The EyeScan module implements a function that moves the sample point for data anywhere in the data eye and measures the number of bit errors at that point. To accomplish this, the EyeScan module uses three other digital modules in addition to an analog phase interpolator and a deserializer. These digital modules are the CDRLF and PI controller, and the eye plot PI controller.
The eye plot PI controller controls the eye-phase interpolator (E PI), under the direction of the EyeScan module. The E PI tracks to the location of the primary PI when no additional ups and downs are requested by the EyeScan module. The EyeScan module can request additional ups and downs be performed on the E PI to create a fixed offset between the E PI and primary PI. The deserializer uses the E PI to sample receive eye data (E data) at times that are at different phases to the normal sampled I and Q data. An up request causes the clock phase delay to increase (moving the clock phase later in time), and a down request causes the clock phase delay to decrease (moving the clock phase earlier in time). The EyeScan module uses this system to measure the bit-error rate at any point in the received data eye.
Note: For more information on EyeScan Module, see Answer Record 67295.