Research And Design Of CDTA-based Current-mode Polyphase Filter

In the low-IF receiver,the image interference is a key problem,and the polyphase filter is widely utilized to suppress it.The polyphase filter,known as a complex filter,affects the performance of the low-IF receiver directly.So,the design of the polyphase filter is significant.In recent years,more polyphase filters which are based on various kinds of active components have been proposed,but there are some shortages in work frequency,circuit complexity and parameters adjustability.So,the design of polyphase filter which possesses high performance has a considerable significance.This paper mainly studies the realization theory of polyphase filter,the design theory of current differencing transconductance amplifier(CDTA)and its application in polyphase filter circuits.Based on theories of polyphase filter and ports charecteristics of CDTA,this paper proposes a novel first-order polyphase filter and a forth-order leapfrog polyphase filter for high work frequency,simple circuit structure and adjustable parameters.The main innovations and study about this dissertation are as follows:1.Firstly,this paper makes a summing up of the polyphase filter design based on different active components,and merit and demerit are concluded and analysed in terms of the used active components,then three design categories of high-order polyphase filter are classified as in terms of synthesis methods.In addition,the classical structure of polyphase filter is deduced and analysed carefully.2.Based on existing CDTA,a novel multi-ouput CDTA(MOCDTA)is proposed by adding transconductance output circuit.Its output stage utilizes super cascade configuration,which could increase the output impedance.Simulation results show that the output impedance is changed from 2.27 M? to 31.15 M?.Then,Based on the proposed MOCDTA,a novel first-order polyphase filter with high center frequency is proposed by using classical structure of polyphase filter.This circuit does not contain resistors and the number of component is lower.The centre frequency could be tuned from 38 MHz to 150 MHz.While the center frequency increasing,the image rejection ratio(IRR)and the centre frequency are increasing meanwhile the bandwidth keeps 20.1 MHz.3.A new signal flow diagram(SFD)of forth-order polyphase filter is proposed,and considering the ports characteristics of MOCDTA,a new circuit of forth-order polyphase filter is realized.In the new circuit,there are no resistors,minimum number of components,and each pair of the center frequency,bandwidth and IRR could be adjusted independently.Based on the above circuit,two high-order polyphase filters with different pass bands are proposed,which are 60MHz-IF high-bandwidth polyphase filter and 35MHz-IF high-bandwidth polyphase filter.In the first polyphase filter whose center frequency is 60 MHz,the pass band is from 46.1 MHz to 68.5MHz,the bandwidth is 22.4 MHz,IRR could be 59 dB,and the IIP3 could achieve 18.58 dBm in the pass band.In the second polyphase filter whose center frequency are 35 MHz,the pass band is from 22.3 MHz to 48.4 MHz,the bandwidth is 26.1 MHz,IRR could be 39 dB,and the IIP3 could achieve 19.02 dBm in the pass band.Furthermore,the characteristics of noise and temperature are simulated and analyzed,the simulation results indicate that the forth-order leapfrog polyphase filter possesses low output noise and stable temperature characteristic.Finally,the work in this paper is summarized and the research direction in the future has been put forward.