with high linearity, variable gain and adjustable bandwidth characteristic.The main works of this thesis are as following:First, the design methodology for optimizing filter parameters is discussed in detail. A multivariable optimization problem is converted to a univariate optimization problem by using parameter normalization approach. This method not only simplifies the optimization process but also gets a more intuitionistic result. Linearity and noise performance of Active-RC cascade biquad is optimized basing on this method.Second, the design realizes adjustable bandwidth and gain and solves the problem of gain error and in band ripple caused by non-ideal effect. Multi-standard and multi-band application requires adjustable band width of the channel select filter. While the big dynamic range of input power requires the base band to have enough gain variation range for optimization the SNR (Signal Noise Ratio) of output signal. Band selection and gain adjustment are realized by switching resistors in resistor arrays and capacitors in capacitor arrays in this design. The revised match resistor array makes gain error effectively controlled in the whole gain range. Tuning segmented resistor according different gain to compensate Q (Quality) factor degradation decreases in band ripple under high gain. FFZC (Feed Forward Zero Compensation) OTA with high gain and high linearity is used in biquad to increase the linearity performance of filter while avoiding extra compensation capacitors use.Third, improve the frequency tuning circuit. The correction on frequency shift due to process variation is more efficient by using the improved frequency tuning circuit. DC offset problem in DCR (Direct Conversion Receiver) is prohibited by DC offset cancellation circuit. Experimental results yield an in band IIP3of over31dBm at0dB gain, a54dB gain range with6dB gain step and a continuous frequency tuning range from0.25MHz to4MHz. In band ripple is less than1.4dB at high gain mode, while gain error and frequency tuning error are no more than3.4%and5%respectively. The design which is fabricated in0.18-μm CMOS process consumes12.6mW power at1.8V supply and occupies1.28mm2.