rf applications engineering technical note pc8236t6 n three circuit configurations for gps application o introduction o circuit d escription o p erformance data
2 introduction necs upc 8236t6n is a silicon germanium carbon (sige:c) mm ic desi gned as low noise amplifier for gps applications. it features low s upply voltage, low n oise f igure and high gain. it also i nclu des an integrated output matching circuit, a robust bandgap regulator , and esd protection circuits. more detailed technical speci fications can be found in upg8236t6n s datasheet , available on cels website: www.cel.com . in the early days of gps applications , most gps receivers were stand - alone devices. in that case , the in - band rf performance specs are usually the critical parameters for a low noise amplifier front end design. the recent trend , however, is the integration of gps receivers into more and more wireless products, such as cel l phones and various short range wireless devices. in these ap plications, there are often strong out - of - band (oob) signal s in the proximity of gps receiver , which can severely degrade the gps rec eiving sensitivity. consequently the oob spec ification s of a fron t - end amplifier are equally important as in - band spec ifica tions for achieving an optimized gps system performance in many applications . generally there are two approaches in dealing with the oob signal interference: i. u se a filter to reduce the oob s ignal strength at the amplifier. ii. i ncrease the linearity, which is usually characterized by iip3 or p1db points, of the amplifier to make it less susceptible to the interference. t his application note describes three circuit configurations for a gps low noise amplifier using UPC8236T6N. each configuration is designed fo r a specific application require ment as follows : normal configuration: op timized for in - band performance. high - pass matching configuration: high rej ection to low frequency signals. high iip3 configuration: improved linearity .
3 circuits description the three circuit configurations and their component values are shown in the following. normal configuration high - pass configuration 1 6 4 5 3 2 b i a s v p s o u t p u t c 2 c 4 v c c i n p u t c 3 c 1 l 1 1 6 4 5 3 2 b i a s v p s o u t p u t c 2 c 4 v c c i n p u t l 1 c 1 c 5 c 3
4 high iip3 configuration component value list component configuration normal high - pass high iip3 c1, pf 1000 5 1000 c2, pf 1 1 1 c3, pf 1000 1000 1000 c4, pf 1000 1000 1000 c5, pf 10000 l1, nh 5.6 5.6 5.6 l2 , nh 0.6 1 6 4 5 3 2 b i a s v p s o u t p u t c 2 c 4 v c c i n p u t c 3 c 1 l 1 l 2
5 performance data the following table lists measured data on a set of circuit boards. test conditions: vcc=vps=2.7v, f=1575mhz parameters configuration normal high - pass high iip3 power gain, db 19.3 18.3 14.9 noise figure, db 0.9 1.0 1.0 input return loss, db 14.3 7.7 8.7 output return loss, db 20.3 22.2 12.6 isolation, db 40.9 40.8 34.9 input p1db point, dbm - 18.5 - 17.2 - 12.6 input ip3 point, dbm - 3.5 - 1.5 +3.2
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