What are input resistance, output resistance, and output resistance
The input resistance is the equivalent resistance seen from the input end of the amplification circuit, and is a performance indicator used to measure the impact of the amplifier on the signal source. The larger the input resistance, the smaller the current taken by the amplifier from the signal source, and the higher the signal voltage obtained from the input end of the amplifier. That is, the less attenuation of the signal source voltage. Us=Rs+Ri * IoRs is the internal resistance of the signal source, and RI is the input resistance of the amplifier.
Therefore, the amplification circuit of instruments such as oscilloscopes and voltmeters used to measure signal voltage should have a large input resistance. If you want to obtain a larger current from the signal source, you should make the amplifier have a smaller input resistance.
The output resistance is the apparent resistance seen from the output of the amplifier. If the amplifier is viewed as a signal source, it is the internal resistance of the signal source. The output resistance is used to measure the strength of the amplifier's load carrying capacity. When the amplifier outputs the amplified signal to the load resistor RL, the amplifier can be equivalent to having an internal resistance R.
The signal source provides output signal voltage and output signal current to RL from this signal source. RO is called the output resistance of an amplifier, which is the equivalent resistance of human communication from the output end of the amplifier to the amplifier itself. If the output resistance RO is very small and meets the condition of RO ≤ RL, then when RL changes over a large range, the output signal voltage can be basically maintained constant.
On the contrary, if the output resistance RO is large and meets the condition of RO ≥ RL, then when RL changes over a large range, the constant output signal current can be maintained. The ability of an amplifier to maintain a constant output signal voltage (or current) under different load conditions is called load carrying capacity. The output resistance RO is a performance indicator that characterizes this ability.
The input impedance of the operational amplifier is very high (greater than 1M or more), so no amount of resistance (1K-100K) in series will affect the actual effect.
This resistor can also be considered as a current limiting resistor, because there is actually no need for current limiting. The internal resistance of the operational amplifier is too high, and the input current itself is extremely small.
