I would like advice on the best solution for a unity gain pre-amp that will be used to detect a signal from a small sensor that is primarily capacitive and then drive a 50 Ohm coaxial cable (2 meters or so in length) to digitize the signal with either a 50 or 1 MOhm impedance down line. Signal bandwidth of interest after digitization will be about 50 MHz but signal content is very broadband due to the signal being impulsive in nature with an initial shock-like rise time and then lasting about 10 microseconds with the dominate signal component < 1 MHz. The sensor has about 6 pF of capacitance at 45 MHz and Z magnitude of about 600 Ohm (These values are properties of the frequency) and there will be about 4-10 cm of copper trace (100 um width) on a polyimide layer between the device and the pre-amp. Input voltages from the sensor to the preamp will peak at 1 to 5 Vpp.
We tried an initial design based on a Analog Devices AD8004 and had problems with DC drift under passive conditions. We also tried a AD8039 but found the frequency response under test conditions was not as flat as we would like to see. Various input impedances were tried from 1k to 100 k without any success for stability when there was just ambient pressure on the hydrophone. Under bench-top conditions with a signal generator as the source, everything looked fine.
I am interested to know what TI products might suit our purposes.
