KCC's Quiz AQQ259 about a tunable gain amplifier

1. Vout =0, alpha = R2/R1+R2
2. alpha = 0, Vout =  -Vin * R2/R1
    alpha = 1, Vout = Vin

1. Vout is 0V at α = R2/(R1+R2)
2. at α = 0: Vout = -Vin * R2/R1
     at α = 1: Vout = Vin * (1-(R2/R1))
...and of course, Vout is limited to +Ecc max. / -Ecc min.

The amplifier has the same voltage applied to the inverting and non-inverting inputs.

Superposition gives the following:

1. alpha= R2/(R1+R2)

2. Vout can span from Vin to (-R2/R1) * Vin

You use the simple relations for an ideal inverting and not inverting opamp. On the non inverting input, you have the partition between (1-alpha)*P and alpha*P, so you end up in the relation Vout= ((-R2/R1) + (1+R2/R1)*alpha)) * Vin. From this relation you can get the answers.

1. R2/R1 = alpha/(1-alpha) => alpha = R2/(R2+R1)
2. Vout=-R2/R1*Vin ... Vin, but it is also limited by Ecc, I am not sure, what does it exactly mean. 

For the dynamic range answer, you also need to take into account Ecc and -Ecc value.

1. 50%

2. -Ecc to +Ecc 

?

Bingo  ; you get it. Congratulations:

Thanks Roland! Agree with your answer 1. But are you sure about question 2? You probably made a typo in an equation when calculating Vout for alpha=1... May be you can recheck?

Bingo retiredEE , you get it! Congratulations!