In circuits with resistors, inductors, and capacitors, the blocking effect on the current in the circuit is called impedance. The impedance is usually represented by Z. It is a complex number. It is actually called a resistor. It is called a reactance. The blocking effect of the capacitor on the alternating current in the circuit is called capacitive reactance. The inductance is a hindrance to the alternating current in the circuit. The resistance of capacitors and inductors to alternating current in the circuit is collectively referred to as reactance. The unit of impedance is ohms. The concept of impedance is not only present in the circuit, but also in the mechanical vibration system.
What is the impedance----input impedanceThe amplifier input sees an equivalent resistor called the input impedance. as the picture shows
Calculation method
Input impedance is the equivalent impedance at the input of a circuit. Add a voltage source U to the input and measure the current I at the input. The input impedance Rin is U/I. You can think of the input as the end of a resistor. The resistance of this resistor is the input impedance.
The input impedance is no different from a normal reactive component, which reflects the amount of resistance to current. For voltage-driven circuits, the higher the input impedance, the lighter the load on the voltage source, and the easier it is to drive without affecting the signal source. For current-driven circuits, the smaller the input impedance, the smaller the input impedance is. The lighter the load on the current source. Therefore, we can think that if the voltage source is used to drive, the larger the input impedance, the better; if it is driven by the current source, the impedance is as small as possible (Note: only suitable for low frequency circuits, at high frequencies) In the circuit, the impedance matching problem should also be considered. In addition, if the maximum output power is to be obtained, the impedance matching problem should also be considered.
What is the impedance----output impedanceUsing the equivalent power theorem, looking at the output of the amplifier can be equivalent to a voltage source and the internal resistance are connected in series. This equivalent internal resistance is called the output resistance.
Calculation method:
1, external resistance short circuit, U / I
2. Let the voltage source be zero, calculate Ro
Regardless of the source or amplifier and the power supply, there is a problem with the output impedance. The output impedance is the internal resistance of a signal source. Originally, for an ideal voltage source (including the power supply), the internal resistance should be zero, or the impedance of the ideal current source should be infinite. Output Impedance This is not the case with voltage sources that require the most attention in circuit design but in reality. We use an ideal voltage source in series with a resistor r to be equivalent to an actual voltage source. This resistor r in series with the ideal voltage source is the internal resistance of the (source/amplifier output/power supply). When this voltage source supplies power to the load, a current I flows through the load and produces a voltage drop of I&TImes;r on this resistor. This will cause the power supply output voltage to drop, which limits the maximum output power (for why the maximum output power is limited, see the following "Impedance Matching" question). Similarly, an ideal current source, the output impedance should be infinite, but the actual circuit is impossible.
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