high performance voltage regulators

Biglee_163

As you can see, it uses an LM317 pre-regulator, but it's more thoughtfully implemented than in the Sulzer and Breakall articles.
就象你看到的，他使用了一个LM317作为预先稳压器，但他比Sulzer 和 Breakall考虑的要周到。

The only quibble I have with the Borbely design is the choice of the LM336 band-gap reference. The main thing about band-gaps is that they can be made with much lower voltage drops than zeners, but they are noisier than a buried zener type reference. Since we don't need the low voltage feature for high-quality audio, I think it's more sensible to go with an LM329 buried zener here. Nevertheless, a band-gap reference is still an improvement over a standard zener both in terms of noise and stability. It's just that a buried zener is even better, if you can afford the higher voltage drop.
唯一模棱两可的是Borbely的设计使用了band-gap(带隙)技术的参考电源LM336。和稳压管相比他们的主要特性是电压跌落要好的多，但他们的噪音要比隐藏型稳压管大。因为温暖在高质量音频系统中并不需要使用低电压的特性，所以我认为使用一个隐藏型稳压管LM329应该更好一些。无论如何，band-gap型参考源的使用仍然是对传统稳压管的噪音以及稳定性的一次改良。如果你可以承受更大的电压跌落的话，一个隐藏型的稳压管似乎更好一点。

Jung Super Regulator
Jung超级稳压器

Finally we come to the Jung regulator. In the first two issues of TAA in 1995, Jung describes his circuit and gives some very detailed test results of it vs. several other linear regulator types. In issue 3, Jan Didden gives a PCB layout for the circuit and gives some advice for applying the regulator circuit. And in issue 4, Gary Galo does some subjective tests on the regulator dropped in as mods to real circuits, with side-bars written by Jung and Didden. If you only want to pick up a few back issues of all the ones I mention, pick up the first two in this series at minimum. The full set of four is very helpful.
最后我们来看Jung稳压器。在1995年TAA杂志发表了两篇文章，Jung描述了他的电路并且和一些线性稳压电源比较所做的非常细节的测试结果。在第3篇文章中，Jan Didden排出了印板并且提出了一些使用建议。在第4次发表中，Gary Galo做了独立测试并改进到接近真实电路，Jung 和 Didden为之写了注解。如果你想回味我提到的版本，最少要看前面2篇文章，所有的4篇文章都是非常有帮助的。

Biglee_163

The major differences in the Jung regulator relative to the original Sulzer design are: better pass transistor (D44H11), different drive scheme for pass transistor, no pre-regulator, better op-amp (AD797), op-amp protection, precision reference (LM329), and remote sensing.
Jung稳压器和Sulzer稳压器最主要的区别是：更好的调整管(D44H11)，调整管不同的驱动电路，没有预先稳压器，更好的运放(AD797)，运放保护，精密参考源(LM329)以及远距检测。

The error amp in the Sulzer regulator effects voltage regulation in a standard way: it varies its output current which changes the voltage drop across the pass transistor. The Jung regulator uses a much different control mechanism. In the Jung regulator, a constant current source (Q2 and assocated parts) pushes current to the base of the transistor, and the error amp sinks as much of this away as is required to maintain the desired output voltage. (The diode inline with the op-amp's output is why it can only sink current.) As I see it, the primary advantage of this configuration is that the CCS indirectly limits the maximum output current of the regulator to a reasonable value. A short across the output of a stock Sulzer regulator would probably destroy the pass transistor.
Sulzer稳压电源中的误差放大器按照标准的方式取得电压调节功能：通过改变输出电流来控制调整管的电压降。Jung稳压器使用了一个不同的稳压机制。在Jung稳压器中，一个恒流源（Q2和关联电路）将电流推到调整管的基极，误差放大器吸收了为保持设定输出电压而要求的电流。（这个连接到运放输出的二极管就是为什么他只能吸收电流的原因）。就如我看到的，这样设计主要的好处是恒流源间接限制了稳压器的最大输出电流并达到一个合理的范围。而老版本Sulzer稳压器在短路输出的情况下将会损坏调整管。

