REP001: Achieving the best balance of IIP3 and gain for AMPS FM mixers

Rapid engineering prototypes are actual circuits that Maxim application engineers build in the lab and conduct product testing. They are the starting point for new RF engineering designs. They are not intended to be used as assessment testing tools.

Goal: Custom-tuning the output matching circuit of this RF mixer operating in the FM (AMPS) signal path to achieve the best balance between best linearity and highest gain.

Use the MAX2320 EV kit to describe the features of the MAX2324 because the features of the MAX2320 are a superset of the features of the MAX2324 and their performance in the cellular frequency band is nearly identical. Note that this IC can be used as a mixer for digital channels (CDMA or TDMA) or in the FM (AMPS) channel, where the output is open-collector. Adjusting the load line changes gain and IIP3 performance (in opposite directions). In this application, the output matching of the FM mixer is optimized to meet the requirements for IIP3.

The MAX2324 low-noise amplifier (LNA) and mixer is designed for CDMA cellular handsets in the cellular band. It can also be used in TDMA, GSM or EDGE applications. It provides two LNA gain states to meet CDMA dynamic range requirements, with switching hysteresis margin between the two states. The MAX2324 contains a total of two mixers: one outputs an analog IF and the other outputs a digital modulation IF. The MAX2324 has buffered VCO inputs and outputs, eliminating the need for additional transmit upconverter VCO buffers.

Schematic of MAX2324 evaluation kit (PDF, 55kB)
Bill of materials, part 1
Bill of materials, part 2