Row-specific SQ2 feedback (fast switching)

The SQ2-Feedback (SQ2FB) output of the MCE, controlled by a DAC can be set to either a constant value or a row-specific set of values switching at row-visit rate. The SQ2FB output is driven by the card plugged into the BC2 slot of the MCE. Either a Bias Card or an Address Card can be plugged into the BC2 slot.

Bias-card-driven SQ2FB

Prior to Rev. F

Bias Cards earlier than Rev. F have a slow opamp at the output followed by 2 sets of kHz range RC filters that limit the output switching frequency to few kHz range and prevents the output from switching at the row-visit rate. Therefore, when these bias cards are used in BC2 slot, only a constant SQ2FB value (one value per array-column) can be specified.

• Relevant mce parameters
  • flux_fb

Rev. F and later

Bias Cards Rev. F and later have faster outputs and they can be switched at row-visit rate. The firmware support for switching SQ2FB values at row-visit rate is added starting revision 5.0.5.

Relevant mce parameters

fb_col0, fb_col1, ..., fb_col31 : each specify up to 41 values, loaded in order when enbl_mux is set to 1

enbl_mux : 0 to have constant outputs, 1 to have switching ouputs

flux_fb  :

row_len  : specifies output switching rate

Software requirements

mas/trunk : r503 or later - servo programs will automatically detect the fast bias card.

mce_script/trunk: r764 or later

Configuration instructions

• When creating mce.cfg:
  • $hw_rev["bc"] = "revE" or greater.
  • $fw_rev["bc"] = 0x5000005 or greater.
  • $card_list should indicate a "bc2" (i.e. not a "bac")
  • mce_status -g should show entries for "bc2 fb_col#" and "sq2 fb_col#" as well as "bc2 flux_fb" and "sq2 fb".
• In experiment.cfg:
  • Set one of
    • config_fast_sq2 = 1; # enable fast-SQ2 switching (and tuning)
    • config_fast_sq2 = 0; # disable fast-SQ2 switching
  • Set
    • hardware_bac = 0; # bc2 is not a bac, it's a bc2.

Address-card-driven SQ2FB

See older instructions here: Fast SQ2 Feedback and TES Biasing with an Address Card

detector bias considerations

Firmware requirement

v5.0.0+

Software requirements

mas/trunk : r439 or later

mce_script/trunk: this has worked for a while...

Configuration instructions

• When creating mce.cfg:
  • $card_list must indicate a "bac" instead of a "bc2"
  • mce_status -g should show entries for "bac fb_col#" and "sq2 fb_col#" and no entries for "bc2"
• In experiment.cfg:
  • Set one of
    • config_fast_sq2 = 1; # enable fast-SQ2 switching (and tuning)
    • config_fast_sq2 = 0; # simulate non-fast-SQ2 bc2 by writing the same FB value for each row.
  • Set
    • hardware_bac = 1; # we are using a bac