The input impedance of AD8283 can be selected between two values of 200 Ohm and 200 kOhm. Considering the fact that this is actually the input impedance of the LNA block at the front end, my questions are as follows:
- Why is the impedance selectable between only two values with a wide gap? Which one should be selected in which situation?
- Is it intended to transfer maximum power into the LNA of AD8283? If so, is there any need to place an impedance matching block between AD8283 and the source device with 100 Ohm differential output impedance, and set the Rin to 200 Ohm?
- Is it intended to create maximum voltage swing at the input of the AD8283? If so, selecting the higher input impedance (200k) should always be preferred. Then why is 200 Ohm available?