Usually, if you wish to management the acquire of an amplifier, you’ll use a variable resistor. You understand, like a quantity management. However what if you wish to management the amplifier’s acquire with a voltage? [Engineering Prof] explains a circuit that may do that utilizing a pair of op amps and a pair of matched JFETs.
The evaluation is easy since you assume the op amps will not be in saturation, so you’ll be able to assume that the op amp will do what it must do to make the enter terminals equal. The left-hand op amp has one enter grounded, so the output will drive the primary FET to make sure the damaging terminal can also be 0V. It’s straightforward to see that the present by R1 should then be the present by the FET, which goes to be the management voltage (which is damaging) divided by R1.
The gate voltage on the primary JFET’s gate is identical because the gate voltage on the second JFET. Since they’re matched, you’ll be able to assume the present by that transistor would be the identical as the primary transistor. For those who make certain the management voltage stays within the linear area of the FET, the system works considerably like a variable resistor.
Complicated? Watch the video under, and it’ll all be clear. We would counsel you simulate it when you actually wish to perceive it. For those who don’t like your simulator in a browser, there are all the time selections.
