X-Stream Operator’s Manual
WM-OM-E Rev I 425
Automatic Gain Control (AGC)
The phase and gain steering algorithm in the DDA’s channel emulation (AGC) will adjust for
changes in the signal after VCO Synch. Read gate tells us where to start looking at the VCO Synch.
Phase is essentially the timing of when a sample is taken, while gain is the levels that are being
searched for as +1 and -1. Thus, when a sample larger than the ideal value is taken, the level
looked for by the emulation is increased. The screen below shows an example of phase and gain
steering.
To start the AGC, we must find the maximum and minimum levels in the VCO Synch, and then
initialize the levels to be searched. Thus, if the pulses are exactly the desired shape, then 1 and -1
will be where expected, with the other levels symmetrically spaced in between.
Note that the VCO Synch must exist in the acquired head signal, or the channel emulation cannot
be run. The phase and gain steering algorithm in the emulation will adjust for changes in the signal
after VCO Synch, assuming it starts correctly.
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