浅谈MOSFET短波功放偏压热补偿设计
ehco 2016-5-4无线电
浅谈MOSFET短波功放偏压热补偿设计
BG8NJW


    短波通信系统中,射频功放(下称PA)是不可或缺的单元,承载着高频功率放大的要务。通常,为提高频谱利用率及信息边带的功率分量,短波通信多采用SSB(单边带)调制方式进行通信,这种调制方式属于线性调制(区别于FM调频等非线性调制)。这样就要求射频功放的增益曲线也要按照线性或近似线性的特性来设计。
    在中小功率(小于300W)的短波射频功放单元中,为兼顾放大器效率与线性度,功率管通常采用ClassAB(甲乙类)推挽结构的电路。射频功放一般效率不高,自身热耗散较大,功放管的工作温度变化范围较宽,为保证电路静态工作点的稳定,在要求不是很低的场合,无一例外都对功放管的偏压加入了自动温度补偿措施。
    随着三菱等厂商一系列射频功率双极型晶体管的全线停产,近年的双极型射频功放管BJT逐步被MOSFET取代,BJT逐渐退出历史舞台(例如常用的2SC1971已被RD06HVF1取代)。MOSFET相比BJT具有输入输出阻抗易匹配,管损小,温度特性好等特点。
因此,本帖主要是对基于MOSFET的短波功放的偏压热补偿方案进行探讨。通过查阅网络和相关书籍,不难发现基本上中小功率PA都是依照如下两种模式进行偏压热补偿设计。
一、正温度系数补偿方案
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    图1中,推动级和强放级均采用了正温度系数补偿措施。4个功放管的G极偏压均串联了一个二极管DAN202U,该二极管为硅高速开关二极管,同1N4148,1N4001一样,在较大的Ifw(正向电流)范围内,正向压降与结温呈良好的线性负相关。因此常被“移作他用”来充当温度传感器。在电路PCB布局中,通常紧贴功率管的散热面安装。图2DAN202U的正向电流与正向压降的结温曲线簇。
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    可以看出,在相同的正向电流下,温度越高,正向压降越低。因为二极管是串联在偏压回路中的,当温度升高,二极管上的压降减小,势必导致MOS管的偏压Vgs升高,因此该电路叫做正温度系数补偿。
    这里题外提一下,由于MOSFET制程中,金属层与半导体之间的氧化层的物理厚度控制精度不高,造成MOS管在线性区的跨导存在较大离散性,即便是同一批次的产品。所以在要求较高的场合,无一例外的对每一个MOS管提供单独的可调的偏压,以获得良好的Idq(漏极静态电流)对称性。

二、负温度系数补偿方案

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    3所示的是另一种偏压补偿设计方案,该方案中,温感二极管1N4001是串接在三端稳压芯片7805的参考电压引脚与地之间。图41N4001的正向电流与正向压降的结温曲线簇。

264116
4

    同理,当温度升高,1N4001的正向压降降低,使7805的参考点降低,输出电压降低,因此该电路叫做负温度系数补偿电路。采用21N4001串联的原因是提高同等温差下的压降变化量。
    那么问题来了,为什么类似的管子型号,类似的电路结构,为什么会采取截然不同的温度补偿措施?带着问题,我们先以RD16HHF1这个30M/16W/16dBMOS功率管设计一个10W的线性功放示例,来看看标准的正向设计流程中,针对MOS管的热补偿设计应该怎么做。
一、明确电路正常工况下的温度波动范围
    民用产品,一般要求将设计指标设计在器件手册规定的MAXIMUM RATINGS限定值的70%以内,那么对于该MOS管,正常工作温度应该控制在-28℃至﹢105℃内,一般按照-20℃至﹢85℃设计。
二、选取正确的直流静态工作点
    对于输出10W功率的AB类功放结构,选取400mAIdq作为其静态工作点(具体的计算计划另开一贴详细叙述)。
三、查阅功率管的Ids-Vds-Tj曲线簇,确定采取何种补偿方向
    经查RD16HHF1DataSheet,该管的Ids-Vds-Tj曲线簇如图5.
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5


