Recently, I was reading a book on Analog CMOS Integrated Circuit Design. During the reading process, there was a sentence that was difficult for me to understand: "The impedance introduced by the current source is infinite." After consulting the information, I understood why it was explained like this.
You can think of it this way: Suppose we now have a simple circuit with a constant current source and a resistor. No matter how the resistance of the added load resistor changes, the current flowing through the circuit should be a constant value (constant current source). Assuming that the voltage drop of the circuit is given, that is to say,
the sum of the resistances in the circuit should be approximately a constant value. In other words, no matter how much load is introduced
, it will not affect the sum of the resistances. So, looking at it this way, the internal resistance of the constant current source is should be approximately infinity.