Low-Jitter GaN E-HEMT Gate Driver With High Common-Mode Voltage Transient Immunity

Abstract

Abstract-An improved gate driver is presented which significantly lowers the output noise of high-precision switch-mode (Class-D) power amplifiers by reducing signal jitter at the output of the power stage tenfold to values below 20 ps. Gate signal jitter in power electronic converters, which introduces wideband noise to the power output, originates mainly from the signal isolators that are required to provide the galvanically isolated gate driver control signals. A low-jitter gate control signal is produced by employing a digital flip-flop, which uses a low-jitter isolated clock, to re-synchronize the jittery gate control signal. By utilizing the clock-enable input of the flip-flop, the gate driver can be rendered immune to high-speed common-mode transients, which is important as the Class-D power amplifier demonstrator system employs fast-switching GaN E-HEMT transistors, where the 400 V switching transients exceed 300 kV µs −1 . The signal to noise ratio of a sinusoidal output signal is measured at 107 dB, which is an improvement of ≈20 dB as compared to the performance of a conventional gate driver.Index Terms-Low-jitter gate driver, common-mode transient immunity (CMTI), low noise switch-mode power amplifier, wide-bandgap gallium nitride power semiconductors, signal to noise ratio (SNR)

Distortion Minimization for Ultra-Low THD Class-D Power Amplifiers

“…As the switching transistors are cooled from the top side, no thermal printed circuit board vias are required, which would otherwise disrupt the commutation loop of the half-bridges. This enables low-inductance commutation loops and fast switching actions with little voltage overshoots and ringing [23]. Fig.…”

“…The gate voltage applied to turn the transistors on is 6 V and -3.3 V to ensure reliable turn-off. The gate control signal is isolated using a low-jitter digital isolator (Si8271, 40 ps RMS jitter, 30 ns delay), which reduces wideband noise in the switched half-bridge output voltages [23], [26].…”

“…16 illustrates, 30 ns of dead time result in a THD of ≈ -100 dB over a wide load current range. Such low dead times are facilitated by the fast half-bridge switching transitions, which take less than 6 ns at a DC-link voltage of 400 V [23]. As the high-side half-bridge power transistor requires an isolated gate control signal, the propagation delay difference (skew) of the two half-bridge gate control signal paths (and the variation of this timing difference, e.g., due to temperature), which is mostly dominated by the digital signal isolators, imposes a practical lower limit to dead time, as it must be guaranteed that a minimum dead time is always ensured to prevent halfbridge shoot-through.…”

“…Another option to further reduce dead time is given by special gate drivers that couple the two gate voltages and make sure that always only one transistor is conducting, while minimizing dead time at the same time [47]. However, this approach increases circuit complexity and affects the gate loop parasitic inductance, which, due to the fast switch-node transitions of the half-bridges and the low GaN HEMT gate threshold voltages, could lead to parasitic transistor turn-on [23]. Other approaches supervise the conduction state of a transistor and communicate it to the complementary gate driver that can then control the switching state accordingly [48], [49].…”

Noise Minimization for Ultra-High SNR Class-D Power Amplifiers

“…2 outlines key noise sources in the context of a switchmode power amplifier, modeled as series-connected voltage or (digital) signal sources. The quantization noise introduced by the limited-resolution PWM [17], as well as the timedomain jitter of the power transistor switching actions [18], are linked to stochastic processes and thus introduce wideband noise of uniform power density [19]. Supply noise, or electromagnetic interference (EMI) from external sources by means of stray fields that couple to the amplifier's circuit, on the other hand, often exhibit spectral components at distinct frequencies.…”