    通过观察图5,可以发现MOSFETRds(on)(漏源导通电阻)温度系数有3个区域,分别是正温度系数区、零温度系数点和负温度系数区,符合微电子理论中对MOSFET导通电阻的描述(具体原理请自行查阅相关资料)。
那么在举例的设计中,Idq=0.4AIdq为静态直流情况下的Ids),落在曲线的负温度系数区,这个时候,对于恒定的Vgs偏压,温度越高,Ids越大。因此需要对Vgs进行热补偿设计来稳定Ids
    从图5红蓝线标识处可以大致得到,为保证Ids恒定为0.4A,当温度从-25升高至+75℃时,偏压Vgs应从4.4V降低到4.2VVgs变化量dVgs0.2V。这时应当采用图3所示电路的负温度系数补偿方案。
    再回头去看一下图41N4148二极管的温度特性,1.85mA正向电流时,温度在150摄氏度范围内变化时,压降变化约为0.28V,应用到设计实例的-25+75℃温区时,压降变化量为0.18V(接近dVgs0.2V),因此图3电路只采用11N4001即可。那么图1的合理性大家就可以自己分析了。
    引申一下,现代较高端的线性功放设计,多采用数控偏压源配合温度传感器来实现温度偏压补偿,这样通过实际器件,实际散热环境的测试模型来实现非常精确的静态工作点稳定。同时可以实现工作点的程控化,例如工作在FM模式的时候可以通过程序瞬间实现负压偏置;也可以在PA高驻波时,瞬间提高偏压使MOS饱和。
    在各大HAM论坛中,对偏压补偿的方式也是众说纷纭,其实完全可以用理论来指导实际。说到这里,相信大家也明白了,对于别人的电路,不要盲目copy,需要具体问题具体分析。不谈静态工作点就乱用补偿方式就是耍流氓。
1N4001.pdf43.0k2次

DAN202U.pdf66.0k3次

RD16HHF1.pdf315k3次
来自 无线电
 
2016-5-4 17:29:28
1楼
echo 大神 + 老乡 重出江湖,前排。
大概看懂了是用1N4001这样的二极管当作温敏探头来反馈调节MOS管吧。
我不是HAM,不过对短波CW有点兴趣,因为国内短波CW基本上都是,7.023MHz,最近也尝试用晶体做了个电路,后级的功放能否用IRFP250n这样的开关管来做
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2楼
类似的我们公司生产的主控里面倒是集成了一个温控,然后内核驱动里面会去实时读取,温度高了就降频,我记得2011年的时候客户提到这种功能大家还觉得没必要,现在才过几年就呵呵了,功耗上去得很快
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ehco(作者)
3楼
引用 smith:
echo 大神 + 老乡 重出江湖,前排。
大概看懂了是用1N4001这样的二极管当作温敏探头来反馈调节MOS管吧。
我不是HAM,不过对短波CW有点兴趣,因为国内短波CW基本上都是,7.023MHz,最近也尝试用晶体做了个电路,后级的功放...
smith大神好 40米波段的CW功放,可以完全按照D类开关电源来做,250管子完全胜任。效率还异常的高。
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4楼
搞懂了原理,才能懂得正向设计。
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5楼
霉帝专利
公开号 US8130039 B2
发布类型 授权
专利申请号 US 13/223,657
公开日 2012年3月6日
申请日期 2011年9月1日
优先权日 2006年5月17日
缴费状态 已支付
公告号 US8031003, US20100156537, US20110309884
发明者 Steven M. Dishop
原受让人 Dishop Steven M
导出引文 BiBTeX, EndNote, RefMan
专利引用 (11), 非专利引用 (11), 被以下专利引用 (3), 分类 (18), 法律事件 (2)
外部链接: 美国专利商标局 (USPTO), 美国专利商标局 (USPTO) 专利转让信息, 欧洲专利数据库 (Espacenet)


264140



US8130039.pdf1.74M11次



设计补偏置母线电压偿温度系数为-6.35mV/℃,可以借鉴参考。


2只硅二极管串联的电压补偿温度系数,大约-4.5mV/℃。
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2016-5-5 12:13:52
ehco(作者)
6楼
引用 hambaby:
公开号 US8130039 B2
发布类型 授权
专利申请号 US 13/223,657
公开日 2012年3月6日
申请日期 2011年9月1日
优先权日 2006年5月17日
缴费状态 已支付
公告号 US8031003,...
呵呵 老兄 美帝这图是不是脱密处理过啊 仔细一看 不对劲啊 不改改没法构成反馈
依靠Q51当二极管用法的话,要求Q51和被偏置管同型号同批次,否则也没啥意义。
还有想请教一下老兄,专利如何保护电路?是对器件型号还是对电路结构进行保护?
264162
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7楼
权利要求(30)

