OPTICALLY INDUCED MEASUREMENT ANOMALIES WITH VOLTAGE-TUNABLE ANALOG-CONTROL MMICS

Monolithic microwave integrated circuits (MMIC's) may be measured unde r relatively high-intensity lighting conditions, Later, when they are packaged, any anomalies found in subsequent measurements could be attr ibuted to unwanted parasitics or box modes associated with the packagi ng. However, optical effects may not always be considered by radiofreq uency (RF) and microwave engineers. For the first time, a qualitative assessment is given for the effects of photonic absorption on three br oad-band voltage-tunable analog-control circuits. Each circuit has a d ifferent function, with each field-effect transistor (FET) operating i n a different mode: a hot FET in a variable-gain amplifier, a cold FET in an analog attenuator, and an FET varactor in an analog phase shift er, All three circuit functions have been implemented using two differ ent FET-based technologies. The first with ion-implanted 0.5-mu m GaAs metal-semiconductor FET's (MESFET's) in circuits operating at either 3 or 10 GHz, The second employs epitaxially grown 0.25-mu m AlGaAs/InG aAs pseudomorphic high electron-mobility transistors (HEMT's) in circu its operating at 38 GHz, All the MMIC's were fabricated using commerci al foundry processes and illuminated under conventional optical micros cope lighting conditions. Prominent error peaks have been found at bia s points unique to the three different circuit topologies, Large error peaks are found with the MESFET-based circuits, while much smaller er ror peaks are achieved with the corresponding pseudomorphic HEMT (pHEM T) based circuits.