GX4002 Datasheet, PDF (42/74 Pages) Gennum Corporation – Dynamic on-chip power management control

The device supports offset measurement of each source through the ADCSRCSEL and
ADCOFFCALEN register controls. ADCOFFCALEN selects the source to zero-out, as
shown in Table 3-2:
Table 3-2: Offset Measurement Sources
ADCOFFCALEN[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Source
0.9V
Ch0 Vertical Eye
Ch1 Vertical Eye
Ch0 Horizontal Eye
Ch1 Horizontal Eye
Ch0 Peak Detector
Ch1 Peak Detector
RSVD
RSVD
RSVD
Temperature Sensor
Supply Sensor
0.45V
1.35V
RSVD
RSVD
ADC Offset Calibration
Input (Vcal)
0.9V
0.9V
0.9V
0.9V
0.9V
0.45V
0.45V
N/A
N/A
N/A
0.9V
0.9V
0.45V
1.35V
N/A
N/A
When a selected source is zeroed-out, the input to the ADC is set to its calibration voltage
(Vcal) as per Table 3-2. The ideal code for that calibration voltage for a given resolution,
can be subtracted from the output code to get the offset. Refer to the formula shown
below:
Offset = ADCOut − (2^{N Vcal} −1)
1.8
Equation 3-1
For example: if the temperature sensor is selected as the source, then it’s Vcal = 0.9V.
Assuming that the ADC resolution (N) is set to 10 bits; by setting ADCOFFCALEN =
“1010”, and reading-out the ADC, (in this example) ADCOUT = 521.
Therefore, Offset = 521 - 511 = 10.
This measured offset can be subtracted from subsequent measurements automatically,
as described in the next section.
GX4002 2x2 14.025Gb/s Crosspoint Switch with Trace
Equalization and Output De-Emphasis
Data Sheet
55972 - 0
March 2012
42 of 74
Proprietary & Confidential