What parts of the circuit are made up of?
There are different types of amplifiers, and the circuit of the amplifier can be composed of the following parts: transistor, bias and stabilization circuit, input and output matching circuit.
1. Bias circuit and stable circuit
Bias and stabilization circuits are two different circuits, but because they are often difficult to distinguish and the design goals same, they can be discussed together.
The operation of the transistor requires a certain bias condition, which we call a static operating point.
This is the foundation of the transistor's foothold and its own "positioning." Each transistor has its own positioning, and its different positioning will determine the working mode, and there are different performances in different positioning.
Some anchor points have small undulations and are suitable for small signal operation; some anchor points have large undulations and are suitable for high power output; some are less available on the positioning point, and the release is pure, suitable for low noise operation; an appropriate offset Point is the basis of normal work. When designing a wideband power amplifier, or when the operating frequency is high, the bias circuit has a large impact on the circuit performance. In this case, the bias circuit should be considered as part of the matching circuit.
There are two major types of bias networks, passive networks and active networks. Passive networks (ie, self-biased networks) typically consist of a resistor network that provides the proper operating voltage and current for the transistor.
Its main drawback is that it is very sensitive to changes in the parameters of the transistor and has poor temperature stability. Active bias networks improve the stability of static operating points and improve temperature stability, but they also have problems such as increased circuit size, increased circuit layout and increased power consumption.
The stabilizing circuit must be in front of the matching circuit because the transistor needs to have the stabilizing circuit as part of itself and then contact the outside world. In the outside world, a transistor with a stable circuit is a "new" transistor. The mechanism of the stabilizing circuit ensures smooth and stable operation of the transistor.
2, transistor
There are many types of transistors, including transistors with multiple structures. Essentially, the operation of a transistor is manifested as a controlled current or voltage source that works by converting the energy of the DC without content into a "useful" output. The DC energy is obtained from the outside world, and the transistor is consumed and converted into useful components.
Different transistors have different "capabilities", such as their ability to withstand power, which is also due to the difference in their ability to obtain DC energy; for example, their response speed is different, which determines how wide and how high it can work in the frequency band; for example, its impedance to the input and output terminals is different, and the external response capability is different, which determines the difficulty of matching it.
3, input and output matching circuit
The purpose of the matching circuit is to choose an acceptable method. For those transistors that want to provide greater gain, the approach is full acceptance and output. This means that the communication between the different transistors is smoother through the interface of the matching circuit. For different amplifier types, the matching circuit is not only a "full acceptance" design method.
Some small tubes with small DC and shallow foundations are more willing to block when they are accepted to obtain better noise performance. However, they cannot block excessive, otherwise they will affect their effects. For some giant power tubes, you need to be cautious when exporting, because they are more unstable. At the same time, certain reservations help them to exert more "not distorted" energy.
Typical impedance matching networks have L-match, π-match, and T-match. Among them, L is matched, which is characterized by simple structure and only two degrees of freedom L and C. Once the impedance transformation ratio and the resonant frequency are determined, the Q value (bandwidth) of the network is determined.
One advantage of a π-matching network is that no matter what kind of parasitic capacitance, as long as it is connected to π-matching network, it can be sucked into the network, which also leads to the universal application of the π-shaped matching network, because in many practical situations, it dominates. The parasitic element of the position is the capacitor. T-shaped matching, when the parasitic parameters of the power supply and the load end are mainly inductive, T-shaped matching can be used to absorb these parasitic parameters into the network.
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