Research And Design For Complex Filter In The Application Of GNSS Receiver

There are several challenges in the design of complex filter:（1）A complex filter,which is able to dispose multi-bands and multi-frequencies,is needed as the gradual expansion of GNSS signal band;（2）In addition,for such a complex filter,it's also extremely significant to design a frequency tuning circuit,which is suitable for all the modes;（3）In the space,this filter tend to operate in extreme situation with high or low temperature.We have to prevent the Quality-factor from changing with the temperature.To the challenges mentioned above,this dissertation studies complex filter and proposes one innovative key technology as well as achieves our expected goals.Firstly,in order to suit the application of GNSS receiver,this complex filter chip is able to receive all the GNSS signals including the GPS,BeiDou,GLONASS and Galileo.It has two centre frequency（4MHz&16MHz）and four bandwidths（2MHz,4MHz,10MHz&20MHz）.What's more,this dissertation introduces the design of frequency tuning circuit,which is based on Delay-locked loop（DLL）technology as well.On the basis of that,it implements a frequency tuning circuit,which is suitable for all the modes through the digital control circuit to the RC array.Secondly,this dissertation also innovatively introduces the combined bias circuit into the bias circuit.Through combining constant-gm with band-gap bias circuit,it makes the temperature coefficient of the complex filter's Q tunable so that by choosing appropriate proportion the Q of the complex filter is able to be stable with the temperature.Finally,on the basis of all the innovative technologies mentioned above,a complex filter chip satisfying all the GNSS signal bands is designed and fabricated in TSMC 0.18μm CMOS process.This chip uses the 5^th-order Chebeyshev architecture and occupies 0.4mm² area.It draws only 9¹4 mA current from 1.8 V supply for all the cases.The measured results indicate that during the range from-25℃to 100℃,gain variation of the complex filter is less than 0.4dB at the 3dB frequency.Meanwhile,for all the modes,it also has tunable gain from 0 dB to 42 dB with step of 6 dB,more than 42dB image rejection,and more than 25 dB rejection.