A 900 MHz Doherty Amplifier Implemented with Lumped

A 900 MHz Doherty Amplifier Implemented with Lumped Elements Y. Zhao, M. Iwamoto, D. Kimball, L. Larson, P. Asbeck University of California, San Diego

Introduction § To increase overall efficiency of RF PA § Use Doherty structure § To shrink circuit size for integration § Use lumped elements to replace transmission lines § To achieve good linearity § Use DSP to control Doherty Amplifier 10/29/202

Agenda § Doherty amplifier architecture § Doherty with lumped elements § Design issues § Simulations § Measurements § DSP application in Doherty amplifier § DSP control mechanism § Measurement Results § Conclusions 10/29/202

Doherty Architecture § Low power range § only Main-PA operates § High power range § Main-PA goes into saturation § Aux-PA turns on Load-line of main amplifier Iout High power operation Low power operation Vout 10/29/202

Lumped Doherty --- Design issues § Size of 90° transmission line § 900 M --- 48 mm § 2. 4 G --- 19 mm Er = 3. 48 § 5. 2 G --- 8. 7 mm § Size of a general PA package 4 mm x 4 mm § Design requirements § Impedance inversion § Phase compensation 10/29/202

Lumped Doherty --- Design issues § C-L-C (9. 1 p. F, 2. 7 n. H) § Impedance inverter § 90 degrees delay § Provide VDD to Aux-PA § Harmonic trap § L-C-L (1. 8 n. H, 15 p. F, 3. 3 n. H) § 90 -degree phase shifter § part of the matching § DC block § L-match (13 p. F, 2. 2 n. H) § Output impedance match § DC block 10/29/202

Lumped Doherty --- Measurement § A Ga. As MESFET-based hybrid Doherty amplifier was built with lumped elements Drain efficiency, PAE and Gain Bandwidth S 21 1 d. B/div 1 d. B Bandwidth ~ 110 MHz § CDMA needs 25 MHz/836 MHz Frequency 50 MHz/Div § 802. 11 b, g need 83 MHz/2. 44 GHz 10/29/202

Lumped Doherty --- Measurement PAE vs. Pout Lumped Doherty vs. a simulated Class AB IS-95 CDMA PDF Lumped Doherty – 14. 1% > 3 X Class AB – 4. 4% 10/29/202

Comparison --- Lumped and distributed Similar PAE performance Slightly narrower bandwidth for lumped Doherty § ADS simulation § Same devices and design § Check 1 d. B bandwidth/900 MHz § the lumped Doherty 130 MHz § the distributed Doherty 150 MHz 10/29/202

Comparison --- Lumped and distributed § Size reduction by using lumped elements is dramatic § Connection lines and components in hybrid circuit can be further shrunk in a IC module schematic Circuit area Quarter-wave lines 10/29/202

Potential problem --- Linearity Non-ideal gain and phase in high power region cause a linearity problem For CDMA signal, ACPR may not be good enough 10/29/202

DSP Linearization Strategy § Gain control System block diagram § Change Vgg 2 according to the instantaneous envelope of the input CDMA signal § Phase control § Baseband phase predistortion § Open loop control with lookup table “Doherty Amplifier with DSP Control to Improve Performance in CDMA Operation, ” 2003 IEEE MTT-S Digest, p 687 -690 10/29/202

Measurement --- linearized IS-95 signal -42 d. Bc § High efficiency is maintained 10 d. B/Div uncorrected § ACPR improvement of up to 9 d. B is achieved; CDMA ACPR specifications are met § Peak power is limited by the device size DSP corrected 0. 5 MHz/Div 10/29/202

Conclusions § Doherty amplifier helps achieve high efficiency over wide output power range § Doherty amplifier with lumped elements shrinks circuit size while maintaining good performance § Linearity of the Doherty amplifier can be substantially improved by DSP to meet the CDMA ACPR specification § A promising approach for CDMA handset and other wireless applications such as 802. 11 10/29/202