A 2 mm x 2 mm HoP-type Power Amplifier for W-CDMA Handset Applications

As a mobile phone is getting smaller and lighter toward a low cost unit (LCU), it is natural that a power amplifier (PA) for handset application has to be implemented in a small footprint. Although a few packaging techniques using multilayer substrate and chip-stacked or chip-embedded assembly have been introduced [1]-[3], it is not easy to minimize PA size economically since the PA should include basically sophisticated MMICs and bulky lumped components for load-matching and other impedance-matching. Practically, PA module size has been reduced up to 3 mm × 3 mm with low cost by commercial manufacturers [4]. In this work, a low cost PA with small form-factor of 2 mm × 2 mm was developed for UMTS band5 handset application, showing good RF performance. Fig. 1 shows a functional diagram of the proposed PA. It consists of one PA MMIC with two external inductors, an integrated Passive Device (iPD), and Helix on Pad (HoP)-type load-matching circuit. The 3-stage PA MMIC was fabricated using 2 μm InGaP/GaAs HBT process and in which input- and interstage-matching circuits are fully integrated except two bulky external inductors. Emitter areas of driver and main stage are 1440 μm2 and 6768 μm2, respectively. To enlarge battery lifetime, the proposed PA bypasses main stage during low output power (Pout) operation by using author’s stage bypass technique [5]. The switching point for power mode selection was chosen to Pout = 16 dBm. The MMIC size is 1.1 mm × 1.06 mm. Two shunt capacitors (C1 and C2) by iPD and load inductance (L3) by HoP are key components in this work. The