REP015: Tuning dual-channel CDMA PA to achieve high linearity

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: To develop cellular CDMA PA application circuits with very high linearity and moderate power added efficiency (PAE).

The characteristics of the MAX2264 high- power amplifier channel and the performance satisfied after tuning in narrowband CDMA are: when P _OUT is +28dBm, the gain is 26.8dB, the efficiency is 28%, ACPR1 = -48.5dBc, ACPR2 = -59.0dBc. These performances demonstrate that the device is operating in a deeply linear mode, as reflected by a reduced PAE of 28%. Typically, components should be tuned to have an efficiency of over 33% and an ACPR1 of at least -44dBc. Use the evaluation board to test the above performance.

The MAX2264 linear RF power amplifier is designed for IS-98-based US cellular band CDMA, PDC, and IS-136-based TDMA modulation modes. For optimal low-power PAE, the MAX2264 uses an on-chip converter to provide a switchable dual-channel amplifier circuit. According to statistical results, CDMA mobile phones work in low-power channels (about +16dBm output) most of the time, which is exactly the situation where PAE needs to be optimized. The PAE of the MAX2264 at low power is typically 12%.

Block diagram of the transmit-path application
Schematic of the MAX2264 evaluation kit (PDF, 24kB)
Measurement test setup