There is a low-pass filter on the op-amp's V+ pin as in the original Sulzer design (R3, C2), but Jung says this is optional. One gets the impression that he'd rather just depend on the power supply ripple rejection behavior of the op-amp. There's some worry that the resistor in this filter could have load-modulated voltage drops across it, thus possibly increasing the ripple at the supply pins. In the fourth article in the series, Gary Galo says he heard a difference between a version with the filter and without, and says he prefers the version with the filter.
和原始Sulzer设计一致，运放的V+端有一个低通滤波器(R3, C2)，但Jung说这个是可选择的。给人的印象是他宁愿依赖运放自身的电源纹波抑制比。有点担心滤波器中的电阻上会有负载调制电压降在上面，这样会影响到运放的电压供应引脚上。在该系列的第4篇文章中，Gary Galo说他听出了有和没有这个滤波器的变化，并说他喜欢选择有滤波器的那个。

Notice that the pass transistor's collector connects directly to the unregulated supply input, not after the low-pass filter like in the original Sulzer circuit. This keeps the high-current path low in impedance and lowers the influence of the output current on the op-amp's power rails.
注意调整管的集电极是直接连接到了非稳压电源的输入处的，而不象原始Sulzer电路一样接在低通滤波器之后。这保持了大电流通路的低输入阻抗并降低对运放供电回路电流的影响。

The diodes on the error amp's inputs protect it from overvoltages. Some op-amps have diodes across the inputs like this already, but even a small discrete diode can pass far more current than the on-chip diodes.
误差放大器输入口的二极管提供了过压保护。一些运放，如象这里使用的，内部已经有了并联在正负输入两端的保护二极管，但即便是外部小二极管，也能比内部二极管通过更大的电流。

There are a few layout considerations pointed out in this series. They aren't part of the circuit design per se, but they are part of the intended implementation. (You could do both of these to the Sulzer variants as well.) First, R2 and R8 do not connect directly to the output of the pass transistor as drawn. Instead, just connect them together and put a wire pad between them. Second, I used two different ground symbols in the schematic; each one is a separate star ground. The two wires from the pass transistor's output and the R2/R8 junction go to the positive side of the load. This allows the error sense circuit to see all errors that happen between the output of the regulator proper and the load. A separate wire from each star ground centerpoint goes to the negative side of the load, so the noise bypassed to ground from the control and sense circuits only mix at the load/sense point, so the error amp can control these errors as well.
在此系列中对排版提出了需要考虑的事项。他们不是每个电路版本的一部分，但他们是必不可少的。（同样适用Sulzer稳压器）首先，R2和R8不要象电路图画的一样直接连接到调整管的的输出点上。相反，将他们连接在一起并放一个焊盘线在两者中间。第二，我在电路中使用了两个接地符号；每个符号是个单独的星型接地。调整管输出点和R2/R8连接点处分别引出两根线走向输出负载的正接点。这样会让误差检测电路可以对整个稳压电源的输出带载而产生的误差感应正确。两个不同的星型地分别引出两根线到负载的负接点，这样从控制和检测电路部分被旁路到地的噪音只有在负载/检测点被混合，所以误差放大器可以同样控制这些误差。

If you do run separate wires from the control and sense grounds to the load, you should also connect the ground of the unregulated section of the power supply to the negative side of the load to avoid a ground loop. Also, beware that there is a risk to remote sensing: it greatly increases the size of the error amp's feedback loop, and it adds significant inductance and probably also capacitance from the long wires into this loop. If you add remote sensing, you must test the power supply for oscillations, especially if you use the fast op-amps that Jung recommends. The fourth article in the series has info on troubleshooting oscillations.
如果你确实使用了两个独立的线从控制和感应地接到了负载上，你应该将非稳压的电源供应的负端也接到负载负端，以避免接地有回路环。同样，要注意远距检测：他极大地提高了误差放大器的反馈回路的反馈程度，并由于接入此回路的长引线的电容而增加了大量的自感应。如果你加上了远距检测，你必须测试电源是否震荡，尤其是使用了Jung推荐的高速运放。第四篇文章已经提供了对付震荡的办法。





