Editing Negative-feedback amplifier (section)

== Feedback amplifier formulas ==
Summarizing the two-port analysis of feedback, one can get this table of formulas.<ref name=":0" />
{| class="wikitable"
|+
!Feedback Amplifier
!Source Signal
!Output Signal
!Transfer Function
!Input Resistance
!Output Resistance
|-
|Series-Shunt (voltage amplifier)
|Voltage
|Voltage
|<math>A_{vf}=\frac{V_o}{V_i}=\frac{A_v}{1+\beta_vA_v}</math>
|<math>R_i(1+\beta_v A_v)</math>
|<math>\frac{R_o}{1+\beta_v A_v}</math>
|-
|Shunt-Series (current amplifier)
|Current
|Current
|<math>A_{if}=\frac{I_o}{I_i}=\frac{A_i}{1+\beta_iA_i}</math>
|<math>\frac{R_i}{1+\beta_i A_i}</math>
|<math>R_o(1+\beta_i A_i)</math>
|-
|Series-Series([[transconductance]] amplifier)
|Voltage
|Current
|<math>A_{gf}=\frac{I_o}{V_i}=\frac{A_g}{1+\beta_zA_g}</math>
|<math>R_i(1+\beta_z A_g)</math>
|<math>R_o(1+\beta_z A_g)</math>
|-
|Shunt-Shunt ([[transresistance]] amplifier)
|Current
|Voltage
|<math>A_{zf}=\frac{V_o}{I_i}=\frac{A_z}{1+\beta_gA_z}</math>
|<math>\frac{R_i}{1+\beta_g A_z}</math>
|<math>\frac{R_o}{1+\beta_g A_z}</math>
|}
The variables and their meanings are

<math>A</math>- gain, <math>I</math>- current, <math>V</math>- voltage,<math>\beta</math>- feedback gain and <math>R</math>- resistance.

The subscripts and their meanings are

<math>f</math>- feedback amplifier, <math>v</math>- voltage,<math>g</math>- transconductance, <math>Z</math>- transresistance, <math>o</math>- output and <math>i</math>- current for gains and feedback and <math>i</math>- input for resistances.

For example <math>A_{vf}</math>means voltage feedback amplifier gain.<ref name=":0" />