Power amplifiers (PAs) represent one of the more critical components in wireless devices and systems. Many techniques have attempted to improve PA linearity and efficiency, including the use of analog feedforward processing and digital signal processing (DSP). But the elegantly simple predistortion linearizers (PDLs) developed by Cigma Technologies (Allendale, NJ) may offer the best combination of improved efficiency and linearity along with savings in amplifier size, cost, and power consumption. Versions of the PDLs are available for both handset and base-station PAs.
The PDL (see figure), introduced earlier this year (see Microwaves & RF, April 2003, p. 33), is essentially a broadband analog circuit that predistorts the amplitude and phase of input signals a PA, so that amplified signals at the PA's output port are highly linear. Because the input signals are optimized, the amplifier can run at high efficiency, and more output power is available from a given design. With greater efficiency, thermal design can be controlled and a smaller amplifier can deliver a desired output-power level.
In general, the base-station PDLs are designed to reduce PA intermodulation distortion (IMD) by as much as 20 dB, and can achieve efficiency as high as 20 percent. They can be used to effective double (increase by 3 dB) usable PA output power, and reduce PA size and cost by as much as 40 percent.
The base-station PDLs are available in bands of 800 to 900 MHz, 1800 to 1900 MHz, and 2400 MHz in three different configurations. The CT-PDL is a basic open-loop (nonadaptive) PDL configuration with some passive circuit loss, but with greater than 14-dB reduction in IMD when applied to single-carrier WCDMA signals. The CT-PDLU is a similar design, but with 0-dB insertion loss. The CT-PDLC is a closed-loop (adaptive) configuration with integral microcontroller.
Like the base-station units, the model CT-PDLH handset PDL is designed to improve PA IMD performance. For a handset, the IMD improvement is applied toward reduced current drain and longer talk time. The CT-PDLH can deliver as much as 50-percent improvement in handset PA efficiency, with a 3-dB increase in handset PA output power and greater than 60-dB dynamic range. The CT-PDLH is available as a discrete device or integrated with a customer's RF integrated-circuit (RF IC) PA. Cigma Technologies, Inc., 40 Boroline Rd., Allendale, NJ 07401; (201) 818-9300, FAX: (201) 818-0400, Internet: www.cigmatech.com.