Reference Circuit 443
REP008: Dual-Band Front-End IC Tuned for CDMA, PCS, and AMPS at a Common 85MHz Low IF
|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: To develop and measure this dual-band triple-mode front-end IC using only 85MHz IF centers for processing PCS, cellular CDMA, and cellular AMPS.
The MAX2323 offers a single-path output for cellular and PCS digital mixers. In this application, the object was to assess performance with a common low IF at 85.38MHz. The high IP2 performance of the PCS mixer combined with the rejection from the RF filter's band edge provided reasonable although not excellent 1/2 IF image rejection. This was an experimental prototype done to assess the limitations of the MAX2320, and the results were surprisingly good, even with a low IF at the PCS band.
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 sensitivity switchover and hysteresis margin. It also comes in a smaller package (28-QFN) and offers increased third-order input intercept.
Schematic of the MAX2323 evaluation kit (PDF, 61kB)
Bill of materials, part 1
Bill of materials, part 2
Bill of materials, part 3