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# 51 signal to noise ratio, noise figure, equivalent input noise of the significance of what?

"Noise" of the simple definition is: "In the process of self-generated signal equipment", these signals are independent of the input signal. Distortion of the signal source to produce the greatest signal strength is not issued simultaneously with the noise intensity as the ratio between the signal to noise ratio, referred to as SNR (Signal / Noise), usually S / N expressed in decibels (dB); noise figure ( M7): refers to the input of the amplifier output signal to noise ratio SNR and 51 datasheet and the ratio of the unit used "dB". The amplifier noise figure is relatively low (such as NF
52. How to understand the output impedance? Much better?

either source or amplifier, power supply has output impedance of the problem, the output impedance is a source of resistance. Originally, for an ideal voltage source (including power), resistance should be 0, or an ideal current source impedance should be infinite. On output impedance, it is relatively easy to "forget." Here, we voltage source, for example in terms of making the problem.

but in reality the voltage source, you can not do this. We used an ideal voltage source in series with a resistor R, a practical approach to the equivalent voltage source. The ideal voltage source and 51 price and series resistance R, is proud of the amplifier output signal source / power of resistance of. When the voltage source to the load, the current I will be too high from the load and 51 suppliers and the resistance to generate U, the voltage drop. This will cause the power output of the voltage drop, which limits the maximum output power (why limit on the maximum output power, see "impedance matching" one asked.) Similarly, an ideal current source output impedance is infinite, but the actual circuit is impossible.

In general, the voltage source output impedance as small as possible, while current source output impedance the better (Note: only suitable for low frequency circuits, high-frequency circuits, but also consider the impedance matching problem , see "impedance matching" one asked. In addition, the requirements limiting or limiting protection of the sources excluded)

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