Jung Super Regulator 2
Jung超级稳压器2代

In the 4/2000 issue of Audio Electronics (successor to TAA), Walt Jung published a new version of his regulator with several improvements over the 1995 circuit:
2000年4月Audio Electronics 杂志( TAA的继任者)发布，Walt Jung针对1995的版本对他的稳压电压进行改进而发表了一个新的版本：

Biglee_163

I've used the same component names as far as possible to aid comparison to the 1995 circuit. I reuse the C2 designation because it's actually the same capacitor on the modified Didden boards, though it has a new role in this circuit. In all other cases, new components have new names.
对比1995年的电路我尽可能使用了相同的元件和名称。我重新使用了C2的设计因为他实际上是在修改的Didden的板上的同样的电容，虽然他在这个电路上有了新的角色。从另一个角度说，新的部件有了新的名称。

The first thing you notice is the LM317 pre-regulator, but I'll talk about that later. Pretend for the moment that the input comes from just before D1.
首先你会注意到的是LM317预先稳压器，但我在稍后谈论他。瞬间的假象是输入是在D1之后。

Far more important is the change to the error amp's power connection. Notice that V+ comes from the output of the power supply. The error amp runs from the regulator's clean output power instead of lightly-filtered unregulated power. Obviously R3 and C2 are no longer needed with this configuration. C3 also had to be removed because you can't use a film bypass cap on the error amp's V+ supply any more because the amp becomes unstable if the output caps' impedance is too low.
另一个重要的改变是误差放大器的电源的连接。注意V+是取自稳压电源的输出。误差放大器使用的是经过稳压的干净的电源而非简单滤波的非稳压电源。显然R3和C2已经在此电路中没有存在的必要了。C3也必须去掉，因为你不能在误差放大器的V+添加更多的薄膜旁路电容，否则由于输出电容的阻抗太低，将使运放变得不稳定。

The diode on the error amp's output is now a 6.8V zener. This helps the regulator start up more reliably. It may be needed in difficult situations in the original Jung circuit, but Jung says it's absolutely essential in this new circuit. If you were to use a regular diode, the the error amp's output is likely to lock up near the negative rail on startup.
误差放大器输出端连接的一个二极管是个6.8V的稳压管。这将使稳压器的启动更可靠。这在Jung的原始版本电路中是恶化境况的需要，但Jung认为他也是这个电路的精华所在。如果你使用了一个稳压二极管，误差放大器的输出在稳压电源启动的时候将接近负供电电压并锁定。

The circuit now uses the AD825. Jung says the AD797 had problems in environments with strong RFI, since its sensitive inputs would rectify the interference and make the output of the error amp unstable. FET input chips are less sensitive to this problem. Emitter-degenerated bipolar input chips are also said to be workable; Jung recommends the AD817. You still want a fairly fast chip for this purpose, and a strong output stage helps.
这个电路现在使用了AD825。Jung认为AD797在较强的RFI（射频干扰）环境下有问题，主要是他敏感的输入端会感应这些信号并导致输出不稳定。FET输入级的运放对这个情况就不那么敏感。发射极接有负反馈电阻的双性型三极管作输入的(运放)芯片在这里也可以工作；Jung推荐AD817。你仍然需要一个相对高速的运放以及一个强壮的输出级的帮助

