With the emphasis today on smaller and lighter cellular phones, battery size and weight is of paramount importance. Talk time, however, must not suffer. Therefore, low DC current consumption is a must. This relates specifically to the power amplifier since it is the main current drain in the handset.
To address this critical demand, two new power amplifier modules have been introduced. The RMPA1963 i-Lo™ and RMPA0963 i-Lo™ power amplifier modules (PAM) are 50 W matched, surface-mount modules targeted at US-PCS CDMA and wireless local loop (WLL), and cellular CDMA, AMPS and WLL applications, respectively. Both module types feature ultra-low DC power consumption for extended battery life, and use novel proprietary circuitry to dramatically reduce amplifier current at low to medium RF output power levels (< 16 dBm), where the handsets most often operate. A simple two-state Vmode control is all that is required to reduce its operating current by more than 50 percent at 16 dBm output power and reduce the quiescent current (Iccq) by as much as 70 percent compared to traditional power-saving methods. No added circuit modifications, such as DC-to-DC converters, are required to achieve this improvement in efficiency. Figure 1 shows a current consumption vs. power output comparison for a conventional PA and the RMPA0963 PAM.
Fig. 1 Current consumption vs. power output comparison
To make conversion to these PAMs more attractive to handset manufacturers, the modules are supplied in a 4 × 4 × 1.5 mm LCC package that is pin-compatible and a drop-in replacement for last generation 4 × 4 mm PAMs that are in wide use today. Thus, the design time for implementing this performance enhancing technology is greatly minimized.
The RMPA1963 and RMPA0963 PAMs are multi-stage GaAs MMICs manufactured using Fairchild’s RF InGaP Heterojunction Bipolar Transistor (HBT) process. As such, the devices use a single positive supply, typically 3.4 Vcc, with a low Vref (2.85 V) compatible with advanced handset chipsets. The devices are internally matched to 50 ? and have DC-blocked RF inputs and outputs. Both PAMs feature industry-standard pinouts. Figure 2 shows their respective functional block diagrams.
Fig. 2 Functional block diagram for the (a) RMPA1963 and (b) RMPA0963 PAMs.
Performance
The RMPA1963 is designed to operate in the 1850 to 1910 MHz frequency range. The PAM is biased at 20 mA DC quiescent current and features a typical gain of 27 dB at +28 dBm output under high-power-mode operation (Vmode=0V) and 20 dB gain at +16 dBm output at low-power-mode (Vmode£2V). Digital power-added efficiency (PAE) at 28 dBm output is typically 38 percent, and 15 percent at 16 dBm output. The adjacent channel power ratio (ACPR) at ±1.25 MHz offset is –50 dBc and –60 dBc at ±2.25 MHz offset for both high power and low power operation.
Fig. 3 Evaluation board schematic.
Under low power mode operation (Vmode£2V), the PAM is designed to deliver maximum linear output power up to 20 dBm. This unique feature allows phone designers to liberally select the low power to high power switching point from 16 dBm to 20 dBm depending on specific phone requirements, while providing sufficient ACPR margin to meet the linearity specifications.
The RMPA0963 PAM is designed for 824 to 849 frequency operation and features similar performance specifications to that of its sister device for CDMA operation. When operating in an AMPS mode its gain is typically 27 dB at +31 dBm output and its analog PAE is 50 percent at high power. Both devices are designed to operate at case temperatures in the range of –30° to +85°C and can withstand a load mismatch of 10:1 with no permanent damage.
Figure 3 shows the need for minimal external components. The device is designed to be flow soldered and proper ESD precautions should be observed during handling. Additional information may be obtained from the company’s Web site at www.fairchildsemi.com.
Fairchild Semiconductor Corp.,
Tyngsboro, MA
(978) 226-2003,
www.fairchildsemi.com