Abstract
It has been known that negative feedback loops (internal and external) in a SiGe heterojunction bipolar transistors (HBT) DC current mirrors improve single-event transient (SET) response; both the peak transient current and the settling time significantly decrease. In the present work, we demonstrate how radiation hardening by design (RHBD) techniques utilized in DC bias blocks only (current mirrors) can also improve the SET response in AC signal paths of switching circuits (e.g., current-mode logic, CML) without any additional hardening in those AC signal paths. Four CML circuits both with and without RHBD current mirrors were fabricated in 130 nm SiGe HBT technology. Two existing RHBD techniques were employed separately in the current mirrors of the CML circuits: (1) applying internal negative feedback and (2) adding a large capacitor in a sensitive node. In addition, these methods are also combined to analyze the overall SET performance. The single-event transients of the fabricated circuits were captured under the two-photon-absorption laser-induced single-event environment. The measurement data clearly show significant improvements in SET response in the AC signal paths of the CML circuits by using the two radiation hardening techniques applied only in DC current mirrors. The peak output transient current is notably reduced, and the settling time upon a laser strike is shortened significantly.
Highlights
Silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs) have received extensive attention for implementation in extreme-environment applications due to their excellent total-ionizing-dose (TID) tolerance, high-speed operation, superb cryogenic performance, and ease of integration in a complementary metal oxide semiconductor (CMOS) platform [1,2,3,4]
Studies have reported that SiGe HBTs are susceptible to single-event phenomena, especially single-event upset (SEU) and single-event transient (SET) [5,6,7], and it is highly critical that the sensitivity of SiGe HBT circuits to single-event effect (SEE) be improved, either via changing the underlying device profile, i.e., radiation hardening by process (RHBP) or circuit
The internal negative feedback created by the emitter degeneration resistor RE is employed in the current mirror of the second current-mode logic (CML) circuit (Figure 2b)
Summary
Silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs) have received extensive attention for implementation in extreme-environment applications due to their excellent total-ionizing-dose (TID) tolerance, high-speed operation (i.e., high unity gain frequency, f T ), superb cryogenic performance, and ease of integration in a complementary metal oxide semiconductor (CMOS) platform [1,2,3,4]. In comparison with the findings in [4], where the mitigation of SETs was observed only at the output of the DC-bias block itself, here we propose that the radiation-hardening of the DC-bias circuitry only results in better SET generated within AC CML circuits in terms of transient peak and duration. This is more attractive in terms of AC operation, since the direct application of hardening techniques to AC (or high-frequency) circuits is likely to lead to a tradeoff of performance degradation such as gain reduction, a noise increase, etc.
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