Comparing the AX508 to the AX502

Sanguine's Andy Wang

The Axiom AX502 was the first fully integrated CMOS Power Amplifier for mobile handsets and had been considered reliable and adopted by many handset manufacturers. To explain it's popularity, as of December 2008, 25 million units of the device have been shipped to their customers.

Recently, Axiom Microdevices, Inc. issued their newest power amplifier, the AX508 power amplifier and with it, expanded their family of GSM/GPRS power amp. In their documentation, Axiom claims the newest product is more powerful and more competitive than its predecessors. The AX508 integrates full quad-band GSM/GPRS functionality on a single integrated circuit (IC), using mainstream Silicon CMOS process technology. Key benefits of the AX508 include improved performance (compared with the earlier AX502), which translates to a longer talk time in handset designs. Axiom also offers a smaller footprint on AX508, by housing the PA in an ultra-low profile micro lead frame package of 5x3.5x0.9 millimeters (mm).

The AX508 is known for its power-added efficiency (PAE) E-GMS of up to 50% at +35dBM, ,according to the datasheet, while the PAE for the AX502 is only 47%. What that means is more power saved by the system and less heat dissipated by the device. The AX508 also features a micro lead frame package with a smaller footprint of 5x3.5x0.9 millimeters (mm), compared with the AX502's package of 5x5x0.9 millimeters (mm).

Package Comparison of the AX508 vs AX502

These particular differences between models seem somewhat small, which brings us to the big question; what are the key differences between AX508 and the AX502? To answer that question, the engineers at Sanguine decided to do decaps on both the AX508 and the AX502 to form a comparison and identify some of the many things you can learn when you look beyond the packaging.

The first difference you notice is the appearance of an additional pad in the AX508 versus the AX502, as seen in the X-ray images shown below.

X-Rays of both Devices - Click on image to enlarge.

Next we take a look at the circuit layout of the two devices. Examining the two images reveals how the AX508 features an additional two test pads and a new, unknown pad.

X-Rays of both Devices - Click on image to enlarge.

The die-mark on AX508 is almost identical with that of the AX502. This includes the same distinguishing marks seen on the AX502 that are seen when taking a much closer look at the circuit schematic. Markings become visible at this close range; like writing of their claim of "the World's First Fully Integrated Cellular Phone Power Amplifier", the names of all their designers, their development team and their technology, and identification of its origin at California Institute of Technology.

Designers get their credit! - Click on image to enlarge.