Effect of changing current sense resistor value in amplifier circuit

I am trying to implement a current output amplifier circuit shown below. Current is measured across sense resistor Rs to adjust input voltage Vin.

Gain: G = -Iout/Vin = R2/(GainIA1 × R1 × RS)

The gain of this circuit is set at 1 with

• R2 = 1 kΩ
• R1 = 100 kΩ
• RS = 0.01 Ω
• RL is the load.

It has an instrumentation amplifier IA1 on the feedback path for less noise and better resolution. The gain of IA1 is also 1.

If I decide to increase resistance of Rs and decrease resistance of R1 while keeping the gain at 1, how would changing sense resistor value affect my system performance?

you formula for gain is not correct,

$$\ \frac{- I_{out}}{V_{in}} = \frac{R_2}{R_1*IA1*R_S}\$$

for your purpose, you need to change R1

• Sorry I updated the question. By changing the resistance of R1 & RS, would that affect the my system performance? Is there any advantage of changing sense resistor value?
– Linh
Nov 19, 2018 at 6:45
• @Linh, by changing R1, input impedance will be change. if you change Rs, you should aware of power dissipation, $P_d = R_s * i^2$,
– M KS
Nov 19, 2018 at 11:11
• What if I keep the same value for R1 and change the value of R2, what should i notice?
– Linh
Nov 19, 2018 at 18:06
• @Linh, I think R2 could just change the loop gain and this cause instability in the loop. I don't know which value this instability happens. you could simulate this circuit for instability region.
– M KS
Nov 19, 2018 at 18:35
• Could you give me more detail on how it causes instability in the loop? Isnt that the point of using negative feedback is to improve stability?
– Linh
Nov 19, 2018 at 22:06