Polar Loop Transmitter T. Sowlati, D. Rozenblit, R. Pullela, M. Damgaard, E. McCarthy, D. Koh, D. Ripley, F. Balteanu, I. Gheorghe

2 6/19/2015 Content Introduction Architectures for EDGE Transmitter Polar Loop Transmitter Measurement results Conclusion

3 6/19/2015 Introduction Time [us] Power [dB] 8-PSK with Gaussian filtering Data rate 3X compared to GMSK Spectrum very similar to GMSK 17 dB amplitude variation EDGE modulation Frequency [kHz] Power [dB] -54dBc -60dBc GMSKEDGEQ I Q I

4 6/19/ Frequency [kHz] Power [dB] Unlike GMSK, EDGE cannot use nonlinear PA For EDGE, PA operating point should be ~ 6dB bellow 1dB compression point. This operating point provides only 3dB margin on Spectral Mask Low Efficiency PA! Introduction (ii) Motivation for our GSM / GPRS / EDGE Transmitter +Preserve high efficiency of the TX chain in GMSK mode +No SAW Filter in TX chain +No mode change in PA between GMSK & EDGE +Improve system efficiency in EDGE Spectral failure due to Compression & AM-to-PM of 0.8°/dB Failure

5 6/19/2015 TX Architectures with Linear PA 2) Direct up conversion with IQ vector modulator 3) Polar modulator prior to the PA 1) Superhet up conversion with IQ vector modulator +Well known techniques with simple interface between Transceiver and PA –Low Efficiency Linear PA for EDGE mode –External Filter to meet noise in RX band –Isolator to maintain EVM under VSWR –Tend to be expensive and bulky solutions Digital Phase VCO PLL  Modulator D/A Digital Amplitude PA Isolator Modulator Driver SAW Filter

6 6/19/2015 Polar with open loop PA amplitude modulation + Very high PA efficiency is possible –Requires linear amplitude control –Sensitive to AM-to-PM in PA –Sensitive to load variations, temperature, supply –Requires isolator after PA to maintain EVM under VSWR –Accurate alignment of AM and PM components is very critical –Dynamic range for power control and power ramping is an issue Required amplitude control range : DCS / PCS > 50 dB GSM 850/900 >48 dB

7 6/19/2015 Polar Loop Transmitter +Very high PA efficiency is possible +Phase and amplitude feedback from PA output +Insensitive to AM-to-PM in PA +Insensitive to load variations, temperature, supply, etc. +No isolator required to maintain good EVM under VSWR +No pre- or post-PA filtering required to meet TX Noise in RX band Main Challenges: –Stability –Noise

8 6/19/2015 Polar Loop Transmitter Block Diagram +Closed Loop Power Control +High Linearity: IM3 < -40dBc +Wide Control Range > 65dB +Constant Gain over Control Range +Low AM-PM +Low Noise

9 6/19/2015 Characteristics of AM / PM loops Dominant poles / zeros are set by external components Variations in loop bandwidth are mostly due to gain variations Loop BW ↑ : Design Tolerance ↑ Loop BW ↓ : Noise ↓ AM LoopPM Loop Loop Gain 40 dB Loop BW 1.8MHz Gain Margin > 14dB> 19dB Phase Margin > 65° Attenuation at 20MHz > 38dB> 40dB

10 6/19/2015 Loop Gain Spectrum at 400KHz offset, Spec: -54dBc EVM (RMS) Spec: 9% EVM (Peak) Spec: 30% Nominal-63dBc1.4%2.9% Nom. – 7dB-55dBc2.1%4.3% Nom. + 10dB-55dBc0.8%1.9% System Simulations AM Loop gain (dB) PM Loop BW ( Normalized ) Spectral Mask at 400kHz Offset (-dBc) Polar Loop Transmitter modeled and simulated using MATLAB, MATHCAD and ADS EVM is not sensitive to mismatch between AM / PM Loops Spectral mask degrades due to mismatch between loops

11 6/19/2015 Power Amplifier - EDGE Specific requirements Same GaAs die as GSM PA. No Mode Select between GMSK / EDGE. Modified Local Power Controller: – Linear Gain Control – Wide Bandwidth Gain Control – Low Noise – No Efficiency Degradation Control Gain20 dB (10V/ V) Control gain variation at max power +/- 3 dB AM to PM 2.5 ° /dB max

12 6/19/2015 Process Info & Die Photos BiCMOS Process: Transceiver / PA Controller 30GHz Ft NPN, 0.35  m CMOS, 3-layer metal GaAs HBT Process: PA 25GHz Ft, 2  m Feature size, 2-layer gold metal Transceiver: 5 mm x 4 mm PA Controller 2 mm x 2 mm PA Module 8 mm x 10 mm

13 6/19/2015 Quad Band GSM / GPRS / EDGE RF Subsystem Transceiver: –RX = 40mA GSM; 50mA DCS –TX = 85mA –SYNTH = 35mA PA Controller –TX = 50mA PA Module – Typical performance Low Band 34.5 dBm = 54% 28.5 dBm = 35% High Band 31.5 dBm = 45% 27.5 dBm = 35% Transceiver PA Module PA Controller Quad Band Evaluation Board

14 6/19/2015 GSM Band – EDGE: Max. Required Power at Antenna (27 dBm)

15 6/19/2015 GSM Band – EDGE: Max. Required Power at Antenna (27 dBm)

16 6/19/2015 GSM Band – EDGE: Max. Required Power at Antenna (27 dBm)

17 6/19/2015 GSM Band – EDGE: Max. Required Power at Antenna (27 dBm)

18 6/19/2015 GSM Band – EDGE: 2dB above Max Required Power at Antenna!

19 6/19/2015 TX Noise in RX Band: Highest Channel & Highest Power Level -79dBm 935 MHz 960 MHz 914.8MHz 5dB/div

20 6/19/2015 Performance under VSWR Requirements: 3:1 - EVM meet spec, RF spectrum allowed to fail spec 6:1 - Maintain the link, EVM and RF spectrum allowed to be corrupted 10:1 - No device damage Measured power at Antenna under VSWR

21 6/19/2015 Without Isolator : + No degradation of EVM ! + Modulation spectrum within spec up to 4:1 VSWR VSWR Measurement EDGE Mode EVM under VSWR Variation Spec Spectral Mask at 400KHz Offset Spec Spectral Mask at 600KHz Offset Spec

22 6/19/2015 System Performance Summary – Low Band

23 6/19/2015 System Performance Summary – High Band

24 6/19/2015 Conclusions A new transmitter architecture has been presented. Closed AM and PM feedback loops ensure very robust performance. High PA efficiency by use of saturated operation. No SAW filter needed to meet TX noise in RX band. No need for Isolator to maintain good EVM under VSWR. Meet or exceed all GSM requirements in Quad Band with both GMSK and EDGE modulated signals.