The current source's default value has been lowered. The D44H11's minimum hFE is 60, so the minimum current from this configuration is about 330mA. If you mirror this circuit for a negative regulator, the complementary D45H11's minimum hFE is 40, so the minimum current would be more like 225mA. You don't want to increase the circuit's output level needlessly because that puts an unnecessary load on the output stage of the error amp.
恒流源的默认电流已被降低。D44H11的最小HFE是60，所以这个电路的最小电流输出大约是330ma。如果你参照这个做个镜像的负稳压电源，互补管D45H11的最小HFE是40，所以最小输出电流大约是225ma。你没有必要增加电路的电流输出能力了，因为这会给误差放大器徒然添加不必要的负载而已。

The LED and its series resistor have been changed to match recommendations by Gary Galo in part 4 of the 1995 series. Galo said these lower the dropout voltage. Jung does mention using the 2N2907 instead of the 2N5087, but he doesn't mention dropout, though Galo said this helped as well.
LED和他串联的电阻是按照1995年Gary Galo在第4篇文章中的推荐而改变的。Galo 认为这将减少压降。Jung提及用2N2907取代2N5087，但没有提及死区电压，而Galo 提到了这个是有帮助的。

And now for that LM317 pre-regulator. Jung's implementation is infinitely more clever than the pre-regulators used by Sulzer and Borbely. Because the LM317 is a floating design, Jung is able to wrap the regulator around the pass transistor so that the output of the preregulator always stays a fixed amount above the output of the pass transistor. The resistor values shown give a 2.3V drop across the preregulator, which should be high enough that you can pull 1.5A from it without hitting dropout. The preregulator reduces the amount of ripple the error amp has to remove, it reduces small errors through the current source, and it takes some of the power dissipation load off the pass transistor. The only downside to the preregulator is that the dropout voltage of the combined regulator rises to something on the order of 5V.
现在来谈论下预先稳压器LM317了。Jung对于预先稳压器的应用显然比Sulzer 和 Borbely高明。因为317是个浮动的设计，Jung可以限制调整管所以预先稳压器的输出总是保持比稳压调整管电流大的一个固定的数值。如图电阻数值将给出一个2.3V的预先稳压器的电压降，这个已经足够高了，可以给出1.5A的电流而没有阻碍。预先稳压器降低了误差放大器必须要消灭的纹波，也减少了恒流源的小误差，并且他承担了一些调整管要承担的耗散功率。使用预先稳压器唯一的缺点是使整个稳压器的压降增大，达到了5V的水平。

The article describes the changes as mods to the Didden circuit boards, so I suspect the boards distributed by audioXpress are still the original design.
这个文章描述了相对Didden电路板做的一些改变，所以我怀疑audioXpress上发表的板是否是原先的设计。

Schematics
原理图

The schematics above are available as a PDF (36K) which will be easier to read than the graphics above.
下面是个PDF连接，应该比看上面的图纸简单一点

Final Comments
总结

In the 2/1974 issue of The Audio Amateur there appeared an article by Walt Jung, "IC Regulated Power". That year also saw the publication of Jung's now-classic book, IC Op-Amp Cookbook. I haven't seen the articles (the 1974 issues of The Audio Amateur are sold out) and I only have the 1986 edition of the book. (Republished with a 1997 copyright date.) Nevertheless, I supeculate by what I see in that edition of the book and what I've read about the 1974 article that Jung had regulators like the archetype at the top of the article in mind way back then. Nevertheless, I think the Sulzer really kicked off a new direction in DIY regulator design.
1974年2月在Audio Amateur上有一篇Walt Jung写的文章，"IC Regulated Power"（IC稳压电源）。现在还可以看Jung发表的至今经典的文章-IC Op-Amp Cookbook（IC运放手册）。我没有读过这文章（1974年发表的杂志卖完了）但我看了1986年的版本。（1997又重新出版）。然而，我盗用了我在书中看到的版本和我在1974年见过的发在文章开头的Jung的原始版本。我也认为Sulzer开创了一个DIY稳压器的设计新方向。