1. An RF power amplifier, comprising:
a first field effect transistor:
having a first gate, a first source, and a first drain,
having an output power rating of at least 200 watts, and
operating with a drain-to-source voltage that is greater than 50 VDC;
a second field effect transistor:
having a second gate, a second source, and a second drain,
having an output power rating of at least 200 watts, and
operating with a drain-to-source voltage that is greater than 50 VDC;
wherein said transistors are configured as a push-pull amplifier;
an RF signal input;
an input transformer connected to the RF signal input, the input transformer having respective balanced outputs connected to the first gate and the second gate;
a broadband output transformer having a first balanced input connected to the first drain, and a second balanced input connected to the second drain, wherein the broadband output transformer has an input to output impedance ratio of 1:4, and further wherein at least some flux cancellation occurs within the broadband output transformer; and
temperature compensating bias circuitry for providing a temperature compensated bias voltage to the first field effect transistor and the second field effect transistor for decreasing the bias voltage of the first field effect transistor and the second field effect transistor as transistor temperature increases, the temperature compensating bias circuitry comprising:
a temperature sensor generating a temperature signal;
a first amplifier having an output providing a first temperature dependent voltage based on the temperature signal;
a second amplifier having an output providing a second temperature dependent voltage based on the temperature signal, wherein the first temperature dependent voltage and the second temperature dependent voltage change at substantially the same rate in response to the temperature signal; and
a potentiometer connected to the output of the first amplifier and the output of the second amplifier such that a voltage across the potentiometer remains substantially constant when the first temperature dependent voltage and the second temperature dependent voltage change; and
a bias output connected to at least one of the first field effect transistor and the second field effect transistor and supplying the temperature compensated bias voltage to the at least one of the first field effect transistor and the second field effect transistor.
2. A modular RF power amplifier system, comprising:
a first amplifier module comprising the RF power amplifier as set forth in claim 1; and
a second amplifier module comprising the RF power amplifier as set forth in claim 1;
wherein outputs from said modules are combined to form a combined RF output.
3. The RF power amplifier of claim 1, further comprising:
an RF output terminal;
an output balun transformer; and
a DC-blocking capacitor, wherein the output balun transformer and the DC-blocking capacitor are connected in series between the broadband output transformer and the RF output terminal,
wherein the broadband output transformer is a transmission line transformer including a cable having a characteristic impedance of approximately or exactly 25 ohms,
wherein the broadband output transformer has balanced outputs and during operation of the RF power amplifier a net flux within the broadband output transformer is substantially zero, and
wherein the output balun transformer has an input to output impedance ratio of 1:1 and a characteristic impedance of approximately or exactly 50 ohms.
4. An RF power amplifier, comprising:
a first plurality of field effect transistors having directly interconnected drains and respective output power ratings of at least 100 watts;
a second plurality of field effect transistors having directly interconnected drains and respective output power ratings of at least 100 watts;
wherein said transistors operate with a drain-to-source voltage that is greater than 50 VDC, and
wherein the first plurality of field effect transistors and the second plurality of field effect transistors together form a push-pull amplifier having an output power rating of at least 400 watts;
an RF signal input;
an input transformer connected to the RF signal input, the input transformer having respective balanced outputs connected to gates of the first plurality of field effect transistors and gates of the second plurality of field effect transistors; and
a broadband output transformer having a first balanced input connected to the drains of the first plurality of field effect transistors, and a second balanced input connected to the drains of the second plurality of field effect transistors, wherein the broadband output transformer has an input to output impedance ratio of 1:4, and further wherein at least some flux cancellation occurs within the broadband output transformer; and
temperature compensating bias circuitry for providing a temperature compensated bias voltage to the first plurality of field effect transistors and the second plurality of field effect transistors for decreasing the bias voltage of the first plurality of field effect transistors and the second plurality of field effect transistors as transistor temperature increases, the temperature compensating bias circuitry comprising:
