How to Design the Reliability of Power Amplifiers Well

author:

How to design and how to do the reliability of power amplifiers is the doubt that many engineers have always had in their minds. For active amplifying circuits such as power amplifiers, the reliability of work is more important than performance indicators in some cases. Let me introduce to you how to design the reliability of the power amplifier well.

In the process of power amplifier circuit design, its reliability is mainly divided into two types: stability and protection. Stability is to prevent self-excitation of the amplifier itself, and protection is to prevent abnormal working conditions or abnormal conditions caused by external circuit abnormal states and environmental problems. damage to the device.

There are two factors that affect the stability of the power amplifier, internal and external, and the internal factor is the problem of the amplifier itself such as packaging.

External factors include many aspects. When the excitation is too large, the amplifier will produce saturation distortion; the PCB layout is unreasonable, the transistor is not well grounded, and the wiring and vias bring distributed parameters, which is easy to cause high-frequency self-excitation; the input and output distances are too close to cause coupling and so on.

For power amplifier protection, it is mainly to prevent damage to the amplifier under extreme conditions. The more common ones are overvoltage breakdown, static electricity, overexcitation, lightning strike, pulse voltage and current, open circuit load and short circuit load, etc.

How to judge the stability of the power amplifier? It is mainly based on the stability factor and the reflection coefficient of the port. When the four reflection coefficients of the port (Γs, ΓL, Γin, Γout) are all less than 1, it is stable; when the stability coefficient K>1, it is stable.

After the power amplifier is stably designed, whether it is effective and reasonable needs to be verified by testing. Methods to test circuit stability include static operating point test and gain test and spectrum observation. Analysis of the stability judgment method: When adjusting the static operating point, observe whether the static current has abnormal jumps; when no input signal is applied to the input terminal, observe whether the output has a signal output with a certain frequency and amplitude.

How to design the stability of the power amplifier is mainly considered from the following aspects when designing the stability:

1. Select the appropriate static working point.

2. Adopt RC negative feedback circuit to form closed-loop control and reduce S21.

3. Connect the feeding inductance with a small resistor in parallel to reduce the Q value of the self-resonant circuit of the inductance or the resonant circuit generated by other parasitic parameters to avoid oscillation.

4. Add π-type attenuation circuit, increase isolation, reduce reflection between stages, and improve S22 and S12.

5. The input end adopts high-pass matching to balance the high-end and low-end gains.

6. The series resistance in the input circuit.

7. When laying out the PCB, ensure that the grounding is good, separate the inductors in series, and avoid thin and long RF traces.

power amplifiers

Application of Ultrasonic Power Amplifier in MEMS Ultrasonic Testing

What is a diode?

Application of Ultrasonic Power Amplifier in MEMS Ultrasonic Testing

What is a diode?