LTC6268-10
Recommended for New Designs
The LTC6268-10/LTC6269-10 is a single/dual 4GHz FET-input operational amplifier with extremely low input bias current and low input capacitance. It also...
Datasheet
LTC6268-10 on Analog.com
LTC6269
Recommended for New Designs
The LTC6268/LTC6269 is a single/dual 500MHz FET-input operational amplifier with extremely low input bias current and low input capacitance. It also features...
Datasheet
LTC6269 on Analog.com
LTC6269-10
Recommended for New Designs
The LTC6268-10/LTC6269-10 is a single/dual 4GHz FET-input operational amplifier with extremely low input bias current and low input capacitance. It also...
Datasheet
LTC6269-10 on Analog.com
Hi,
I would like to ask about the following issue that occurred when designing the LTC6268-10 as a TIA.
I designed the circuit shown in the attached image using KiCad 7. This circuit is a transimpedance amplifier (TIA) that converts input current into voltage. Therefore, for performance testing, it is necessary to input a current. I inserted a 10kΩ resistor in series with the output of a function generator (10mV) to adjust the circuit’s input so that 1μA of current flows. Since the feedback resistor in this circuit is 10kΩ, the output voltage should theoretically be 10mV. However, the expected amplification was not observed.
Additionally, I inserted a 10kΩ resistor at the non-inverting input to account for the bias current, but I am unsure whether this had any effect. Furthermore, changing this 10kΩ resistor to 0Ω did not affect the output, and the amplification issue remained.
I would like to understand why this situation is occurring. I appreciate any guidance you can provide.
Also, could you share the recommended PCB layout? The layout described in the datasheet is too abstract, making it difficult to implement in my design.
Hi yms ,
Do you have a scopeshot of how your output looks like? Also have you tried increasing the input current say 100uA or increase feedback resistor to 20kohm-100kohm and check for output? (I would recommend removing that 0.1pF cap on feedback too just to make the circuit simple unless your circuit needs compensation for stability).
Also can you measure the voltage at the IN- node just to check?
For the resistor at non-inverting pin, this device has very low bias current (3fA) so it has minimal effect on your output (since you are just using 10kohm feedback resistor).
Here's some LT Spice simulation of your simple circuit.
Thanks and Best Regards,
Kenneth