Between the 1995 and 2000 articles, Jung published two intermediate circuits. The first was in EDN Jan. 2, 1997, "Regulator Excels in Noise and Line Rejection". The second was in Electronic Design Analog Applications Issue June 23, 1997, "Low-Noise Power for Analog Circuits", which you can download from Walt Jung's web site.
在1995和2000年的文章中，Jung发布了两篇中间电路。一篇是1997年1月2日的，"Regulator Excels in Noise and Line Rejection"，第二篇是1997年6月23日发布在analog电子设计文档的"Low-Noise Power for Analog Circuits"，你可以从Jung的网站下载他。

Jeffrey Jenkins offered some helpful technical help with this article, which has been incorporated since the original publication.
Jeffrey Jenkins在本文中提供了许多有帮助的设计，这些已经成为原始发表的一些组成部分了。

Biglee_163

jung regulators are a little bit too complicated as it requires a high-speed opamp, which is hard to come by.
Jung的稳压器有一点复杂主要是他要求的高速运放很难得到

however, you can implement a jung regulator quite simply.
然而，你可以简单地仿制一个Jung稳压器

here is one example.
这里是一个例子

special note: V1 is a 2v led, v3 is a 20v zener (you may use a different one depending on your needs).
特别指出：V1是个2V LED，V3是个20V的稳压管（用可以使用不同的稳压管取决于你的需求）

it looks pretty much like a regular power supply.
他看上去非常象个稳压电源

a) input stage: q2/q3 form the differential input stage. V3 the zener provides a reference voltage. r2 provides bias to the zener, and r6/c2 form a low-pass filter to filter out zener noise.
a)输入级：q2/q3 组成差分输入级。V3稳压管提供参考电压。r2提供稳压管的偏置，r6/c2组成一个低通滤波器来滤除稳压管噪音

r4/r8 forms the feedback to the input stage. C1 drops all the a/c on the base of Q2 to increase the gain for output ripple.
r4/r8组成输入级的反馈。C1降低所有Q2基极上增加输出纹波的增益的交流成分

b) Q4 forms the voltage ampliciation stage, R10 is the emitter regenerator resistor.
b)Q4组成电压放大级，R10是发射极负反馈电阻

the load of Q4 is a constant current source (q1, r1, c1, and r4). This helps improve gain for the amplifier.
Q4的负载是个恒流源(q1, r1, c1, and r4). 这有助于提高放大器增益。

c) M1 is the output mosfet (it can be a bipolar transistor as well).
c)M1是输出mosfet (也可以使用双极性管）

as you can see, when fed with 50v dc + 20v ripple (40% ripple content), and driving into 8ohm load (3.7amp), the output is rock solid at between 29.43371v to 29.43387v, or a ripple content of 1-29.43371/29.43387=0.0005%. or a 37,000x improvement.
正如你所见，当输入50V直流加上20V纹波（40%纹波成分），并且驱动8欧姆负载的状况下（3.7安培电流），输出牢靠地在29.43371v 到o 29.43387v之间，纹波范围1-29.43371/29.43387=0.0005%，或者 37,000x抑制

Biglee_163

as locky_z pointed out, this is essentailly a power amplifier.
就如locky_z兄弟指出的，这实际上是个功率放大器
if you feed audio signal to V3, you get audio output on R7.
如果你给V3输入音乐，你可以从R7得到音乐输出
like any other audio amplifiers, you can improve it.
和其他音频放大器一样，你可以改进他
the first problem is that the current in the input stage varies with output voltage or ripple.
第一个问题是输入级的电流随着输出电压或者纹波而变化
so we can replace R3 with a constant current source.
所以我们可以使用一个恒留源来代替R3
slightly better ripple rejection: output ripple from 29.369185v to 29.369257v, or a ripple content of 0.0002%, and ripple rejection of 80,000x.
些微的纹波抑制改善：输出纹波从29.369185v到 29.369257v，纹波比0.0002%，抑制比80000X
very good.
很好

