Difference between Conditional and unconditional stability of Amplifier

This page on Conditional vs unconditional stability describes difference between Conditional and unconditional stability of Amplifier. It also covers amplifier stability factor K.

Amplifier stability factor

Unconditional stability in amplifier occurs when K >=1

Here no input and output termination possible which would make the transistor unstable.

Conditional stability in amplifier occurs when K<1 and stability depends on source and load terminations. In this case stability circles are required to check which terminations make the device stable and which not.

How one can determine that amplifier is unstable? - Unstable amplifier will have high narrowband gain peak at certain frequency. - Also one can find noise, linearity and port impedance poor here.

RF K-factor Calculator

Refer RF K-Factor Calculator>> for more information on how to calculate K-factor based on complex S parameters S11, S22, S12 and S21.

EXAMPLE of RF K-factor calculator:
INPUTS: S11(magnitude,angle)= (0.2552, 156.2o) ;
S22(magnitude,angle)= (0.1544, -95.3o);
S12(magnitude,angle)= (0.0994, 41.5o);
S21(magnitude,angle)= (5.636, 53.1o);
OUTPUT: RF Amplifier K-factor (Stability factor) = 1.0618

S11_magnitude (input1) :

S11_angle (input2) :

S22_magnitude (input3) :

S22_angle (input4) :

S12_magnitude (input5) :

S12_angle (input6) :

S21_magnitude (input7) :

S21_angle (input8) :

RF Amplifier K-Factor (Output) :

*Note: Enter values in INPUT boxes and Press CALCULATE button to check OUTPUTS.

RF and Wireless Terminologies