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There is one main configuration which needs to be made during use of the AD-FMCOMMS1-EBZ - to use or not to use the RF section. When not using the RF section of the board, the analog interface is directly to the ADC inputs and DAC outputs. (The RF section is not powered down, so it still consumes the same amount of power).
The following “jumpers” are solder jumpers - typically three pads, where a solder blob is places across two of the pins. (This is as good as you can do for RF signals, and still have jumpers). Without these connected in either the RF or bypass direction, the inputs and outputs will be floating, and the performance will suffer… :)
Don't change these very often - as the pads will wear out from the heat, and you will damage the card.
This is the default configuration option (the way it is tested and shipped). For performance characteristics when in this configuration, check the specifications section.
This will connect the differiantial input (JP1.2, JP2.2, JP3.2, JP7.2) of the AD9643 to either the SMB Header (J13, J11 via JP1.1, JP2.1, JP3.1, JP7.1) or to the output of the AD8366 (via JP1.3, JP2.3, JP3.3, JP7.3). This can be found on page 3 of the schematic.
This will connect the jumpers found on page 8 of the schematic.
Like mentioned above - don't do this very often (or better yet, at all) - the boards are not designed to take excess heat on these pads, and they will lift off, and destroy the functionality of the board.
The performance of the card in this configuration is shown below.
Note: that the ADC configuration does NOT go down to DC, due to:
The physical configuration of the resistors normally sets the name of the attenuator circuit, with the “pi attenuator” above being so named because in its unbalanced form it resembles the shape of the Greek letter “p” (Pi) which has two vertical bars connected at the top by a third bar forming the restiveness shape.
In the FMComms1 design, the input and output impedance are always equal, that is ZIN = ZOUT. In this case, it is placed in series between the signal source and the load to provide the required amount of attenuation. Various on line calculators are avalible to help determine the values of the resistors.
There are a three pi attenuators in the design:
The default build of these attenuators is 0dB attenuation. (2 resistors are Do Not Insert and the remaining is a 0 ohm.)