Biglee_163

another way to improve the open loop gain of a differential pair is to use a current mirror.
另一个提高差分电路开环增益的途径是使用电流镜电路

q5/q6 is the added current mirror and r11/r12 the degeneration resistors.
q5/q6是个增加的电流镜，r11/r12 是本地负反馈电阻

ripple? well, from 29.4101561v to 29.4101468v, or ripple of 0.00003%, ripple rejection of 632,000x.
纹波？好，从29.4101561v 到 29.4101468v，0.00003%，纹波抑制比632000X

you cannot beat that, can you?
你不能打败他，是吗？

Biglee_163

most amps have great psrr at low frequencies but poor psrr at high frequencies.
大部分放大器对低频有很好的电源纹波抑制比而高频就不行了
so how will our amp do?
那么我们的放大器怎么样呢？
I fed it with a 20vp 20khz ripple, rather than the 100hz ripple we have been using.
我给他输入20Khz20V的纹波，而不是刚才使用的100hz的。
here is its ripple output for the last version with a current mirror.
这是使用了电流镜的最后版本的输出纹波
output ripples from 29.41006v to 29.41023v, or 0.00058% ripple, for a ripple rejection of 34,000x.
输出纹波从29.41006v 到 29.41023v，0.00058%纹波，34000X纹波抑制比
not bad at all.
还不赖

Biglee_163

further improvement?
更多改进？
a) replace R4 with a tl431 + 2 resistors.
将R4用tl431和2个电阻取代
b) replace the zener with a tl431 + 2 resistors.
将稳压管用tl431和2个电阻取代
c) add a floating pre-regulator, like in jung super regulator 2.
加浮动预先稳牙器，象Jung super reguler 2代一样
d) use two small signal mosfets for q2/q3 and dial up the current.
用两个小信号mosfet取代Q2/Q3并且提高电流
e) add a protecton diode for M1.
为M1增加保护二极管

etc.
等等

Biglee_163

what I would NOT recommend this power supply?
我不推荐这个放大器吗？不是一个功率放大器
NOT in a power amp.

小鬼头

Biglee_163的翻译已非常好.


为方便大家阅读,利用版主的编辑权对 Biglee_163 的帖子作了分行处理,即插入空行.

还校正了几处翻译上容易造成误解的地方:

the pass transistor     电源调整三极管(原译为 传输三极管)
sensing 和sense  译为检测可能更好(原译为感应)
a moving coil preamp     动圈唱头前置放大器
bang-gap     带隙技术(用于制作电压源的专门技术或工艺,如TL431就是)
a buried zener    原译隐藏型稳压管,不恰当,但我忘了应怎么译(应是与雪崩型稳压二极管相区别),故保留原译.
Emitter-degenerated bipolar input chips    发射极接有负反馈电阻的双性型三极管作输入的(运放)芯片(原译为发射极耦合的双极性管输入的芯片)

the dropout voltage 楼主译为死区电压,我改为压降.

Some op-amps have diodes across the inputs like this already, but even a small discrete diode can pass far more current than the on-chip diodes.
      这一句原译得不够明晰.改译为:   一些运放，如象这里使用的，内部已经有了并联在正负输入两端的保护二极管，但即便是外部小二极管，也能比内部二极管通过更大的电流。

C3 also had to be removed because you can't use a film bypass cap on the error amp's V+ supply any more because the amp becomes unstable if the output caps' impedance is too low.
     这句也修改一下,译得更易懂:    C3也必须去掉，因为你不能在误差放大器的V+添加更多的薄膜旁路电容，否则由于输出电容的阻抗太低，将使运放变得不稳定。

The diode on the error amp's output is now a 6.8V zener. This helps the regulator start up more reliably. It may be needed in difficult situations in the original Jung circuit, but Jung says it's absolutely essential in this new circuit. If you were to use a regular diode, the the error amp's output is likely to lock up near the negative rail on startup.
    这段我不知道该怎么改.总感觉还可以译得更好:  误差放大器输出端连接的一个二极管是个6.8V的稳压管。这将使稳压器的启动更可靠。这在Jung的原始版本电路中是恶化境况的需要，但Jung认为他也是这个电路的精华所在。如果你使用了一个稳压二极管，误差放大器的输出在稳压电源启动的时候将接近负供电电压并锁定。


PS:还有一些小改动,不能尽录.

