# LTC6269-10 Supports 100 ohm feedback resistance

I am building light balancing circuit.  For higher bandwidth, I need lower feedback resistance (i.e) 100 ohm.  When I use feedback resistance of 100 ohm and feedback capacitance of 2 pF. I am facing ringing effect. So, how do we select the capacitance according to the resistor. Will the opamp IC LTC6269-10 works with the feedback resistance 100 ohm. I am attaching my circuit.

• Hi,

Can you provide more details on your requirements?

It seems like your net input current is 0, is that correct?

What is your expected output voltage? What is your target transimpedance gain?

ADI has a tool called photodiode wizard tool in this link and will help you to determine if LTC6269-10 is suitable for your requirements and the tool will also help you with the recommended design values of feedback R and C.

• Yes, Net current should be 0. I1 and C1 is the equivalent circuit of Photodiode 1, I2 and C2 is the equivalent circuit of Photodiode 2. The circuit is basically lightt balancing detection circuit. So, if light is equal, Output will be 0 V. If the light coming of the two photodiodes are equal. I need to use Rf of 100 ohm because  I want to make this circuit work in higher bandwidth.

• Hi Vilashini,

The resistor has nothing to do with it, look carefully at this condition:

Cf and Cin capacitors set the noise gain at high frequencies. This condition is not met in your circuit

Regards,

Kirill

• CIN = CPD + CCM + CDM

CPD = Photodiode capacitance

CCM = Common Mode Capacitance of Amplifier

CDM = Differential Mode Capacitance of Amplifier

CIN = 0.25 pF + 100 fF + 450 fF

= 0.8 pF

CIN/Cf >= 10

0.8 pF / 0.025 pF = 32 which is greater than 10. But  I am facing same type of error.

• Hi,