Abstract: Reference design (RD) shows a dual-band, triple-mode CDMA front-end IC tuned to provide +20dBm in low-gain high-linearity mode. The RD features a CDMA low-noise amplifier (LNA) that is also useful for TDMA, GSM, EDGE, and WCDMA applications.The MAX2323 LNA/mixer is featured.
Rapid Engineering Prototypes are real circuits that Maxim application engineers have built and measured in our labs. They can provide a starting point for new RF designs. They are not available as evaluation kits.
Objective: For this dual-band triple-mode front-end IC, to experimentally tune for the best-possible cellular LNA linearity available in CDMA low-gain high-linearity mode.
The project requirement was to custom-tune to obtain cellular LNA low-gain high-linearity performance of +20dBm IIP3, as well as to match the analog and the digital (cellular/PCS) mixer output ports both to 85.38MHz IFs. Note that this was a one-time experimental "limits-of-performance" design, which is difficult to achieve routinely. The LNA bias resistor was adjusted carefully along with the IF output matching circuit. The LNA input match was varied as well, but care was taken not to upset the mid-gain and high-gain noise figures. The LNA output match was not varied. It demonstrates the extremely versatile application designs that can be developed using these SiGe FE ICs.
The MAX2323 low-noise amplifier (LNA) plus mixer is designed for dual-band CDMA cellular-phone handsets, but it can also be used in dual-band TDMA, GSM, EDGE, or WCDMA applications. It differs from its predecessor (the MAX2320) by adding a third "mid-gain" state for the cellular-band LNA that improves switchover hysteresis margin. It also comes in a smaller package (28-QFN) and offers increased third-order input intercept.
Tested Circuit 
