The Temperature Dependence of a GaAs pHEMT Wideband IQ Modulator IC

Kiyoyuki IHARA  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.3   pp.366-372
Publication Date: 2008/03/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.3.366
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
Keyword: 
IQ modulator,  temperature dependence,  EVM,  direct conversion,  GaAs,  pHEMT,  

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Summary: 
The author developed a GaAs wideband IQ modulator IC, which is utilized in RF signal source instruments with direct-conversion architecture. The layout is fully symmetric to obtain a temperature-stable operation. However, the actual temperature drift of EVM (Error Vector Magnitude) is greater in some frequency and temperature ranges than the first generation IC of the same architecture. For applications requiring the precision of electric instrumentation, temperature drift is highly critical. This paper clarifies that linear phase error is the dominant factor causing the temperature drift. It also identifies that such temperature drift of linear phase error is due to equivalent series impedance, especially parasitic capacitance of the phase shifter. This effect is verified by comparing the SSB measurements to a mathematical simulation using an empirical temperature-dependent small-signal FET model.