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Company Confidential 1 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Failure Analysis and Solution of PCS RC2 and EVDO Single Tone Desense Failures Feb 13, 2008
Company Confidential 2 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Root causes for RC2 STD failures and EVDO STD RC2 for PCS band seems to be the worst case for STD test b/c call box asks for more device output power for the radio link than RC3,RC4,RC5. Greater output power increases TX level in RX chain which causes worst STD performance. (phenomena is called Cross Modulation) Secondly, because of duplex filter performance, the middle channels near CH675 has less TX power rejection (from TX to RX ports) than top or bottom channels. Filter rejection directly affects STD performance. Finally, there is hole in shield can where duplex filter is located, that is designed to radiate TX power away from RX circuits. When battery is placed over the hole, TX signal couples onto metallic battery and then travels back to RX circuit which degrades STD performance. Since dummy battery is plastic, RF radiates through the material instead of coupling which actually helps to improve STD tests.
Company Confidential 3 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Duplex Filter Isolation performance from TX to RX ports Middle channel rejection of TX signal is worst than top or bottom. This is why we see STD performance at middle channel worst than at bottom or top channels. (TX freq is 1850- 1910MHz) Unfortunately, this duplex filter from Avago is the best filter on the market in terms of overall performance.
Company Confidential 4 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Nokia 6205 Device shield can, and battery coupling effect. When battery is used in device, RF power from transmitter is not allowed to radiate out of phone. Purpose of this hole originally was to allow TX power to radiate a bit so that it would not couple onto shield can and travel to receiver circuit and jam the receiver during STD case. But in effect, if the battery is inserted, it acts as coupling mechanism that is similar to shield can. Because Nokia with dummy battery, the STD failure could not be seen during testing. TX RX
Company Confidential 5 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials STD Solution Solution is to place electromagnetic absorber material onto the PCS duplex filter. This small absorber (.5mm thick) material on top of the duplex filter will allow the radiated TX power to be dissipated into the patch instead of coupling onto battery and then back to receiver circuits. Size of absorber is only 3.8 X 3.8 mm^2.
Company Confidential 6 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Material Characteristics - NEC Flex Suppressor material.Type K4E 500MHz-5GHz range 10dB coupling attenuation at 1GHz Operating temp of -25 to 85 deg C RoHS Compliant, Lead free Adhesive backing Data sheet attached
Company Confidential 7 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Production Feasibility of Flex Absorber Absorber can be pre cut to size for easy and simple installation in production after SMD process. Adhesive backing can adhere directly to duplex filter. One of the labels will then be placed over the hole/flex material to prevent consumer tampering.
Company Confidential 8 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials PCS 1X: STD(RC2), Sensitivity, Power, IMD results from testing with battery, 3 Devices Measured. Improvement of minimum 2dB after adding absorber on 3 devices.
Company Confidential 9 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials PCS EVDO: STD, Sensitivity, Power, IMD results from testing with battery, 3 Devices Measured. Improvement of minimum 1.5dB after adding absorber on 3 devices. Margin is increased
Company Confidential 10 © 2005 Nokia V1-Filename.ppt / yyyy-mm-dd / Initials Conclusion and Recommendation Battery inserted to device affects the STD performance b/c of filter rejection, more difficult RC2 power requirement, and coupling of TX signal to RX circuits by way of real battery. Solution is to use absorber material to mitigate TX radiation to RX chain specifically in STD test case. Absorber solution can be easily manufactured in production. Tests results in 1X show no effect to Sensitivity, Max Power, IMD performance, but improves STD. EVDO data can be shown later but preliminary results show no degradation of DO parametric, but actually shows improvement of STD at PCS Ch750.
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