The ratio of amplifier output to input is the amplification factor, and the unit is "times", such as 10 times amplifier and 100 times amplifier. When the unit is changed to "decibel", the magnification is called gain, which is two names of a concept. DB is basically a proportional value, that is, the unit of expression of multiples. That is, the relative difference between the test data and the reference standard.
Calculation formula: db =10log (p1/p2) = 20log (v1/v2) (p stands for power and v stands for voltage). The formula for converting the magnification into decibel is: 20×lgA, where A is the magnification, so when the magnification of the circuit is 85, the conversion formula is: 20× LG85 = 20×1.929 = 38.588 dB. That is, k (unit: dB) = 20×lgA, that is, the magnification a = 10 (db/20).
Two definitions of dB:
1. Definition of decibel number of Voltage (current) amplification: K=20lg(Vo/Vi), where k is the decibel number of amplification, vo is the amplified signal output, and Vi is the signal input.
2. Definition of decibel number of Power amplification: K= 10lg(Po/Pi), where k is the decibel number of amplification, po is the amplified signal output, and Pi is the signal input.
3. K>0 means that the signal is amplified, K=0 means that the signal passes, and k
With the increase of input frequency, the voltage amplification factor of the amplifier circuit will decrease, and the position where the voltage amplitude decreases to 0.707 times of the maximum value is the cutoff frequency. At this time, the power value is exactly half of the maximum power, so it is also called half power point.
It is expressed in decibels as a drop of 3dB (calculated by voltage amplitude: 20Log (0.707) = -3dB, calculated by power: 10log(0.5)=-3dB), and the corresponding frequency is called the upper cut-off frequency, which is often called -3dB bandwidth.