Chapter 10 511
Controller Section
12-Bit Flash ADC
12-Bit Flash ADC
The flash ADC (U22) converts the analog video signal into 12-bit digital
values at a fixed rate of 12 megasamples per second.
When measuring voltages or waveforms on the Fast ADC of the A2
controller assembly, connect the ground (or common) lead to the
ground-plane trace associated with the shield. This digital ground
plane is totally isolated from the chassis.
1. Press
PRESET on the spectrum analyzer and set the controls as
follows:
Center frequency ..................................................... 300MHz
Span .................................................................................0Hz
Reference level ......................................................... −20dBm
Log/division ..............................................................5dB/DIV
Sweep time .................................................................... 20ms
2. Connect the CAL OUTPUT to the INPUT 50Ω connector.
3. Pins 2 through 13 (ADC0-ADC11) of U22 should all be high (logic 1),
corresponding to an ADC digital count of 255 for the analog input of
+2 volts or greater.
4. Disconnect the CAL OUTPUT signal from the INPUT 50Ω
connector.
5. Pins 2 through 13 (ADC0-ADC11) of U22 should all be low (logic 0),
corresponding to an ADC digital count of zero for the analog input of
0 volts or less.
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