a temperature sensor generating a temperature signal;
a first amplifier having an output providing a first temperature dependent voltage based on the temperature signal;
a second amplifier having an output providing a second temperature dependent voltage based on the temperature signal, wherein the first temperature dependent voltage and the second temperature dependent voltage change at substantially the same rate in response to the temperature signal; and
a potentiometer connected to the output of the first amplifier and the output of the second amplifier such that a voltage across the potentiometer remains substantially constant when the first temperature dependent voltage and the second temperature dependent voltage change; and
a bias output connected to at least one of the first plurality of field effect transistors and the second plurality of field effect transistors and supplying the temperature compensated bias voltage to the at least one of the first plurality of field effect transistors and the second plurality of field effect transistors.
5. A modular RF power amplifier system, comprising:
a first amplifier module comprising the RF power amplifier as set forth in claim 4; and
a second amplifier module comprising the RF power amplifier as set forth in claim 4, wherein outputs from said modules are combined to form a combined RF output.
6. The RF power amplifier of claim 4, further comprising:
an RF output terminal;
an output balun transformer; and
a DC-blocking capacitor, wherein the output balun transformer and the DC-blocking capacitor are connected in series between the broadband output transformer and the RF output terminal,
wherein the broadband output transformer is a transmission line transformer including a cable having a characteristic impedance of approximately or exactly 25 ohms,
wherein the broadband output transformer has balanced outputs and during operation of the RF power amplifier a net flux within the broadband output transformer is substantially zero, and
wherein the output balun transformer has an input to output impedance ratio of 1:1 and a characteristic impedance of approximately or exactly 50 ohms.
7. An RF power amplifier, comprising:
a push-pull amplifier, the push-pull amplifier comprising a first field effect transistor and a second field effect transistor; and
temperature compensating bias circuitry for providing a temperature compensated bias voltage to the first field effect transistor and the second field effect transistor for decreasing the bias voltage of the first field effect transistor and the second field effect transistor as transistor temperature increases, the temperature compensating bias circuitry comprising:
a temperature sensor generating a temperature signal;
a first amplifier having an output providing a first temperature dependent voltage based on the temperature signal; and
a potentiometer connected to the output of the first amplifier such that a voltage across the potentiometer remains substantially constant when the first temperature dependent voltage changes; and
a bias output connected to at least one of the first field effect transistor and the second field effect transistor and supplying the temperature compensated bias voltage to the at least one of the first field effect transistor and the second field effect transistor.
8. The RF power amplifier of claim 7, wherein the temperature compensating bias circuitry further comprises a second amplifier having an output providing a second temperature dependent voltage based on the temperature signal,
wherein the first temperature dependent voltage and the second temperature dependent voltage change at substantially the same rate in response to the temperature signal, and
wherein the potentiometer is connected to the output of the first amplifier and the output of the second amplifier such that a voltage across the potentiometer remains substantially constant when the first temperature dependent voltage and the second temperature dependent voltage change.
9. The RF power amplifier of claim 8, further comprising a follower transistor connected to the potentiometer, wherein the follower transistor generates the bias output.
10. The RF power amplifier of claim 7, wherein the temperature sensor is a transistor.
11. The RF power amplifier of claim 7, wherein the temperature sensor comprises a temperature sensor integrated circuit.
12. The RF power amplifier of claim 7, further comprising a temperature output signal transmitting a temperature of the RF power amplifier.
13. The RF power amplifier of claim 7, further comprising a transistor dump signal for deactivating at least one of the first field effect transistor and the second field effect transistor.
14. The RF power amplifier of claim 7, wherein the first field effect transistor includes a first gate, a first source, and a first drain,
wherein the second field effect transistor includes a second gate, a second source, and a second drain, the RF power amplifier further comprising:
a broadband output transformer having a first balanced input and a second balanced input, wherein the broadband output transformer has an input to output impedance ratio of 1:4, and further wherein at least some flux cancellation occurs within the broadband output transformer;
