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对于第2节提出的电路,其输出脉宽可调范围有限,需要新的电路结构,实现更大的输出脉宽可调范围。仍使用GaN HEMT搭建输入级,采用共源极结构。共源极结构将输入信号反相,需要添加一级再一次反相。从单片集成的角度考虑,P沟道GaN器件无疑是最好的选择,但P型GaN的空穴迁移率低,不利于制备P沟道功率器件。另一种办法是使用耗尽型和增强型的N沟道GaN器件构成反相器,但存在长时间导通的支路,受到散热与功耗的限制。最终选取Si PMOS与电阻构成中间级,如图7所示。最终的PCB尺寸为13 mm×11 mm。
除输入信号脉宽外,其他测试条件与前文一致。输入脉宽为10~100 ns,步长为30 ns,将示波器测试结果导出并绘制波形,如图8所示。最窄输出光脉宽由示波器示数读出,为8.4 ns,此时输出光脉冲峰值功率为8.3 W,脉宽可调至100 ns以上。电源电压升至20 V,输入脉宽100 ns时,输出光峰值功率可达46.6 W。
测试结果表明,电路实现了更大的输出光脉宽可调范围。选取的M2响应速度较慢,在栅极电压较低时导通电阻较大,导致输出光脉冲上升沿的时间较长。可以选用响应速度更快、导通电阻更低的PMOS,使上升沿更加陡峭。
表1展示了文中提出电路与相关参考文献所提出电路的比较。脉冲宽度为输出光脉宽范围,峰值功率为输入脉宽100 ns时的输出光脉冲峰值功率,且参考文献[4]与[6]中激光器放电回路电压大于文中使用的20 V。测试采用GaN HEMT的尺寸分别为2.5 mm×1.5 mm、0.9 mm×0.9 mm,Si PMOS尺寸为2.8 mm×1.2 mm,若采用3.2节中的集成方法,集成的预期尺寸小于(2.5+0.9) mm×(1.5+0.9) mm。
表 1 对照表
Table 1. Comparison table
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GaN器件的优点使得全GaN电路单片集成受到国内外广泛的研究。高校与企业陆续开发了基于不同增强型技术的集成工艺平台。其中,台积电提出了基于P-GaN增强型技术的100 V/650 V GaN-on-Si的工艺平台[13],可以集成电阻、二极管、低压逻辑晶体管、高压功率晶体管等元件。Chen等[14]提出了一款基于GaN工艺的电路,集成了驱动器及650 V增强型GaN HEMT。
第2节中提出的驱动电路,其所使用的电子元件除储能电容外,只有少数的晶体管和电阻,基于GaN工艺,容易实现单片集成,图9为其集成工艺结构示意图。
目前大多GaN外延片具有AlGaN势垒层,可以直接制备GaN HEMT,电阻与GaN HEMT制备工艺兼容,不需额外的工艺步骤。因此,整个驱动电路采用GaN HEMT的制备工艺即可完成单片集成。
第3.1节提出的电路比第2节提出的电路多出Si PMOS和电阻,采用Si PMOS工艺制备,电路中除电容外的其余元件采用GaN HEMT工艺制备,将两部分集成,即可完成电路的集成。集成方式采用3D堆叠式封装,将面积小的管芯倒扣在另一管芯上,笔者所在课题组已进行相关研究[6]。
Adjustable narrow pulse laser drive circuit using GaN HEMT
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摘要: 为实现纳秒级的输出光脉宽,使用GaN HEMT作为激光器放电回路的开关管。由于GaN HMET的栅极总电荷小,提出使用小尺寸的GaN HEMT建立驱动电路的输入级,响应控制信号,控制放电回路开关管。搭建电路驱动860 nm激光器,并进行测试。放电回路电源电压为12 V,测试结果显示,最大输出光脉宽8.8 ns对应大于8 W的峰值功率,输出最小光脉宽为4 ns。为实现更大的脉宽可调范围,设计另一款电路并测试。该电路实现输出光脉宽大于8.4 ns可调,在电源电压20 V、输入信号脉宽100 ns的条件下,输出光峰值功率可达46 W。电路尺寸分别为10 mm×6 mm和13 mm×11 mm,为实现进一步小型化,对设计的电路提出了集成方法。提出的电路结构简单、容易实现集成且成本低,为窄脉冲激光器驱动电路的设计提供了新的思路。Abstract: GaN HEMT is used as the switch of the discharge circuit to achieve nanosecond pulse width. Due to the low total gate charge of GaN HMET, a GaN HEMT with small size is used to build the input stage of the driver circuit to respond to the control signal and control the discharge circuit switch. The circuit is built to drive the 860 nm laser and tested. The power supply voltage of the discharge circuit is 12 V, and the test results show that the maximum output pulse width of 8.8 ns corresponds to a peak power greater than 8 W, and the minimum output pulse width is 4 ns. Another circuit is designed and tested to achieve a larger pulse width adjustable range. The circuit realizes adjustable pulse width greater than 8.4 ns of output light. When the power supply voltage is 20 V and the pulse width of the input signal is 100 ns, the output optical peak power can reach 44 W. The area of the circuit is 10 mm×6 mm and 13 mm×11 mm. In order to realize further miniaturization of the drive circuit, a integration method is proposed for the two designed circuits. The proposed circuit is simple in structure, easy to realize integration and low in cost, which provides a new idea for the design of narrow pulse laser drive circuit.
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Key words:
- semiconductor laser /
- driver circuit /
- GaN HEMT /
- narrow pulse /
- miniaturization
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表 1 对照表
Table 1. Comparison table
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