DAC and PLL Programming
PCVisionplus
Hardware Reference
4–3
Rev 02; February 8, 2002
4.1.3 DC Restore Reference DAC
This DAC programs the clamp voltage (PCLAMP) used to DC Restore the AC coupled video input. The incoming
video signal is sampled during the back porch and is clamped to the voltage level programmed in this DAC.
The voltage of this DAC should be set to match the negative reference voltage of the ADC. The voltage swing of the
DAC is 0 to 2.5 Volts. The 13-bit DAC produces 8192 voltage steps with 2.5/8192=0.3 mV steps. The default DAC
setting for 1.75 Volts is 0x1666 (5734 decimal).
Desired Clamp Level = 1.75 V
DAC value = (desired clamp voltage level) / (2.5 V / 8192)
= 1.75/0.000305 = 5734 = 0x1666
Data
Output Voltage
0x00
0 mV
0x01
0.3 mV
0x02
0.6 mV
. . .
. . .
0x1FFF
2.5 V
4.1.4 Sync Stripper Horizontal Line Rate
This DAC programs the voltage used to define the horizontal line rate of the Sync Stripper. The Reference voltage for
this DAC is +2.5 Volts. The 13-bit DAC produces 8192 voltage steps with 2.5/8192=0.3 mV steps. The formula for
calculating the sync stripper DAC value is:
DAC Value = (1.7 – (line rate in KHz) / 45 KHz) ) / 0.000169
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