Working frequency limits (F) :
Show amplifier satisfies the working frequency limits of various index. The working frequency limits with effective amplifier may be more than the working frequency limits of the definition.
Power gain (G) :
Show amplifier outputs the ratio of power and power input, the unit is commonly used " DB " .
Gain evenness spends (Δ G) :
Point to fall in constant temperature, inside limits of whole job frequency, the limits that amplifier gain changes. Gain evenness spends express by next type (see a picture 1) :
Graph 1
Δ G= ± (Gmax-Gmin) / 2dB
Δ G: Gain evenness is spent
Gmax: Gain -- the extent maximum of frequency sweep curve
Gmin: Gain -- the scope of frequency sweep curve is the least value
Noise coefficient (NF) :
Noise coefficient is to show input end believes comparing of a confusion of voices and amplifier output end to believe the ratio that a confusion of voices compares, the unit is commonly used " DB " .
Noise coefficient expresses by next type: A confusion of voices of letter of NF=10lg(input end is compared / a confusion of voices of output end letter is compared)
The noise coefficient in amplifier is lower (for example NF<1) below the circumstance, normally the noise coefficient of amplifier uses noise temperature (T) will express.
The relation of noise coefficient and noise temperature is: T= (NF-1) T0 or NF=T/T0+1
T0- absolutely temperature (290K)
The conversion table of noise coefficient and noise temperature (see a picture 2)
1 decibel compresses a dot to output power (P1dB) :
Amplifier has a linear and dynamic range, inside this limits, the output power of amplifier increases along with power input linear. This kind of amplifier says for linear amplifier, of these two power comparing is power gain G. Increase as power input continuity, amplifier is entered nonlinear area, its output power follows the addition of power input no longer and linear increases, that is to say, its output the cost that power predicts under place of small signal gain. The output power when dropping gain to lower than linear gain 1dB normally is worth a definition to reduce a point to output the 1dB of power, express with P1dB. (see a picture 3)
Below typical situation, when power exceeds P1dB, gain will drop quickly and achieve the biggest or completely saturated output power, its are worth bigger than P1dB 3-4dB.
3 rank cut nod (IP3) :
Those who measure amplifier is nonlinear characteristic, the simplest method is to measure 1dB to compress bit of power n P1dB. Another very popular method is to use two apart the 5 adjacent signal to 10MHz, when these two signal that are F1 and F2 when frequency add an amplifier, the output of this amplifier contained these two signal not only, and the intermodulation weight that also included frequency to be Mf1+nf2 (IM) , here, call M+n the rank number of intermodulation heft. When medium and saturated n, removing those who control function normally is the most adjacent of fundamental frequency 3 rank heft (see a picture 4) .
Because 3 rank till distortion very severe drop is rising to control function, so commonly used 3 rank cut are nodded (IP3) come token intermodulation distortion (see a picture 3) . Point of 3 rank check is a when describe amplifier linear rate main index. 3 rank cut nod the model of power to be worth taller than P1dB 10-12dB. IP3 can get through measuring IM3, computational formula is:
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