Hi Team, seeking some inputs for a customer.
The inverted input of the IVC is connected to a photodiode, and I am using the 10pF internal capacitor for the integrator.
The photodiode is illuminated with an optical pulse train (75us on/75us off). I am testing the circuit using an Agilent oscilloscope and the integrated output signal is amplified LT1919 programmable opamp, gain = 4) and measured using 10 bits ADC.
I am using the configuration shown in figure 3a of the datasheet. The control pulses are as per Figure 3b.
I have the following questions:
1) The output shows the triangular integrated pulse, as should be, but it presents a zero crossing, i.e., change signal around 1/3 of the pulse width. I could not understand why this happens. It seems the input current changes the signal during the pulse.
2) Using the timing diagram from figure 3b, during the second Hold time (10us on that example), the signal should be held and the ADC reading should be done during that time. However, the signal goes to zero very quickly. After 10us, the signals go almost to zero. It seems the signal hold does not occur. I do not understand why the HOLD function does not perform as described on the datasheet.
Thank you.
-Mark
