Memory Effect in HPAs
■Over the past 5-10 years, gallium nitride (GaN) technology has become an increasingly popular selection for those wishing to purchase solid state high power amplifiers for satellite uplink applications. GaN-based SSPAs have not only supplanted traditional applications dominated by their gallium arsenide (GaAs) based predecessors, such as the maritime and milsatcom markets, they have also been readily considered for wideband and multi-carrier applications long dominated by TWT-based amplifiers. This is all possible because GaN devices are capable of providing power that GaAs devices cannot, and on a more cost effective basis. However, a challenge has arisen for SSPA manufacturers selling into these new multi-carrier and wideband markets: a phenomenon which directly impacts the linear performance of SSPA transmissions, dubbed “memory effect.”
■The end result of memory effect is that it impairs the expected intermodulation performance of the HPA, sometimes by as much as 10 dB. This requires the user to back off the output power by more than the expected amount, negatively impacting the link budget and/or the overall performance of the earth station. Memory effect is not necessarily limited to GaN devices. It can also affect GaAs based SSPAs. However, GaAs SSPAs are rarely used in applications where the effect manifests itself, since they are predominately used in single-carrier operations. The issue has never manifested itself in TWTAs, at least to a significant or measurable level.
●ADVANCE SUMMARY
■Memory Effect is a phenomenon that can negatively affect output linear RF power, primarily when GaN BUCs are used in multicarrier applications.
■The degree to which output power is affected is determined by tonal spacing and number of carriers.
■CPI has mapped this behavior using IMD sweeps and spectral regrowth charts.
■CPI has mitigated this effect in its own GaN-based products. Other manufacturers may or may not be aware of this issue.
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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29 April 2019 |
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