I'm trying to design high gain, low collector current Common Emitter amplifier.
As far as I know, this is well known CE amp for high gain.
Is there anything I can do for low-current consumption? And I would really appreciate it if you let me know the methods to decide resistor values for high-gain, low-current
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3\$\begingroup\$ This is a typical "class A" type amplifier. The #1 drawback to this type of amplifier is its current consumption (the idle current has to be at least as large as the maximum drive current). The only real way to decrease this is to switch to a different class of amplifier. This link may help \$\endgroup\$– evildemonicCommented May 11, 2023 at 19:26
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2\$\begingroup\$ What do you consider low current? What do you consider high gain? \$\endgroup\$– GodJihyoCommented May 11, 2023 at 20:39
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\$\begingroup\$ The maximum voltage gain of a common emitter amplifier is independent of the current drawn. It's only dependent on the Early effect. It's a different matter when you're trying to drive a load, which you haven't specified. \$\endgroup\$– LetterSizedCommented May 12, 2023 at 14:59
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\$\begingroup\$ egekod - Hi, What are you doing? You have been changing your question after answers were given (please don't do that), then you put things back as they were. Do you need help with using the site? We can try to help, if you explain what you are trying to do. Thanks. \$\endgroup\$– SamGibson ♦Commented May 12, 2023 at 15:17
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\$\begingroup\$ egekod - You have just removed the part which was the apparent main question originally, where you had asked: "Is there anything I can do for low-current consumption?" As I said above, please don't change the question after answers have been received, as it can invalidate those answers. In this case, your first answer mainly addressed the low current consumption question, so you cannot now remove it. || As I asked above, please explain what you are trying to achieve by your changes to the question. Thanks. \$\endgroup\$– SamGibson ♦Commented May 12, 2023 at 15:31
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2 Answers
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One way to reduce current consumption in a CE amp is to use self-biasing instead of voltage divider biasing.
Basically you remove R2, and connect R1 to the collector instead of the positive supply. Now all of the bias current goes into the base instead of some being shunted to ground. It also makes biasing pretty easy, since it adjusts itself to some degree it's rather forgiving of resistor values.
Something like this for instance will give you around 45 dB of gain at around 500 uA current draw. Note that it needs to be followed by a stage with high input impedance, typically at least 10 times the collector resistance (indicated by the 100k load here), the following stage can be something like an emitter follower as it only needs current gain.
simulate this circuit – Schematic created using CircuitLab
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A transistor with high gain has high distortion. This transistor is not clipping. Negative feedback reduces the distortion and reduces the gain:
