User talk:Djhk

Fully differential op amp
(a copy of Talk:Circuit Idea/Simple Op-amp Summer Design)

DavidCary has written:

Can Dieter's procedure be applied to a fully differential amplifier? At first glance, I'm guessing that there's one minor and one major change:
 * Use equal feedback resistors Rf, one from the + output to the - input, and one from the - output to the + input. Connect the "common" input to the appropriate voltage source. (minor change to the " difference amplifier" )
 * The sum of the gains = zero in a properly-designed fully differential amplifier circuit. (Right? major change)

Wrong! Daisy's theorem states that the sum of ALL gains is equal to one. This applies to the +out node, the -out node, or any other node. If we add two sets of gains, each of which has a sum of +1, how do we get a sum of zero. Is 1+1 = 0 ?

If that process looks good, please move it to Electronics/Op-Amps. (Should we mention fully differential amplifiers on this Circuit Idea/Simple Op-amp Summer Design page? ) --DavidCary 23:15, 5 November 2007 (UTC)
 * Calculate resistor values for each input, using Ri = Rf / |desired gain|.
 * For inputs with positive gain, connect the calculated resistor value between that input and the + input on the amplifier.
 * For inputs with negative gain, connect the calculated resistor value between that input and the - input on the amplifier.
 * If all your inputs are differential pairs, then the sum of all the gains is now zero. Done. Otherwise add a ground resistor to bring the total gain to zero.

Shadow's design procedure only applies to Voltage feedback op-amps. It does not apply to Current mode op-amps, nor to video amps. Please keep the name. This is Shadow's procedure. It's not a trick. The procedure only applies to the General Summing Amplifier. The gain equation is derived via VSA analysis and simplified for large op-amp gain. Don't confuse this aproach with the comedy of error approach typically used in electronics.