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It is aiming at active MIMO (multiple input multiple output) antenna arrays, where using a top-side cooled amplifier (‘PA’ upside-down in diagram right) allows all heat to be extracted from one side of a simple PCB, leaving its other side available for the antennas.
The aim is to cut the weight of each enclosure required for the base station to under 23kg (20kg is the 2023 target, said NXP) to allow one person to lift and install them. Lighter weight and lower wind-induced loading also allows lighter supporting structures to be used.
Conventional construction using its bottom-cooled amplifiers requires more height, said NXP
The first products, available today, are A5M34TG140-TC, A5M35TG140-TC and A5M36TG140-TC – the latter will be supported by a development board series.
These combined LDMOS and GaN technologies, and are aimed at 200W 32-transmit 32-receive (32T32R) radios covering 3.3 to 3.8GHz, delivering 31dB gain and 46% efficiency over 400MHz of instantaneous bandwidth, claimed NXP.
Spanning the tops of multiple hot top-side cooled packages brings with it the challenge of compensating for package height variation – in this case across 32 to 64 power amplifiers and any other ICs on the RF PCB that need cooling.
How does the company propose that designers deal with this?
“NXP recommends a gap filler type thermal conductive material,” NXP RF power product manager Gavin Smith told Electronics Weekly. “Typical gap distance should be kept to a minimum, and not to exceed 0.5mm based on the thermal resistance vs thickness trade-off.”
This allows 0.1mm for package tolerance and 0.4mm for application tolerance.
And what type of thermally-conductive material?
“A high performance, low thermal resistance material in the range of 6 to 25W/mK, depending on the application, is recommended”, replied Smith.
Is there a suggested part number for the thermally conductive compliant material?
“NXP is working on identifying a few specific products on the market,” he said. “However, narrowing down to just a few will likely prove difficult as the end applications will vary. We plan to have an app note to provide customers further guidance.”
At the tine of writing, no information on NXP’s three top-cooled RF amplifiers was available, but this link should be live by the time you, dear reader, have access to this article.
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