March 6, 2017
RF engineers are continually challenged when designing RF front-ends for mobile devices. A higher number of frequency bands (up to 40), including Wi-Fi and Bluetooth, jammed into one device; fewer SKUs (stock keeping units) — all can make design tricky. In some cases, difficult coexistence requirements can go from being a minor inconvenience to a nightmare. And that's before designing for new standards, such as Power Class 2.
Power Class 2 is a new LTE power standard that gained 3GPP certification in December 2016, as part of an industry initiative to add high-performance user equipment (HPUE) and improve 2.5 GHz LTE TDD coverage worldwide. Higher frequency signals can't travel as far, so cellular carriers needed a way to achieve higher power output. Power Class 2 was the answer.
Initially, the 3GPP spec for Power Class 3, the previous standard, limited mobile-to-tower uplink of Band 41 to 23 dBm nominal output power. This definition helped ensure backward compatibility with prior technologies (GSM/UMTS) so that network deployment topologies could remain similar.
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Learn more about HPUE and Power Class 2:
However, TDD-LTE Band 41 does not have any 3GPP legacy technologies associated with it, so it does not have to be backward compatible. This allowed the 3GPP to define a new power standard — Power Class 2 — and increase the power output for TDD Band 41.
Power Class 2 allows for output power levels of 26 dBm — double the maximum output power previously defined by Power Class 3. (See the figure below.)
The increase in output power to Power Class 2 compensates for greater propagation losses at the higher TDD frequencies, enabling carriers to maintain cell coverage without adding expensive infrastructure. This is a win-win for both the user experience and the carriers — but it's a challenge for device manufacturers.
As RF front-end complexity grows, the overall insertion loss link budget increases. Designing using traditional discrete components and redundant matching only adds to the link budget. The new Power Class 2 requirement (i.e., output power to 26 dBm) further complicates the RF design.
When designing their front-ends, RF engineers need to use the following:
But there's good news. From the RF front-end module perspective, analysis shows that TDD B41 at 26 dBm actually improves the PA contribution to battery life. There is also up to 30% improvement in cell coverage in B41 TD-LTE with a single carrier.
As RF design engineers, we must work to reduce these matching losses and system link budgets as much as possible. Qorvo uses two strategies to achieve this:
RF front-end design will continue to get more difficult as bands increase, frequencies go higher, and capacity solutions like carrier aggregation expand. Power Class 2 is a challenge, but one an RF engineer can meet if partnering with the most knowledgeable RF suppliers. Using high-performance Qorvo BAW filter technology and a highly integrated design approach like RF Flex and RF Fusion will help handset designers be more efficient and successful in a shorter amount of time.
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