Other Parts Discussed in Thread: TINA-TI, LMH6401
We have received an inquiry from our customer as follows.
We are trying to use an LMH5401 in one of our designs and neither our design, nor the EVM produces what the data sheet says it should. Need to figure out why that's so.
We are trying to use the LMH5401 in our design. Our frequency range is 30 MHz to 6 GHz. What we find is that the system seems to have a rapid roll off at frequencies of more than about 4 GHz. We've tried the designs in the data sheet and also the 5401EVM and none of them produce the performance as specified in the data sheet.
As a starter the data sheet says that Figure 1 was derived from measurements made using the EVM. We cannot reproduce that graph for the 2V/V and 4V/V curves using the schematics provided in the data sheet Figure 56 and the EVM. That would be a good starting point. Also we actually need to cascade two or more amps to get the gain required and we find that cascading more than one amp drops the 3 dB frequency very fast. Even the TI-spice seems to show this behavior so there seems to be something that's not mentioned in the data sheet. For instance does this part have a very high input capacitance?
Thank you for your support!