a first DC-blocking transformer connected between the first balanced input and the first drain; and
a second DC-blocking transformer connected between the second balanced input and the second drain.
15. The RF power amplifier of claim 14, wherein each one of the broadband output transformer, the first DC-blocking transformer, and the second DC-blocking transformer include a cable having a characteristic impedance of approximately or exactly 25 ohms.
16. The RF power amplifier of claim 14, wherein the first DC-blocking transformer provides a negative feedback signal to the first field effect transistor, and wherein the second DC-blocking transformer provides a negative feedback signal to the second field effect transistor.
17. The RF power amplifier of claim 14, further comprising another transformer, which provides negative feedback signals to the first field effect transistor and the second field effect transistor.
18. The RF power amplifier of claim 14, further comprising
an RF output terminal; and
an output balun transformer connected between the broadband output transformer and the RF output terminal.
19. An RF power amplifier, comprising:
a push-pull amplifier, the push-pull amplifier comprising a first field effect transistor having a first drain and a second field effect transistor having a second drain;
a broadband output transformer having a first balanced input and a second balanced input;
a first DC-blocking transformer connected between the first balanced input and the first drain; and
a second DC-blocking transformer connected between the second balanced input and the second drain.
20. The RF power amplifier of claim 19, further comprising temperature compensating bias circuitry for providing a temperature compensated bias voltage to the first field effect transistor and the second field effect transistor for decreasing the bias voltage of the first field effect transistor and the second field effect transistor as transistor temperature increases.
21. The RF power amplifier of claim 19, wherein each one of the broadband output transformer, the first DC-blocking transformer, and the second DC-blocking transformer include a cable having a characteristic impedance of approximately or exactly 25 ohms.
22. The RF power amplifier of claim 19, wherein the first DC-blocking transformer provides a negative feedback signal to the first field effect transistor, and wherein the second DC-blocking transformer provides a negative feedback signal to the second field effect transistor.
23. The RF power amplifier of claim 19, further comprising another transformer, which provides negative feedback signals to the first field effect transistor and the second field effect transistor.
24. The RF power amplifier of claim 19, wherein the broadband output transformer has an input to output impedance ratio of 1:4, and further wherein at least some flux cancellation occurs within the broadband output transformer.
25. The RF power amplifier of claim 24, further comprising
an RF output terminal; and
an output balun transformer connected between the broadband output transformer and the RF output terminal.
26. The RF power amplifier of claim 19, wherein the broadband output transformer has unbalanced outputs and an input to output impedance ratio of 1:1.
27. The RF power amplifier of claim 26, further comprising
an RF output terminal; and
an unbalanced-to-unbalanced transformer connected between the broadband output transformer and the RF output terminal.
28. The RF power amplifier of claim 27, wherein the unbalanced-to-unbalanced transformer has an input to output impedance ratio of 1:4.
29. An RF power amplifier, comprising:
a first amplifier module comprising a first push-pull amplifier including a plurality of field effect transistors and a first output balun transformer, wherein an output impedance of the first amplifier module is 25 ohms;
a second amplifier module comprising a second push-pull amplifier including a plurality of field effect transistors and a second output balun transformer, wherein an output impedance of the second amplifier module is 25 ohms;
a combiner connected to the first amplifier module and the second amplifier module, the combiner comprising an unbalanced-to-unbalanced output transformer having an input-to-output impedance ratio of 1:4,
wherein the combiner combines an output from the first amplifier module and an output from the second amplifier module into a combined signal,
wherein the combined signal is supplied to the unbalanced-to-unbalanced output transformer, and
wherein an output impedance of the combiner is 50 ohms.
30. The RF power amplifier of claim 29, wherein the first amplifier module includes a plurality of DC-blocking transformers, and wherein the second amplifier module includes a plurality of DC-blocking transformers.

该专利原文中的权利要求。
关于专利保护情况,这个大虫可能比较有发言权,俺也是一知半解……
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2016-5-6 08:22:24
8楼
引用 hambaby:
1. An RF power amplifier, comprising:a first field effect transistor:having a first gate, a first source, and a first dr...
看起来这个权利要求的主权项有6项,实际上仍然只有一项。其它属于从属权利要求。
保护范围要看整个权利要求,从属权利要求其实是具体描述和限定主权项的范围。
事实上该权利要求中,温度补偿电路不具有独立的权利。
楼主的理论综述可以认为是该领域技术人员公知的设计思想和设计方法,也不存在专利问题。即使补偿系数设计为6.25mV/℃也没有任何问题。
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