VITESSE
SEMICONDUCTOR CORPORATION
High-Speed Octal
Programmable Timing Generator
Figure 3: Fine Vernier Calibration DAC Programming
One Test/Calibration Cycle
Shift Data Into
Calibration Register
SHIFT
1
DCLK
2
3
4
5
6
1
2
3
4
5
6
Hold Data In
Calibration Register
Data Sheet
VSC6048
DIN
5
4
3
2
1
0
X
X
X
X
X
5
4
3
2
1
0
X
X
X
X
DAC_WR
CAL_DAT
(internal)
ADR[2:0]
Vernier 0 DAC Data
Vernier 1 DAC Data
Address for Vernier 0
Address for Vernier 1
DAC Calibration
Each fine vernier must be calibrated to a 1240ps span, one step (10ps) shorter than the 800MHz period
(1.25ns). This is accomplished by setting the fine vernier to maximum delay and adjusting the 6-bit calibration
DAC until the desired range has been achieved.
The calibration data is transferred into the device through a 3-bit serial interface. Refer to Figure 3 for the
programming sequence. Typical DCLK frequencies are 1MHz to 10MHz. Once the calibration value has been
transferred into the device, the data is written into the specified DAC by the rising edge of DCLK when
DAC_WR is HIGH. The address lines must remain stable from the enable of SHIFT to one cycle after the dis-
able of DAC_WR.
DAC Application
There are three DAC_REF pins on this device. Each pin supplies the reference for two or three calibration
DACs. In order to reduce crosstalk between verniers through the DAC_REF supply, it is recommended that
each DAC_REF pin be isolated from each other. This will reduce crosstalk between the the three channel
groups, however, it will not effect crosstalk between verniers within each group.
Table 3: DAC Reference Pin Identification
DAC_REF Pin #
1
18
40
Vernier Channels
0, 1, 2
3, 4
5, 6, 7
Outputs
Each channel has a differential ECL output. The output of the verniers is falling edge active. The shift reg-
ister propagates a 2ns pulse. The fine vernier then stretches the pulse width based on the programmed delay.
Page 4
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
G52335-0,Rev.4.0
8/28/00
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