激光鼠

Biglee_163 辛苦了

millwood

Biglee_163 辛苦了!

the sad truth about discrete regulated power supply is that a lot of the regulator ICs have incorporated those ideas. Take a typical 317 or 431 and you will tons of similarities between them and the circuits here. the difference is that the ICs tend to have a lot more transistors for a more precision applications.

so my suggestion is that unless you absolutely have to have a super stable rail voltage (very rare in audio application) or huge output current, just use one of those ICs - costwise you cannot compete with those ICs.

小鬼头

millwood 请收PM.

顺便顶一把

小鬼头

原帖由 millwood 于 2007-12-14 20:05 发表
the sad truth about discrete regulated power supply is that a lot of the regulator ICs have incorporated those ideas. Take a typical 317 or 431 and you will tons of similarities between them and the circuits here. the difference is that the ICs tend to have a lot more transistors for a more precision applications.

so my suggestion is that unless you absolutely have to have a super stable rail voltage (very rare in audio application) or huge output current, just use one of those ICs - costwise you cannot compete with those ICs.

译一下:

对于分立件电源来说,有点悲哀的事实是大量的稳压IC都已使用了上面的那些方法.拿典型的LM317或TL431三端稳压IC来说,你将看到,他们的内部线路与这里的分立件线路中有很多相似之处.不同的是IC往往是为了更精确的用途而使用大量的晶体管.

因此我的建议是,除非你绝对需要超稳定的电源电压(这在音响中是很少的)或者很强的电流输出,否则你一般使用稳压IC就足够应付你的需要-----也因为你不能与这些IC比赛.

输入电龙

根没说一样.
鄙视你

WYSheng1123

locky_z

原帖由 Biglee_163 于 2007-12-14 18:23 发表
another way to improve the open loop gain of a differential pair is to use a current mirror.
另一个提高差分电路开环增益的途径是使用电流镜电路

q5/q6 is the added current mirror and r11/r12 the ...

除了用上述办法，最后还有一个不推荐的办法来提高差分电路开环增益，就是增加一点正反馈Rf。

摘自一本书上的话：
用正反馈使输出电阻为0
  在负反馈回路中加入正反馈会产生意外的效果，如果正反馈加在回路放大器的一级，且反馈量达到了在一般情况下会引起震荡的临界点，那么这时的负反馈回路就像增益无穷大一样。但在这里不会产生震荡，并且负反馈系统的输出阻抗是0。如果再进一步增大正反馈，使之超过在一般情况下会引起震荡的反馈量，那么系统仍然是稳定的，但此时输出阻抗变成负的。但Zout=0的正反馈量是很严格的，难以准确维持这种状态，
  但事实上，为改善线路对Vi变化的性能，只需进行隔离，而不必增大回路增益，尽管更大的回路增益也能改善这个性能，但从各方面来看，不宜采用很大的回路增益。应用较大的回路增益的主要优点就是提高了输出对于放大器增益变化的稳定性，使实际输出电压与按照基准典雅的某个简单比例所计算出来的数值更相符合，同时减少输出阻抗。

所以我觉得想更加提高Vo对Vi变化的免疫力，除了用电流镜等方法提高回路增益之外，隔离Vi也是一个较好的方法，例如：
1.调整管采用自举沃尔曼（共基-共集电极输出），就象浮动预先稳牙器一样
2.Q1采用更进恒定的威廉逊恒流源，

老土

挖个好帖出来学习。

QQ虫

我就喜欢看这样的文章，对我的工作也有很大的帮助！非常感谢楼主。

anmon

不错的，要学习