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e310: Added some doc comments on frontend tuning

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Martin Braun 2017-06-27 14:32:04 -07:00
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@ -436,7 +436,8 @@ For more advanced IMU based applications please refer to the <a href="https://gi
Please see the \ref page_gpio_api for information on configuring and using the GPIO bus.
\subsection e3x0_hw_audio Audio connectors
\subsection e3x0_hw_audio Audio connectors (if populated)
The E3x0 2.5 mm Audio Jack TRRS pins are assigned as follows: Tip=Mic, Ring1=Right, Ring2=Left, Sleeve=GND.
\image html TRRS.png "Audio Jack"
@ -544,6 +545,22 @@ Both transmit and receive can be used in a MIMO configuration. For
the MIMO case, both receive frontends share the RX LO, and both transmit
frontends share the TX LO. Each LO is tunable between 50 MHz and 6 GHz.
As there is a single LO for each direction (RX and TX), this means that both
channels need to use the same LO frequency (i.e., both RX channels share an LO
frequency, and both TX channels share an LO frequency). If the two channels
are supposed to receive on different frequencies, the digital tune stages need
to be used for that. The two frequencies will need to be within the currently
selected master clock rate, and the final bandwidths need to be chosen
carefully. Example: Assume the master clock rate is set to 50 MHz, and we want
to receive at 400 MHz and 440 MHz. We can set the LO to 420 MHz, which will
sample the spectrum from 395 MHz to 445 MHz. The LO offsets for both channels
need to be 20 MHz and -20 MHz respectively. However, the final bandwidth should
be less than 10 MHz (preferably lower), or the signals would exhibit aliasing.
Because both channels share an LO, tuning one channel can possibly affect the
other channel. It is advisable to read back the actual, current frequency from
software before assuming the device is tuned to a specific frequency.
\subsubsection e3x0_dboard_e310_gain Frontend gain
All frontends have individual analog gain controls. The receive