Active gate driving has been demonstrated to beneficially shape switching waveforms in Si-and SiC-based power converters. For faster GaN power devices with sub-10-ns switching transients, however, reported variable gate driving has so far been limited to altering a single drive parameter once per switching event, either during or outside of the transient. This paper demonstrates a gate driver with a timing resolution and range of output resistance levels that surpass those of existing gate drivers or arbitrary waveform generators. It is shown to permit active gate driving with a bandwidth that is high enough to shape a GaN switching during the transient. The programmable gate driver has integrated high-speed memory, control logic, and multiple parallel output stages. During switching transients, the gate driver can activate a near-arbitrary sequence of pull-up or pull-down output resistances between 0.12 and 64 Ω. A hybrid of clocked and asynchronous control logic with 150-ps delay elements achieves an effective resistance update rate of 6.7 GHz during switching events. This active gate driver is evaluated in a 1-MHz bridge-leg converter using EPC2015 GaN FETs. The results show that aggressive manipulation of the gate-drive resistance at sub-nanosecond resolutions can profile gate waveforms of the GaN FET, thereby beneficially shaping the switch-node voltage waveform in the power circuit. Examples of open-loop active gate driving are demonstrated that maintain the low switching loss of constant-strength gate driving, while reducing overshoot, oscillation, and EMI-generating highfrequency spectral content.
/ has previously been proposed as a temperature indicator for Si and SiC devices, however, the evaluation of its viability for GaN devices is challenging as known current sensors introduce significant unwanted parasitic inductance. This work presents a figure-of-eight magnetic field sensor (∞-sensor) that permits, for the first time, highbandwidth floating current sensing, with negligible insertion impedance and influence on switching performance, in highspeed GaN and SiC switching circuits. The pair of coils are connected in a way that the measurement is immune to currents outside of the sensing region. The simulated bandwidth of the sensor, taking into account the loading by the probe connected to its output, is 225 MHz. The insertion inductance is 0.2 nH, and the insertion resistance is 4.2 mΩ at 100 MHz. This sensor is used to investigate the temperature dependency of turn-on di/dt in a 650 V, 52 mΩ GaN device. It is found that both average and peak turn-on di/dt decrease with temperature. Peak di/dt appears to be the preferred temperature indicator due to its high sensitivity and linearity.
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