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math&science
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are the input impedances for both inverting and non-inverting amplifiers infinity?
What's the full part number of the opamp? The transistors that I'm referring to are inside the opamp -- that's how an opamp is made. Take a look at the datasheet for your opamp, or the one for a simple LM741, for example. In addition to listing the input characteristics of the opamp, they will usually show you a simplified equivalent circuit. That will show you approximately how they have built the opamp out of transistors, resistors and capacitors on the monolithic opamp IC.math&science said:but i was using a 411 amplifier and not transistors
Well, the LF411 has JFET input transistors, and its DC input resistance is listed as 10^12 Ohms typical. That's pretty high, but not infinite. The datasheet doesn't list input capacitance, unfortunately, but guess it's around 10pF and that gives about -j160kOhms of impedance, definitely not infinite.math&science said:Oh, I see what you're saying. I used an LF411. I guess my question was more of a theoretical one. Would it be infinity theoretically for both types?
An input impedance for amplifiers is the measure of the resistance that the amplifier presents to the source of the input signal. It is an important characteristic of amplifiers as it determines the amount of current that will flow into the amplifier from the source.
The main difference between input impedances for inverting and non-inverting amplifiers is the way in which the input signal is connected. In an inverting amplifier, the input signal is connected to the inverting input terminal, while in a non-inverting amplifier, the input signal is connected to the non-inverting input terminal. This results in different input impedance values for the two types of amplifiers.
The input impedance for inverting amplifiers is calculated as the parallel combination of the feedback resistor and the input resistor, while for non-inverting amplifiers, it is calculated as the input resistor itself. The formula for calculating input impedance for both types of amplifiers is Zin = Rf || Rin, where Rf is the feedback resistor and Rin is the input resistor.
Having a high input impedance for amplifiers is important as it allows the amplifier to draw less current from the input source, resulting in less loading on the source. This is especially crucial for sensitive input sources, as a low input impedance can cause distortion and affect the accuracy of the input signal.
In theory, yes, the input impedance for amplifiers can be infinity. This means that the amplifier will draw no current from the input source, resulting in no loading on the source. However, in practical applications, the input impedance for amplifiers is limited by the properties of the components used and can only reach very high values, but not infinity.