REP028: MAX2251 Cellular (Linear) RF PA Performs Well in AMPS FM Operation
Rapid engineering prototypes are real circuits that Maxim application
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kits.
Objective: To test and verify the cellular-band MAX2251 linear RF Power Amplifier for AMPS-only operation.
Two tests were conducted at 3.4 Vcc; one optimized for gain, and the other for efficiency. At 836MHz band-center, 26.4dB gain was achieved, with the original TDMA match remaining unchanged. This resulted in AMPS power-added efficiency (PAE) of 45% with +31.5dBm output (917mA Icc). Changing the output match to get better PAE by moving C12 along the output transmission line lowered gain to 25.4dB for AMPS, but increased PAE to 51.4% at +31.5dBm output (806mA Icc). The tests were conducted in the US Cellular band.
The MAX2251 is a low-voltage linear power amplifier designed for TDMA/AMPS dual-mode phone applications. The device delivers over +30dBm of linear power in TDMA operation. It features an on-chip shutdown mode which reduces operating current to 1µA(typ) and eliminates the need for an external supply switch. The MAX2251 needs no external reference voltage, no bias circuitry and only a few external matching components. External bias resistors eliminate wasted "safety-margin" current and allow current throttleback at lower output power levels, thus maintaining the highest possible efficiency at all power levels. The MAX2251 is packaged in an ultra-compact (2.06mm x 2.06mm) chipscale package (CSP).
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